PDS_VERSION_ID = PDS3 RECORD_TYPE = FIXED_LENGTH RECORD_BYTES = 2880 FILE_RECORDS = 180 ^IMAGE = "JGM50C01.IMG" INSTRUMENT_HOST_NAME = "MARS GLOBAL SURVEYOR" TARGET_NAME = "MARS" INSTRUMENT_NAME = "RADIO SCIENCE SUBSYSTEM" DATA_SET_ID = "MGS-M-RSS-5-SDP-V1.0" ORIGINAL_PRODUCT_ID = "MARS50C.A01" PRODUCT_ID = "JGM50C01.IMG" PRODUCT_RELEASE_DATE = 1998-01-15 DESCRIPTION = "This file contains a digital map of Mars gravity accelerations derived from radio tracking of the Mariner 9 and Viking Orbiter spacecraft. The map is vertical gravity in milligals (1 milligal = 0.01 mm/s/s) at the surface referenced to a sphere of 3394.2 km radius. There are no Mars Global Surveyor data included in this model. This is considered to be the baseline (pre-MGS) Mars model for the JPL Gravity Science Team, under the direction of W.L. Sjogren. The model was constructed from 325,005 observations, summarized in the table below. The data were divided into 372 spans or independent arcs (covering 1142 days) based on considerations of data coverage and timing of maneuvers. Spacecraft Number Average Arc Total of Arcs Length Observations (days) ---------- ------- ----------- ------------ Mariner 9 50 72 55984 Viking 1 189 96 157125 Viking 2 133 96 111896 ---------- ------- ------------ Total 372 325005 For each arc certain parameters were determined: the spacecraft state (position and velocity), a solar radiation pressure coefficient, Doppler biases for each station over the arc to account for frequency biases, and the mismodeling of the effects of the troposphere and ionosphere on the Doppler signal. The a priori force model that was used included the GMM-1 (Goddard Mars gravity model; archived here as GGM50A01.SHA), and included the third-body perturbations due to the Sun, all the planets (including Earth), the solar radiation pressure perturbation, and appropriate relativistic effects. The DE200 set of planetary and lunar ephemerides was used in the analyses. The model is defined in the IAU 1994 coordinate frame [DAVIESETAL1995]. The data were weighted at 2 to 5 mm/s. Although each data arc was typically fitted to the level of 1 mm/s, the data were downweighted in this fashion in order to attenuate the power of the high degree terms, and account for any systematic mismodeling that might still be present in the data. The solution was also derived using a power law rule (Kaula constraint of 13 x 105/L2) [KAULA1966], where L is the spherical harmonic degree. Without this constraint, the high degree terms develop excessive power. A degree strength a priori was also used in selected areas at the poles and Olympus Mons. This is a spatial constraint and is described in [KONOPLIV&SJOGREN1995], in which a detailed report is presented for the entire determination of this gravity field. In the process of deriving the model, extensive experiments were performed in order to select the a priori weights for the sets of data in the solution - and care was taken to downweight or delete data that produced spurious signals in the anomaly maps. The gravity anomalies in this model were evaluated at the Martian surface - assumed to be spherical with radius 3394.2 km. START_ORBIT_NUMBER and STOP_ORBIT_NUMBER are reserved for MGS orbits." START_ORBIT_NUMBER = "N/A" STOP_ORBIT_NUMBER = "N/A" START_TIME = 1971-11-14T00:00:00 STOP_TIME = 1980-08-07T23:59:59 SOFTWARE_NAME = "GRVMAP;V1.0" PRODUCT_CREATION_TIME = 1995-02-17T12:34:56.789 PRODUCER_ID = "MARS GRAVSCI TEAM" /* Structure Objects */ OBJECT = IMAGE LINES = 180 LINE_SAMPLES = 360 SAMPLE_TYPE = "IEEE REAL" SAMPLE_BITS = 64 OFFSET = 0.0E+00 SCALING_FACTOR = 1.0E+00 DESCRIPTION = "The Digital Map contains values of vertical gravity in milligals (1 milligal = 0.01 mm/s/s). The true values can be obtained by multiplying the sample in the map by SCALING_FACTOR and then adding OFFSET. " END_OBJECT = IMAGE OBJECT = IMAGE_MAP_PROJECTION ^DATA_SET_MAP_PROJECTION = "DSMAP2.CAT" COORDINATE_SYSTEM_TYPE = "BODY-FIXED ROTATING" COORDINATE_SYSTEM_NAME = PLANETOCENTRIC MAP_PROJECTION_TYPE = "SIMPLE CYLINDRICAL" A_AXIS_RADIUS = 3394.20 B_AXIS_RADIUS = 3394.20 C_AXIS_RADIUS = 3394.20 FIRST_STANDARD_PARALLEL = "N/A" SECOND_STANDARD_PARALLEL = "N/A" POSITIVE_LONGITUDE_DIRECTION = "EAST" CENTER_LATITUDE = 0.0 CENTER_LONGITUDE = 0.0 REFERENCE_LATITUDE = 0.0 REFERENCE_LONGITUDE = 0.0 LINE_FIRST_PIXEL = 1 LINE_LAST_PIXEL = 180 SAMPLE_FIRST_PIXEL = 1 SAMPLE_LAST_PIXEL = 360 MAP_PROJECTION_ROTATION = 0.0 MAP_RESOLUTION = 1.0E+00 MAP_SCALE = "N/A" MAXIMUM_LATITUDE = 89.5 MINIMUM_LATITUDE = -89.5 EASTERNMOST_LONGITUDE = 179.5 WESTERNMOST_LONGITUDE = -179.5 LINE_PROJECTION_OFFSET = 89.5 SAMPLE_PROJECTION_OFFSET = 179.5 END_OBJECT = IMAGE_MAP_PROJECTION END