PDS_VERSION_ID = PDS3 LABEL_REVISION_NOTE = "2014-06-01, S. MURCHIE, edited; 2014-06-03, J. WARD, edited; 2014-09-11, S. MURCHIE, edited" RECORD_TYPE = STREAM OBJECT = DATA_SET DATA_SET_ID = "MESS-H-MDIS-5-RDR-HIE-V1.0" OBJECT = DATA_SET_INFORMATION DATA_SET_NAME = "MESS MDIS MAP PROJ HIGH-INCIDENCE BASEMAP EAST RDR V1.0" DATA_SET_TERSE_DESC = "High solar incidence angle basemap illuminated from the east reduced data records for the MDIS camera system on MESSENGER." DATA_SET_COLLECTION_MEMBER_FLG = "N" DATA_OBJECT_TYPE = "IMAGE" START_TIME = 2004-08-19T18:01:23 STOP_TIME = NULL DATA_SET_RELEASE_DATE = 2015-03-06 PRODUCER_FULL_NAME = "CHRISTOPHER HASH" DETAILED_CATALOG_FLAG = "N" CITATION_DESC = "C. Hash, MESS MDIS MAP PROJ HIGH-INCIDENCE BASEMAP EAST RDR V1.0, NASA Planetary Data System, 2015" ABSTRACT_DESC = " Abstract ======== The Mercury Dual Imaging System (MDIS) consists of two cameras, a Wide Angle Camera (WAC) and a Narrow Angle Camera (NAC), mounted on a common pivot platform. This dataset includes Map Projected High- Incidence Angle Basemap Illluminated from the East RDRs (HIEs) which comprise a global map of I/F measured by the NAC or WAC filter 7 (both centered near 750 nm) during the the Extended Mission at high incidence angles to accentuate subtle topography, photometrically normalized to a solar incidence angle (i) = 30 degrees, emission angle (e) = 0 degrees, and phase angle (g) = 30 degrees at a spatial sampling of 256 pixels per degree. The HIE data set is a companion to the Map Projected High-Incidence Angle Basemap Illluminated from the West RDR (HIW) data set. Together the two data sets are intended to detect and allow the mapping of subtle topography. They complement a Basemap Data Record (BDR) data set also composed of WAC filter 7 and NAC images acquired during the Primary Mission at moderate/high solar incidence angles centered near 68 degrees, and an Low Incidence Angle (LOI) data set also composed of WAC filter 7 and NAC images acquired during the Extended Mission at lower incidence angles centered near 45 degrees, analogous to the geometry used for color imaging. The map is divided into 54 'tiles', each representing the NW, NE, SW, or SE quadrant of one of the 13 non-polar or one of the 2 polar quadrangles or 'Mercury charts' already defined by the USGS. Each tile also contains 5 backplanes: observation ID; BDR metric, a metric used to determine the stacking order of component images, modified for the higher incidence angle centered near 78 degrees; solar incidence angle; emission angle; and phase angle." DATA_SET_DESC = " Data Set Overview ================= A major imaging campaign for MDIS in MESSENGER's primary mission was acquisition of a global data set at low emission angles for cartographic purposes, and moderate to high incidence angles that highlight topography. Those images were mosaicked into basemap data records (BDRs). The HIE data set is complementary in that it highlights low-relief topography that is less evident. The illumination from the east favors asymmetric topography more steeply sloped to the east than to the west. The companion HIW data set favors asymmetric topography more steeply sloped to that west than to the east. The file names developed for this PDS archive are restricted to a maximum 36-character base name and 3 character extension name with a period separating the file and extension names. Also known as the '36.3' format, this is compliant with the ISO 9660 Level 2 specification (maximum of 40 characters), which is required by PDS. The MDIS HIE products have a '22.3' format and thus remain within the PDS specification parameters. Map tiles are named based on the quadrant of the Mercury chart they span: MDIS_ppp_rrrPPD_Hxxddv.IMG where: ppp = product type = HIE rrr = resolution in pixels/degree (PPD) Hxx = Mercury chart designation dd = quadrant within Mercury chart (NW, NE, SW, or SE), or a polar chart (NP, SP)e limits v = version number The following is an example file name with a description of the individual components: MDIS_HIE_256PPD_H03NE0.IMG For this image: Product type = HIE (HIE) Resolution = 256 pixels/degree (256PPD) Mercury chart = Shakespeare (H03) Quadrant = Northeast (NE) Version = 0 The HIE directory, present in the HIE archive volume, contains MDIS Map Projected High Incidence Angle Basemap Illuminated from the East Reduced Data Records (HIEs). The HIEs are organized into subdirectories based on the Mercury Chart containing the HIE. Latitude and longitude limits of the Mercury Charts are: Quadrangle Subdirectory Lat. (degrees) Long. (deg. east) H-1 Borealis H01 65 to 90 0 to 360 H-2 Victoria H02 22.5 to 65 270 to 360 H-3 Shakespeare H03 22.5 to 65 180 to 270 H-4 Liguria