PDS_VERSION_ID = PDS3 LABEL_REVISION_NOTE = "2006-09-19, S. MURCHIE 2007-01-17, S. MURCHIE 2007-05-09, S. MURCHIE 2007-08-17, S. MURCHIE 2007-11-19, S. MURCHIE" RECORD_TYPE = STREAM OBJECT = DATA_SET DATA_SET_ID = "MRO-M-CRISM-3-RDR-TARGETED-V1.0" OBJECT = DATA_SET_INFORMATION DATA_SET_NAME = "MRO CRISM TARGETED REDUCED DATA RECORD V1.0" DATA_SET_COLLECTION_MEMBER_FLG = "N" DATA_OBJECT_TYPE = {"TABLE", "IMAGE"} START_TIME = "N/A" STOP_TIME = "N/A" DATA_SET_RELEASE_DATE = UNK PRODUCER_FULL_NAME = "SCOTT MURCHIE" DETAILED_CATALOG_FLAG = "N" ARCHIVE_STATUS = "IN QUEUE" CITATION_DESC = "Murchie, S., Mars Reconnaissance Orbiter Compact Reconnaissance Imaging Spectrometer for Mars Targeted Reduced Data Record, MRO-M-CRISM-3-RDR-TARGETED-V1.0, NASA Planetary Data System, 2006." DATA_SET_TERSE_DESC = "Targeted Reduced Data Records for IR and VNIR image cubes for CRISM (Compact Reconnaissance Imaging Spectrometer for Mars)." ABSTRACT_DESC = "This dataset is intended to include IR and VNIR data from the CRISM instrument on MRO, processed to several different levels. The core structure parallels that of an EDR with a multiband image and a text file containing frame-specific housekeeping information for each of the concatenated image frames in the multiband image. However the image data has been converted to units of radiance using level-4 and level-6 CDRs, and analog housekeeping items in the text file (voltages, currents, and temperatures) have been converted into physical units using a level-6 CDR. Both files share a common label. A TRDR may also contain separately labeled multiband images in which radiance has been processed to I/F (radiance divided by (pi * solar flux at 1 AU * heliocentric distance^2)), Lambert albedo, or a set of derived spectral parameters (summary products) that provide an overview of the data set. The summary products include Lambert albedo at key wavelengths, or key band depths or spectral reflectance ratios. To create Lambert albedo or most summary products, estimated corrections for atmospheric, photometric, and thermal effects are applied to the I/F data using corrections given in ADRs. The formulations for all of the summary products have been validated using data from Mars Express/OMEGA." DATA_SET_DESC = " Data Set Overview ================= This volume contains portions of the CRISM Targeted Reduced Data Record (TRDR) Archive, a collection of multiband images from the Compact Reconnaissance Imaging Spectrometer for Mars on the Mars Reconnaissance Orbiter spacecraft. Images consist of data calibrated to units of radiance or I/F plus a text file with housekeeping information, and optionally image data to which further corrections have been applied. Image data are in sensor space and non-map-projected. The data are stored with PDS labels. This volume also contains an index file ('imgindx.tab') that tabulates the contents of the volume, ancillary data files, and documentation files. It may also contain browse images in PNG format, and HTML documents that support a web browser interface to the volume. For more information on the contents and organization of the volume set refer to the aareadme.txt file located in the root directory of the data volumes. Parameters ========== CRISM observing scenarios are constructed using a set of key variables ('configurations') which include the following. (All are selectable separately for the VNIR and IR detectors. Only a subset of the configurations represent 'scene' data, as indicated by the keyword MRO:ACTIVITY_ID. Only scene data that are aimed at Mars are processed to TRDRs. Only those configurations that affect the contents or dimensionality of a TRDR are discussed below): Image source: Image data may be generated using digitized output from the detector, or using one of up to seven test patterns. Only data from the detector are processed to a TRDR. Pixel binning: Pixels can be saved unbinned or binned 2x, 5x, or 10x in the spatial direction. No pixel binning in the spectral direction is supported. Data with any pixel binning configuration may have a corresponding TRDR, but the pixel binning configuration will affect the dimensionality of the TRDR. Row selection: All detector rows having useful signal can be saved, or alternatively an arbitrary, commandable subset of rows can be saved. The number of rows with useful signal is 545, 107 in the VNIR and 438 in the IR. The nominal number of rows for multispectral mode was 73, 18 in the VNIR and 55 in the IR prior to 10 Dec 2006. On that date an extra channel was added to the VNIR for a total of 19. For each detector, there are four options of channel selection to choose from rapidly by command: hyperspectral (545 total channels), multispectral (73 total channels prior to 10 Dec 2006, 74 total channels on and after 10 Dec 2006), and two sets of expanded multispectral (84 and 92 channels prior to 10 Dec 2006, 85 and 93 channels on and after 10 Dec 2006). An analogy is a car radio preset button. New options are set by uploading a data structure to the DPU. Data with any wavelength selection may have a corresponding TRDR, but the wavelength selection affects the wavelength continuity and dimensionality of a TRDR. Calibration lamps: 4095 levels are commandable in each of two lamps at each focal plane, and in two lamps in the integrating sphere. All lamps can be commanded open-loop, meaning that current is commanded directly. For the integrating sphere only, closed loop control is available at 4095 settings. For closed loop control, the setting refers to output from a photodiode viewing the interior of the integrating sphere; current is adjusted dynamically to attain the commanded photodiode output. Note: lamps reach maximum current at open- or closed-loop settings <4095. Only data for which the calibration lamps are off may be processed to a TRDR. Shutter position: Open, closed, or viewing the integrating sphere. The shutter is actually commandable directly to position 0 through 32. In software, open=3, sphere=17, closed=32. NOTE: during integration and testing, it was discovered that at positions <3 the hinge end of the shutter is directly illuminated and creates scattered light. Position 3 does not cause this effect, but the other end of the shutter slightly vignettes incoming light. Only data in which the shutter is open, and at position 3, may be processed to a TRDR. Pointing: CRISM has two basic gimbal pointing configurations and two basic superimposed scan patterns. Pointing can be (1) fixed (nadir-pointed in the primary science orbit) or (2) dynamic, tracking a target point on the surface of Mars and taking out ground track motion. Two types of superimposed scans are supported: (1) a short, 4-second duration fixed-rate ('EPF-type') scan which superimposes a constant angular velocity scan on either of the basic pointing profiles, or (2) a long, minutes-duration fixed-rate ('target swath-type') scan. Pointing configuration affects the contents but not the dimensionality of a TRDR. Processing ========== The CRISM data stream downlinked by the spacecraft unpacks into a succession of compressed image frames with binary headers containing housekeeping. In each image, one direction is spatial and one is spectral. There is one image for the VNIR focal plane and one image for the IR focal plane. The image from each focal plane has a header with 220 housekeeping items that contain full status of the instrument hardware, including data configuration, lamp and shutter status, gimbal position, a time stamp, and the target ID and macro within which the frame of data was taken. These parameters are stored as part of an Experiment Data Record (EDR), which consists of raw data, or a Targeted Reduced Data Record, or TRDR, the 'calibrated' equivalent of an EDR. The data in one EDR or TRDR represent a series of image frames acquired with a consistent instrument configuration (shutter position, frame rate, pixel binning, compression, exposure time, on/off status and setting of different lamps). Each frame has dimensions of detector columns (spatial samples) and detector rows (wavelengths, or bands). The multiple image frames are concatenated, and are formatted into a single multiple-band image (suffix *.IMG) in one file, plus a detached list file in which each record has housekeeping information specific to one frame of the multiple-band image (suffix *.TAB). The text file is based on the 220 housekeeping items. Five of the items are composite in that each byte encodes particular information on gimbal status or control. These separate items are not broken out, except for the gimbal status at the beginning, middle, and end of each exposure, from which gimbal position is broken out (3 additional items). The housekeeping is pre-pended with 10 additional frame-specific items useful in data validation, processing, and sorting, for a total of 233 items per frame. Further information can be found in the data product SIS in the DOCUMENT directory. The multiple-band image has dimensions of sample, line, and wavelength. The size of the multiple-band image varies according to the observation mode but is deterministic given the macro ID. A typical multiple-band image might have XX pixels in the sample (cross-track) dimension, YY pixels in the line (along-track) dimension, and ZZ pixels in the wavelength dimension, where: XX (samples) = 640/binning, where 640 is the number of columns read off the detector, and binning is 1, 2, 5, or 10; YY (lines) = the number of image frames with a consistent instrument configuration; and ZZ (bands) = the number of detector rows (wavelengths) whose read-out values are retained by the instrument. Once data are assembled into EDRs, they are calibrated into TRDRs. Image data are converted to units of radiance using level-4 and level-6 CDRs, and analog housekeeping items in the text file (voltages, currents, and temperatures) have been converted into physical units using a level-6 CDR. Both files share a common label. The calibration algorithms are discussed at length in an Appendix in the CRISM Data Products SIS. A TRDR may also contain separately labeled multiband images in which radiance has been processed to one of the following: I/F (radiance divided by (pi * solar flux at 1 AU * heliocentric distance^2)), Lambert albedo, or a set of derived spectral parameters (summary products) that provide an overview of the data set. The summary products include Lambert albedo at key wavelengths, or key band depths or spectral reflectance ratios. To create Lambert albedo or most summary products, estimated corrections for atmospheric, photometric, and thermal effects are applied to the I/F data using corrections given in ADRs. The formulations for all of the summary products have been validated using data from Mars Express/OMEGA. The sequence of processing that creates a TRDR is as follows: (a) EDRs are assembled from raw data. (b) The radiance multiband images in TRDRs are created from the EDRs and Calibration Data Records, or CDRs, using a calibration algorithm discussed at length in an Appendix in the CRISM Data Products SIS. (c) Gimbal positions are extracted from the EDR housekeeping and formatted as a gimbal C kernel. (d) Using the gimbal C kernel and other SPICE kernels, DDRs are created. The surface intercept on the MOLA shape model is calculated for each spatial pixel (sample at the reference detector row). The angles of this pixel relative to the equatorial plane and reference longitude constitute the latitude and longitude of the pixel. For that latitude and longitude, solar incidence, emission, and phase angles are determined at a surface parallel to the areoid but having a radius from planetary center equivalent to that of the surface intercept of the shape model. Solar incidence and emission are also determined relative to the shape model itself. Using the latitude and longitude of the surface intercept of each spatial pixel, TES bolometric albedo and thermal inertia are retrieved from global map products, and resampled into CRISM sensor space using nearest neighbor resampling. The same procedure is used to retrieve MOLA elevation, and the local slope magnitude and slope azimuth of the MOLA elevation model. (e) Optionally, radiance is converted to I/F by dividing by (pi * solar flux at 1 AU * heliocentricdistance^2)). Solar flux is maintained in a level 4 CDR, and solar distance is written in the label to the radiance image. (f) Optionally, I/F is converted to Lambert albedo to allow rapid identification of new ROIs and to quickly assess the information content of targeted observations. Some or all of the following corrections may be made: I/F is divided by cosine of the solar incidence angle The estimated contribution to and attenuation of the signal by atmospheric aerosols is removed. The estimated attenuation of the signal by atmospheric aerosols is removed. The thermal emission from longer IR wavelengths is removed. These corrections depend on local weather conditions, and they leverage the fact that Martian weather tends to be highly repeatable year to year [SMITHETAL2002, SMITHETAL2003, SMITH2004] That climatic record and its predicted effects on surface spectra are recorded in a special data product called Ancillary Data Records, or ADRs. An ADR is a hyperdimensional binary table containing reference information used by algorithms that correct at-sensor radiance to Lambert albedo of the surface, with atmospheric and thermal effects 'removed.' The axes of an ADR are physical parameters that may describe some scene. The parameters may be extracted from the label of a TRDR radiance image or from a DDR. The axes include latitude, longitude, solar longitude, incidence, emission, or phase angle, TES bolometric albedo, TES thermal inertia, MOLA elevation, MOLA slope magnitude, or MOLA slope azimuth. To correct a given spatial pixel in a TRDR for its climatologically predicted atmospheric and thermal effects, that spatial pixel's physical values from the DDR are used as coordinates to locate within the ADR a multiplicative correction from I/F to Lambert albedo. The corrections are pre-computed using DISORT modeling [STAMNESETAL1988] of the expected effects of the atmosphere and thermal emission under different illumination conditions, based on TES climatology as a function of latitude, longitude, and solar longitude. Four different algorithms of varying complexity and fidelity have been developed to apply the ADR corrections. Which algorithms are used are indicated by the keywords MRO:ATMO_CORRECTION_FLAG, MRO:THERMAL_CORRECTION_MODE, and MRO:PHOTOCLIN_CORRECTION_FLAG. Once data have been acquired during the primary science phase and the algorithms' performance has been evaluated, one of the four algorithms may be adopted or modified for pipeline production of special products. CRISM standard data products and the supplementary browse products are defined and described in greater detail in the Data Products Software Interface Specification and the Data Archive Software Interface Specification in the DOCUMENT directory. Details of DN to radiance conversion ==================================== FLIGHT AND GROUND CALIBRATION DATA: ---------------------------------- All calibration matrices are stored in 'calibration data records' or CDRs, separate from the main algorithm coded in software. There are two general classes of calibration matrices, those derived from ground data and updated infrequently if at all, and those that represent highly time-variable properties of the instrument. Examples of the former include the constants needed to uncompress data, correct non-linearity, or correct bias for effects of detector or focal plane electronics temperature. Examples of the latter include bias and IR thermal background, which depend on detector and spectrometer housing temperature respectively. There are two formats for storing the values in the matrices, distinguished by the levels of processing. Level 6 CDRs, or CDR6s, are tabulated numbers in ASCII format, and level 4 CDRs, or CDR4s, are images each derived from a collection of flight or ground calibration measurements. Calibration matrices that are highly time variable will be measured inflight, and include the following. For the VNIR detector bias is measured directly, with the shutter closed and at the same integration time as accompanying measurements of Mars. For the IR, shutter-closed measurements also include thermal background. The bias is therefore measured for the IR detector by taking data at several integration times and extrapolating to zero exposure. The step function, a discontinuity in measured bias at some detector row, is modeled deterministically as a function of integration time. Currently, the default is to take a VNIR bias measurement with every observation and IR bias observations several times daily. Masks of bad pixels, whose occurrence depends on detector temperature, will be created in concert with bias images. IR thermal background is the response of the IR detector to 'glow' of the inside of the instrument predominantly at >2300 nm. The change in spectrometer housing temperature that perturbs thermal background by the equivalent to read noise is about 0.02K, whereas the spectrometer housing is predicted to change by several degrees over the course of an orbit. Therefore shutter-closed IR measurements will be taken interspersed within all observations, at an interval of approximately once per 3 minutes. To correct any given frame of scene data, bracketing shutter-closed measurements are interpolated in time. The onboard integrating sphere serves as the radiance reference against which CRISM's radiometric responsivity as a system is pegged. The frequency of its measurement is driven by the timescales of change of instrument characteristics which must be calibrated out using the sphere. The most rapidly varying radiometric characteristic is responsivity of the VNIR detector at its longer wavelengths, which changes by the equivalent of noise in the data in tens of seconds due to the thermostatic cycling of VNIR detector temperature. Measuring the sphere this frequently is impractical, so this effect is corrected instead using telemetered temperature of the VNIR detector and ground calibration results. The next most rapidly changing characteristic is IR detector responsivity at its longest wavelengths, which is also a function of temperature. The default to calibrate this effect is to take sphere observations on day- and night-side segments of several orbits per day, each observation consisting of illuminated images with the sphere lamp under closed-loop control, and unilluminated images to measure the sphere's blackbody background (which must be subtracted out). Pixel-to-pixel variations in VNIR detector responsivity are measured monthly using bland regions of Mars. RADIOMETRIC CALIBRATION: Radiometric calibration to units of radiance involves uncompressing data, correcting instrument artifacts, subtracting bias and background, dividing by exposure time, and converting of the result of these steps to units of radiance by comparing against a radiometric reference. This approach explicitly uses measurements of the internal integrating sphere. The general equation to reduce measurements of Mars to units of radiance, using ground and flight calibration measurements, is: RD(x,lambda) = M(x,lambda,Hz)( ( K(x,lambda,Hz)( D14lambda( DN(x,lambda,TV,TW,TI,TJ,T2,Hz,t) ) - BiaT(x,lambda,TV,TW,TI,TJ,Hz,t) ) / t - Bkgd(x,lambda,TI,T2,Hz) - Scat(x,lambda,TV,TI,T2,Hz) ) / RST(x,lambda,TV,TI,T2,T3,S) ) Subscripts define the variables on which calibration coefficients depend, and include the following: x is spatial position in a row on the focal plane, in detector elements. lambda is position in the spectral direction on the focal plane, in detector elements. Hz is frame rate, and implicitly includes with it compression configuration including wavelength table and binning mode TI, is IR detector temperature in degrees K. TV is VNIR detector temperature in degrees K. T2, is spectrometer housing temperature in degrees K. T3 is temperature of the integrating sphere in degrees K. TJ is IR focal plane board temperature in degrees K. TW VNIR focal plane board temperature in degrees K. t is integration time in seconds. s is choice of sphere bulb, side 1 (controlled by IR focal plane electronics) or side 2 (controlled by VNIR focal plane electronics). Discussion of the various instrument effects being corrected is including in the 'Confidence Level Note' below. All of the input temperatures come from instrument housekeeping, and are monitored by the focal plane electronics. Temperatures