PDS_VERSION_ID = PDS3 RECORD_TYPE = FIXED_LENGTH RECORD_BYTES = 122 FILE_RECORDS = 1327 ^SHADR_HEADER_TABLE = ("JGM50C01.SHA",1) ^SHADR_COEFFICIENTS_TABLE = ("JGM50C01.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 = "SHGMARS50C.A01" PRODUCT_ID = "JGM50C01.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 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. The gravity model was produced by the Jet Propulsion Laboratory Gravity Science Team under the direction of William L. Sjogren. 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 = 1995-02-22T01:02:03.456 PRODUCER_FULL_NAME = "WILLIAM L. SJOGREN" PRODUCER_INSTITUTION_NAME = "JET PROPULSION LABORATORY" PRODUCT_VERSION_TYPE = "PRELIMINARY" PRODUCER_ID = "MGS GRAVSCI TEAM" SOFTWARE_NAME = "SHAGRV;V1.0" /* 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 = 1325 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