PDS_VERSION_ID = PDS3 RECORD_TYPE = STREAM OBJECT = TEXT INTERCHANGE_FORMAT = ASCII PUBLICATION_DATE = 2001-09-01 NOTE = "N/A" END_OBJECT = TEXT END 1. Introduction ------------- This document provides an overview of the Near Earth Asteroid Rendezvous (NEAR) X-ray Spectrometer (XRS) instrument. The XRS Level 3 data products in this archive include daily time series of spectra collected by the instrument along with selected spacecraft engineering and instrument configuration and orbital ephemerides. Supporting documentation includes the specifics of how these data were generated. 2. Description of XRS Calibrated Level 3 Products ---------------------------------------------- The Level 2 data product comprises the time series of the XRS instrument'science data in physical units. At each integration time the instrument Data Processing Unit (DPU) samples instrument spectra accumulated during the integration period as well as instrument and engineering configurationinformation. Ground processing activities at the University of Arizona produce Derived Engineering and Spatial Ephemerides information. The Level-2 data are then combined into integral products within a relational database and exported as an integral Level-2 product. Each XRS Level-2 record is comprised of the following logical data units: Spectra: 4, (256 Channel) Spectra (UNF, MG, AL, SOL) UNF = Unfiltered: Asteroid Pointing MG = Magnesium: Asteroid Pointing AL = Aluminum: Asteroid Pointing SOL = Solar: Sun Pointing Instrument HouseKeeping: Instrument Rates and activity Engineering Housekeeping: Engineering Configurations Derived Engineering: Ground derived data products Spatial Orbital Ephemerides Each XRS Level-3 record is comprised of the same logical data units however, the spectra are summed from a set of level-2 integral records with selected averaging of all housekeeping and spatial ephemerides information. 3. File Formats ------------ The XRS Level 2 integral data are BINARY files the describe the integrated composition of spectral, orbital ephemerides, instrument configuration and derived products for each XRS integration period. Descriptions of each integral file comes with a detached PDS header label. A header label file describes attributes specific to each integration. Each header references a common label file for each integral file. An observation log file is included also an ASCII table described by its corresponding detached label. All text files (*.TXT 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 format of each Level-2 BINARY record file is: Example: x2000125051326.dat where x = X-ray Spectrometer 2000 = Year 125 = Julian Day 05 = hour 13 = minute 26 = second .dat = file extension The Level-3 record file name is "xsummary.txt" and is contained in each flare directory. The file is of type TEXT. The contents is generally as follows. * each spectra has 256 values (counts) * 2 sets of spectra, first on target and the second is calibration * 2 sets of parameters, first on target and the second is calibration * s/c information for each of two detectors * followed by averaged: engineering, coverage area and solar information For the complete description of the XRS Level-2 and 3 products see: "The Near Earth Asteroid Rendezvous, X-ray Spectrometer, Level-2 Requirements Specification": May 25, 2001 In the DOCUMENT Section. For the PDS submission Level-3 Integral products have been exported on specific to the occurence of solar flares which have been noted to provide the highest signal to noise spectra. Each flare in the Level-3 summary record XRS data collection will be stored in a directory specific to each of the selected flares directory comprised of variable number`s of integral Level-2 records plus a Level-3 summary record. The directory format is listed below in the directory elaboration. 4. Directory Contents ------------------ Files on this volume are organized into a series of subdirectories below the top-level directory. The following table shows the structure and content of these directories. In the table, directory names are enclosed in square brackets ([]). [DATA] | |- DATAINFO.TXT Desc. of files in the DATA dir. This file. |- [FLARE_2000_05_04] Flare from May 4, 2000 | | |-*.(lbl,dat) Flare Binary integrations, label files | | |-xsummary.txt Level-3 Summary file | | [FLARE_*] Other flares | | |-*.(lbl,dat) Flare Binary integrations, label files | | |-xsummary.txt Level-3 Summary file | ..... | 5. Cognizant Persons ----------------- NEAR/XRS data were provided by Jacob Trombka, NEAR XGRS Team Leader: Jacob Trombka Building 2, Rm# 165 Code 691, Astrochemistry Branch NASA/Goddard Space Flight Center Greenbelt, MD 20771. jack.trombka@gsfc.nasa.gov 301-286-5941 This volume was designed and produced by: Tim McClanahan Building 2, # 166 Code 691, Astrochemistry Branch NASA/ Goddard Space Flight Center Greenbelt, MD 20771