are corrected for electronics noise by substituting for temperatures, currents, and voltages in the image headers the corresponding values at the same spacecraft time from the low-speed telemetry stored in 'ST' CDR6s. This step is performed because the low-speed telemetry maintains a fixed timing relative to instrument current variations on 1-second cycles, whereas the image headers do not; this makes the electronics noise more easily calibrated in the low-speed telemetry. The raw digital values are corrected for effects of frame rate and variable current loads, including lamps and coolers, using additive and multiplicative coefficients maintained in the 'HD' CDR6, and then scaled to physical units using other coefficients maintained in the 'HK' CDR6. The terms in the equation and their sequential application are as follows: Data decompression. D14lambda converts from raw 8- or 12-bit DNs to 14-bit DNs. This is accomplished by inverting the 12-to-8-bit LUT using the 'LI' CDR6, then dividing by the gain and adding the offset used onboard, whose values are contained in the 'PP' CDR6. Bias subtraction. BiaT(x,lambda,TV,TW,TI,TJ,Hz,t) is detector bias derived as described above from flight measurements, and stored as a 'BI' CDR4. For the VNIR, it is just a decompressed shutter-closed measurement. For the IR, it is the zero-exposure intercept of the pixel-by-pixel fit of 14-bit DN to exposure time in the bias measurements, added to the bias step function stored in the 'BS' CDR6. Bias is corrected for changes in focal plane electronics and detector temperature since the time of bias measurement, using telemetered detector and electronics temperature and the 'DB' and 'EB' CDR6's respectively. Electronics artifacts correction. K(x,lambda,Hz) applies the bad pixel, detector ghost, and detector nonlinearity corrections. This is actually a composite of four distinct steps. The bad pixel mask, stored as a 'BP' CDR4, is constructed from a bias measurement. Two distinct types of pixels are flagged, noisy pixels and pixels with elevated bias; once data are units of radiance bad pixels are interpolated across bilinearly. Noisy pixels are defined as those whose noise level significantly degrades the effective SNR of the calibrated data. Thresholds for flagging detector elements as 'noisy' are stored in the 'AS' CDR6. The noise is calculated from the standard deviation of pixel DN levels between different frames in the short-exposure bias measurement, and stored in a 'UB' CDR4. The noise for each pixel is compared to the threshold in the 'AS' product and if the value is larger, the pixel is declared bad. Pixels with elevated bias are treated in a wavelength- dependent fashion, such that they are flagged if their bias is sufficiently high that a bright scene would cause them to saturate. (This is done instead of just examining scene data and looking for saturation, because when pixels are binned spatially, saturation of one of the component pixels is not obvious.) The 'AS' CDR6 also contains 14-bit saturation limits, and limiting 14-bit scene DNs for different combinations of frame rates and exposure times corresponding to sphere observations and targeted and multispectral observations of Mars. For each pixel, bias from the 'BI' product is added to the expected 14-bit DN from the 'AS' product, and if the saturation limit is crossed, the pixel is declared bad. The correction for detector ghosts subtracts the scaled, bias- removed DN from each quadrant from every other quadrant of the detector. Scaling coefficients are stored in the 'GH' CDR6. The nonlinearity correction scales bias- and ghost-removed DN to account for nonlinearity in detector response. Detector- averaged scaling coefficients are stored in the 'LI' CDR6. Pixel-dependent nonlinearity at higher frame rates can be corrected using one of two methods. The primary method is to use the onboard integrating sphere for IR data, and bland regions of Mars for VNIR data. (The sphere is comparable in brightness to Mars in the IR, but much dimmer in the VNIR.) For IR data, pixel-to-pixel effects are partly corrected by imaging the sphere at the same frame rate. For the VNIR a non-uniformity matrix, or flat-field, the 'NU' CDR4, is constructed from images of bland regions of Mars having average albedo and illumination. Several thousand frames of different scenes along-track are averaged to remove effects of non-uniform illumination of the surface due to topography, and the spatial image at each wavelength is normalized by its mean value. The non-uniformity correction is used with VNIR sphere or scene images processed to this point. A backup approach is to use the focal plane lamps, along with a ratio image of lamp illumination to an external flat field (stored in the 'RA' CDR4). This approach is less desirable due to the spatial non-uniformity of focal plane lamp illumination of the detector. Background subtraction. Bkgd(x,lambda,TI,T2,Hz) is a 'BK' CDR4 constructed by applying the D14, BiaT, and K corrections to a shutter-closed IR measurement interspersed with Mars measurements. The actual background subtracted from a scene measurement is a time-weighted average of preceding and subsequent 'BK' shutter-closed measurements, to allow for the continuous variation of IR thermal background as spectrometer housing temperature changes. Scattered light subtraction. Scat(x,lambda,TV,TI,T2,Hz) is the stray light subtraction, and includes two components. The first component is glare from the gratings, which produces a low level of light at a distance of tens or more of pixels from a source. For the VNIR detector, this component of scattered light is measured directly at each row of the detector as the mean level in the scattered light columns at a given row. The locations of the scattered light and scene pixels are stored in the 'DM' CDR4. It is then extrapolated across the detector using a function based on signal at the shortest wavelengths (UV), which is dominated by scatter. The shape of he function varies as a function of wavelength. For the IR detector, transient bad pixels render this correction noisy so instead this correction was derived using a bland, dusty scene on Mars, applying the correction both to the scene and to the accompanying sphere measurement. The extrapolation across the field of view uses a function resempling that at the longest VNIR wavelengths. The correction was then median filtered and multiplied into the sphere radiometric model. Given the derivation of the IR scattered light correction, it is most accurate for uniformly illuminated scenes. The second component of scattered light is the second-order light leaked through zone 3 of the IR order sorting filter. This is removed by scaling and subtracting the measured signal at second order wavelengths from the measured first-order signal in zone 3. For each detector row (wavelength), which second- order rows to use and their weightings are stored in the 'LL' CDR4. Responsivity correction using sphere data. RST(x,lambda,TV,TI,T2,T3,S) is spectral responsivity derived from onboard sphere calibration images. It is calculated by processing a sphere measurement through the aforementioned steps with two exceptions, and dividing by exposure time to create an 'SP' CDR4. The exception is that the background image is taken looking into the unilluminated sphere instead of with the shutter closed, in order to subtract out the blackbody radiation of the sphere's structure. The 'SP' product is corrected for non-reproducibility in shutter position by measuring the 'peak' in sphere DN/ms near VNIR detector row 232, and scaling a multiplicative correction stored in the 'SH' CDR4 by the magnitude of that peak. The SP CDR4 is divided by the sphere spectral radiance model stored in the 'SS' CDR4 to derive a snapshot of instrument responsivity. The model uses as an input the choice of sphere bulb, and the telemetered sphere temperature to account for temperature-dependence of the photodiode that drives the sphere's closed loop control. The actual responsivity applied to any scene measurement is a time-weighted average of responsivities derived from preceding and subsequent sphere measurements, to allow for continuous variation in temperatures of the sphere and IR detector. In the case of the VNIR detector, interpolated responsivity is further corrected for differences in detector temperature from the times of sphere measurement, using telemetered detector temperatures and the 'TD' CDR4. M(x,lambda,Hz) applies the detector mask in the 'DM' CDR4, flagging non-scene data (e.g. scattered light and masked pixels) with a value of 65535. This is a standard value for missing or 'bad' (saturated) data. Converting radiance to I/F. RD(x,lambda) is the observed spectral radiance in W/m2/steradian/um at the instrument aperture, and is the output of the preceding steps for a scene measurement. That radiance may be converted to I/F by dividing by squared solar distance (stored in EDR and TRDR labels) and the solar irradiance model stored in the 'SF' CDR4. That model is itself derived convolving a predicted solar spectrum with the measured center wavelength (stored in the 'WA' CDR4) and spectral bandpass (stored in the 'SB' CDR4) of every detector element. Data ==== DATA DESCRIPTION: There is only one data type associated with this volume, the Targeted Reduced Data Records or TRDRs. The TRDR consists of the output of one of the constituent macros associated with a target ID that contains scene data (Mars or other). Not all EDRs are processed to TRDR level; those containing bias, background, sphere, or calibration lamp data are processed instead to CDRs. Only scene EDRs are processed to the TRDR level. The TRDR contains one or more multiple-band images (suffix *.IMG). One matches the dimensions of the multiple-band image of raw DN in an EDR, except that the data are in units of radiance. The size of the multiple-band image varies according to the observation mode but is deterministic given the ID of the command macro used to acquire the data. Appended to the multiple-band image is a binary table of the detector rows that were used, as selected by the wavelength filter. This is a one-column table, with each row containing one detector row number expressed as a 16-bit unsigned integer values, most