Data Set Information
DATA_SET_NAME CLEM1 LUNAR GRAVITY V1.0
DATA_SET_ID CLEM1-L-RSS-5-GRAVITY-V1.0
NSSDC_DATA_SET_ID
DATA_SET_TERSE_DESCRIPTION
DATA_SET_DESCRIPTION Data Set Overview : The gravitational signature of the Moon was determined from velocity perturbations of the Clementine spacecraft as measured from the Doppler shift of the S-band radio tracking signal. Clementine was tracked by NASA's Deep Space Network (DSN) at Goldstone, California, Canberra, Australia, Madrid, Spain, as well as by the Pomonkey, Maryland, tracking station operated by the Naval Research Laboratory. The tracking data were used to determine the Clementine orbit about the Moon, as well as the lunar gravity field [ZUBERETAL1994]. A detailed description of how the Clementine orbits were computed and an assessment of their quality can be found in [LEMOINEETAL1995B]. The Clementine data were combined with S-band tracking observations from Lunar Orbiters 1, 2, 3, 4, and 5 and from the Apollo 15 and 16 subsatellites [KONOPLIVETAL1993B]. With the exception of the Lunar Orbiter 4 and Lunar Orbiter 5 spacecraft, these spacecraft lacked the global coverage of Clementine (LO-4 and LO-5 were placed in near polar, elliptical orbits of the Moon), but most had lower periapsis altitudes and thus provided distributed regions of short-wavelength resolution in the vicinity of spacecraft periapses (generally +/- 40 degrees latitude). There are seven gravity products in this archive. These include a 70-th degree and order spherical harmonic gravitational field model, designated Goddard Lunar Gravity Model 2 (GLGM-2), and digital gridded maps of the Free-air gravity anomalies (at 1 and 0.25 degree resolution), Free-air gravity errors, Bouguer gravity anomalies, Geoid anomalies, Geoid anomaly errors, and effective crustal thicknesses. Data : There are 3 data types for the gravity products found on this volume: tabular, array, and image data. The file containing the spherical harmonic coefficients of the Moon's gravity field (GLGM-2) is in tabular format, with each row in the table containing the degree index m, the order index n, the coefficients Cmn and Smn, and the uncertainties in Cmn and Smn. The gridded digital maps of Free-air gravity anomalies (at 1 and 0.25 degree resolution), Free-air gravity errors, Bouguer anomalies, Geoid anomalies, Geoid anomaly errors, and crustal thicknesses are ASCII 2-D data arrays. There is also a byte-scaled image of each of the gridded products. Parameters : The gravitational signature of the Moon was determined from velocity perturbations of the Clementine spacecraft, Lunar Orbiters and Apollo 15 and 16 subsatellites as measured from the Doppler shift of the S-band radio tracking signal. The Clementine Doppler data from the DSN stations were acquired with a count interval of 10 seconds. Data from the Pomonkey station were also at a 10 second count interval. Most of the historic Doppler data were at a count interval of 60 seconds. The Free-air gravity anomalies of the Moon (in milligals, mGals, where 1 mGal : 0.01 mm/s^2) are evaluated at the surface, and are determined from the GLGM-2 solution. The Free-air gravity errors are also in mGals. Bouguer anomalies, determined by subtracting the gravitational attraction of the surface topography from the free-air anomaly, are in mGals. Geoid anomalies and errors are in meters. Crustal thicknesses, assuming a constant-density crust and mantle, are in kilometers. Processing : The GLGM-2 gravity solution consists of 708,854 observations, of which 361,794 were contributed by Clementine. The data were divided into 392 spans or independent arcs based on considerations of data coverage and timing of maneuvers. The table below summarizes the number of observations and arcs from each spacecraft: Satellite Number Avg. Arc Total Observations of Arcs Length (hours) Lunar Orbiter-1 48 21.76 44,503 Lunar Orbiter-2 62 16.38 68,732 Lunar Orbiter-3 68 17.77 61,852 Lunar Orbiter-4 11 70.16 48,734 Lunar Orbiter-5 51 33.74 47,690 Apollo-15 subsatellite 81 16.76 44,096 Apollo-16 subsatellite 35 4.55 31,453 Clementine 36 44.16 361,794 Total 392 708,854 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 [KONOPLIVETAL1993B] gravity model, and included the third-body perturbations due to the Sun, the Earth, and all the planets, the solar radiation pressure perturbation, the Earth-induced and solar-induced solid lunar tides (assuming a k2 value of 0.027, as derived by previous investigators), and appropriate relativistic effects. The DE200 set of planetary and lunar ephemerides was used in the analyses. The data in GLGM-2 were weighted at 1 to 3 cm/s, with the exception of the Clementine data, which had a data weight of 0.5 cm/s (because of their high quality). Although each data arc was typically fit 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 15 x 10e-5/L^2), where L is the spherical harmonic degree. Without this constraint, the high degree terms develop excessive power. In the process of deriving GLGM-2, 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. (GLGM-2 is the 309th in the series of lunar gravity solutions that have been developed in the course of this work since just prior to the Clementine mission). The gravity anomalies in this model were evaluated at the lunar surface. Ancillary Data : N/A Coordinate System : The coordinate system for the gravity data, and the coefficients in the GLGM-2 gravity field, is selenocentric, center of mass, longitude positive east. The location of the pole and the prime meridian are defined as per the reference from [DAVIESETAL1992B], with corrections for two of the terms. alpha_0 : 270.000 + 0.003 T - 3.878 sin E1 - 0.120 sin E2 + 0.070 sin E3 - 0.017 sin E4 delta_0 : 66.541 + 0.013 T + 1.543 cos E1 + 0.024 cos E2 - 0.028 cos E3 + 0.007 cos E4 W : 38.317 + 13.1763582 d + 3.558 sin E1 + 0.121 sin E2 - 0.064 sin E3 + 0.016 sin E4 + 0.025 sin E5 E1 : 125.045 - 0.052992 d E2 : 250.090 - 0.105984 d E4 : 176.625 + 13.340716 d The quantities E3 and E5 are listed incorrectly in the reference, and were corrected by [DAVIESETAL1993B, personal communication to the Clementine Science Team]. The correct values are: E3 : 260.008 + 13.012001 d E5 : 357.529 + 0.985600 d where T : interval in Julian centuries (36525 days) from the standard epoch. d : interval in days from the standard epoch. W : location of the prime meridian in degrees. alpha_0 and delta_0 are the standard equatorial coordinates, in degrees, with equinox J2000 at epoch J2000 (right ascension and declination). Standard Epoch is 2000 January 1.5 or Julian Date 2451545.0 TBD. Software : N/A Media/Format : The Clementine gravity dataset will be available electronically via the World-Wide Web and anonymous FTP transfer. File types include ASCII and binary formats. Formats will be based on standards established by the Planetary Data System (PDS).
