PDS_VERSION_ID = PDS3 RECORD_TYPE = STREAM OBJECT = TEXT NOTE = "XGRS BROWSE Directory information file" PUBLICATION_DATE = 2001-06-19 END_OBJECT = TEXT END /******* BROWINFO.TXT ********* Date: May 30, 2001 Introduction: ------------- This file describes the contents of the BROWSE partition of the Near Earth Asteroid Rendezvous (NEAR), X-ray and Gamma-ray Spectrometer (XGRS) submission to NASA's Planetary Data System (PDS). The data included are derived from the operation of the NEAR X-ray spectrometer and are meant for use as an initial reference tool for future science investigation. The BROWSE directory contains the high level results of all XRS data collected during the periods that the NEAR spacecraft was below 50 km distance from the surface of the 433 Eros asteroid which comprise the most optimal sampling conditions for the XRS experiment. The results are in the form of daily image histograms (JPEGS) of spectra collected for the Solar pointing and Unfiltered asteroid pointing detectors as well as an image (JPEG) comprised of 6-orthogonal views of the asteroid surface in asteroid body fixed coordinates. The map is generated by virtually positioning and orienting the sun, spacecraft, instrument pointing and asteroid in a 3-D model specific to the time the sample is collected. Counts collected in the XRS asteroid pointing detector are then projected back to the model for each integration. Total counts accumulations are then color coded and an image is generated for each of the six orthogonal views of the model. Ancillary data are also included that provide a textual summary of the daily averages of spatial ephemerides and instrument specific information. The XGRSBROWSE.HTML file is a browser developed to integrate a view of each of the daily images that were generated for the XRS low altitude sampling. This facility provides a calendar date reference to each day. Time tags are all based on UTC base time. Directory Contents: ------------------- BROWINFO.TXT ; Overview of PDS XGRS BROWSE Directory XGRSBROWSE.HTML ; Browsable Calendar Style index for Daily Images ./COV_MAP ; Daily coverage caps (JPEG Images) ./HIST ; Daily histograms (JPEG Images) ./SOLAR ; Solar Pointing Detector (JPEG Images) ./UNFIL ; Unfiltered Pointing Detector (JPEG Images) ./DAILY_SUMMARY ; Summary:Spatial Ephemerides, daily coverage map ./D_HTML ; Daily html reference files that integrate and display each day of browse data Description of Contents: ------------------------ 1. COV_MAP: ------- This directory contains images that were generated using a software application called Spec3d. The application can produce coverage maps of the surface of all data collected during a specified time interval by simulating the position of the spacecraft and the XRS asteroid pointing instrument field of view with respect to the asteroid surface. A coverage map is produced by discretely accumulating all occurrences of the field of view with respect to the surface and color coding the number of occurrences of the field of view on each plate in the 7500 plate asteroid model. Each image is rendered by taking the six orthogonal views of the asteroid map, in asteroid body fixed coordinates and projecting each orthogonal view to its appropriate position in the image. The image may be printed, cut, and folded into a six sided rectangular block. An associated text file is included that contains daily averages of spatial ephemerides information. 2. ./HIST: ----------- This directory contains images that were generated using the XRS quicklook application. The application can take spectral data and generate a false color image of the sequence of spectra (X-axis), versus the spectral channel or energy (Y-axis). The intensity in each channel is color coded using the color table COLORTBL.TXT by calculating the Log base 10 of the counts in each channel and normalizing by the distance between the maximum and minimum values in each histogram divided by 256 colors. Note: A dynamic averaging algorithm is run during the generation of each histogram to reconcile the differences between the number of spectra and channels to be displayed versus the available screen space. So: * Color assignments and averaging intervals may be different from one histogram to another. Color assignments are blue for low #'s of counts in each channel to yellow for high numbers of counts in each channel. See the color scale in the lower left of each image. A. ./HIST/SOLAR: Solar Histograms contain the information from the XRS solar pointing detector. Each histogram contains the time sequenced daily solar activity. Low energy channels are at the bottom of the histogram. Spectra are sequenced in time from left to right and rendered into a histographic image. Each Solar Histogram contains: Date of Generation: ; Upper right Histogram ; Left Center Log base 10 Normalized color scale ; Lower Left Spectral Type ; = Solar Number of Channels in Histogram ; = 256 Channel Binning Interval ; 1 = no