significant bit first. Other multiple-band images may contain I/F, Lambert albedo, or derived summary products. The I/F and Lambert albedo images, if present, parallel the structure of the radiance image except lack the list file. The summary products image has the same spatial dimensions, but a different dimension in the spectral direction and it lacks that table of row numbers. Each of these three multiple-band images has its own label. There are 45 summary parameters, as follows: SURFACE PARAMETERS: from Lambert albedo NAME: R770 PARAMETER: 0.77 micron reflectance FORMULATION *: R770 RATIONALE: rock/dust ratio NAME: RBR PARAMETER: red/blue ratio FORMULATION *: R770 / R440 RATIONALE: rock/dust ratio NAME: BD530 PARAMETER: 0.53 micron band depth FORMULATION *: 1 Ð (R530/(a*R709+b*R440)) RATIONALE: crystalline ferric minerals NAME: SH600 PARAMETER: 0.60 micron shoulder height FORMULATION *: R600/(a*R530+b*R709) RATIONALE: select ferric minerals NAME: BD640 PARAMETER: 0.64 micron band depth FORMULATION *: 1 Ð (R648/(a*R600+b*R709)) RATIONALE: select ferric minerals, especially maghemite NAME: BD860 PARAMETER: 0.86 micron band depth FORMULATION *: 1 Ð (R860/(a*R800+b*R984)) RATIONALE: select ferric minerals NAME: BD920 PARAMETER: 0.92 micron band depth FORMULATION *: 1 Ð ( R920 / (a*R800+b*R984) ) RATIONALE: select ferric minerals NAME: RPEAK1 PARAMETER: reflectance peak 1 FORMULATION *: wavelength where 1st derivative=0 of 5th order polynomial fit to R600, R648, R680, R710, R740, R770, R800, R830 RATIONALE: Fe mineralogy NAME: BDI1000VIS PARAMETER: 1 micron integrated band depth; VIS wavelengths FORMULATION *: divide R830, R860, R890, R915 by RPEAK1 then integrate over (1 - normalized radiances) RATIONALE: crystalline Fe+2 or Fe+3 minerals NAME: BDI1000IR PARAMETER: 1 micron integrated band depth; IR wavelengths FORMULATION *: divide R1030, R1050, R1080, R1150 by linear fit from peak R between 1.3 - 1.87 microns to R2530 extrapolated backwards, then integrate over (1 - normalized radiances) RATIONALE: crystalline Fe+2 minerals; corrected for overlying aerosol induced slope NAME: IRA PARAMETER: 1.3 micron reflectance FORMULATION *: R1330 RATIONALE: IR albedo NAME: OLINDEX PARAMETER: olivine index FORMULATION *: (R1695 / (0.1*R1050 + 0.1*R1210 + 0.4*R1330 + 0.4*R1470)) - 1 RATIONALE: olivine will be strongly +; based on fayalite NAME: LCPINDEX PARAMETER: pyroxene index FORMULATION *: ((R1330-R1050) / (R1330+R1050)) * ((R1330-R1815) / (R1330+R1815) RATIONALE: pyroxene is strongly +; favors low-Ca pyroxene NAME: HCPXINDEX PARAMETER: pyroxene index FORMULATION *: ((R1470-R1050) / (R1470+R1050)) * ((R1470-R2067) / (R1470+R2067) RATIONALE: pyroxene is strongly +; favors high-Ca pyroxene NAME: VAR PARAMETER: spectral variance FORMULATION *: find variance from a line fit from 1 - 2.3 micron by summing in quadrature over the intervening wavelengths RATIONALE: Ol & Px will have high values; Type 2 areas will have low values NAME: ISLOPE1 PARAMETER: -1 * spectral slope1 FORMULATION *: (R1815-R2530) / (2530-1815) RATIONALE: ferric coating on dark rock NAME: BD1435 PARAMETER: 1.435 micron band depth FORMULATION *: 1 - ( R1430 / (a*R1370+b*R1470) ) RATIONALE: CO2 surface ice NAME: BD1500 PARAMETER: 1.5 micron band depth FORMULATION *: 1 Ð ( ((R1510+R1558)*0.5) / (a*R1808+b*R1367) RATIONALE: H2O surface ice NAME: ICER1 PARAMETER: 1.5 micron and 1.43 micron band ratio FORMULATION *: R1510 / R1430 RATIONALE: CO2, H20 ice mixtures NAME: BD1750 PARAMETER: 1.75 micron band depth FORMULATION *: 1 - ( R1750 / (a*R1660+b*R1815) ) RATIONALE: gypsum NAME: BD1900 PARAMETER: 1.9 micron band depth FORMULATION *: 1 - ( ((R1930+R1985)*0.5) / (a*R1857+b*R2067) ) RATIONALE: H2O, chemically bound or adsorbed NAME: BDI2000 PARAMETER: 2 micron integrated band depth FORMULATION *: divide R1660, R1815, R2140, R2210, R2250, R2290, R2330, R2350, R2390, R2430, R2460 by linear fit from peak R between 1.3 - 1.87 microns to R2530, then integrate over (1 - normalized radiances) RATIONALE: pyroxene abundance and particle size NAME: BD2100 PARAMETER: 2.1 micron band depth FORMULATION *: 1 - ( ((R2120+R2140)*0.5) / (a*R1930+b*R2250) ) RATIONALE: monohydrated minerals NAME: BD2210 PARAMETER: 2.21 micron band depth FORMULATION *: 1 - ( R2210 / (a*R2140+b*R2250) ) RATIONALE: Al-OH minerals NAME: BD2290 PARAMETER: 2.29 micron band depth FORMULATION *: 1 - ( R2290 / (a*R2250+b*R2350) ) RATIONALE: Mg,Fe-OH minerals (at 2.3); also CO2 ice (at 2.292 microns) NAME: D2300 PARAMETER: 2.3 micron drop FORMULATION *: 1 - ( (CR2290+CR2320+CR2330) / (CR2140+CR2170+CR2210) ) (CR values are observed R values divided by values fit along the slope as determined between 1.8 and 2.53 microns - essentially continuum corrected)) RATIONALE: hydrated minerals; particularly clays NAME: SINDEX PARAMETER: Convexity at 2.29 _m due to absorptions at 1.9/2.1 microns and 2.4 microns FORMULATION *: 1 Ð (R2100 + R2400) / (2 * R2290) (CR values are observed R values divided by values fit along the slope as determined between 1.8 - 2.53 microns (essentially continuum corrected)) RATIONALE: hydrated minerals; particularly sulfates NAME: ICER2 PARAMETER: gauge 2.7 micron band FORMULATION *: R2530 / R2600 RATIONALE: CO2 ice will be >>1, H2O ice and soil will be about 1 NAME: BDCARB PARAMETER: overtone band depth FORMULATION *: 1 - ( sqrt [ ( R2330 / (a*R2230+b*R2390) ) * ( R2530/(c*R2390+d*R2600) ) ] ) RATIONALE: carbonate overtones NAME: BD3000 PARAMETER: 3 micron band depth FORMULATION *: 1 - ( R3000 / (R2530*(R2530/R2210)) ) RATIONALE: H2O, chemically bound or adsorbed NAME: BD3100 PARAMETER: 3.1 micron band depth FORMULATION *: 1 - ( R3120 / (a*R3000+b*R3250) ) RATIONALE: H2O ice NAME: BD3200 PARAMETER: 3.2 micron band depth FORMULATION *: 1 - ( R3320 / (a*R3250+b*R3390) ) RATIONALE: CO2 ice NAME: BD3400 PARAMETER: 3.4 micron band depth FORMULATION *: 1 - ( (a*R3390+b*R3500) / (c*R3250+d*R3630) ) RATIONALE: carbonates; organics NAME: CINDEX PARAMETER: gauge 3.9 micron band FORMULATION *: ( R3750 + (R3750-R3630) / (3750-3630) * (3920-3750) ) / R3920 - 1 RATIONALE: carbonates ATMOSPHERIC PARAMETERS: from I/F NAME: R440 PARAMETER: 0.44 micron reflectance FORMULATION *: R440 RATIONALE: clouds/hazes NAME: IRR1 PARAMETER: IR ratio 1 FORMULATION *: R800 / R1020 RATIONALE: Aphelion ice clouds vs. seasonal or dust NAME: BD1270O2 PARAMETER: 1.265 micron band FORMULATION *: 1 - ( (a*R1261+b*R1268) / (c*R1250+d*R1280) ) RATIONALE: O2 emission; inversely correlated with high altitude water; signature of ozone NAME: BD1400H2O PARAMETER: 1.4 micron band depth FORMULATION *: 1 - ( (a*R1370+b*R1400) / (c*R1330+d*R1510) ) RATIONALE: H2O vapor NAME: BD2000CO2 PARAMETER: 2 micron band FORMULATION *: 1 - ( R2010 / (a*R1815+b*R2170) ) RATIONALE: atmospheric CO2 NAME: BD2350 PARAMETER: 2.35 micron band depth FORMULATION *: 1 - ( (a*R2320+b*R2330+c*R2350) / (d*R2290+e*R2430) ) RATIONALE: CO NAME: IRR2 PARAMETER: IR ratio 2 FORMULATION *: R2530 / R2210 RATIONALE: aphelion ice clouds vs. seasonal or dust NAME: BD2600 PARAMETER: 2.6 micron band depth FORMULATION *: 1 - ( R2600 / (a*R2530+ b*R2630) ) RATIONALE: H2O vapor NAME: R2700 PARAMETER: 2.70 micron reflectance FORMULATION *: R2700 RATIONALE: high aerosols NAME: BD2700 PARAMETER: 2.70 micron band depth FORMULATION *: 1 - ( R2700 / (R2530*(R2530/R2350)) ) RATIONALE: CO2; atmospheric structure (accounts for spectral slope) NAME: IRR3 PARAMETER: IR ratio 3 FORMULATION *: R3750 / R3500 RATIONALE: aphelion ice clouds vs. seasonal or dust Note *: 'a', 'b', 'c', 'd', 'e' in band depth formulations represent fractional distances between wavelengths wavelength; for example, given BD(c), a band depth at a central wavelength 'c' with nearby continuum points defined at shorter and longer wavelengths 's' and 'l': BD(c) = 1 - R(c) / (a*R(s) + b*R(l)), where a = 1 - b and b = (lambda(c) - lambda(s)) / (lambda(l) - lambda(s)) DATA DIMENSIONALITY: The size of the multiple-band image varies according to the observation mode but is deterministic given the ID of the onboard macro the generated the data. A typical multiple-band image might have XX pixels in the sample (cross-track) dimension, YY pixels in the line (along-track) dimension, and ZZ pixels in the wavelength dimension, where: XX=640/binning, where binning is 1, 2, 5, or 10, and dark is the number of masked and scattered light pixels YY=the number of frames of data taken by the macro, and ZZ=the number of rows (wavelengths) that are retained by the instrument. The data in a TRDR do not have optical distortions removed. In one column, the projection onto Mars' surface may vary by as much as +/-0.4 not-binned detector elements in the XX dimension depending on position in the FOV (distortions are worst at the edges of the VNIR and IR FOVs). For a single wavelength, its location in the ZZ direction may vary by as much as +/-1 not-binned detector elements depending on wavelength and position in the XX direction (distortions are worst at the short- and long- wavelength ends of the IR detector). To correct for optical distortions, multiband images may be resampled in the spectral or spatial direction. Three types of resampling may have occurred: (a) resampling in the wavelength direction occurs using nearest-neighbor resampling, as coded in the PS CDR; (b) resampling in the spatial direction, to remove differences in spatial scale with wavelength or band, is done with bicubic interpolation using the CM CDR; and (c) VNIR data may be rescaled to match the slightly different magnification of the IR spectrometer, also using bicubic interpolation and the CM CDR. A resampled TRDR is distinguished by values of the keywords MRO:SPATIAL_RESAMPLING_FLAG, MRO:SPATIAL_RESCALING_FLAG, and MRO:SPECTRAL_RESAMPLING_FLAG. Components of the TRDR are generated at a different times and therefore may have non-synchronous version numbers. The list file can be created nearly as soon as data are received. The radiance or I/F multiple-band image requires bracketing sphere observations to process and so it might be delayed by days. Construction of the summary product or Lambert albedo multiband images requires an accompanying DDR. Thus, following the protocol for DDR creation, version 0 summary product or Lambert albedo TRDR images represent values based on predicted pointing, generated to provide quick-look information. Version 1 and subsequent versions are based on actual, reconstructed pointing. Ancillary Data ============== There are various types of ancillary data provided with this dataset: 1. SPICE kernels, used to contruct observational geometry, are available in the GEOMETRY directory. See GEOMINFO.TXT for more details. 