PDS_VERSION_ID = PDS3 LABEL_REVISION_NOTE = "2014-06-01, S. MURCHIE, edited; 2014-06-11, J. WARD, edited; 2014-09-11, S. MURCHIE, edited; 2016-02-12, S. MURCHIE, edited" RECORD_TYPE = STREAM OBJECT = DATA_SET DATA_SET_ID = " MESS-H-MDIS-5-RDR-RTM-V1.0" OBJECT = DATA_SET_INFORMATION DATA_SET_NAME = "MESS MDIS MAP PROJ REGIONAL TARGETED MOSAIC RDR V1.0" DATA_SET_TERSE_DESC = "Regional mosaics of targeted images acquired by the MDIS WAC or NAC camera for regions of interest." DATA_SET_COLLECTION_MEMBER_FLG = "N" DATA_OBJECT_TYPE = "IMAGE" START_TIME = 2004-08-19T18:01:23 STOP_TIME = 2015-04-30T11:07:43 DATA_SET_RELEASE_DATE = 2016-05-06 PRODUCER_FULL_NAME = "CHRISTOPHER HASH" DETAILED_CATALOG_FLAG = "N" CITATION_DESC = "C. Hash, MESS MDIS MAP PROJ REGIONAL TARGETED MOSAIC 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 include regional mosaics of targeted observations directed at specific regions of interest. Four types of targeted observations are included: (a) WAC 3-color targeted observations acquired mainly during the primary mission, to complement 1 km/pixel 8-color mapping with a higher spatial resolution 3-color product; (b) WAC observations of targets that were observed repeatedly at different photometric geometries in order to improve photometric models of Mercury; these were observed initially in 8 color and since early 2013 in 11 colors; (c) WAC 8- or 11-color science targeted observations; and (d) NAC image strips acquired either for high-resolution imaging of morphology or as context for MASCS or MLA observations. The images in each observation share a common SITE_ID in the file name and PDS label. The SITE_ID corresponds to a targeting request entered into a database, in response to which a series of images was acquired. There is one SITE_ID for each time the region of interest is observed; thus for photometry targets, the same geographic region of interest is covered by many sets of images, each set sharing a common SITE_ID and distinct photometric geometry. Each mosaic is map projected in an orthographic projection, and contains one or more image planes. NAC mosaics contain 4 backplanes: observation ID, solar incidence angle, emission angle, and phase angle. WAC color products contain 3 backplanes: solar incidence angle, emission angle, and phase angle." DATA_SET_DESC = " Data Set Overview ================= A major activity on MESSENGER has been acquisition of enhanced observations pointed at special regions of scientific interest, so-called targeted observations. Mostly these are directed at features for which higher-resolution morphological or multispectral imaging or denser spectral sampling could help in geological characterization or hypothesis testing. Other imaging is acquired as context for MLA or MASCS measurements, or to characterize photometric properties of Mercury's surface. These observations are scattered throughout the CDR data set linked by the SITE_ID in their PDS label. In the RTM data set, the images for each SITE_ID are collected, coregistered if they are multispectral, map projected, and photometrically corrected to a standard geometry of incidence angle i=30 degrees, emission angle e=0 degrees, and phase angle g=30 degrees. All map projections are orthographic and near the native resolution of the images to preserve spatial resolution. RTM products are named based on their SITE_ID, OBSERVATION_ID of the first image, and number of image bands: MDIS_ppp_cbb_siteid_observationid_v.IMG where: ppp = product type = RTM c = camera (W WAC or N NAC) bb = bands (01, 03, 08, 11 depending on type of observation) siteid = a 6-digit integer giving the unique SITE_ID of the region covered by the product observationid = image observation ID of the first image (lowest ID) v = version number The following is an example file name with a description of the individual components: MDIS_RTM_N01_000276_1214047_0.IMG For this image: Product type = RTM (RTM) Camera = NAC (N) Bands = 1 (01) SITE_ID = 276 (000276) OBSERVATION_ID = 1214047 Version = 0 The RTM directory, present in the RTM archive volume, is organized into subdirectories based on camera/band (cbb from the file name) followed by year and day of year with the naming format: MDIS_RTM_CBB/YYYY_DDD where C = camera (W WAC or N NAC) BB = bands (01, 03, 08, 11 depending