H04 22.5 to 65 90 to 180 H-5 Apollonia H05 22.5 to 65 0 to 90 H-6 Kuiper H06 -22.5 to 22.5 288 to 360 H-7 Beethoven H07 -22.5 to 22.5 216 to 288 H-8 Tolstoj H08 -22.5 to 22.5 144 to 216 H-9 Solitudo H09 -22.5 to 22.5 72 to 144 Criophori H-10 Pieria H10 -22.5 to 22.5 0 to 72 H-11 Discovery H11 -65 to -22.5 270 to 360 H-12 Michelangelo H12 -65 to -22.5 180 to 270 H-13 Solitudo H13 -65 to -22.5 90 to 180 Persephones H-14 Cyllene H14 -65 to -22.5 0 to 90 H-15 Bach H15 -90 to -65 0 to 360 An HIE: - Consists of map-projected photometrically normalized I/F CDRs mosaicked into a basemap map tile; - Contains image data in I/F corrected photometrically to i=30 degrees, e=0 at a resolution of 256 pixels per degree (~166 m/pixel at the equator); - Represents one latitude-longitude bin in a global map; - Is composed of images acquired with by the NAC or by the WAC in filter 7, both centered near 750 nm; - Contains images acquired as part of the high-incidence angle basemap campaign for which SUBSOLAR_LONGITUDE is located east of the images's CENTER_LONGITUDE; and - Contains 5 backplanes: (a) observation id, (b) BDR metric, modified for the optimal incidence angle to be 78 degrees instead of 68 degrees, (c) solar incidence angle, (d) emission angle, and (e) phase angle. Versions ======== Version numbers of HIEs increment on reprocessing or addition of new data. Polar tiles are in polar stereographic projections, other tiles in equirectangular projection. Version 0 is released at PDS release 13. Parameters ========== MDIS observing variable pertaining to the HIEs are as follows. Pixel Binning: Some HIE images are unbinned and 1024x1024 pixels. Some images are 2x2 pixel binned in the focal plane hardware (also known as 'on-chip' binning), resulting in 512 x 512 images. The WAC was used to acquire HIE images from lower altitudes, and the NAC was used at higher altitudes. Within the altitude range for either camera, on-chip binning was used within the lower portion of the range, to control data volume and to manage data flow on the spacecraft. No MP binning was used. 12-8 bit compression: Images are read off the detector in 12-bit format. 12 bit images may converted to 8 bit images using one of eight lookup tables (LUTs). All images collected as part of the HIE basemap have been converted to 8 bits. FAST/DPCM compression: All images are compressed losslessly using FAST/DCPM compression as they are read out of the DPU, to conserve recorder space. Once the data are written to the recorder, they can be uncompressed and recompressed more aggressively in the MP. Wavelet compression: Images may be integer wavelet transform- compressed in the MP, typically at 3:1 for color data and 4:1 for monochrome data, but any value from 1 to 32 can be used. The initial configuration in Mercury orbit was to perform 12 to 8 bit conversion using LUT0 for the WAC and LUT2 for the NAC, with a wavelet compression ratio of 8:1 for monochrome imaging and 4:1 for color imaging. Initial images exhibited unexpectedly visible compression artifacts. Beginning 19 April 2011, LUT0 and LUT2 were replaced with LUT1 which better preserves image dynamic range, and compression ratios were decreased to 4:1 or less for monochrome data and 3:1 or less for color data where possible. Lossless compression was used when downlink allowed. Exposure Control: The exposure time of MDIS images can be set manually by command, or automatically by the software. In manual mode, exposure times from 1-989, 1001-1989, ..., to 9001-9989 ms are available. In autoexposure mode the exposure time of the next image is computed by the DPU software, and cannot exceed 989 ms in duration. If the time of the next image occurs before the calculation can be completed, and pixel binning or filter position change, then the algorithm compensates for predicted changes in scene brightness and filter transmission using an onboard data structure. All images in HIEs were acquired using automatic exposure. Pointing: The MDIS imagers are mounted on a pivot platform, which is itself mounted to the MESSENGER spacecraft deck. The pivot platform is controlled by a stepper motor, which is controlled by the Data Processing Unit (DPU). The pivot platform can move in either direction. The total range of motion is 240 degrees, limited by mechanical 'hard' stops, and is further constrained by 'soft' stops applied by the software. The nominal pointing position for MDIS is defined as 0 degrees, aligned with the spacecraft +Z axis and the boresight for several other instruments. The range of the soft stops is set to 40 degrees in the spacecraft -Y direction (toward the MESSENGER sunshade) and +50 degrees in the +Y direction (away from the sunshade). The