2. The BROWSE directory contains browse images in PNG format, and HTML documents that support a web browser interface to the volume. See BROWINFO.TXT for more details. Coordinate System ================= The cartographic coordinate system used for the CRISM data products conforms to the IAU planetocentric system with East longitudes being positive. The IAU2000 reference system for Mars cartographic coordinates and rotational elements was used for computing latitude and longitude coordinates. Media/Format ============ The CRISM archive will be made available online via Web and FTP servers. This will be the primary means of distribution. Therefore the archive will be organized as a set of virtual volumes, with each data set stored online as a single volume. As new data products are released they will be added to the volume's data directory, and the volume's index table will be updated accordingly. The size of the volume will not be limited by the capacity of the physical media on which it is stored; hence the term virtual volume. When it is necessary to transfer all or part of a data set to other media such as DVD for distribution or for offline storage, the virtual volume's contents will be written to the other media according to PDS policy, possibly dividing the contents among several physical volumes." CONFIDENCE_LEVEL_NOTE = " Confidence Level Overview ========================= Four major sources of uncertainty in the interpretation of radiance, I/F, or Lambdert albedo images in TRDRs include: (a) Random noise in the data due to statistical uncertainties in counting photons. This is manifested as noisy calibrated data. Noise is most significant in darker areas. Typically, the signal to noise ratio at <2500 nm is 400 in bright areas and 200 in dark areas, in the constituent observations, before pixel binning. (b) Optical distortion can affect spectra of small-scale features. In one column, the projection onto Mars' surface may vary by as much as +/-0.4 not-binned detector elements in the XX dimension depending on position in the FOV (distortions are worst at the edges of the VNIR and IR FOVs). For a single wavelength, its location in the ZZ direction may vary by as much as +/-1 not-binned detector elements depending on wavelength and position in the XX direction (distortions are worst at the short- and long-wavelength ends of the IR detector). In other words, different wavelengths include slightly different combinations of signal from spatially adjacent pixels, so that compositional interpretations of features near the scale of a pixel are weakly wavelength-dependent. Also, wavelengths drifts across the field of view. Compositional interpretations based on exact wavelengths of absorptions may thus be weakly spatially dependent. The resampling approach outlined above can remove much of this uncertainty. To correct for optical distortions, multiband images may be resampled in the spectral or spatial direction. Three types of resampling may have occurred: (a) resampling in the wavelength direction occurs using nearest-neighbor resampling, as coded in the PS CDR; (b) resampling in the spatial direction, to remove differences in spatial scale with wavelength or band, is done with bicubic interpolation using the CM CDR; and (c) VNIR data may be rescaled to match the slightly different magnification of the IR spectrometer, also using bicubic interpolation and the CM CDR. A resampled TRDR is distinguished by values of the keywords MRO:SPATIAL_RESAMPLING_FLAG, MRO:SPATIAL_RESCALING_FLAG, and MRO:SPECTRAL_RESAMPLING_FLAG. (c) In order to distinguish spectrally similar minerals that have different geological implications for their environments of formation, adequate spectral resolution is necessary. This requires sufficiently high density spectral sampling, as well as a sufficiently narrow full width half maximum (FWHM) of the instrument response in the spectral direction. This 'slit function,' the effective bandpass for a single detector element, represents the convolution of spectral sampling and the point-spread function in the spectral direction. CRISM's benchmark is distinguishing the minerals montmorillonite and kaolinite, which form in hydrothermal environments under different temperature regimes [SWAYZEETAL2003]. The requirements for this are (a) <20 nm FWHM and (b) sampling of the spectrum at this is smaller increments. CRISM's spectral sampling requirement is <10 nm/channel to provide oversampling, and the actual performance is better at 6.55 nm/channel. FWHM is 8 nm in the VNIR across the FOV. In the IR it increases from 10 nm at short wavelengths to 15 nm at the longest wavelengths at the center of the FOV, and broadens by about 2 nm at 0.8 degrees from the center of the field of view. Outside +/-0.9 degrees from the center of the field of view the telescope is slightly vignetted, so further degradation is expected at extreme field angles. Although the spectral sampling and resolution meet requirements, their variation across the field-of-view must be accounted for when comparing with rock and mineral analog spectra. (d) There are several instrument artifacts that are corrected in the calibration pipeline. Residual errors in the corrections will introduce systematic errors into the data. Seven most significant artifacts were found early enough during calibration either to be corrected, or to be characterized sufficiently to be largely removed during processing. First, the boundary of zones 1 and 2 of the VNIR order sorting filter is a joint between two distinct glasses with different indices of refraction. When illuminated during detector-level tests, it was found to cause significant (>10%) scattered light at shorter wavelengths (<670 nm). This was correcting by replacing the VNIR focal plane assembly with the flight spare, onto which a narrow black stripe was painted to shadow the joint. The black stripe attenuates the light from 610-710 nm and causes a dip in response at those wavelengths. In the processed data, the are two major effects: signal to noise ratio is decreased, and non-reproducibility of the exact position of the shutter when observing the sphere causes shifting of the shadow in the wavelength direction. Measurement and correction of this effect are discussed below. Second, the linearity of both detectors was found to be extraordinarily sensitive to the bias voltage applied. Upon discovery of this during detector-level testing, the voltage was modified from 5 to 4.8 V to lessen the effect. The residual non-linearity is characterized in a level 6 CDR and removed during calibration. Third, CRISM's gimbal housing has a gap between two segments of its planet facing radiator, in order to simultaneously maintain the cooler bodies at >248K and the optics at about 213K. During ad hoc testing for scattered light (performed by walking a flashlight around the gimbal housing with a mounted but unaligned VNIR detector), a sneak path for undispersed light to the VNIR detector was discovered. This was easily fixed by covering the VNIR FPA with thermal blanketing, but the result was a heat leak from the FPA to the spectrometer housing, raising spectrometer housing temperature to near is maximum desired value of -75C. To remediate the heat leak, VNIR operating temperature was modified from -20C, intended originally, to -60C. Fourth, the original 'open' position for the shutter at step 0 of 33 was found to create a ghost image of the scene approximately 1 degree out of the FOV in the cross-slit direction, with a magnitude up to 10-30% of the primary scene. This was remediated by a software fix, in which 'open' was redefined to position 3, which moves the origin of the ghost image to an angle further from the FOV at which it is baffled by the telescope. Secondary artifacts created by this fix are discussed in more detail below. Fifth, zone 1 of the IR order sorting filter was found to have a red leak at >4200 nm, beyond CRISM's nominal wavelength range but within the spectral range at which the detector responds. Hence, thermal background is unexpectedly large at 1000-1700 nm in the IR. This was discovered too late for redesign of the filter; the main effect is decreased - but still high - SNR at the affected wavelengths. Sixth, it was intended originally that the maximum wavelength would be 4050 nm - compared to MRO's requirement of =>3600 nm - in order to cover the center of the strong carbonate band at 3980 nm. Due to tolerances in the manufacturing process, the peak response of the zone 3 linearly variable filter was mismatched from the peak required for 4050 nm light to fall on the detector. The mismatch was greater than the 80-nm bandpass of the filter. To maintain responsivity at >2700 nm, a long- wavelength cutoff of 3920 nm was accepted to properly align the filter with light dispersed from the gratings. Finally, the spectrometer slit - which defines the mapping of wavelengths to detector rows as well as the spatial FOV - is mounted on a curved surface whose axis of curvature is parallel to the wavelength direction. The slit assembly is fixed with pins through holes whose diameters are oversized to provide margin for fastening the assembly. During instrument-level vibration testing, the slit assembly shifted in the wavelength direction by the tolerance in the hole diameters, shifting wavelength calibration by about 15 nm in both the VNIR and IR. Although vibration testing exceeded expected launch vibrations by about 50%, additional shifting of the slit assembly during launch cannot be ruled out. If it occurred, it can will be calibrated out using the measured positions of Martian atmospheric gas absorptions. All except one of remaining artifacts are relatively minor and/or have straightforward (though sometimes tedious) corrections, discussed below. The coefficients needed for each correction are maintained in a level 4 or level 6 CDR, and applied during calibration of EDRs to TRDRs. The leak of second order light into the >2800 nm wavelength