Index of /volume/nxersf_2002

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[DIR] Parent Directory - [DIR] calib/ 29-Aug-2002 10:44 - [DIR] catalog/ 29-Aug-2002 10:44 - [DIR] data/ 29-Aug-2002 10:44 - [DIR] document/ 29-Aug-2002 10:45 - [DIR] index/ 29-Aug-2002 10:45 - [TXT] aareadme.txt 21-Jun-2002 12:05 19K [   ] voldesc.cat 26-Aug-2002 11:06 4.2K [PDS catalog file]
PDS_VERSION_ID  REAM                                                          
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 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.                               
                                                                              
At the end of the orbital mission, the NEAR spacecraft was                    
maneauvered to perform a final landing on the surface of the                  
433 Eros asteroid.  Upon NEAR's successful landing, it was found              
that not only had the spacecraft remained intact, but it had also             
maitained an attitude capable of maintaining limited                          
communications contact with NASA's Deep Space Network (DSN) and               
simultaneously having the Gamma-ray spectrometer pointed to the               
surface.  At that time NEAR mission scientists proposed an                    
extension to the NEAR mission which included turning on the                   
Gamma-ray spectrometer to produce long duration, in-situ,                     
integrations of the spectrometer to generate high resolution                  
results.                                                                      
                                                                              
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.                                
                                                                              
                                                                              
2. Documentation                                                              
   _____________                                                              
                                                                              
This document provides an overview of the Near Earth Asteroid                 
Rendezvous Gamma-Ray On-asteroid Level 3 document archive.  These             
documents describe the design, development, implementation,                   
calibration and operations of the NEAR GRS instrument.  The                   
directory contains references for 2 documents that could not be               
included in this archive due to copyright concerns and are cited              
in the REF.CAT file in the CATALOG directory.                                 
                                                                              
An additional publication specific to the analysis of the GRS                 
on-asteroid data has been submitted to Meteoritics and                        
Planetary Science for publication in Fall 2001.                               
                                                                              
Elemental Composition from Gamma-Ray Spectroscopy of the NEAR-                
Shoemaker Landing Site on 433 Eros.  Larry Evans et. al.                      
                                                                              
Additional documentation is found in the DOCUMENT directory,                  
including a document describing the GRS instrument calibrations.              
                                                                              
3. Volume Set 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. As a result two Level-3 summary files were                  
generated as follows:                                                         
                                                                              
4. CD-ROM Format                                                              
   _____________                                                              
                                                                              
The CD-ROM has been formatted so that a variety of computer systems           
(e.g.,PC, Macintosh, and Sun) may access the data. Specifically, it           
is formatted according to the ISO-9660 level 1 Interchange Standard.          
For further information, refer to the ISO-9660 Standard Document:             
RF# ISO 9660- 1988, April 15, 1988.                                           
                                                                              
This CD-ROM does not contain any Extended Attribute Records (XAR).            
Thus, VAX/VMS users may have some problems accessing files on this            
volume.                                                                       
                                                                              
5. File Formats                                                               
   ____________                                                               
                                                                              
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:                          
                                                                              
6. Volume 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 ([]).                         
                                                                              
      FILE                  CONTENTS                                          
                                                                              
  Top-level directory                                                         
   |                                                                          
   |- AAREADME.TXT          The file you are reading.                         
   |                                                                          
   |- [DATA]                                                                  
   |   |- DATAINFO.TXT      Description of files in the DATA directory.       
   |   |- ONSURNS1.TAB      On Aster. NAI, ANTI, NAI1, NAI1 Integ.            
   |   |- ONSURBS1.TAB      On Aster. BGO Integration                         
   |   |- ONSURNA1.TAB      On Aster. NAI Ancillary information               
   |   |- ONSURBA1.TAB      On Aster. BGO Ancillary information               
   |   |                                                                      
   |                                                                          
   |- [DOCUMENT]            GRS Documentation file.                           
   |   |- DOCINFO.TXT       Description of files DOCUMENT directory.          
   |-  |- GRS_REQS_7_2.DOC  NEAR-GRS L-2 Requirement Specs (MS Word)          
   |-  |- GRS_REQS_7_2.LBL  Label file for GRS L-2 Reqs Doc versions          
   |-  |- GRS_REQS_7_2.TXT  Reduced form, NEAR GRS Reqs specs. (ASCII)        
   |-  |- GRS_REQS_7_2.JPG  Reqs. saved as multi-page Jpeg file.              
   |-  |- GRS_REQS_7_2.TIF  Reqs. saved as multi-page TIF file.               
   |-  |- GRS_REQS_7_2_*    Individual pages NEAR GRS L-2 Reqs. Spec.         
   |   |-                   Also included label file each TIF image           
   |   |-                   Saved as 1 page per TIF file, * = Page #          
   |   |- [INSTRUMENT]      Includes XGRS_DEFINITIONS file                    
   |   |- [OBSERVATION_LOG] Has various logs and user guide.                  
   |   |- [GRS_RESULTS]     Includes explanation of abundances and various    
   |   |                    figures from MAPS paper                           
   |                                                                          
   |- [CATALOG]                                                               
   |   |- CATINFO.TXT       Catalog directory information                     
   |   |- INSTHOST.TXT      Instrument design information                     
   |   |- MISSION.CAT       NEAR Mission related information and refs         
   |   |- PERSON.CAT        Personnel associated with this submission         
   |   |- REF.CAT           References to other publications                  
   |   |- GRSURFL3.CAT      Description of this GRS dataset                   
   |   |- XGRSINST.CAT      Instrument related Information                    
   |                                                                          
                                                                              
7. Whom To Contact For Information                                            
   _______________________________                                            
                                                                              
For questions concerning this data set collection:                            
                                                                              
     Planetary Data System (PDS)                                              
     Small Bodies Node (SBN)                                                  
     Astronomy Department                                                     
     University of Maryland                                                   
     College Park, MD 20742                                                   
                                                                              
     NEAR/XGRS Science Team                                                   
     Code 691, Astrochemistry Branch                                          
     NASA / Goddard Space Flight Center                                       
     Greenbelt, MD 20771                                                      
     WWW Site: http://leptpm.gsfc.nasa.gov/near.html                          
     Electronic mail addresses: jack.trombka@gsfc.nasa.gov,                   
                                tim.mcclanahan@gsfc.nasa.gov                  
                                                                              
8. Cognizant Persons                                                          
   _________________                                                          
                                                                              
NEAR/XGRS 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