Averaged HEND Data (AHD)

The Mars Gamma-Ray Spectrometer Averaged High-Energy Neutron Data (HEND) data set is a collection of data tables that contain an average counting rate and the associated engineering data for each of the five neutron signals that are obtained by the High-Energy Neutron Detector's four individual detectors. These data have been summed by signal over 5-degree by 5-degree latitude and longitude cells on the Martian surface over a time period of 15 degrees of solar longitude (, or also called "L-sub-S" in the Data Interface). Thus the HEND data have been binned both spatially and temporally in the PDS Data Interface output files.

The spatial constraint for AHD data is a 5-degree latitude by 5-degree longitude bin. Latitudes and longitudes are calculated for each pixel based on the spacecraft position at the midpoint of the collection interval.

The temporal constraint for AHD data is measured by 15-degree increments of , which is equivalent to a Martian week. AHD product data files contain a table of one 15-degree of temporal bin, with one record per spatial bin. The AHD data files are grouped by Martian year and .

The AHD product data is presented in a table corresponding to a 5-degree by 5-degree grid. There are 36 latitude bands and 72 longitude bands, thus 2592 grid cells. Each cell corresponds to one row in the table. The first 72 rows in the table are the data for the 5 degree latitude band centered at 87.5 degrees north latitude, the second 72 rows are the data for the band centered at 82.5 degrees north latitude, and so on. Within each band, longitude increases eastward from the cell centered at 2.5 degrees east longitude to the cell centered at 357.5 degrees east longitude.


Neutron Signals of Interest

The five neutron signals of interest are:

  1. The Small Detector (SD), with an energy range of 0.4 eV to 1 keV

  2. The Medium Detector (MD), with an energy range of 10 eV to 100 keV

  3. The Large Detector (LD), with an energy range of 10 eV to 1 MeV

  4. The Inner Scintillator (IN_SC_LOW), with a neutron pulse height of 1 MeV to 2.5 MeV, and

  5. The High Inner Scintillator (IN_SC_HIGH), with a neutron pulse height of greater than 2.5 MeV.

Each of these GRS HEND detectors collects a new spectrum (also called a pixel, or frame) approximately every 20 seconds, or 360 times per orbit. About 4,200 spectra are received daily. The AHD is intended to be the second intermediate data product available for the HEND portion of the GRS dataset. These data whould be useful to scientists who are experienced in neutron spectroscopy.

For more information, see the
  • AHD Data Set Description

  • HEND Data Processing Document.
Both of the above documents are in the section of the AHD Data Interface pages.

Obtaining Averaged HEND Data, Step by Step

For new users, this web page provides help in a step-by-step way, and will walk you through a session using the GRS Data Interface to obtain Gamma-Ray Spectrometer Averaged HENDData (AHD).

Before You Download...

Before you execute any query using the GRS Data Interface, please do the following to prepare:

  1. Decide which type of data you wish to download. Remember that Averaged Data (also called "Calibrated Data") is an intermediate product that has been processed. Uncalibrated data, on the other hand, is raw data that has had timing and spatial data added. For more detailed information on the data products, see the data product links on the left menu bar.
  2. Consider your connection speed to the internet and your computer's system resources such as disk space and RAM when deciding how many days of data to download per file. It is best to choose time spans on the scale of a week or several weeks at most for Corrected Gamma spectra, for example, due to the large output file sizes. On any type of data it is best to choose one month or less time spans to maximize the download time and prevent overloading your system's resources.
  3. Decide on the beginning and ending dates and times for the data you wish to download. Keep in mind the flight phases of the spacecraft, and when the desired data was created in the spacecraft's timeline.
  4. Decide on the geographical area of interest, delimited by Martian latitude and longitude, if applicable.

Once you have performed the above four steps, you are ready to begin downloading data.

Mouse clicking instructions are included for the PC-style, two-button mouse. (Left-click) means to click on an icon or text with the left mouse button. Macintosh users have a one-button mouse typically, and should click once with their mouse when (Left-click) is in the instructions. UNIX users with three-button mouses should also use their left mouse button to (Left-click).