range of the IR detector is the only major correction. Electronics Effects =================== Housekeeping errors: Both responsivity and bias of the VNIR and IR detectors have to be corrected for small differences in detector temperature between measurements of scenes and measurements of internal calibration sources. The required detector temperature measurement precision is approximately 0.3K. Relatively late during calibration, it was found that raw values of temperatures telemetered by the IR focal plane electronics (including both redundant detector temperatures) were being perturbed by up to 2K by changes in current loads on the board. These variations in current result from normal operations like changing frame rate, running lamps, or running a cooler. A large number of ground calibration frames afforded many cases in which loads changed while temperature remained constant, and these cases occurred over temperatures that span the operating range, allowing derivation of the correction of telemetry values at each frame rate to their corresponding values at 1 Hz. These corrections are maintained in a level 6 CDR. Errors in this correction will propagate into corrections for detector temperature as discussed below. Electronics ghost: Both detectors, but especially the VNIR detector, are subject to a weak ghost image of any illuminated spot into its corresponding location in every other of the four 160-column quadrants of the of the 640-column detector. This is a small effect at the <1% level, and is removed by scaling the image of each quadrant by an empirically determined value that is nonlinearly related to signal level, and then subtracting the scaled quadrant image from that of every other quadrant. The scale factors are maintained in a level 6 CDR. To the uncertainties in measurement, each of the four quadrants in a detector behaves only slightly differently. There is a minimal effect of frame rate, but ghost magnitude is apparently unaffected by detector temperature. Errors in this correction could be manifested as anomalously dark or bright spots exactly one-fourth of the detector width away (160 samples, 80 2x-binned samples, 32 5x-binned samples, or 16 10x-binned samples. Detector-averaged non-linearity: As mentioned previously, both detectors exhibit slightly nonlinear response to input signal. This was characterized using a matrix of measurements at each frame rate, in which both the level of a well-calibrated light source and exposure time were varied. Both types of modulation of total signal produce indistinguishable results. This testing has been repeated inflight by imaging a focal plane lamp at multiple exposure times at each frame rate. Nonlinearity is described in a level 6 CDR by a logarithmic function of bias- and ghost-corrected DN; corrections for flight data scale DN level by the ratio of relative responsivity at that DN to the responsivity at a reference DN level. Errors in the linearity correction are most likely to be manifested processed data in the following ways: anomalously high or low value at the extreme wavelengths in either the VNIR or IR detector inaccuracy in the ratio of values at wavelengths inside and outside strong absorptions (2700 nm CO2, 3000 nm H2O) Pixel-dependent non-linearity: At higher frame rates (15 and 30 Hz), the detector-averaged behavior described above appears inadequate to fully characterize nonlinearity, and individual pixels exhibit slight variations. These are corrected using known, smooth fields of approximately the same brightness as Mars. In the IR the onboard integrated sphere provides a sufficiently high signal to measure and remove this effect. In the VNIR the sphere's signal is not sufficient at all wavelengths, and instead smeared measurements of Mars are used to construct the correction. Errors in this correction would appear a systematically low or high wavelengths (bands) when observed at a particular detector column. Optical Effects =============== Shutter position irreproducibility. In order to illuminate the spectrometer slit's full 2.12 degree field of view, CRISM's telescope illuminates a circular region of slightly larger diameter surrounding the slit. The base of the shutter, on the hinge end, just protrudes into the illuminated area. At position 0, originally intended as the 'open' position, the reflective rear surface of the shutter provides the detectors an unbaffled view of the scene approximately 1 degree from the center of the field of view in a cross-slit direction, creating an out-of-focus 'ghost' image of that location. Moving the shutter through successive steps redirects the angle from which the ghost image originates to further from the center of the FOV. At position 3, the angle from which the ghost image originates is baffled by the telescope, and the ghost disappears. To remediate the ghost image, the open position of the shutter is defined in software to position 3. At position 3 the shutter attenuates up to 10% of the light coming from an external scene, depending on the wavelength. The short- wavelength zone of the VNIR grating and the long-wavelength zone of the IR grating are blocked preferentially. In frames that view the integrating sphere, ratioing successive views of the sphere (between which the shutter is moved) creates a distinctive wavelength-dependent pattern in which brightness of the sphere is non-repeatable by up to a few percent. This is explained by a small (about 0.1 degree) non-reproducibility in the angle at which the sphere is viewed and the fact that, unlike the external scene, the spectrometer's view of the sphere is vignetted by the sphere's aperture. With a slight shift in shutter position, the cone of sphere light entering spectrometer optics shifts. The filling of dual zone gratings changes slightly, decreasing responsivity at long VNIR wavelengths and short IR wavelengths. Also, the shadow of the black strip on the VNIR order-sorting filter zone boundary shifts, creating a distinctive trough and peak pattern at detector rows 222-235 (approximately 605-690 nm). Because this effect is so characteristic as a function of wavelength, it is easily correctable. Ratios of different sphere observations during ground calibration are used to create a multiplicative correction to a sphere image as a function of wavelength, that is maintained in a level 4 CDR. In flight data to be corrected, the magnitude of the peak near VNIR row 235 is measured. The correction is scaled by the magnitude of the peak, and it is multiplied by the data. The VNIR row 235 peak is used to scale the corrections for both the VNIR and IR. Errors in this correction would lead to high or low values especially at 600-700 nm, with the error being systematic within a group of observations processed using a single sphere observation, but random between such groups of observations. Put differently, the systematic errors would change every few orbits. To the limits of measurement error, the small irreproducibility of shutter position at the 'open' position has no measurable effect on external scene data. IR second order leakage: Zone 3 of the IR order sorting filter admits up to 3% of the 2nd order light from the grating, at wavelengths 1400-1950 nm, that falls at detector rows whose nominal wavelengths are 2800-3900 nm. The leakage peaks at a nominal wavelength of 3400 nm. Due to the falloff of both the solar spectrum and the Martian reflectance spectrum with increasing wavelength, the relative magnitude of the leakage to the signal in zone 3 is enhanced so that it becomes tens of percent of the total signal in that wavelength range. Ground testing provided sufficient data for an empirical correction for this effect, in which scaled values of signal at second-order wavelengths are subtracted from first-order (nominal) wavelengths. The correction is maintained in a level 4 CDR. Errors in this correction would be manifested in processed data as a negative positive additive component to the values from 2760-3920 nm, centered and strongest at 3400 nm. Temperature Effects =================== Bad pixels: The IR detector is operated at cryogenic temperature to minimize dark current and bias level of the detector. With increasing detector temperature, not all pixels accrue an elevated bias level or dark current - the latter of which adds noise due to its electron counting statistics - at the same rate. The most susceptible pixels, within which effective SNR or available dynamic range are adversely impacted, are 'bad pixels.' Bad pixels are identified routinely during internal calibrations, and recorded in level 4 CDRs. In the contruction of TRDRs, bad pixels are interpolated over. The effect on processed data is local wavelength-dependent 'blurring,' but the locations are known in the bad pixel masks. Appearance of a new bad pixel not recorded in a level 4 CDR would result in an anomalous and/or noisy value at a particular wavelength (band) at the same detector column (sample) position. Bias levels: Bias is the response of the detector to zero input signal from light or thermal background, and includes two components. One component is a fixed pattern that varies pixel-to-pixel +/-25 14-bit DN's, and has a weak columnar organization. The second component is a step function of about 20 14-bit-DNs that occurs at some row of the detector. The row at which this occurs moves systematically with frame integration time. The fixed-pattern component of bias depends on frame rate, differing by about 100 14-bit DNs between frame rates. It also varies with detector temperature and temperature of the focal plane electronics. To the limits of measurement uncertainty, the temperature dependence itself is independent of quadrant or frame rate. Bias is routinely measured via dedicated calibrations and recorded in level 4 CDRs, and is adjusted for changes in detector or focal plane electronics temperature based on telemetered temperatures, using scaling factors maintained in level 6 CDRs. The step function is modeled and removed using a function described in a 6 CDR. Errors in the temperature corrections to bias would be manifested in processed data as a negative positive additive component to the values at all wavelengths. Errors in removal of the step function would be manifested in processed data as systematically