chan. avg. File Name with Calendar Date ; Lower Right Solar events transition in time from blue and green color coded regions to red and yellow starting in the low channels and extend to higher channels as the spectrum hardens. Solar events typically build quickly and dissipate more slowly. B. ./HIST/UNFIL: UNFILTERED Histograms contain the information from the XRS Unfiltered asteroid pointing detector. Each histogram contains the time sequenced daily results. Low energy channels are at the bottom of the histogram. Spectra are sequenced in time from left to right and rendered into a histographic image. Each UNFILTERED Histogram contains: Date of Generation: ; Upper right Histogram ; Left Center Log base 10 Normalized color scale ; Lower Left Spectral Type ; = Solar Number of Channels in Histogram ; = 256 Channel Binning Interval ; 1 = no chan. avg. File Name with Calendar Date ; Lower Right 3. ./DAILY_SUMMARY ------------- For each coverage map generated (COV_MAP) a text file is generated that contains summary information about the spatial ephemerides convolved in each coverage map. Averages of the spatial ephemerides such as angles, instrument integration times, and the numbers of asteroid on-pointing and off pointing occurrences of the instrument boresite during the day. Blue areas of the map contain low numbers of coverage and red is high. 4. ./D_HTML -------- A directory for the daily HTML reference files. Referenced from the MAIN.HTML in the ./BROWSE directory. 5. Daily Image Review Notes: The purpose of the XGRSBROWSE.HTML browser is to allow the direct correlation of the solar activity and fluorescence collected. The top two images in each daily image browser are the XGRS Unfiltered and Solar Histograms. Since the fluorescence collected in the XRS asteroid pointing detector is a function of many factors such as orbital geometry, instrument pointing, solar activity (flux), how much of the XRS field of view on the surface is illuminated, incidence angle, emission angle, and instrument configuration, the fluorescence detection can be viewed as largely circumstantial. In the daily representations the two images have identical sample time resolution in both the X-axis and Y-axis. Solar flares, seen in the top image as (Yellow and Red) vertical oblong blotches on a (blue green background) may or may not be correlated to fluorescence detection in the second image (Unfiltered). EXAMPLE: -------- An Example of fluorescence detection is on May 4, 2000. During the day 1723 XRS spectral integrations were collected as noted by the 1723 in the right of each of the top two images. During the first part of the day an M-class solar flare took place at approximately hour 04 minute 45, (UTC). The solar fluorescence is noted in the top image as the first vertical yellow stripe (Left to right). In the Unfiltered image, directly below, fluorescence is noted in the asteroid pointing detector as a vertical strip, of the same time resolution, bright yellow at the bottom part of the image and transitioning to red in the higher energies. A second event in the day occurs approximately mid day, where the solar detector briefly turned itself off due to high flux conditions, (blue vertical streak). Surface fluorescence is also noted in the Unfiltered image directly below. a. At times the images have bright yellow vertical streaks in them. This is usually due to the presence of bad telemetry packets having not been caught by the Data Quality Index flag (DQI). The presence of these streaks can shift the distribution of colors allocated in an image to lower than expected (blue and green) missing the typical reds and yellows of the highest intensity data. b. In the Solar monitor image some images have both PIN and GAS detector solar spectra interleaved in a ping pong mode. In the image this looks like interleaved vertical stripes. Engineering flags from the datasets can identify these periods. See the the NEAR XRS Level 2 requirements specifications. c. In the Unfiltered data a horizontal color break occurs about channel 57 in the image. This is due to the discriminator setting. d. Color changes in the images are a function of counts distributions being mapped to 256 available colors. Different images will change in color based on counts distribution variance. e. Solar monitor angle also changes significantly during the course of the mission, but constrained to be below 40 degrees from directly pointing at the sun for power considerations. The change in the solar detector pointing angle alters the performance of the solar detector as low energy counts are lost due to collimator influences. The issue is currently being modeled by XRS team members. f. There will be occurrences where there may not be daily correlated histograms or coverage maps or summaries available for each day. Possible reasons include telemetry dropouts, instrument down time or other processing related reasons. 6. 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