Data Set Information
DATA_SET_NAME NEAR NLR LEVEL 3 DATA PRODUCTS V1.0
DATA_SET_ID NEAR-A-NLR-6-EROS-MAPS-MODELS-V1.0
NSSDC_DATA_SET_ID
DATA_SET_TERSE_DESCRIPTION
DATA_SET_DESCRIPTION Data Set Overview : The NEAR Laser Rangefinder (NLR) Level 3 Data Products includes spherical harmonic shape and gravity models, and gridded maps or images of those models. Parameters : Spherical harmonic models are tables of coefficients GM, Cmn, and Smn. ASCII data type (SHA) formats are defined. Each file contains 2 tables: a header table containing general parameters for the model (gravitational constant, its uncertainty, degree and order of the field, normalization state, reference longitude, and reference latitude) and a coefficients table (degree m, order n, coefficients Cmn and Smn, and their uncertainties). Gridded Digital Map files are image representations of shape and other parameters. Gravity and topographic values may be displayed using this data type. Data are formatted as PDS image objects. Processing : The Level 2 NLR profiles in the 200 by 200 km orbital phases and lower are the source of the NLR shape models. Where two ground tracks intersect, the residual is calculated by linear interpolation between adjacent shots. The crossover residuals are used as a measure of data quality and can be used to remove systematic errors in spacecraft ephemeris and pointing. Crossover corrections are implemented in two stages via the software described in [NEUMANNETAL2001], as modified for NLR. The first stage adjusts for long-wavelength errors due to mis-modeled ephemeris and pointing, at a period of four cycles per asteroid revolution. The second stage adjusts higher-frequency errors at a period of ~5 minutes, primarily due to residual pointing mismodeling. Adjustments are iterated until the crossover residual root-mean-square error is less than 10 m. The adjusted profiles are merged by binning observations within a given grid cell, uniformly spaced in longitude and latitude. The median value and the number of observations in each bin comprise the gridded data product. The gravity field coefficients were obtained by solving systems of equations with thousands of unknowns. Radio tracking data in long arcs delimited by propulsive maneuvers, occultations, etc. were used in solutions that were obtained iteratively and by least squares. Data : Data are stored on CD-WO volumes. A CD volume was created for delivery of data to PDS. ASCII spherical harmonic models are stored in the /LEVEL3/SHA directory with file names of the form NLRknnnv.SHA, where nnn is a 3-character modifier specified by the data producer, v is a version identifier, and k is replaced by G for gravity field or T for topography/shape field, and SHA denotes that this is an ASCII file of spherical harmonic coefficients. Gridded map products are stored in the /LEVEL3/IMG directory. Each image is a binary array of 16-bit integers with one image line per file record. The image file name is in the form NLRnnnvk.IMG, where nnn is the bin size, v is a version identifier, and k is replaced by C for counts or R for radius, and IMG denotes that this is a PDS image object. For example, a one-eighth degree resolution topography image would be named NLR125vR.IMG. Its format would be described by a detached PDS label in the file NLR125vR.LBL. An ASCII tabular file containing global shape data of Eros, including the latitude and longitude of the NLR laser bounce point, the radius, and the number of observations (counts) can be found in the /LEVEL3/ASCII directory. Ancillary Data : None. Coordinate System : NLR data files use an EROS centered body-fixed coordinate system with positive east longitude. The transformation from inertial (J2000) coordinates to body-fixed is represented by the project-supplied SPICE format attitude and orientation files used to generate level 2 data products. Software : None. Media/Format : The archival data set was written on CD-WO by the NEAR/NLR Project. The CD-WO volumes conform to ISO 9660 Level 2 standards.
DATA_SET_RELEASE_DATE 2001-07-13T00:00:00.000Z
START_TIME 2000-03-05T12:00:04.000Z
STOP_TIME 2001-02-12T07:04:01.000Z
MISSION_NAME NEAR EARTH ASTEROID RENDEZVOUS
MISSION_START_DATE 1996-02-17T12:00:00.000Z
MISSION_STOP_DATE 2001-02-28T12:00:00.000Z
TARGET_NAME EROS
TARGET_TYPE ASTEROID
INSTRUMENT_HOST_ID NEAR
INSTRUMENT_NAME NEAR LASER RANGEFINDER
INSTRUMENT_ID NLR
INSTRUMENT_TYPE ALTIMETER
NODE_NAME Small Bodies
ARCHIVE_STATUS ARCHIVED
CONFIDENCE_LEVEL_NOTE Overview : Data in this archive have been reduced as part of mission data analysis activities of the NEAR/NLR Science Team. Review : This archival data set was reviewed by the NEAR/NLR Science Team prior to final submission to the Planetary Data System (PDS). Prior to creation of the final version of the archival data set, key elements of the archive were distributed for preliminary review. These included electronic versions of example PDS labels, example data files, CATALOG files, and other relevant documentation. These materials were distributed to PDS personnel, the experiment investigator, and others, as appropriate. Data Coverage and Quality : These volumes contain gravity and shape models and gridded maps generated from NEAR data collected through February 2001. The NEAR data included tracking results from the EROS Orbit Phase. GTM0180A.SHA contains the coefficients for a 180x180 degree and order shape model produced at Goddard Space Flight Center. A full error analysis is included. Internal consistency, as measured by crossover point misfit, is generally better than 10 m. NLRG016A.SHA is a spherical harmonic gravity field model complete to degree and order 16. NLR125AR.IMG is a gridded shape map of Eros at a resolution of 0.125 by 0.125 degrees, based on altimetry data acquired by the NLR instrument. The data include edited NLR observations from 200-km orbits and lower, using the NLR393 orbit solutions produced at NASA-GSFC. NLR125AC.IMG is a data file that accompanies the shape map of Eros NLR125AR.IMG at a resolution of 0.125 by 0.125 degrees. It contains the number of observations per pixel that have been used to produce the NLR shape data product. The data include edited NLR observations from 200-km orbits and lower. NLR100.TAB is a 1 degree resolution tabular data file that contains global shape data of Eros, including the latitude and longitude of the NLR laser bounce point, the radius, and the number of observations (counts). Limitations : There is NO gravity covariance matrix on these volumes. This product is useful in understanding the errors in the gravity solution. The gravity field covariance represents the complete error description for the gravity field solution, including the coefficient variances (sigmas^2), and the correlations between all the coefficients. This product was not available at the time this archive was completed. The file and documentation will be available at a later date on the World Wide Web/Internet at the following URL: http://pds-geophys.wustl.edu/pds/near_nlr.
CITATION_DESCRIPTION Neumann G., D. Smith, NEAR NLR LEVEL 3 DATA PRODUCTS V1.0, NEAR-A-NLR-6-EROS-MAPS-MODELS-V1.0, NASA Planetary Data System, 2001.
ABSTRACT_TEXT NLR Level 3 Data Products includes spherical harmonic shape and gravity models, and gridded maps or images of those models.
PRODUCER_FULL_NAME DAVID E. SMITH
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