on type of observation) YYYY = year of the beginning of acquisition of the first image in the observation DDD = day of year of the beginning of acquisition of the first image in the observation An RTM: - Consists of map-projected photometrically normalized I/F CDRs assembled into a regional mosaic; - Contains image data in I/F corrected photometrically to i=30 degrees, e=0 degrees, g=30 degrees at a resolution close to the native resolution of the imaging data; - Is composed of images acquired by the NAC or through multiple spectral filters by the WAC; - Contains images acquired during a targeted observation of one region of interest denoted by a site ID; and - NAC mosaics contain 4 backplanes: (a) observation id, unique to each image, (b) solar incidence angle, (c) emission angle, and (d) phase angle. WAC color products contain 3 backplanes: (a) solar incidence angle, (b) emission angle, and (c) phase angle. Versions ======== Version numbers of RTMs increment on reprocessing. - Version 0 is released at PDS release 13. It is built from version 4 CDRs projected onto a sphere using version 0 DDRs. It uses a Hapke-form photometric correction, with different parameters for low- and high-incidence angle products. - Version 1 is released at PDS release 15 at end of mission. It uses version 5 CDRs projected onto a digital elevation model using version 1 DDRs. It uses a Kasseleinen-Shkuratov photometric correction with a common set of parameters among all data products. Parameters ========== MDIS observing variables pertaining to the RTMs are as follows. Pixel Binning: Some RTM 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, only where needed to increase image cadence and along-track overlap. MP binning was used only for WAC photometric targets to control data volume. 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). Typically, WAC multispectral images are 12 bits except and NAC image strips 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 spacecraft main processor (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, especially for WAC multispectral observations. 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. Most images in RTMs were acquired using automatic exposure, with an upper limit on exposure time to limit image smear. 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 targeted observations, the pointing of the pivot varied depending on the type of target and whether the observation was coordinated with MASCS or MLA. NAC image strips are mostly pointed at low to moderate emission angles, and solar incidence angles near 68 degrees. However NAC images taken to provide context for MASCS or MLA observations are pointed close to the +Z axis coaligned with the appropriate other instrument. WAC targeted 3- or 11-color image sequences are typically targeted at low solar incidence angles with constrained emission angles. WAC 8- or 11-color image sequences targeted for photometry have whatever pointing is required in order to meet specified bounds on incidence, emission, or phase angle for the particular region of interest. 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. RTMs may consist of only NAC images, or WAC images in 3, 8, or 11 filters. The usage of filters in types of WAC observations is given below: Filter Filter Center Bandpass 3- 8- 11- Number letter wavelength width color color color in file (nm) (nm) name 1 A 698.8 5.3 x 2 B 700 600.0 3 C 479.9 10.1 x x 4 D 558.9 5.8 x x 5 E 628.8 5.5 x x 6 F 433.2 18.1 x x x 7 G 748.7 5.1 x x x 8 H 947.0 6.2 x 9 I 996.2 14.3 x x x 10 J 898.8 5.1 x x 11 K 1012.6 33.3 x 12 L 828.4 5.2 x x Processing ========== A sequence of processing creates an RTM 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 RTM, 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 RTMs 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. 