pivot position can be commanded in intervals of 0.01 degrees within this range. During acquisition of the HIE basemap, the pivot was used to point the WAC or NAC to low emission angles on the surface, at times when the solar incidence angle was close as possible to 78 degrees. Filter selection: The WAC imager contains a 12 position filter wheel to provide spectral imaging over the spectral range of the CCD detector. WAC filter 7 (750 BP 5) was chosen to complement the NAC because its bandpass within that of the NAC lessens any discontinuities that might result from regional variations in spectral slope. Processing ========== A sequence of processing creates an HIE from CDRs and DDRs. A Derived Data Record (DDR) consists of multiband images whose line and sample dimensions and coordinates correspond one-for-one with those of a CDR. It has 5 bands of data used to help create an HIE, including for every image pixel: (a) latitude, (b) longitude, (c) incidence angle, (d) emission angle, and (e) phase angle. The DDRs are an intermediate product used to create HIEs and other map products, are defined as a distinct data product in the MDIS CDR/RDR Software Interface Specification, and are delivered to the PDS beginning with delivery 11. The sequence of processing is as follows: (a) Experiment Data Records (EDRs) are assembled from raw data. (b) Radiance images are created from the EDRs and calibration files. (c) Radiance is converted to I/F CDRs by dividing by (pi * solar flux at 1 AU * heliocentricdistance^2). (d) I/F is photometrically corrected to i = 30 degrees, e = 0 degrees. (e) Gimbal positions are extracted from the spacecraft housekeeping and formatted as a gimbal C kernel. (f) Using the gimbal C kernel and other SPICE kernels, DDRs are created. The surface intercept on a sphere of Mercury's radius is calculated for each spatial pixel. 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. (g) I/F corrected to i = 30 degrees, e = 0 degrees is map projected into HIEs using the latitude and longitude information in the DDRs. The same procedure is used on DDRs to assemble the backplanes with derived information. They are appended to the image band in the following order: OBSERVATION_ID BDR metric Solar Incidence Angle Emission Angle Phase Angle where OBSERVATION_ID is taken from the CDR label, the ordinal number of the image among MDIS images taken post-launch. The values for all backplanes are those for the filter 7 image within the color sequence. The BDR metric or stacking order ('which image is on top') was first defined for BDRs. For HIEs, the objective is to have 'on top' those images with high spatial resolution, low emission angle, and a solar incidence angle as close as possible to 78 degrees. This incidence angle was defined was chosen to highlight subtle topographic shading. An image taken as part of the high-incidence angle campaign is included in the HIE products if its value of SUBSOLAR_LONGITUDE is located eastward less than 90 degrees from CENTER_LONGITUDE. Stacking order is determined by evaluating at camera boresight a modified version of the BDR metric that favors incidence angles near 78 degrees instead of 68 degrees as for BDRs. This metric represents both spatial resolution and image geometry; lowest values for the metric represent the 'best' image. The 'worst' complete, map- projected image with the highest value for the metric is laid into the HIE first; then the complete image with the second-highest value is laid in second, overwriting the first image where the coverage coincides, and so on until the complete 'best' image with the lowest value for the metric is on top. There are 3 expressions for the modified BDR metric depending on latitude greater or less than 65 degrees and solar incidence angle greater or less than 78 degrees. (a) Where abs(lat) <= 65 degrees and i => 78 degrees, the metric is: PIXEL_SCALE / (cos e * ( cos ( flatten_factor * i) / cos ( flatten_factor * 78 ) ) ) where i is solar incidence angle, e is emission angle, lat is planetocentric latitude, and flatten_factor is set to 0.85 to de-emphasize low solar incidence angles. (b) Where abs(lat) <= 65 degrees and i < 78 degrees, the metric is: PIXEL_SCALE / (cos e * (cos 78 / cos i)) (c) Where abs(lat) > 65 degrees, the metric is: PIXEL_SCALE / (cos i * cos e ) where i is solar incidence angle, e is emission angle. In each case, the value of PIXEL_SCALE is limited not to be below approximately 166 meters so that unfavorably illuminated images with high spatial resolutions not captured at the resolution of an HIE do not overwrite more favorably illuminated images. The photometric correction applied to MDIS WAC and NAC images used to create HIE mosaics (from