positive or negative feature at the same wavelength (band) position at all spatial (sample) positions. Sphere radiance: Under closed-loop control, the brightness of either of the integrating sphere's lamps is measured by a Si photodiode that adjusts current up or down to reach a commandable brightness goal. The responsivity of the Si in the photodiode is affected by temperature at >900 nm, becoming more sensitive to light at warmer temperatures. So, as sphere temperature increases and the Si becomes more photosensitive, the same commanded goal requires less lamp current. Sphere radiance is modeled based on ground calibration at different operating temperatures, which were measured by comparing against stable external sources. Output radiance for each sphere bulb at the commanded brightness goal is calculated at every pixel of each detector as a function of telemetered sphere temperature; model coefficients are maintained in level 4 CDRs. Errors in the basic sphere model will be manifested in processed data as errors in the long wavelength-scale shape of the spectrum. Errors in the temperature correction will appear similarly, and will be most significant at shorter wavelengths. Detector responsivity: Both the VNIR and IR detectors exhibit dependence of their spectral responsivities on detector temperature. In the VNIR detector, the +/-1K thermostatic cycling of the detector heater on the timescale of minutes affects responsivity at >900 nm by up to a few percent, due to the temperature-dependence of Si photosensitivity at those wavelengths. These differences in responsivity are corrected using a function of telemetered detector temperature, whose coefficients are maintained in a level 4 CDR. Errors in this correction will appear in processed data as systematically too high or too low values at >900 nm, more so at the longer wavelengths. In the IR detector, the longest wavelengths (especially zone 3) exhibit a cyclical pattern of responsivity variation as a function of wavelength. The pattern is interpreted as Fabry-Perot fringes due to interference by long-wavelength light that penetrates the HgCdTe detector material which - at those wavelengths - is only a few wavelengths thick. The pattern shifts systematically as a function of detector temperature due to thermal expansion of the detector material, creating responsivity differences at about the 5% level. The change in temperature required to introduce these artifacts at the level of noise in the data is near 0.25K. To correct for this, the sphere will be measured repeatedly as detector temperature changes, and the sphere used as a relatively stable reference against which to calibrate out these effects. Errors in this correction will lead to residual, high spectral frequency (about 25-nm period) ripples in the values at 2760-3920 nm. Post-calibration Corrections ============================ In data calibrated to Lambert albedo, atmospheric conditions are assumed for a given latitude, longitude, solar longitude, and elevation, based on TES climatology. Actual weather conditions, especially aerosol composition and abundance, may vary. The pronounced artifacts of errors in the assumed atmospheric conditions are errors in spectral slope and in the depth and shape of absorption features due to water ice near 1.4, 1.9, and 3 microns. VNIR Calibration Versions ========================= Version 0 was the first version of VNIR radiometric calibration applied to flight data. Five major sources of inaccuracy and image artifacts were identified. The first arose from the method by which scattered light from the grating was extrapolated from scattered light columns across the scene. A simple linear interpolation was applied, and this underestimated the total scattered light within the scene. When this procedure was applied to ground calibration data to derive a model for sphere radiance, results include an unrealistically red spectral slope. When applied to flight measurements of Mars and the integrating sphere, results include residual cross-track (along-slit) color variations. The second problem arose from the choice of which sphere bulb to use as the primary calibration source. Originally it was the bulb controlled by the VNIR focal plane electronics. However, for unknown reasons, this bulb yields much greater scatter from the grating than does the bulb controlled by the IR focal plane electronics. Residuals within the shadow of zones 1 and 2 of the wavelengths order sorting filter led to a large negative artifact at 600-700 nm. The third problem arose from low light levels in the sphere at <560 nm. That is, measured sphere signal levels are low enough that they introduced systematic noise at short wavelengths into observations calibrated using them. The fourth problem arose from propagated statistical errors in sphere measurements used to calibrate the data. That is, corrections for all of the artifacts outlined above require a series of algebraic operations each of which propagates small errors or effects of noise. The sphere data require more corrections, and at lower-signal wavelengths the residual errors at each detector element are manifested as a spuriously high or low value at the corresponding wavelength and spatial position. This can appear as wavelength-dependent striping in the along-track direction. Fifth, it was discovered that the bias varies image to image, leading to striping in the cross-track direction in processed data. Version 1 used an arbitrary scaling across of scattered light from the grating across the field of view, in an attempt to remediate the first two effects. It proved unsuccessful, and was abandoned after validation of the first observations to which it was applied. Version 2 addresses and largely corrects each of the five major problems with version 0. First, there is a more sophisticated extrapolation from the scattered columns. At short wavelengths, the distribution is measured from measured signal at UV wavelengths. The detector is nearly unresponsive to UV signal from Mars, so in most regions the nominally UV wavelengths instead provide a measure of the scattered light at the corresponding position along the slit. This gradually transitions with longer wavelength to a linear extrapolation between the scattered light columns, as with version 0. This correction is applied both to ground calibration data used to derive the sphere radiance model, and to flight scene and sphere data. Second, the sphere bulb controlled by the IR focal plane electronics is used as the primary radiometric reference, because the lower scattered light from it is more easily corrected and leaves lesser artifacts at low-signal wavelengths. Third, calibration of the data is handled differently at <560 nm and at >560 nm. At longer wavelengths, sphere measurements and the sphere radiance model traceable to ground measurements are used to determine a snapshot of detector responsivity, and apply that to scene data to derive radiance. This is appropriate because of temperature dependendence of optical throughput, especially the beamsplitter, at >560 nm. At shorter wavelengths, responsivity is derived directly from ground calibration measurements, and low-signal sphere data are not used. The approach has consistently yielding nearly identical, continuous results at the wavelengths at which the two approaches overlap, about 530-600 nm. Fourth, to eliminate propagation of statistical errors in processing of sphere data, the sphere-derived responsivity at each wavelength is averaged. Correction for spatial nonuniformity occurs using a Mars flat-field calibration and the NU CDR derived from it. Fifth, to remove frame-to-frame variations in bias, an additive correction is applied to each frame while still in units of DN, to make the physically masked columns at the edge of the detector zero after dark subtraction. There are two alternate versions of VNIR version 2 specifically for special types of observations. The bland Mars scenes used to measure non-uniformity are processed to version 9 TRDRs. The version 9 processing is the same as version 2 except it doesn't include the non-uniformity correction. Deimos, Phobos, and any other pointlike or compact targets like stars are processed to version 8 TRDRs. The major difference in the processing for such scenes is that within-scene scattered light from the grating is much less, so the correction for intra-scene scattered light is skipped. The VNIR version 8 processing uses special version 8 'SS' and 'NU' CDR4s. Known Issues with VNIR Radiometric Calibration ============================================== Version 2 has been validated using observations of the MER Spirit and Opportunity landing sites, with PANCAM measurements that were modeled at the top of the atmosphere using CRISM viewing geometry and solar longitude. Five artifacts or data quality concerns remain. (a) Radiance at <410 nm is typically low, because there is not much signal at those wavelengths and they are most susceptible to artifacts from scattered light subtraction. (b) Some artifact at the wavelengths of the filter zone boundary. In some parts of the field of view at sharp brightness contrasts it extends to 644-684 nm. (c) Scenes with large coverage by ice, especially near either edge of the field of view, have more significant artifacts from the scattered light correction because, unlike typical Martian soils, ice has significant UV reflectance and that decreases accuracy of the correction. Typical effects may include degradation at wavelengths below 480 nm and above 1010 nm. (d) Due to spectral smile, mineralogic absorptions located where instrument response varies steeply with wavelength exhibit variation with field angle. This is most prominent with Fe mineral absorptions near 900 nm. IR Calibration Versions ========================= Version 0 was the first version of IR radiometric calibration applied to flight data. Five major sources of inaccuracy and image artifacts in version 0 are known. The first originated from inadequacy of the bad pixel correction. On ground, three types of bad pixels were observed: hot with high dark current, dead with no response, and noisy. Based on that the bad pixel correction was planned to use dark measurements to identify bad pixels. Inflight, a new type of bad pixel was