DATA_SET_DESCRIPTION 
Data Set Overview
=================
The gravitational signature of the Moon was determined from
velocity perturbations of the Lunar Prospector (LP) spacecraft as
measured from the Doppler shift of the Sband radio tracking
signal. LP was tracked by NASA's Deep Space Network (DSN) at
Goldstone, California, Canberra, Australia, and Madrid, Spain.
The tracking data were used to determine the LP orbit about the
Moon, as well as the lunar gravity field [KONOPLIVETAL1998].
The LP data were combined with Sband tracking observations from
Lunar Orbiters 1, 2, 3, 4, and 5 and from the Apollo 15 and 16
subsatellites [KONOPLIVETAL1993B] and from Clementine
[LEMOINEETAL1997].
In advance of the LRO mission, the Lunar Prospector and other
historical tracking data were reanalyzed and the GLGM3 model was
developed. The model is documented in a JGR paper
[MAZARICOETAL2010]. In addition, the GLGM3 model was extended to
degree 200 using a LineofSight (LOS) analysis technique
[HANETAL2011] to produce the LPE200 model.
Data
====
There are 2 data types for the gravity products found on this
volume: tabular and array data. The files containing the
spherical harmonic coefficients of the Moon's gravity field
(GLGM3150, LPE200) are in tabular (ASCII) and array (BINARY)
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 binary array file is a
littleendian, row ordered upper triangular matrix.
Coordinate System
=================
The coordinate system for the gravity data, and the coefficients
in the GLGM3150 and LPE200 gravity fields is selenocentric, center
of mass, longitude positive east. The location of the pole and
the prime meridian are defined by the principal axes as given by
the integrated lunar librations of DE421 [WILLIAMSETAL2008].
Processing
==========
The GLGM3 gravity solution consists of 4,324,171 observations, of
which 3,570,901 were contributed by LP. The data were divided
into 1225 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 Total Periapsis Apoapsis
of Arcs Observ. (km) (km)
Lunar Orbiter1 70 48,575 50 1830
Lunar Orbiter2 90 77,726 50 1870
Lunar Orbiter3 73 62,264 50 1820/320
Lunar Orbiter4 32 48,688 2700/75 6000/4000
Lunar Orbiter5 70 42,916 100/170 1750/2000
Apollo15 subsatellite 93 52,500 75 160
Apollo16 subsatellite 46 42,579 30 190
Clementine 40 378,022 370 2960
LP (nominal) 184 2,198,751 90 110
LP (extended) 127 1,372,150 25 45
Total 1225 3,570,901
For each arc certain parameters were determined: for example, the
spacecraft state (position and velocity), solar radiation pressure
coefficients, Doppler biases for each station over the arc to
account for frequency biases, and increments in velocity to
account for spacecraft manuevers. The DE421 set of planetary and
lunar ephemerides was used in the analyses.
Average data fits and the final effective data weight for each set
of the data in the solution are as follows:
Satellite Avg. RMS of fit Eff. Data Wt.
(cm/s) (cm/s)
Lunar Orbiter 1 0.24 3.16
Lunar Orbiter 2 0.11 3.16
Lunar Orbiter 3 0.07 3.16
Lunar Orbiter 4 0.05 0.55
Lunar Orbiter 5 0.21 0.49
Apollo 15 subsatellite 0.12 0.95
Apollo 16 subsatelite 0.15 0.32
Clementine 0.31 1.34
Lunar Prospector (nom) 0.02 1.41
Lunar Prospector (ext) 0.25 3.78
Media/Format
============
This data set is stored online at the Planetary Data System
(http://pds.nasa.gov/) and may be downloaded using a web browser
or FTP software. A copy may be requested on physical media if
downloading is not possible. The Planetary Data System maintains
backup copies of this data set on various media.

CONFIDENCE_LEVEL_NOTE 
Confidence Level 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.
[KONOPLIVETAL2001] provides a detailed description of the Lunar
Prospector tracking data. The overall data accuracy was about
0.3 mm/s but there was some variability due to antenna type
(34 m vs. 26 m). In addition during the extended mission,
[KONOPLIVETAL2001] reports that multipath signals make the LP
Doppler data closer to the poles more noisy. We note that
[KONOPLIVETAL2001] applied a deweighting scheme (cf pp.5 of
[KONOPLIVETAL2001]) due to convergence of the ground tracks. No
such deweighting by latitude was performed with GLGM3.
Errors in the Freeair gravity anomalies computed from the full
error covariance to 150x150 range from a minimum of 2.4 mGals on
the nearside equator to a maximum of 78.1 mGals on the mid
latitude regions of the lunar farside. The lunar nearside is
characterized by errors of 230 mGals. The lunar farside is
characterized by errors of 30 to 78 mGals. Similarly errors in the
geoid, computed from the full error covariance to 150x150 range
from a minumum of 0.1 meters on the nearside to a maximum of 24.8
meters on the midlatitude regions of the farside. On the
nearside, the geoid errors are under 8 meters. Geoid errors on the
lunar farside range from 8 to 25 meters. These errors are computed
as commission error to degree 150, and do not include omission
error (the contribution of error from degrees higher than 150).
Review
======
The volume containing the LP gravity dataset was formally
reviewed by the PDS in October 2011.
Data Coverage/Quality
=====================
Lunar Prospector is the first circular polar orbiter for the Moon
in a low altitude orbit of 100 km. The only previous low altitude
data (about 100 km) was from the Lunar Orbiters and the Apollo
subsatellites at low inclination (which provide coverage at < 30
degrees of latitude). Lunar Orbiters 4 and 5 provided some near
equatorial data at low altitude from their polar eccentric orbit,
but no low altitude data for the high latitudes. Clementine, with
its eccentric nearfive hour orbit, had a periapse altitude of 415
km and so provided long wavelength information on the gravity
field.
Because of the Moon's synchronous rotation, spacecraft cannot be
directly tracked from Earth over a large part of the lunar
farside, so there is no tracking data from 120 to 240 degrees
longitude in the +/ 70 degree latitude band.
Limitations
===========
See Data Coverage/Quality above.
