MGN RSS Gravity Data Records (GRAV)
GRAV – Gravity Data Records
Instrument: Magellan Radio Science
PDS Data Set ID: MGN-V-RSS-5-GRAVITY-L2-V1.0 (In the “gravity” and “images” subdirectories) DOI: 10.17189/1522521Citations of DOI: 10.17189/1522521
PDS4 Bundle:urn:nasa:pds:magellan_gravityDOI: 10.17189/bbn0-je09
For more information about RSS GRAV products, see the GRAV Data Set Description.
The Radio Science Subsystem (RSS) Gravity Data Records (GRAV) data products include spherical harmonic gravitational field models and digital gravity maps of the Bouguer anomalies, free-air gravity anomalies, free-air gravity errors, geoid anomalies, and geoid anomaly errors.
The gravitational signature of Venus was determined from velocity perturbations of the Pioneer Venus Orbiter (PVO) and the Magellan spacecraft as measured from the Doppler shift of the S-band and X-band ratio tracking signal. The Doppler data from the Deep Space Network (DSN) stations were acquired with count intervals of 1 minute and 10 seconds.
The free-air gravity anomalies (in milligals, mGals, where 1 mGal = 0.01 mm/s2) are evaluated at the surface. The free-air gravity errors are also in mGals. Geoid anomalies and errors are in meters. Bouguer anomalies, determined by subtracting the gravitational attraction of the surface topography from the free-air anomaly, are in mGals.
The free-air gravity values are given by the radial (or vertical) acceleration at the reference surface. This is the radial gradient of the gravity potential. The reference surface is a sphere with radius 6051.0 km. The GM for the potential expansion is 324858.5897 km3/s2 (from the 120th degree and order gravity field solution).
The Bouguer map is the actual free-air gravity minus the theoretical free-air gravity from the topography with no compensation. The acceleration difference is at the reference surface of 6051.0 km. The reference radius for the topography field is 6051.848044 km.
The gravity solution consists of over 3,304,000 observations, of which 204,000 were contributed by PVO. The data were divided into independent arcs based on considerations of data coverage and timing of maneuvers. For each arc certain parameters were determined: the spacecraft state (position and velocity), a solar radiation pressure coefficient, Doppler biases for each station of 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 model that was used included the Konopliv et al., 1993 (doi:10.1029/93GL01890) gravity model, and included the third-body perturbations due to the Sun, the Earth, and all the planets, the solar radiation pressure perturbation, the solar-induced solid tides, and appropriate relativistic effects. The DE403 planetary ephemeris was used in the analyses.
GRAV data files. Unless otherwise noted, files have a detached PDS label (.XML in PDS4 and .LBL in PDS3):
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urn:nasa:pds:magellan_gravity:gravity Collection (.DAT unless otherwise noted) |
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shgj120p |
Coefficients and related data for the MGNP120PSAAP Spherical Harmonic model of the Venus gravity field (ASCII), with an attached PDS3 label and deattached PDS4 label. |
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shgj120u |
Coefficients and related data for a spherical harmonic model of the Venus gravity field (binary). |
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shgj180u |
Coefficients and related data for the MGNP180U Spherical Harmonic model of the Venus gravity field (ASCII), with an attached PDS3 label and deattached PDS4 label. |
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bouguer |
A digital map of Venus Bouguer anomaly derived from radio tracking of the Magellan spacecraft. |
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bouggrd |
A 180 line by 360 sample ASCII array of free-air gravity accelerations. |
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freeair |
A digital map of Venus gravity accelerations derived from radio tracking of the Magellan spacecraft. |
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fairgrd |
A 180 line by 360 sample ASCII array of free-air gravity accelerations. |
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fairerr |
A 180 line by 360 sample ASCII array of the errors in the free-air gravity accelerations. |
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geoid |
A digital map of Venus geoid derived from radio tracking of the Magellan spacecraft. |
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geoidgrd |
A 180 line by 360 sample ASCII array of geoid anomalies. |
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geoiderr |
A 180 line by 360 sample ASCII array of the errors in the geoid anomalies. |
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bouggrd |
A 180 line by 360 sample byte-scaled image of bouguer gravity anomalies. |
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fairgrd |
A 180 line by 360 sample byte-scaled image of free-air gravity accelerations. |
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fairerr |
A 180 line by 360 sample byte-scaled image of the errors associated with the free-air gravity accelerations. |
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geoidgrd |
A 180 line by 360 sample byte-scaled image of geoid anomalies. |
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geoiderr |
A 180 line by 360 sample byte-scaled image of the errors associated with the geoid anomalies. |
In ODE, GRAV products have the following product IDs (in the same order as the table above):
GRAVITY Collection
shgj120p
shgj120u
shgj180u
bouguer
bouggrd
freeair
fairgrd
fairerr
geoid
geoidgrd
geoiderr
IMAGES Collection
bouggrd
fairgrd
fairerr
geoidgrd
geoiderr