DATA_SET_RELEASE_DATE 1996-01-01T00:00:00.000Z
START_TIME 1994-02-19T12:00:00.000Z
STOP_TIME 1994-05-03T12:00:00.000Z
MISSION_NAME DEEP SPACE PROGRAM SCIENCE EXPERIMENT
MISSION_START_DATE 1991-11-19T12:00:00.000Z
MISSION_STOP_DATE 1994-05-07T12:00:00.000Z
TARGET_NAME MOON
TARGET_TYPE SATELLITE
INSTRUMENT_HOST_ID CLEM1
INSTRUMENT_NAME RADIO SCIENCE SUBSYSTEM
INSTRUMENT_ID RSS
INSTRUMENT_TYPE RADIO SCIENCE
NODE_NAME Geosciences
ARCHIVE_STATUS ARCHIVED
CONFIDENCE_LEVEL_NOTE Overview : The data noise on the historic Doppler data ranged from 0.3 to several mm/s, depending on the arc, and most of the data were at a count interval of 60 seconds. The Clementine Doppler data from the DSN stations had a data noise of 0.25 mm/s with a count interval of 10 seconds. Clementine was also tracked by a 30 meter antenna of the Naval Research Lab in southern Maryland. These data were also at 10 second count interval and had a data noise of 2.5 to 3.0 mm/s. Errors in the Free-air gravity anomalies from GLGM-2 ranged from 17-24 mGals over the equatorial nearside (+/- 30 degrees latitude), 32-36 mGals over the equatorial farside, and 40-45 mGals over the high-latitude farside. The relative errors in Clementine topography are governed by the orbital accuracy, of order 10 m and the Lidar noise, of order 40 m, which translates to a 5 mGal error in the Bouguer anomaly. Errors in the Geoid range from 4-24 meters. Gridded digital maps showing the errors associated with the Free-air gravity and Geoid anomalies are included in the archive. Review : The volume containing the Clementine gravity and topography datasets was reviewed by Clementine mission scientists and by PDS. Data Coverage/Quality : The Clementine data now provide the most powerful constraint on the low degree and order field, and strongly determine the low degree harmonics, as well as the sectoral terms of the lunar gravity field through degree 20. The historical data from the Lunar Orbiters and the Apollo-15 subsatellite provided distributed regions of higher resolution coverage in the equatorial regions (+40 degrees N to -40 degrees S). This is a consequence of the lower periapse altitude of these satellites: the Lunar Orbiters were placed in eccentric orbits with periapse altitudes as low as 30 km, but more typically between 60 to 100 km. The Apollo-15 subsatellite was located in a near-circular, retrograde orbit (inclination of 152 degrees) with a mean altitude of 100 km. Clementine, with its eccentric near-five hour orbit, in contrast had a periapse altitude of 415 km. Because of the Moon's synchronous rotation, spacecraft cannot be directly tracked from Earth over a large part of the lunar far side, so there is no tracking data from 120 to 240 degrees longitude in the +/- 45 degree latitude band. Limitations : See Data Coverage/Quality above.
CITATION_DESCRIPTION Lemoine, F. G. R., CLEM1 LUNAR GRAVITY V1.0, CLEM1-L-RSS-5-GRAVITY-V1.0, NASA Planetary Data System, 1996
ABSTRACT_TEXT The gravitational signature of the Moon was determined from velocity perturbations of the Clementine spacecraft as measured from the Doppler shift of the S-band radio tracking signal. Clementine was tracked by NASA's Deep Space Network (DSN) at Goldstone, California, Canberra, Australia, Madrid, Spain, as well as by the Pomonkey, Maryland, tracking station operated by the Naval Research Laboratory. The tracking data were used to determine the Clementine orbit about the Moon, as well as the lunar gravity field [ZUBERETAL1994]. A detailed description of how the Clementine orbits were computed and an assessment of their quality can be found in [LEMOINEETAL1995B].
PRODUCER_FULL_NAME FRANK G. R. LEMOINE
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