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_in_AU^2). (d) I/F is photometrically corrected to i = 30 degrees, e = 0 degrees, g = 30 degrees. (e) Gimbal positions are extracted from the spacecraft housekeeping and formatted as a gimbal C kernel. (f) Using the pivot C kernel and other SPICE kernels, DDRs are created. The surface intercept on a model of Mercury's surface 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 RTMs 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 (if applicable) 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 stacking order ('which image is on top') is that the first image in time is map projected first, the second image in time overlays the first, and so on, so that the last image overlays all others and is 'on top'. The photometric correction applied to MDIS images to create version 0 RTMs is based on bi-directional reflectance equations formulated by [HAPKE1993]. The general equation for I/F is given by: I/F=(w/4)[mu_not'/(mu' +mu_not')]{[1+B(g)]P(g)- 1+H(mu_not')H(mu')}S(i,e,g,theta) where w is single scattering albedo, i is incidence angle, e is emission angle, g is phase angle, p(g) is the single particle scattering function, theta is a parameter representing macroscopic roughness, and mu_not' and mu' are modified versions of the cosines of the incidence and emission angle that take into account effects of theta. H(mu_not') and H(mu') describe approximations to the Chandrasehkar H-functions. The surface roughness function, S(i,e,g,theta), modifies the radiative transfer equation to account for surface roughness. In addition, a Henyey-Greenstein function is used to describe the single particle scattering function p(g). The form of the Henyey-Greenstein function used corresponds to the form utilized in the USGS ISIS software, and is given by: p(g)=c(1-b^2)(1-2b cos(g)+b^2)^(-3/2) + (1-c)(1-b^2)(1+2b cos(g)+b^2)^(-3/2), where g is the phase angle, b is the scattering amplitude parameter, and c is the partition parameter between forward and backward scattering. In version 0 RTMs, no single set of Hapke parameters was found that yields close matches for corrected I/F across boundaries of images taken at different photometric geometries, for both the 3- and 8-color maps taken predominantly at low solar incidence angles (average, about 45 degrees) included in MDRs and MD3s, and monochrome maps taken predominantly at high solar incidence angles (BDRs, HIEs, HIWs). Therefore map products emphasizing low or high incidence angles initially used different sets of photometric parameters optimized for each to minimize seams between images. RTMs were acquired at different photometric geometries depending on the type of observation. NAC image strips were acquired predominantly at high solar incidence angles like BDRs/HIEs/HIWs and therefore all use those parameters; WAC multispectral images were acquired predominantly at low solar incidence angles like MDRs/MD3s and therefore use their parameters instead. VERSION 0 PHOTOMETRIC CORRECTION FOR WAC TARGETED OBSERVATIONS: The parameters used, those for the MDR/MD3 photometric correction, were derived by modeling data acquired from multiple regions between 24 degrees and 46 degrees south latitude and 330 degrees and 353 degrees east longitude. These regions sample incidence angle (i), emission angle(e), and phase angle (g) coverage commensurate with low incidence angle mapping campaigns, plus additional supplementary observations intended to expand the phase angle range. The data from each of the regions was combined into a single data set and a single set of parameters derived for each filter. The photometric measurements were modeled using a least squares grid search routine over the available 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. Derivation of the photometric correction involved: (1) calculating the reflectance at the observed geometry for each pixel in each image (Ro), (2) calculating the reflectance at i=30 degrees, e=0 degrees, g=30 degrees (R30), (3) calculating the correction factor (R30/Ro), and (4) applying the correction factor to each pixel within each image. The Hapke model parameters used are listed below for each WAC filter included in 3-, 8- or 11-color RTMs, where w is the single scattering albedo, theta is the surface roughness parameter, and b and c are the Heyney-Greenstein single particle scattering function parameters defined above. filter, wavelength, w, b, c , theta F, 433.2, 0.151360115, 0.155099698, 0.126102310, 14.60131926 C, 479.9, 0.169685245, 0.147410229, 0.106108941, 14.74522393 D, 558.9, 0.197384444, 0.136483073, 0.081821900, 14.78008707 E, 628.8, 0.218696307, 0.129164430, 0.070385011, 14.65283436 A, 698.8, 0.237307445, 0.124224188, 0.068452363, 14.44035788 