PDS_VERSION_ID = PDS3 RECORD_TYPE = STREAM OBJECT = DATA_SET DATA_SET_ID = "NEAR-A-GRS-3-EDR-EROS/SURFACE-V1.0" OBJECT = DATA_SET_INFORMATION DATA_SET_NAME = "NEAR GRS SPECTRA EROS ON ASTEROID" DATA_SET_COLLECTION_MEMBER_FLG = "N" DATA_OBJECT_TYPE = SPECTRUM START_TIME = 2001-02-19T16:59:24 STOP_TIME = 2001-02-28T17:49:37 DATA_SET_RELEASE_DATE = 2001-07-15 PRODUCER_FULL_NAME = "JACOB TROMBKA" DETAILED_CATALOG_FLAG = "N" DATA_SET_DESC = " Introduction ============= This document provides an overview of the Near Earth Asteroid Rendezvous Gamma-Ray Spectrometer, On asteroid Level 3 data archive. This volume contains science data products from observations acquired by the Near Earth Asteroid Rendezvous (NEAR) Gamma-ray Spectrometer (GRS) instrument. The following documentation and dataset describes the dataset and documentation delivered as part of the NEAR XGRS instrument team delivery to NASA's Planetary Data System. Volume Information ================== It was found that the on surface attitude of the spacecraft did not facilitate the use of the fixed high gain antenna and the low gain antenna was used for the duration of the on-surface mission. As a result available telemetry rates did not facilitate the downlink of the full complement of instrument, engineering and ancillary information with priority being given to selected spectra. The first two days of on-surface activity were used to calibrate the detectors to account for deviations of temperature between orbital and on surface operations. Adjustments were then made to the instrument high voltage to improve the energy gain in the escape peak spectra. In this configuration, several long term integrations were collected and spectra from the 2 longest integration times (total duration = 586320 sec) were summed for (NAI, ANTI, NAI1, and NAI2) spectra. The higher counting rate BGO spectrum was taken and from a single integration of (total duration = 346480 secs). Each of set of spectra were corrected for channel rollover which occured in several instances due to long integration times causing accumulations of counts in some channels to exceed and rollover the maximum numerical range of the 2 byte channel. Higher counting rates in the lower energies of each spectrum incurred multiple rollovers and algorithms were developed to rectify this effect. A second correction made to the on-surface spectra is the removal of differential non-linearities (DNL) contained within the spectra. The effect being high frequency spikes in channels spaced at regular intervals within the spectrum. (DNL)`s were removed using a 3rd order polynomial fit and smoothing function for a sliding boxcar of 21 channels through each raw spectrum. The result is then provided as a GRS Level-3 spectrum. The GRS on asteroid Level 3 data are contained in ASCII TABLE`s files that contain corrected spectra and associated ancillary information specific to each integration as a seperate table. All TABLE files (*.TAB files) and detached labels (*.LBL files) on this volume,are stream format files, with a carriage return (ASCII 13) and a line feed character (ASCII 10) at the end of each line. This allows the files to be read by the MacOS, DOS, and UNIX operating systems. An example and description of the content and format of the two on asteroid Level-3 record files described below. File 1: ONSURNAS.TAB - Asteroid Surface Position (Lat, Lon) West Longitude - Starting time tags (MET) for each summed integrations - End (MET) - Energy Calibration - Instrument Attitude ONSURNSS.TAB - 4 Spectra (NAI, ANTI, NAI1, NAI2) - Summed from From 2 seperate Integrations (total duration = 586320 sec) File 2: ONSURBAS.TAB - Starting time tags (MET) for the single BGO integration - End (MET) - Energy Calibration - Asteroid Surface Position (Lat, Lon) West Longitude - Instrument Attitude ONSURBSS.TAB - 1 Spectrum, BGO - Starting time tags for the summed BGO integration - Summed from From 2 seperate Integrations (total duration = 346480 sec) These products are located in in the DATA directory: Coordinate System ================= All products were derived in the Asteroid Body Fixed Coordinate System Software ======== Requirement Specifications For Level-2 Parameters Required Stored or Derived by The Near Earth Asteroid Rendezvous (NEAR) Gamma-Ray Spectrometer (GRS) Ground System Media ====== CD-ROM " CONFIDENCE_LEVEL_NOTE = " Overview ======== Data in this archive have been reduced as part of mission data analysis activities of the NEAR XGRS Science Team. Data of questionable validity have been omitted from the solutions. Review ====== This archival data set was reviewed by the NEAR XGRS Team prior to submission to the Planetary Data System (PDS). It was one of several data sets included in a comprehensive review by the PDS Small Bodies Node in August 2001, prior to PDS acceptance and ingestion. Data Coverage and Quality ========================= The data included in this archive were collected during the NEAR orbital phase from 2001-02-19 to 2001-02-28. Limitations =========== None " END_OBJECT = DATA_SET_INFORMATION OBJECT = DATA_SET_TARGET TARGET_NAME = "EROS" END_OBJECT = DATA_SET_TARGET OBJECT = DATA_SET_HOST INSTRUMENT_HOST_ID = "NEAR" INSTRUMENT_ID = "GRS" END_OBJECT = DATA_SET_HOST OBJECT = DATA_SET_REFERENCE_INFORMATION REFERENCE_KEY_ID = "CHENGETAL1998" END_OBJECT = DATA_SET_REFERENCE_INFORMATION END_OBJECT = DATA_SET END