urn:nasa:pds:context:instrument:hirise.mro 1.0 1.7.0.0 Product_Context 2016-10-01 1.0 extracted metadata from PDS3 catalog and modified to comply with PDS4 Information Model urn:nasa:pds:context:instrument_host:spacecraft.mro::1.0 instrument_to_instrument_host McEwen, A.S., E.M. Eliason, J.W. Bergstrom, N.T. Bridges, W.A. Delamere, J.A. Grant, V.C. Gulick, K.E. Herkenhoff, L.Keszthelyi, R.L. Kirk, M.T. Mellon, S.W. Squyres, N. Thomas, C.M. Weitz, MRO's High Resolution Imaging Science Experiment (HiRISE). J. Geophys. Res. 2007. reference.MCEWENETAL2007 Snyder, J.P., Map Projections - A Working Manual, U.S. Geol. Surv. Professional Paper 1395, 1987. reference.SNYDER1987 HIGH RESOLUTION IMAGING SCIENCE EXPERIMENT Imager not applicable not applicable Instrument Overview =================== The High Resolution Imaging Science Experiment (HiRISE) is one of the remote sensing instruments on the Mars Reconnaissance Orbiter (MRO) spacecraft that acquires orbital observations of the Martian surface during a two earth-year primary mapping phase. MRO, successfully launched in August 2005, arrived at Mars in March 2006. Following orbit insertion the spacecraft went into an aerobraking period to achieve a 250 x 315 kilometer near-polar orbit suitable for the Primary Science Phase (PSP) mapping that started in November 2006. Since the start of PSP HiRISE has been continuously operating acquiring 5-20 observations per day. The HiRISE camera is a pushbroom imaging system featuring a 0.5 m aperture telescope with a 12 m focal effective length and 14 CCD detectors capable of generating images of up to 20,000 cross-scan observation pixels (exclusive of overlap pixels) and 65,000 unbinned scan lines. The HiRISE instrument capabilities include the acquisition of: (1) observations of the Mars surface from orbit with a ground sampling dimension between 25 and 32 cm/pixel, depending on the orbital altitude, along with an intrinsic point spread function of 1.4 pixels (full width at half maximum assuming no spacecraft jitter) and high signal-to-noise ratio (SNR), (2) high-resolution topographic data from stereo observations with a vertical precision of ~0.2 m over areas of ~5x5 pixels (~1.5 m), and (3) observations in 3 colors with high radiometric fidelity. A key instrument design feature includes Charge Couple Device (CCD) detectors with up to 128 lines of Time Delay and Integration (TDI) to create high (>100:1) SNR in the Red filter bandpass anywhere on Mars. At the nominal 300 km MRO orbital altitude the instrument can acquire image swaths of approximately 6 kilometers cross-orbit and 20 kilometers along-orbit. Scientific Objectives ===================== The high-level science objectives of MRO are to 1) characterize the current climate and mechanisms of climate change, 2) determine the nature of complex layered terrain, 3) identify water-related landforms, 4) search for sites showing evidence for aqueous and/or hydrothermal activity, and 5) identify and characterize sites with the highest potential for landed science and sample return by future missions. Given these objectives, the key HiRISE capabilities in order of priority are: 1) Achieve the best possible spatial resolution and detection of surface features. With a ground sampling dimension between 25 and 32 cm/pixel along with a narrow point-spread function (PSF) and high signal to noise ratio (SNR) we can detect most 1-meter-scale objects or landforms with dimensions of 2 meters. The HiRISE PSF is less then 2 pixels wide at half max when spacecraft jitter is negligible. 2) Achieve high-resolution topographic data from stereo images and Digital Elevation Models (DEMs). HiRISE can achieve a vertical precison of ~0.2 m over areas of ~5x5 pixels (~1.5 meters). 3) Acquire observations in three colors with high radiometric fidelity, for photometric studies such as identification of color/albedo units and photoclinometry. Calibration and Measured Parameters =================================== The radiometric calibration-correction procedure is described here at a high level. A detailed description will be provided in a future HiRISE calibration paper. The radiometric calibration correction is performed on each individual HiRISE channel file (EDR) correcting for instrument offset, dark current, gain, then converting to I/F reflectance. The first step in the calibration, carried out by the ISIS (Integrated Software for Imagers and Spectrometers, http:/isis.astrogeology.usgs.gov/hical) hiclean program, corrects for instrument dark current and offset. The hiclean program uses the ancillary calibration data (dark and mask pixels) that accompany the science data to compute corrections in both the column (sample) and row (line) directions. The mask pixels, positioned at the start of the instrument output, provide dark current information for each column. The dark pixels, positioned at the end of each image row, capture the time dependent dark current and offset instrument drift. The ISIS program then applies an intra-channel B0 (additive dark current matrix) and A0 (multiplicative gain matrix) correction for each column in the image array. The hical then converts the pixel values to I/F (intensity/flux, I/F = 1 for a 100% ideal lambertian reflector viewed normal to the surface) as described below: For: H = dark current and offset corrected image, output of hiclean B0 = intra-channel dark current correction (TDI & BIN dependent) A0 = intra-channel gain correction (TDI and BIN dependent) G = global gain correction, normalizes CCD/channels L = observation line time I = I/F conversion factor at Sun-Target distance of 1.5 AU AU = Mars-to-Sun distance (AU) at time of observation Z = radiometrically corrected image in I/F units The correction is: Z = ([H-(B0?L)]/L)?A0?G*I*(1.5/AU)2 Instrument instabilities result in radiometric mismatches requiring additional corrections for the varying column-to-column, channel-to- channel, and CCD-to-CCD sensitivities. Residual column-to-column variations are corrected by first computing the mean value for each column in an image array. The mean-value one-dimensional array is then high-pass filtered to eliminate low- frequency information due to scene content. The result of the high pass filter is then subtracted from the image array. CCD channels are adjusted to