NAC and WAC G filter images) is based on the bi-directional reflectance equations formulated by [HAPKE1993]. These equations use a Henyey-Greenstein function to describe the single particle scattering function (p(alpha)). The form of the Henyey- Greenstein function used corresponds to the form utilized in the USGS ISIS software, and is given by: p(alpha)=c(1-b^2)(1-2b cos(alpha)+b^2)^(-3/2) + (1-c)(1-b^2)(1+2b cos(alpha)+b^2)^(-3/2), where alpha is the phase angle, b is the scattering amplitude parameter, and c is the partition parameter between forward and backward scattering. As of the writing of this file, no single set of parameters for the Hapke-based photometric correction has been found that yields close matches for corrected I/F across boundaries of images taken at different photometric geometries, for both the color maps taken predominantly at low solar incidence angles (average, about 45 degrees) that are included in 8-Color Map Projected Multispectral RDRs (MDRs), 3-Color Map Projected Multispectral RDRs (MD3s), and 5-Color Map Projected Multispectral RDRs (MP5s), as well as for the monochrome maps taken predominantly at high solar incidence angles that are included in BDRs, HIEs, and HIWs. Therefore MDRs/MD3s/MP5s and BDRs/HIEs/HIWs are constructed using different sets of photometric parameters optimized for each to minimize seams between images. The parameters for the HIE Hapke photometric correction were derived by modeling whole-disk observations of Mercury taken at a large number of photometric geometries during the Mercury flybys using different filters in the wide-angle camera. Those data were modeled using a least squares grid search routine over the available model parameter space. The model parameter values were individually plotted as a function of wavelength over the MDIS filter central wavelength values. A polynomial trend was fit to each parameter as a function of wavelength. The polynomial trend value at each filter central wavelength was then used as the model parameter values for determining the photometric correction. The Hapke model parameters used for the global monochome map stored in HIEs is given in the table below, where w is the single scattering albedo, theta is the surface roughness parameter, and b and c are the Henyey-Greenstein single particle scattering function parameters defined above. For the monochrome basemap in HIEs, photometric behavior of Mercury in NAC images is assumed to be equivalent to that in the WAC G filter. WAC filter, wavelength, w, b, c , theta G, 749 , 0.278080114, 0.227774899, 0.714203968, 17.76662946 Data ==== There is one data type associated with this volume, HIEs consisting of mosaicked, photometrically corrected WAC filter 7 (G filter) CDRs and NAC CDRs, appended with 5 backplanes describing the component CDRs, their native spatial sampling scale, and their photometric geometries. Ancillary Data ============== There may be one type of ancillary data provided with this dataset: 1. There may be a BROWSE directory containing browse images in PNG and/or GeoTIFF format, and HTML documents that support a web browser interface to the volume. See BROWINFO.TXT in that directory for more details. Coordinate System ================= The cartographic coordinate system used for the MDIS data products conforms to the J2000 celestial reference frame for star imaging, and the IAU planetocentric system with East longitudes being positive for planetary surfaces. The IAU2000 reference system for cartographic coordinates and rotational elements was used for computing latitude and longitude coordinates of planets. However a Mercury radius of 2440.0 km is used which may be slightly different from the IAU value. Media/Format ============ The MDIS archive is organized and stored in the directory structure described in the Mercury Dual Imaging System (MDIS) Calibrated Data Record (CDR) and Reduced Data Record (RDR) Software Interface Specification (SIS). The contents of the archive, along with fiduciary checksums, are compressed into a single 'zip archive' file for transmittal to the PDS Imaging node. The zip archive preserves the directory structure internally so that when it is decompressed the original directory structure is recreated at the PDS Imaging node. The zip archive is transmitted to the PDS Imaging node via FTP to the URL specified by the node for receiving it." CONFIDENCE_LEVEL_NOTE = " Confidence Level Overview ========================= Known issues of concern are described below. 