PDS_VERSION_ID = PDS3 RECORD_TYPE = FIXED_LENGTH RECORD_BYTES = 122 FILE_RECORDS = 1325 ^SHADR_HEADER_TABLE = ("GGM50A02.SHA",1) ^SHADR_COEFFICIENTS_TABLE = ("GGM50A02.SHA",3) INSTRUMENT_HOST_NAME = "MARS GLOBAL SURVEYOR" TARGET_NAME = "MARS" INSTRUMENT_NAME = "RADIO SCIENCE SUBSYSTEM" DATA_SET_ID = "MGS-M-RSS-5-SDP-V1.0" OBSERVATION_TYPE = "GRAVITY FIELD" ORIGINAL_PRODUCT_ID = "SHGGMM-1.A01" PRODUCT_ID = "GGM50A02.SHA" PRODUCT_RELEASE_DATE = 1998-12-17 DESCRIPTION = "This file contains coefficients and related data for a Spherical Harmonic model of the Mars gravity field. Input data were from radio tracking of the Mariner and Viking spacecraft. There are no data from Mars Global Surveyor in this model, though the model serves as a baseline for future MGS models which will eventually be dominated by MGS measurements. The model was constructed from 232,323 observations, summarized in the table below. The data were divided into 270 spans or independent arcs (covering 1142 days) based on considerations of data coverage and timing of maneuvers. Spacecraft Periapsis Inclination Number Average Arc Total Altitude of Arcs Length Observations (km) (deg) (days) ---------- --------- ----------- ------- ----------- ------------ Mariner 9 1500 64.4 32 4.3 49878 Viking 1 1500 38.2 29 4.2 31393 Viking 1 300 39.1 95 4.8 63977 Viking 2 1400 55.4 12 3.8 11878 Viking 2 1500 75.1 11 4.7 10467 Viking 2 778 80.1 54 3.8 35375 Viking 2 300 80.2 37 4.2 29355 ---------- ------- ------------ Total 270 232323 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 (for the 300 km periapsis altitude arcs) a drag coefficient was adjusted on each day. The a priori force model that was used included a preliminary gravity solution obtained from the analysis of these data, a 50 x 50 solution designated mgm0340. In addition, third body perturbations were modeled, the solar radiation pressure perturbation was applied, and the appropriate relativistic perturbations in the measurement model, and the force model were included. The JPL DE-96 set of planetary and lunar ephemerides was used in these analyses. GGM50A02.SHA, differs from its predecessor, GGM50A01.SHA, in that the coordinate frame has been rotated to the IAU 1991 coordinate frame [DAVIESETAL1992] and the coefficients have been rescaled to a new reference radius (3396 km). The input data were weighted at 0.8 to 4.1 cm/s, and the data weights were calibrated using the subset calibration method of [LERCH1991]. Although each data arc was typically fitted to the level of a few 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. The gravity model was produced by the Goddard Space Flight Center Gravity Science Team under the direction of David E. Smith. For more information see [SMITHETAL1993]. The file contains two ASCII tables: a header table and a coefficients table, both defined below." START_ORBIT_NUMBER = "N/A" STOP_ORBIT_NUMBER = "N/A" START_TIME = 1971-11-14T00:00:00 STOP_TIME = 1980-08-07T23:59:59 PRODUCT_CREATION_TIME = 1993-11-25T00:00:00.000 PRODUCER_FULL_NAME = "DAVID E. SMITH" PRODUCER_INSTITUTION_NAME = "NASA/GODDARD SPACE FLIGHT CENTER" PRODUCT_VERSION_TYPE = "FINAL" PRODUCER_ID = "MGS GRAVSCI TEAM" SOFTWARE_NAME = "SOLVE, VERSION 9301" /* Structure Objects */ OBJECT = SHADR_HEADER_TABLE ROWS = 1 COLUMNS = 8 ROW_BYTES = 137 ROW_SUFFIX_BYTES = 107 INTERCHANGE_FORMAT = ASCII DESCRIPTION = "The SHADR header includes descriptive information about the spherical harmonic coefficients which follow in SHADR_COEFFICIENTS_TABLE. The header consists of a single record of eight (delimited) data columns requiring 137 bytes, a pad of 105 unspecified ASCII characters, an ASCII carriage-return, and an ASCII line-feed." OBJECT = COLUMN NAME = "REFERENCE RADIUS" DATA_TYPE = ASCII_REAL START_BYTE = 1 BYTES = 23 FORMAT = "E23.16" UNIT = "KILOMETER" DESCRIPTION = "The assumed reference radius of the spherical planet." END_OBJECT = COLUMN OBJECT = COLUMN NAME = "CONSTANT" DATA_TYPE = ASCII_REAL START_BYTE = 25 BYTES = 23 FORMAT = "E23.16" UNIT = "N/A" DESCRIPTION = "For a gravity field model the assumed gravitational constant GM in km cubed per seconds squared for the planet. For a topography model, set to 1." END_OBJECT = COLUMN OBJECT = COLUMN NAME = "UNCERTAINTY IN CONSTANT" DATA_TYPE = ASCII_REAL START_BYTE = 49 BYTES = 23 FORMAT = "E23.16" UNIT = "N/A" DESCRIPTION = "For a gravity field model the uncertainty in the gravitational constant GM in km cubed per seconds squared for the planet. For a topography model, set to 0." END_OBJECT = COLUMN OBJECT = COLUMN NAME = "DEGREE OF FIELD" DATA_TYPE = ASCII_INTEGER START_BYTE = 73 BYTES = 5 FORMAT = "I5" UNIT = "N/A" DESCRIPTION = "The degree of model field." END_OBJECT = COLUMN OBJECT = COLUMN NAME = "ORDER OF FIELD" DATA_TYPE = ASCII_INTEGER START_BYTE = 79 BYTES = 5 FORMAT = "I5" UNIT = "N/A" DESCRIPTION = "The order of the model field." END_OBJECT = COLUMN OBJECT = COLUMN NAME = "NORMALIZATION STATE" DATA_TYPE = ASCII_INTEGER START_BYTE = 85 BYTES = 5 FORMAT = "I5" UNIT = "N/A" DESCRIPTION = "The normalization indicator. For gravity field: 0 coefficients are unnormalized 1 coefficients are normalized 2 other." END_OBJECT = COLUMN OBJECT = COLUMN NAME = "REFERENCE LONGITUDE" POSITIVE_LONGITUDE_DIRECTION = "EAST" DATA_TYPE = ASCII_REAL START_BYTE = 91 BYTES = 23 FORMAT = "E23.16" UNIT = "DEGREE" DESCRIPTION = "The reference longitude for the spherical harmonic expansion; normally 0." END_OBJECT = COLUMN OBJECT = COLUMN NAME = "REFERENCE LATITUDE" DATA_TYPE = ASCII_REAL START_BYTE = 115 BYTES = 23 FORMAT = "E23.16" UNIT = "DEGREE" DESCRIPTION = "The reference latitude for the spherical harmonic expansion; normally 0." END_OBJECT = COLUMN END_OBJECT = SHADR_HEADER_TABLE OBJECT = SHADR_COEFFICIENTS_TABLE ROWS = 1323 COLUMNS = 6 ROW_BYTES = 107 ROW_SUFFIX_BYTES = 15 INTERCHANGE_FORMAT = ASCII DESCRIPTION = "The SHADR coefficients table contains the coefficients for the spherical harmonic model. Each row in the table contains the degree index m, the order index n, the coefficients Cmn and Smn, and the uncertainties in Cmn and Smn. The (delimited) data require 107 ASCII characters; these are followed by a pad of 13 unspecified ASCII characters, an ASCII carriage- return, and an ASCII line-feed." OBJECT = COLUMN NAME = "COEFFICIENT DEGREE" DATA_TYPE = ASCII_INTEGER START_BYTE = 1 BYTES = 5 FORMAT = "I5" UNIT = "N/A" DESCRIPTION = "The degree index m of the C and S coefficients in this record." END_OBJECT = COLUMN OBJECT = COLUMN NAME = "COEFFICIENT ORDER" DATA_TYPE = ASCII_INTEGER START_BYTE = 7 BYTES = 5 FORMAT = "I5" UNIT = "N/A" DESCRIPTION = "The order index n of the C and S coefficients in this record." END_OBJECT = COLUMN OBJECT = COLUMN NAME = "C" DATA_TYPE = ASCII_REAL START_BYTE = 13 BYTES = 23 FORMAT = "E23.16" UNIT = "N/A" DESCRIPTION = "The coefficient Cmn for this spherical harmonic model." END_OBJECT = COLUMN OBJECT = COLUMN NAME = "S" DATA_TYPE = ASCII_REAL START_BYTE = 37 BYTES = 23 FORMAT = "E23.16" UNIT = "N/A" DESCRIPTION = "The coefficient Smn for this spherical harmonic model." END_OBJECT = COLUMN OBJECT = COLUMN NAME = "C UNCERTAINTY" DATA_TYPE = ASCII_REAL START_BYTE = 61 BYTES = 23 FORMAT = "E23.16" UNIT = "N/A" DESCRIPTION = "The uncertainty in the coefficient Cmn for this spherical harmonic model." END_OBJECT = COLUMN OBJECT = COLUMN NAME = "S UNCERTAINTY" DATA_TYPE = ASCII_REAL START_BYTE = 85 BYTES = 23 FORMAT = "E23.16" UNIT = "N/A" DESCRIPTION = "The uncertainty in the coefficient Smn for this spherical harmonic model." END_OBJECT = COLUMN END_OBJECT = SHADR_COEFFICIENTS_TABLE END