G, 748.7, 0.249052388, 0.122256228, 0.072924183, 14.27068804 L, 828.4, 0.265449469, 0.121966502, 0.090225001, 14.02954160 J, 898.8, 0.277789564, 0.124805212, 0.115960759, 13.90988549 H, 947.0, 0.285371188, 0.128609684, 0.139801777, 13.91310187 I, 996.2, 0.292068663, 0.133854741, 0.167852540, 14.00895011 K, 1012.6, 0.293865419, 0.135640972, 0.176741965, 14.05611393 For all wavelengths, the width of the opposition surge, h, is 0.09 and the strength of the opposition surge, B0, is 3.086. VERSION 0 PHOTOMETRIC CORRECTION FOR NAC TARGETED OBSERVATIONS: The parameters used, for the BDR/HIE/HIW 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 RTMs containing NAC images 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. 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 The width of the opposition surge, h, is 0.09 and the strength of the opposition surge, B0, is 3.086. VERSION 1 PHOTOMETRIC CORRECTION FOR ALL TARGETED OBSERVATIONS: In version 1 RTMs delivered at the end of the mission, a different photometric correction is used for all filters and all geometries, a Kasseleinen-Shkuratov function described by [DOMINGUEETAL2016]. The form of the function is given as: I/F = AN*exp[-(g*mu)]{c_sub_l[2cos i/(cos i + cos e)]+[1-c_sub_l]cos i} where AN is normal albedo at a given wavelength, and mu and c_sub_l are wavelength-dependent parameters. Their values were fit using multiple regions between 24 degrees and 46 degrees south latitude and 330 degrees and 353 degrees east longitude. These regions sample incidence angle (i), emission angle(e), and phase angle (g) coverage commensurate with global mapping campaigns. In addition whole-disk Mercury images taken at a large number of geometries during the Mercury flybys expand the phase angle range. Parameter values were fit in the same manner as the parameters for the Hapke model. The values are given in the table below: WAC Filter, Wavelength, AN, mu, c_sub_l F 430 6.92413210E-02 6.37228563E-01 6.28836906E-01 C 480.4 7.98153978E-02 6.21777913E-01 6.27629117E-01 D 559.2 9.10849913E-02 5.97475375E-01 6.18544492E-01 E 628.7 9.86118777E-02 5.80013748E-01 6.22758382E-01 A 698.8 1.05807514E-01 5.68069278E-01 6.35596439E-01 G 749 1.11116798E-01 5.62741989E-01 6.42377921E-01 L 828.6 1.19413553E-01 5.56997602E-01 6.36801364E-01 J 898.1 1.25034169E-01 5.49548099E-01 6.17408232E-01 H 948 1.26684133E-01 5.38610109E-01 6.09847145E-01 I 996.8 1.24975849E-01 5.19691856E-01 6.30847041E-01 K 1010 1.23758640E-01 5.12689614E-01 6.45356466E-01 Data ==== There is one data type associated with this volume, RTMs consisting of mosaicked, photometrically corrected WAC 3-, 8-, or 11-color or NAC CDRs, appended with 4 backplanes describing the component CDRs and their photometric geometries. Ancillary Data ============== There may be two types of ancillary data provided with this dataset: 1. The EXTRAS directory in the RTM archive contains a list of all SITE_IDs targeted by MDIS or other instruments, describing their latitude/longitude coordinates and the motivation for their targeting. This list is the primary mechanism for tracing the science rationale for acquisition of the data in the RTM. 2. There may be a BROWSE directory containing browse images in PNG and/or GeoTIFF format. 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. In version 0 RTMs, the IAU2000 reference system for cartographic coordinates and rotational elements is used for computing latitude and longitude coordinates of planets. However a Mercury radius of 2440.0 km is used. In version 1 RTMs, the value for Mercury radius is updated to 2439.4 km. 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 was examined by a peer review panel prior to its acceptance by the Planetary Data System (PDS). The peer review was 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 RTM products. Briefly, the following criteria are met: (a) The data represent a scene and not the instrument test pattern, as indicated by data quality index (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 a targeted observation directed at the SITE_ID on which the RTM is based. The OBSERVATION_ID for a part of an RTM is a pointer back to the WAC filter 7 or NAC image used for that part of the RTM. Version 0 RTMs are based on version 4 CDRs which correct a number of earlier