Data Set Overview : 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 the Derived Data Record (DDR) information for all valid, calibratible images acquired during flybys and orbit around Mercury, for which the target is Mercury and at least part of the image falls on the surface of the planet. These conditions represent a subset of all the images in the Calibrated Data Record or CDR dataset. The filename parallels that of the corresponding CDR, where:  'pcrnnnnnnnnnf_tt_v', where  p : product type : D derived c : camera (W WAC or N NAC) r : spacecraft-clock-partition-number minus 1 [0, 1] for pre- or post-spacecraft-clock-reset nnnnnnnnn : Mission Elapsed Time (MET) counter taken from the image header (and same as original compressed filename from SSR). f : Filter wheel position (A, B, C, D, E, F, G, H, I, J, K, L, U) for the WAC. It is M for the NAC, which has no filter wheel. tt : data type (DE derived) v : version number  The data exist in a format paralleling that of the raw or calibrated data: images have the same line and sample dimensions, and information in attached PDS labels is updated to convey differences in units and processing history. This dataset also includes ancillary data files that tabulate the contents of the volume and documentation files.  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.   Versions :  Version numbers of DDRs increment on reprocessing or updates to pointing information used to create the products.  In version 0 DDRs, latitude and longitude are calculated using the best-determined spacecraft and instrument pointing values, spacecraft position, and camera model recorded in SPICE kernels, and an ellipsoidal model of the planet surface. For version 1 DDRs, c-smithed kernels and a global digital elevation model (DEM) are used, with the DEM derived using a least-squares bundle adjustment of common features, measured as tie point coordinates in overlapping NAC and WAC-G filter images.   Parameters : MDIS observing variables pertaining to the DDRs are as follows.  Pixel Binning: Some 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. Images can be further compressed 2x2 using the MP, in addition to DPU binning, yielding 256x256 images. The dimensions of the DDR are controlled by the types of pixel binning applied to the source image.  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. The position of the pivot is a key input to calculation of values in the DDR image planes.   Processing :  A Derived Data Record (DDR) consists of a multiband image whose line and sample dimensions correspond one-for-one with those of a CDR. It has 5 bands of data used to help create map- projected products, including for every image pixel: (a) latitude, (b) longitude, (c) solar incidence angle, (d) emission angle, and (e) phase angle. The focal lengths and optical distortions that control the static field of view of each of the WAC and NAC are recorded in the instrument (I) kernel. Pivot positions are extracted from the spacecraft housekeeping and formatted as a pivot C kernel. Spacecraft attitude is formatted as a spacecraft C kernel. Spacecraft position is recorded in an SP kernel. Planetary constants including orbital elements are recorded in the PC kernel. Using these kernels and SPICE software, the surface intercept on a shape model of Mercury is calculated for each spatial pixel. The angles between a vector from the center of the planet to the pixel's surface intercept and either the equatorial plane or reference longitude constitute the latitude and longitude of the pixel, respectively. For that latitude and longitude, solar incidence, emission, and phase angles are evaluated for the time that the image was taken. For calculation of the photometric angles, it is assumed that locally the surface is a part of a spherical shell.   Data : There is one data type associated with this volume, DDRs consisting of 5 image planes describing the latitude, longitude, and photometric geometries of each pixel in MDIS WAC and NAC images of the planet Mercury.   Ancillary Data :  There are no ancillary data provided with this dataset.   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. A Mercury radius of 2440.0 km was used for data products delivered prior to delivery 15. In delivery 15, that value 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 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 DDRs generated for the image. 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) Mercury occupies at least part of the image.  The information in DDRs has systematic errors resulting from the following issues.  (1) TIME VARIATIONS IN MDIS ATTITUDE. The orientation of MDIS relative to the spacecraft reference frame was determined inflight using star calibrations to solve for WAC-NAC coalignment, the orientation of the pivot plane, and the origin of the reported pivot position within the plane. However these alignments can be affected by thermal state of the spacecraft, or by any other events that potentially shift the position of the MDIS base relative to the spacecraft star cameras that generate the attitude measurements. Mercury and Venus flybys are thermally benign. However in Mercury orbit there are thermal perturbations from which errors in reported MDIS attitude of up to 350 microradians might be expected. Regular star calibrations are conducted in orbit and indicate up to two or more types of time variation in attitude of an image relative to a given reported pivot position: (a) A one-time shift of WAC and NAC image alignment occurred near the time of Mercury orbit insertion, several hundred microradians in magnitude. This is being addressed in an updated frames kernel. The shift for the WAC was first describe in a frames kernel released in conjunction with release 9. The frames kernel in conjunction with release 11 and the first release of DDRs also includes the shift of NAC image alignment near the time of orbit insertion. (b) In addition to the shift of WAC and NAC image orientation near the time of orbit insertion, subsequent gradual drift is observed in the WAC from star calibration images. That is addressed by modifications to the pivot C kernel that incorporate that drift as part of the pivot attitude, for simplicity. Limited star calibrations that determine the relative alignments of the WAC and NAC during the orbital phase of the mission indicate that the two fields of view drift together, so a single modified pivot C kernel is used to describe the pointing for both cameras.  (2) POINTING UNCERTAINTY. MDIS pivot C-kernels generated prior to September 2009 were based on counting steps of the pivot motor. There is periodicity at the scale of 3 degrees of pivot rotation in the relationship between pivot step size and physical angle, leading to reported pivot geometries being in error by up to 350 microradians in early versions of the pivot C kernel. Inflight tests during 2009 supported development of an alternative calculation of pivot angle using the pivot position resolver; this approach is included in MDIS pivot C kernels since MDIS release 5 (images through Mercury flyby 3). The uncertainties in pivot attitude in latter kernels are of the order of 35 microradians.  Uncertainty in spacecraft pointing is by requirement less than 350 microradians, but unofficial estimates from the guidance and control team suggest a more typical value near 70 microradians. When convolved with error in pivot pointing, this results in the majority of error in knowledge of image pointing (exclusive of thermal distortion or time variations that can be calibrated out).  An additional and generally larger source of error in map projection of MDIS images acquired during Mercury orbit may be uncertainty in spacecraft position. At low altitudes that source of error dominates, whereas at high altitudes pointing error dominates, such that in either case typical errors in map projection from the best reconstructed spacecraft position are expected to be smaller than 1 km.  In the end-of-mission delivery 15 of SPICE files and version 1 DDRs, these errors are reduced by controlling images 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.  (3) TEMPERATURE-DEPENDENCE OF WAC and NAC FOCAL LENGTH. The star calibrations used to track the position of the MDIS pivot base, augmented by special calibrations using fields with high spatial densities of stars, sample much of the range of thermal environments experienced in orbit. Analyses of these data showed that focal length of each camera is correlated with temperature of the focal plane housing 'FOCAL_PLANE_TEMPERATURE', and that focal length varies over the cameras' operating temperature range by several parts in 10,000. This dependence is included in an updated delivery of the instrument kernel associated with PDS release 11.   Limitations : None