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 ========================= Only a subset of raw EDR data are calibrated to CDRs and then incorporated into HIE products. Briefly, the following criteria are met: (a) The data represent a scene and not the instrument test pattern, as indicated by DQI byte 0. (b) The exposure time is greater than zero (zero exposures occur in some images due to software features), as indicated by DQI byte 1. (c) Less than 20 percent of the image is saturated (empirically this is a threshold dividing wholly corrupted images from everything else). (d) The target of the image is MERCURY. (e) The image was taken as part of the high incidence angle basemap campaign represented by HIE data products, as indicated within an observation table used internally at the MESSENGER Science Operations Center. Also, the imaged surface is illuminated from the east, such that the value of SUBSOLAR_LONGITUDE is <= 90 degrees eastward of CENTER_LONGITUDE. HIEs are based on version 4 CDRs which correct a number of earlier calibration artifacts. Some issues still remain. The OBSERBATION_ID for a part of a HIE is a pointer back to the WAC filter 7 or NAC image used for that part of the HIE. Those images may be subject to some or all of the following issues. (1) COMPRESSION ARTIFACTS. Images may be integer wavelet transform- compressed in the MP, typically at 3:1 for color data and 4:1 for monochrome data, but any value from 1 to 32 can be used. The initial configuration in Mercury orbit was to perform 12 to 8 bit conversion using LUT0 for the WAC and LUT2 for the NAC, with a wavelet compression ratio of 8:1 for monochrome imaging and 4:1 for color imaging. Initial images exhibited unexpectedly visible compression artifacts. Beginning 19 April 2011, LUT0 and LUT2 were replaced with LUT1 which better preserves image dynamic range, and compression ratios were decreased to 4:1 or less for monochrome data and 3:1 or less for color data where possible. Lossless compression was used when downlink allowed. Images that are part of HIE products typically were compressed 4:1 or losslessly. (2) RADIOMETRIC ACCURACY. The responsivities used to convert DNs to radiance are based on ground calibrations that were validated by comparison of MDIS with MASCS-VIRS measurements of Venus and Mercury. Except for 3 of the 12 filters, WAC radiances based on ground calibrations yielded a similar spectral shape with a 10-15% difference in absolute value. Filters 3 and 6 (at 480 and 433 nm) were systematically too low and too high respectively, so the responsivites used to calibrate them were adjusted empirically to improve correspondence with MASCS-VIRS. In addition WAC filter 2 (clear filter) radiances have not been validated. The relative accuracy of NAC and WAC filter 7 data (which correspond in central wavelength) were examined by comparing nearly simultaneous images taken during the Mercury 2 flyby and the NAC calibration was adjusted empirically to produce agreement. Both the NAC and WAC have CCDs whose responsivity to different wavelengths of light varies with CCD temperature. Inflight including Mercury orbit the CCD operating temperature range is typically -10C to -45C; however ground calibration measurements were acquired only at +23C, -31C, and -34C rendering the initial characterization of the temperature dependence inaccurate especially below -34C. M1 and M2 measurements of comparable surfaces, acquired at CCD temperatures of -34C to -43C, were used to improve the calibration of CCD temperature dependence over the lower end of the temperature range, and this correction was applied to version 3 CDRs. In version 4 CDRs, an additional update to responsivity improved temperature dependence over the full operating range. The correction was derived empirically by fitting as a function of CCD temperature the median values of images acquired at a wide range of temperatures but a narrow range of photometric geometries. (3) SCATTERED LIGHT. In the NAC, scattered light from out-of-field sources is an issue. The geometry contributing most of the scatter is 1-2 fields-of-view sunward of the NAC boresight. For a very large, evenly illuminated source that overfills the field-of-view by a factor of several, ray-trace studies supported by testing during Venus flyby 2 suggest that 2-7% of the radiance measured in the field-of-view will have come from out-of-field sources. The spatial pattern of the scatter is variable, due to diffuse reflections off the internal instrument housing. The WAC is subject to scattered light originating from within the field-of-view or just outside it. In overexposed images, the source is evidently multiple reflections off of 13 optical surfaces (2 sides of each of 4 lenses, the spectral filter, and the CCD cover glass, as well as the CCD surface itself). The scatter becomes worse at longer wavelengths. Just off the limb of a large extended source near 