calibration artifacts. Version 1 RTMs are based on version 5 CDRs. The following issues may affect the component images. (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. (2) RADIOMETRIC ACCURACY. The radiometric calibration of the WAC was updated several times over the mission to iteratively reduce residuals from 3 sources of error: (a) time-variable responsivity of the detector, (b) residuals in the flat-field correction, and (c) residuals in the correction to responsivity for detector temperature. For multispectral products, the residuals from time-variable responsivity initially led to distinct seams; correction of this artifact is treated in more detail below. 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 from Mercury orbit at a wide range of temperatures but a narrow range of photometric geometries. The flat field was updated empirically using the median of hundreds of photometrically corrected images of relatively bland field-filling images of Mercury. In version 5 CDRs, a new, final temperature correction used all Mercury images satisfying the illumination criteria. A new, final flat-field correction was derived similarly to the updated correction used in version 4, except using more images and a Kasseleinen-Shkuratov photometric correction. (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. One source is 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. (4) TIME-VARIABLE WAC RESPONSIVITY. During Mercury orbit it was recognized that filter-dependent changes in WAC responsivity on the order of +/- 15% occurred over timescales as short as several days. Because those variations were not consistent from filter to filter, they led to spurious spectral features, which were particularly conspicuous near 750 nm. The cause(s) of these variations in responsivity are not known, but they could include transient radiation effects on the detector or electronics, aging of filters, periodic deposition and burn-off of contaminants on filters, or incorrect recording of exposure time. An initial empirical correction for images acquired in the first year of operations was developed and utilized in version 4 WAC CDRs used to create version 0 RTMs. For version 5 WAC CDRs in delivery 15 at end of mission, an updated correction covers the full duration of the orbital phase. Overlaps between color image sets in color mapping campaigns were used to derive a multiplicative correction factor for each filter and for each Earth day (2-3 orbits). Version 1 RTMs use CDRs with this updated correction. An analysis of overlap among individual images shows that residual differences (which include errors from calibration, scattered light, and possible incomplete correction of photometric variation) average <2% for the majority of the planet. (5) UNCONTROLLED MOSAIC PROJECTED ONTO A SPHERE. Version 0 RTMs 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. Version 1 RTMs are constructed from images controlled using c-smithed kernels and a global digital elevation model (DEM), both derived using a least-squares bundle adjustment of common features, measured as tie point coordinates in overlapping NAC and WAC-G filter images of Mercury at favorable solar incidence and emission angles. Empirically, misregistration errors between images decreased generally to the pixel scale of the map (0.2 km) in most locations. Derivation of smithed kernels and the DEM for end of mission data products is described by [BECKERETAL2016]. (6) INACCURACY IN THE PHOTOMETRIC CORRECTION. The Hapke correction applied to version 0 RTMs required the use of illumination-dependent parameters implying the possibility of systematic inaccuracy. As shown by [DOMGINUEETAL2016] the Kasseleinen-Shkuratov correction used in version 1 RTMs greatly reduces residuals between images acquired at different photometric geometries, implying reduced systematic errors. 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 OBJECT = DATA_SET_REFERENCE_INFORMATION REFERENCE_KEY_ID = "HAPKE1993" END_OBJECT = DATA_SET_REFERENCE_INFORMATION OBJECT = DATA_SET_REFERENCE_INFORMATION REFERENCE_KEY_ID = "DOMINGUEETAL2016" END_OBJECT = DATA_SET_REFERENCE_INFORMATION OBJECT = DATA_SET_REFERENCE_INFORMATION REFERENCE_KEY_ID = "BECKERETAL2016" END_OBJECT = DATA_SET_REFERENCE_INFORMATION END_OBJECT = DATA_SET END