radiometrically match at the seam where the two channels come together. The CCDs are then radiometrically matched one to the other by matching the overlapping areas of adjacent CCDs. Detectors ========= The HiRISE focal plane system consists of 14 independently commanded CCD arrays housed in a focal plane substrate of aluminum-graphite composite material collocated with CCD Processing and Memory Modules (CPMM). Each CCD has 2048 pixels (12x12 ?m) in the cross-scan direction and 128 TDI elements (stages) in the along-orbit direction. The 14 staggered CCDs overlap by 48 pixels at each end (except the outside ends). Electronics =========== The CCD Processing and Memory Module (CPMM) electronics minimizes the number of active and passive components that contribute to noise. The analog signal processing chain between the CCD output amplifier and the 80 Mega Samples per Second 14 bit (pixel value range 0-16,383) Analog to Digital (A/D) converters have been designed so that they add less noise than the CCD while being radiation tolerant and reasonably low power. Each of the 14 CPMM's uses a radiation-hardened Xilinx Virtex 300E Field Programmable Gate Array (FPGA) to perform the control, signal processing, lookup table compression, data storage, maintenance, and external Input/Output. The FPGA is Static Random Access Memory (SRAM) based using a Flash Serial Programmable Read Only Memory (SPROM) for configuration upon power-up. The SPROM and FPGA are reconfigurable so design changes can be applied. Filters ======= HiRISE is a three-color imaging system acquiring observational data in blue-green (band center: 500 nm, bandwidth: 200 nm), red (band center: 700 nm, bandwidth 300 nm), and near infrared (band center: 900 nm, bandwidth 200 nm). Optics ====== The HiRISE design is an all-reflective three mirror astigmatic telescope with lightweight Zerodur optics and a graphite-composite structure. The Cassegrain design with relay optic and two fold mirrors is optimized for diffraction-limited performance. Instrument Modes and Operational Conisderations =============================================== The 14 CCD detector arrays can be independently commanded offering flexibility for how a HiRISE image observation can be acquired. Power requirements on the HiRISE instrument allow all 14 CCD detectors to be simultaneously operated. Not all 14 CCDs need to simultaneously operate to acquire an observation. Depending on the type of observation the color filter CCDs may not need to participate in the observation, for example if color data is not required to satisfy the observational intent. If a narrower cross-orbit swath is desired, the observation may have fewer red- filter CCDs operating. Several data compression methods can be employed to optimize data return. The first compression method uses pixel binning where adjacent pixels in an image are summed equally in the cross-scan and down-scan pixel dimensions (permitted values: unbinned, 2, 3, 4, 8, 16). Binning reduces data volume and increases the pixel SNR, a useful option in low illumination viewing conditions. Different binning modes can be specified for each CCD. A typical HiRISE red-filter observation might acquire unbinned image data for the CCDs in the central portion of the observation where the primary target of interest is located while the peripheral CCDs may be binned to create a context for the primary target. With this flexibility, HiRISE operations can make optimal use of the available data-return volume. A second data compression method converts the 14-bit data stream (16- bit/pixel storage) to 8-bit pixels thereby reducing the returned data volume of an observation by half. The conversion to 8-bit pixels employs look-up tables (LUT) translating the 14-bit values to 8-bit. There are 28 onboard command-selectable LUTs available. Additionally, an on-the-fly LUT can be defined using commanded instrument parameters. Linear and non-linear (square root) methods can be used to define the LUT. A third data compression method employs a lossless data compression system not part of the HiRISE instrument hardware. MRO's Solid State Recorder (SSR) receives and stores data from the HiRISE instrument. A Fast and Efficient Lossless Image Compression System (FELICS) FPGA board is located on the interface between the HiRISE instrument and the SSR to enable compression of the image data before storage on the SSR and subsequent data transmission back to Earth. The FELICS algorithm is expected to offer compression ratios ranging 1.7:1 to 2.0:1. FELICS compression is applied only to 8-bit pixel data thereby requiring the LUT translation to be additionally used. Additional commanding parameters specify the number of post-binned image lines, TDI stages, and the line exposure duration. The number of post-binned image lines defines the areal extent of an observation in the down-orbit direction while the number of commanded CCDs defines the cross-orbit areal extent. The number of lines is limited by the instrument buffer space available for storing image data (63,000 unbinned lines for 14-bit data, 126,000 lines for 8-bit data). The number of TDI stages specifies how many TDI down-scan sensors to integrate while acquiring an image observation (permitted values are 8, 32, 64, and 128). The binning mode, viewing conditions, and spacecraft jitter are considerations when determining the optimal number of TDI stages. TDI stages improperly selected may cause image saturation or images with poor SNR. High-albedo targets acquired under bright lighting conditions may cause image saturation for 128 TDI stages. Conversely, observations with low lighting conditions, such as polar observations, might use a larger number of TDI stages to increase the SNR. If large pixel binning were commanded then the number of TDI stages would be reduced to prevent image saturation. Finally, the number of TDI stages impacts the effect of spacecraft jitter on the point-spread function (PSF) of the image pixels. Effects of spacecraft jitter are reduced for fewer TDI stages but also reduce SNR. The line time specifies the time between the generation of successive lines. The adjustment of this parameter matches the TDI readout with the boresight groundtrack velocity. Line time is the same for all CCDs for a given observation.