PDS_VERSION_ID = "PDS3" FILE_NAME = "JGM75A01.SHB" RECORD_TYPE = FIXED_LENGTH RECORD_BYTES = 512 FILE_RECORDS = 260600 ^SHBDR_HEADER_TABLE = ("JGM75A01.SHB",1) ^SHBDR_NAMES_TABLE = ("JGM75A01.SHB",2) ^SHBDR_COEFFICIENTS_TABLE = ("JGM75A01.SHB",93) ^SHBDR_COVARIANCE_TABLE = ("JGM75A01.SHB",184) SPACECRAFT_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" PRODUCT_ID = "JGM75A01.SHB" PRODUCT_RELEASE_DATE = 1999-05-01 DESCRIPTION = " This file contains formal error covariance 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 product is a set of four binary tables: a header table, a names table, a coefficients table, and a covariance table. Definitions of the tables follow. The MGS75A gravity model is delivered in the Spherical Harmonics Gravity Binary Data Record (SHGBDR) 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 = "SHBGRV;V1.0" OBJECT = SHBDR_HEADER_TABLE ROWS = 1 COLUMNS = 9 ROW_BYTES = 56 INTERCHANGE_FORMAT = BINARY DESCRIPTION = "The SHBDR Header includes descriptive information about the spherical harmonic coefficients which follow in SHBDR_COEFFICIENTS_TABLE. The header consists of a single record of nine data columns requiring 56 bytes. The Header is followed by a pad of binary integer zeroes to ensure alignment with RECORD_BYTES." OBJECT = COLUMN NAME = "REFERENCE RADIUS" DATA_TYPE = IEEE_REAL START_BYTE = 1 BYTES = 8 UNIT = "KILOMETER" DESCRIPTION = "The assumed reference radius of the spherical planet." END_OBJECT = COLUMN OBJECT = COLUMN NAME = "CONSTANT" DATA_TYPE = IEEE_REAL START_BYTE = 9 BYTES = 8 UNIT = "N/A" DESCRIPTION = "For a gravity field model the 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 = IEEE_REAL START_BYTE = 17 BYTES = 8 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 = MSB_INTEGER START_BYTE = 25 BYTES = 4 UNIT = "N/A" DESCRIPTION = "Degree of the model field." END_OBJECT = COLUMN OBJECT = COLUMN NAME = "ORDER OF FIELD" DATA_TYPE = MSB_INTEGER START_BYTE = 29 BYTES = 4 UNIT = "N/A" DESCRIPTION = "Order of the model field." END_OBJECT = COLUMN OBJECT = COLUMN NAME = "NORMALIZATION STATE" DATA_TYPE = MSB_INTEGER START_BYTE = 33 BYTES = 4 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 = "NUMBER OF NAMES" DATA_TYPE = MSB_INTEGER START_BYTE = 37 BYTES = 4 UNIT = "N/A" DESCRIPTION = "Number of valid names in the SHBDR Names Table. Also, the number of valid coefficients in the SHBDR Coefficients Table." END_OBJECT = COLUMN OBJECT = COLUMN NAME = "REFERENCE LONGITUDE" POSITIVE_LONGITUDE_DIRECTION = "EAST" DATA_TYPE = IEEE_REAL START_BYTE = 41 BYTES = 8 UNIT = "DEGREE" DESCRIPTION = "The reference longitude for the spherical harmonic expansion; normally 0." END_OBJECT = COLUMN OBJECT = COLUMN NAME = "REFERENCE LATITUDE" DATA_TYPE = IEEE_REAL START_BYTE = 49 BYTES = 8 UNIT = "DEGREE" DESCRIPTION = "The reference latitude for the spherical harmonic expansion; normally 0." END_OBJECT = COLUMN END_OBJECT = SHBDR_HEADER_TABLE OBJECT = SHBDR_NAMES_TABLE ROWS = 5773 COLUMNS = 1 ROW_BYTES = 8 INTERCHANGE_FORMAT = BINARY DESCRIPTION = "The SHBDR Names Table contains names for the solution parameters (including gravity field coefficients) which will follow in SHBDR_COEFFICIENTS_TABLE. The order of the names in SHBDR_NAMES_TABLE corresponds identically to the order of the parameters in SHBDR_COEFFICIENTS_TABLE. Each coefficient name is of the form Cij or Sij where i is the degree of the coefficient and j is the order of the coefficient. Both indices are three- digit zero-filled right-justified ASCII character strings (for example, C010005 for the 10th degree 5th order C coefficient, or S002001 for the 2nd degree 1st order S coefficient). The eighth byte in the table is an ASCII blank used to ensure that the row length is equal to RECORD_BYTES. Names of other solution parameters are limited to 8 ASCII characters; if less than 8, they will be left-justified and padded with ASCII blanks. The Names Table itself will be padded with ASCII blanks, if necessary, so that its length is an integral multiple of RECORD_BYTES." OBJECT = COLUMN NAME = "PARAMETER NAME" DATA_TYPE = CHARACTER START_BYTE = 1 BYTES = 8 UNIT = "N/A" DESCRIPTION = "The name of the coefficient or other solution parameter, left- justified and padded with ASCII blanks (if needed) to 8 characters." END_OBJECT = COLUMN END_OBJECT = SHBDR_NAMES_TABLE OBJECT = SHBDR_COEFFICIENTS_TABLE ROWS = 5773 COLUMNS = 1 ROW_BYTES = 8 INTERCHANGE_FORMAT = BINARY DESCRIPTION = "The SHBDR Coefficients Table contains the coefficients and other solution parameters for the spherical harmonic model. The order of the coefficients in this table corresponds exactly to the order of the coefficient and parameter names in SHBDR_NAMES_TABLE. The SHBDR Coefficients Table will be padded with double precision DATA_TYPE zeroes so that its total length is an integral multiple of RECORD_BYTES." OBJECT = COLUMN NAME = "COEFFICIENT VALUE" DATA_TYPE = IEEE_REAL START_BYTE = 1 BYTES = 8 UNIT = "N/A" DESCRIPTION = "A coefficient Cij or Sij or other solution parameter as specified in the SHBDR Names Table." END_OBJECT = COLUMN END_OBJECT = SHBDR_COEFFICIENTS_TABLE OBJECT = SHBDR_COVARIANCE_TABLE ROWS = 16666651 COLUMNS = 1 ROW_BYTES = 8 INTERCHANGE_FORMAT = BINARY DESCRIPTION = "The SHBDR Covariance Table contains the covariances for the spherical harmonic model coefficients and other solution parameters. The order of the covariances in this table is defined by the product of the SHBDR Names Table with its transpose, except that redundant terms are omitted on their second occurrence. The SHBDR Covariance Table will be padded with double precision DATA_TYPE zeroes so that its total length is an integral multiple of RECORD_BYTES." OBJECT = COLUMN NAME = "COVARIANCE VALUE" DATA_TYPE = IEEE_REAL START_BYTE = 1 BYTES = 8 UNIT = "N/A" DESCRIPTION = "The covariance value for the coefficients and other solution parameters specified by the product of SHBDR_NAMES_TABLE with its transpose, after omitting redundant terms." END_OBJECT = COLUMN END_OBJECT = SHBDR_COVARIANCE_TABLE END