1 field-of-view in size, like Venus or Mercury, measured radiance increases with wavelength from 2% to 7% of the value measured on the extended source. The value decreases with distance off the target more quickly at longer than at shorter wavelengths, but remains at 1% hundreds of pixels from the source. Conversely, light must be scattering from bright parts of an image to dark parts of an image. Averaged over sources tens of pixels in area, and away from abrupt brightness contrasts, scattered light affects shapes of spectra measured from WAC data at least at the 1-2% level, worse near brightness boundaries or for small, bright crater ejecta. The expected effect is enhanced brightness at <650 nm in dark areas, and decreased brightness at >650 nm in small bright areas. At the time this file was last updated, a forward model of the expected WAC scatter from a given scene was being derived using optical design software modeling CCD structure and hardware, with magnitudes of scatter calibrated against flight measurements. The long-term objective is to iteratively subtract from the whole image the scatter expected to originate from each small area on the CCD and its immediate surroundings. (4) TIME-VARIABLE WAC RESPONSIVITY FOLLOWING PROBABLE CONTAMINATION. Beginning 24 May 2011, WAC response to light decreased by different amounts in each filter, most in the shortest- and longest-wavelength filters. Subsequently response increased slowly over several months approaching previous values. This is believed to result from deposition and subsequent bakeoff of a contaminant on the MDIS outer optic. The deposition may have resulted from MESSENGER's first period with periapsis of its orbit near the sub-solar longitude at planet perihelion. The correction is maintained as a look-up table, derived empirically by comparing median properties of WAC images taken within a narrow range of photometric geometries. Correction for this event is first applied in version 4 CDRs, for the WAC only. For the global monochrome map stored in the HIEs, data acquisition followed the contamination event and early bake-off. (5) TIME-VARIABLE FILTER TRANSMISSIVITY FOLLOWNG RECOVERY FROM CONTAMINATION. Following the apparent recovery of responsivity about 1 year after orbit insertion and 10 months after the 'contamination event', response in several filters - especially 6 and 7 (F and G) - began to fall again relative that response through other filters. This trend continued for more than another year. It was determined that the rate of falloff in response was related to the amount of time the filter was 'in position' for imaging; generally MDIS is pointed in the direction of the illuminated surface of Mercury. It is speculated that intense radiance from Mercury caused loss of transmission in the affected filters. A correction is maintained as part of the same look-up table derived to track dissipation of the contaminant. It is derived empirically by comparing median properties of overlapping WAC color image sequences. (6) UNCONTROLLED MOSAIC PROJECTED ONTO A SPHERE. Version 0 HIEs were constructed by uncontrolled mosaicking, projecting the image data onto a sphere. Systematic errors in spacecraft position and in knowledge of spacecraft and MDIS attitude, systematic errors in range to the surface due to ignoring topography, and systematic errors in latitude and longitude due projecting onto a sphere instead of a shape model will all contributed to mosaicking errors. In general these are expected to be under 1 km but locally might exceed 4 km. The interested user is referred to the CDR Data Set Catalog File for a more extended discussion of sources of geometric error. (7) INACCURACY IN THE PHOTOMETRIC CORRECTION. As explained above, the photometric correction applied to HIEs is only preliminary. Known inaccuracies are most severe at high incidence and high emission angles. Also because a different photometric correction is used in MD3s, MP5s and MDRs than for the monochrome maps stored in BDRs, HIEs, and HIWs, the radiometric content of the data products is not comparable quantitatively. Limitations =========== None" END_OBJECT = DATA_SET_INFORMATION OBJECT = DATA_SET_MISSION MISSION_NAME = "MESSENGER" END_OBJECT = DATA_SET_MISSION OBJECT = DATA_SET_TARGET TARGET_NAME = "MERCURY" END_OBJECT = DATA_SET_TARGET OBJECT = DATA_SET_HOST INSTRUMENT_HOST_ID = MESS INSTRUMENT_ID = {"MDIS-NAC","MDIS-WAC"} END_OBJECT = DATA_SET_HOST OBJECT = DATA_SET_REFERENCE_INFORMATION REFERENCE_KEY_ID = "HAWKINSETAL2007" END_OBJECT = DATA_SET_REFERENCE_INFORMATION OBJECT = DATA_SET_REFERENCE_INFORMATION REFERENCE_KEY_ID = "HAWKINSETAL2009" END_OBJECT = DATA_SET_REFERENCE_INFORMATION END_OBJECT = DATA_SET END