PDS_VERSION_ID = PDS3 RECORD_TYPE = FIXED_LENGTH RECORD_BYTES = 122 FILE_RECORDS = 2927 ^SHADR_HEADER_TABLE = ("JGM75A01.SHA",1) ^SHADR_COEFFICIENTS_TABLE = ("JGM75A01.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 = "MGS75A" PRODUCT_ID = "JGM75A01.SHA" PRODUCT_RELEASE_DATE = 1999-05-01 DESCRIPTION = " This file contains coefficients and related data for the MGS75A Spherical Harmonic model of the Mars gravity field. MGS75A was derived from radio tracking of the Mariner 9, Viking 1 Orbiter, Viking 2 Orbiter, and Mars Global Surveyor spacecraft. MGS Doppler and ranging data were collected during the Orbit Insertion subphases of Aerobraking 1, Science Phasing Orbit 1, and Science Phasing Orbit 2 (through 1998-09-20). Although there are approximately 4000 Mariner 9, 14000 Viking, and 134000 MGS observations incorporated in the solution, the observations do not provide uniform coverage. The Mariner 9 data are from a very eccentric orbit with periapsis altitudes of 1400 km and periapsis latitudes near equatorial (very high altitudes over the poles). The Viking data are much better with periapsis altitudes of 300 km; but the latitudes of periapsis were almost all in the northern hemisphere (only a few at 40 degrees south with an orbit inclination of 40 degrees. The MGS data provide excellent new coverage over the north polar region with periapsis latitudes ranging from 65-85 degrees north and altitudes of 180 km. But the southern hemisphere gravity remains very poorly defined and at about the same state of knowledge as before MGS (Konopliv and Sjogren, Jet Propulsion Laboratory Publication 95-5, 1995). The reduction procedure was the same as described in Konopliv and Sjogren (1995); however the coordinate frame and constants are from the published IAU 1991 J2000 system. The main contribution from the MGS data is the resolution of the north polar region where feature resolution is about 200-300 km. Correlation of gravity with surface imaging and MOLA topography is not one to one, but some areas do correlate -- such as Chasma Boreale, which follows a gravity low as one might expect. For additional details see an article planned for publication in Science in late 1999. This file is a pair of ASCII tables: a header table and a table of 5772 coefficients (plus a value for GM). Definitions of the tables follow. The MGS75A gravity model is delivered in the Spherical Harmonics Gravity ASCII Data Record (SHGADR) and is produced by the Mars Global Surveyor Gravity Science Team at JPL under the direction of William L. Sjogren." START_ORBIT_NUMBER = 1 STOP_ORBIT_NUMBER = 572 START_TIME = 1997-09-12T00:00:00.000 STOP_TIME = 1998-09-23T23:59:59.999 PRODUCT_CREATION_TIME = 1999-05-01T00:00:00.000 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" 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 kilometers 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 kilometers 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 = 2925 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