identified, whereby a detector element abruptly develops high dark current, then abruptly returns to normal. At least 2 percent of pixels, and probably more, display this behavior at some time. This was manifested as sharp, wavelength-dependent striping in the along-track direction in image data. The second problem originated from incomplete correction of bad pixels in ground calibration measurements used to derive the sphere radiance model. This was manifested as diffuse, wavelength-dependent striping in the along-track direction in image data. The third problem was spuriously high radiances near the boundaries of the order sorting filters, especially at 1630-1680 and 2690-2770. A lesser spuriously high radiance occurred at 1800 nm. Spuriously high values also occurred at <1050 nm. The fourth problem was 'bumps' in radiances at 1370 and 1850 nm, water vapor in the beam and adsorbed water on ground calibration sources was under-corrected. The fifth problem was that the correction for leaked second order light at >2700 nm was not implemented in version 0. Version 1 partially corrected problems with version 0 but did not close out known IR calibration issues. First, within-scene bad pixels were identified were interpolated over. For each scene, the entire scene was collapsed to one median frame matching the layout of the detector. Then a median filter was run in the spatial direction. The difference between the median image and the filtered median image was calculated, and detector elements having more than a 1.4 standard deviation difference were identified as bad pixels. These were replaced throughout the scene by the average of the adjacent non-bad pixels at the same wavelength. Second, artifacts in the sphere radiance model were removed using a Mars flat-field calibration and the NU CDR derived from it. However this is not done within strong atmospheric absorptions near 1400, 1600, 2000, and 2700 nm because spectral smile would introduce new artifacts. Third, systematically high radiances at the filter zone boundaries were corrected by smoothing the sphere radiance model. Fourth, the 'bumps' in radiances at 1370 and 1850 were corrected by performing an approximate atmosphere removal on bland, dusty terrain at the summit of Olympus Mons. The magnitude of the 'bumps' was estimated, and the appropriate multiplicative correction to the sphere model to remove them was applied. Version 2 added six further corrections for outstanding issues identified in version 1. First, in version 1, incomplete correction for water vapor in the spectra of ground calibration sources had introduces a 'bump' in radiance at 2550-2650 nm. This wavlength is on the edge of a strong 3-micron absorption in Mars; spectrum, so Olympus Mons observations could not be used to estimate a correction. Instead this artifact was corrected using observations of Deimos, which lacks a 3-micron band. The magnitude of the 'bump' was estimated, and the appropriate multiplicative correction to the sphere model to remove them was applied. Second, smoothing of the sphere radiance model that had been used in version 1 was performed in an attempt to correct anomalously high derived Mars radiances in the 2 channels closest in wavelength to 2700 nm. Third, in version 2 leaked second order light at >2700 nm was corrected. This was performed by subtracting scaled radiances from one-half the wavelength using the 'LL' CDR4s. Fourth, in version 1, the bad pixel correction had been set to too sensitive a threshold, so that abrupt brightness boundaries often triggered the bad pixel correction, leading to aliasing at those boundaries. The threshold for identifying a bad pixel in the median-scene image was increased from 1.4 to 2.4 standard deviations in version 2. Fifth, slight misalignment of the instrument aperture with the ground calibration source intruduced systematic error into the sphere radiance model. This preferentially affected wavelengths below 1500 nm, and in version 1 scene radiances it had introduced a broad, sigmoidal-shaped bump centered near 1400 nm. For version 2, this effect was modeled using grating theory, and a correction for it was applied to the sphere radiance model. Sixth, in version 1, no attempt had been made to remove scattered light from the grating at IR wavelengths, either in scene data or in observations of the internal integrating sphere. The effect was overestimation of IR scene radiance at <1900 nm. In version 2, the correction was introduced. However, unlike the VNIR correction for grating scatter, for the IR detector transient bad pixels render a correction of this form noisy. Instead this correction was derived using a bland, dusty scene on Mars, applying the correction both to the scene and to the accompanying sphere measurement. The extrapolation across the field of view uses a function resembling that at the longest VNIR wavelengths. The correction was then median filtered and multiplied into the sphere radiometric model. Given the derivation of the IR scattered light correction, it is most accurate for uniformly illuminated scenes. There are two alternate versions of IR version 2 specifically for special types of observations. The bland Mars scenes used to measure non-uniformity are processed to version 9 TRDRs. The version 9 processing is the same as version 2 except it doesn't include the non-uniformity correction. Deimos, Phobos, and any other pointlike or compact targets like stars are processed to version 8 TRDRs. The major difference in the processing for such scenes is that within-scene scattered light from the grating is much less, so the correction for intra-scene scattered light is skipped. The IR version 8 processing uses special version 8 SS CDR4s. Known Issues with IR Radiometric Calibration ============================================ Due to spectral smile, mineralogic absorptions located where instrument response varies steeply with wavelength exhibit variation with field angle. This is most prominent at the edge of atmospheric gas absorptions near 1400 and 2000 nm. Summary of VNIR and IR 'bad channels' ===================================== The following channels can be routinely excluded: VNIR: wavelengths less than 410, 644-684, greater than 1023 nm IR: wavelengths less than 1021 nm, 2694 and 2701 nm, and greater than 3924 nm The following channels may be 'degraded' and their quality is observation-dependent. Caution is recommended but the data may be valid. VNIR: Wavelengths less than 442 nm (due to artifacts from scattered light correction in very contrasty scenes) Wavelengths greater than or equal to 970 nm (radiances are observed to misalign with IR radiances; the reason is uncertain but may be related to uncorrected effects of beamsplitter temperature) IR: Wavelengths less than 1047 nm radiances are observed to misalign with IR radiances; the reason is uncertain but may be related to uncorrected effects of beamsplitter temperature) Wavelengths 2660-2800 nm (the reason is uncertain but may be due to problems with correction of water vapor in measurements of the ground calibration sources) Wavelengths greater than 3700 nm (there is a scene dependent turndown in radiances beyond 3700 nm due to unknown causes) Review ====== This archival data set will be examined by a peer review panel prior to its acceptance by the Planetary Data System (PDS). The peer review will be conducted in accordance with PDS procedures. Data Coverage and Quality ========================= For each observation, every EDR is compared against frame-by-frame predictions of commanded instrument state. The results of the comparison are written as a data validation report that accompanies the EDRs for that observation. In the case of a hardware or configuration discrepancy (shutter position, lamp status or level, pixel binning, frame rate, channel selection, power status of detectors), processing of the image data to TRDR level does not occur in order to avoid introducing invalid results, and DDRs are not created. Also, missing frames or portions of frames are replaced with a value of 65535 (this cannot be a valid data value). That portion of the EDR is not further processed, and it also is propagated to a value of 65535 in all layers of the TRDR. Only a subset of instrument configurations represent 'scene' data, as indicated by the keyword MRO:ACTIVITY_ID. Only scene data aimed at Mars have corresponding DDRs. Limitations =========== None." END_OBJECT = DATA_SET_INFORMATION OBJECT = DATA_SET_TARGET TARGET_NAME = "MARS" END_OBJECT = DATA_SET_TARGET OBJECT = DATA_SET_HOST INSTRUMENT_HOST_ID = "MRO" INSTRUMENT_ID = "CRISM" END_OBJECT = DATA_SET_HOST OBJECT = DATA_SET_MISSION MISSION_NAME = "MARS RECONNAISSANCE ORBITER" END_OBJECT = DATA_SET_MISSION OBJECT = DATA_SET_REFERENCE_INFORMATION REFERENCE_KEY_ID = "BUGBYETAL2005" END_OBJECT = DATA_SET_REFERENCE_INFORMATION OBJECT = DATA_SET_REFERENCE_INFORMATION REFERENCE_KEY_ID = "LEESETAL2005" END_OBJECT = DATA_SET_REFERENCE_INFORMATION OBJECT = DATA_SET_REFERENCE_INFORMATION REFERENCE_KEY_ID = "MELLONETAL2000" END_OBJECT = DATA_SET_REFERENCE_INFORMATION OBJECT = DATA_SET_REFERENCE_INFORMATION REFERENCE_KEY_ID = "MURCHIEETAL2004" END_OBJECT = DATA_SET_REFERENCE_INFORMATION OBJECT = DATA_SET_REFERENCE_INFORMATION REFERENCE_KEY_ID = "MURCHIEETAL2006" END_OBJECT = DATA_SET_REFERENCE_INFORMATION OBJECT = DATA_SET_REFERENCE_INFORMATION REFERENCE_KEY_ID = "PELKEYETAL2005" END_OBJECT = DATA_SET_REFERENCE_INFORMATION OBJECT = DATA_SET_REFERENCE_INFORMATION REFERENCE_KEY_ID = "SILVERGLATE&FORT2004" END_OBJECT = DATA_SET_REFERENCE_INFORMATION OBJECT = DATA_SET_REFERENCE_INFORMATION REFERENCE_KEY_ID = "SMITH2004" END_OBJECT = DATA_SET_REFERENCE_INFORMATION OBJECT = DATA_SET_REFERENCE_INFORMATION REFERENCE_KEY_ID = "SMITHETAL1999" END_OBJECT = DATA_SET_REFERENCE_INFORMATION OBJECT = DATA_SET_REFERENCE_INFORMATION REFERENCE_KEY_ID = "SMITHETAL2002" END_OBJECT = DATA_SET_REFERENCE_INFORMATION OBJECT = DATA_SET_REFERENCE_INFORMATION REFERENCE_KEY_ID = "SMITHETAL2003" END_OBJECT = DATA_SET_REFERENCE_INFORMATION OBJECT = DATA_SET_REFERENCE_INFORMATION REFERENCE_KEY_ID = "SWAYZEETAL2003" END_OBJECT = DATA_SET_REFERENCE_INFORMATION OBJECT = DATA_SET_REFERENCE_INFORMATION REFERENCE_KEY_ID = "TROLLETAL2005" END_OBJECT = DATA_SET_REFERENCE_INFORMATION END_OBJECT = DATA_SET END