Creating a Query for Averaged HEND Data (AHD)

  1. Left-click) once on . All the calibrated products available will appear as a clickable list:




  2. After the selections are displayed and open, (Left-click) on the Averaged HEND menu item. Then the AHD data type will then be highlighted with the darker grey-purple:

    In the right-hand side of the GRS Data Node window, a description of the chosen data type will appear, including descriptions of all field (column) types in that particular data, the units of each field (column), and other information.


  3. If you would like to print the column-field information about this type of data, (Right-Click) in the Column Descriptions area, and use your web browser's ability to "Open this Frame in a New Window." You may then print from that new window. This will give you a hard-copy description of all of the column descriptions, their units of measure, etc. Return to the main GRS Data Node window before proceeding.


  4. To enter the dates or other database query criteria, click on the button to continue.

    Note that data entry areas appear that allow you to constrain your database query by time, or constrain it by spatial region (if available). Also, an option to exclude data marked bad is offered.


  5. Enter your latitude and longitude constraints. The Data Interface allows you to Constrain by Spatial Region. Note the following area for changing the latitude and longitude:



    If you do not wish to select the entire planet, proceed to the next step. If you wish to select the entire planet, go to step 9.

  6. Click on the link to activate the Latitude-Longitude Chooser. The following new window will appear:




  7. Now you may enter the latitude and longitude in one of two ways:

    1. By pointing and clicking. You will draw an imaginary box, from the upper-left corner of the region you wish to specify, to the lower-right corner. This is identical to drawing a box in a drawing program on your computer.

      Place the mouse cursor over the MOLA image of Mars. Notice that the mouse cursor turns into a crosshair ().

      Locate the cursor on the upper-left corner of the region box you wish to draw.

      Click and hold the (Left-Mouse) button. Pull down and to the right, until you reach the lower-right corner of your desired rectangular area. The corresponding coordinates will appear in the latitude and longitude data entry area below the MOLA map.

    2. By entering the latitude and longitude manually in the data entry area below the map:

      Click in the area. Type in the starting latitude of your region of interest, from +90 (Martian North Pole) to -90 (Martian south pole).

      Click on the area. Type in the ending latitude of your region of interest.

      Click on the area. Type in the starting longitude in degrees East around Mars, from 0 degrees to 360 degrees.

      Click on the area. Type in the ending longitude of your region of interest.

    In either case, note that you may not specify a region that spans the 360-degree longitude mark. As an example, you may not specify a region from 350 degrees to 20 degrees in longitude. This area of interest would have to be split into two regions, one from 350 degrees to 360 degrees, and the other from 0 degrees to 20 degrees.

  8. Click on the button after the correct longitude and latitude of your region of interest are entered.



    Enter your starting constraints for the date and time. The next two steps will select the start time and stop time for your data query, and the following section appears in the PDS Data Interface.



    Note that under this Constrain by Time section, the following categories appear:


    The Start Time and Stop Time define the time period you wish to compile data for by date, with an assumed time of midnight GMT on each date. The time period as defined by the angle of the Martian orbit, or , which is also called "L-sub-S" in the Data Interface. In the Range, you may view or specify the time period by the number of days or the value of the angle.

    Pulldown menus provide pre-selected dates for starting and ending dates, with a set time of midnight for each.


  9. (Left-click) on the year, date and degrees of under the UTC Start Time and choose the desired value:


  10. (Left-click) on the year, date and degrees of under the UTC Stop Time and choose the desired value:


  11. Check the range value. (Left-click) on the range pull-down menu and make any adjustments:


    Note that the range may be viewed by the number of days or angle of the Martian orbit ().


  12. Decide whether to exclude bad data, or not. If you leave the box checked as shown:



    Data marked as bad will NOT be included in your data set. If you wish to include bad data, (Left-click) once on the box to un-check it. It is almost always recommended that bad data be excluded.

    For an explanation of bad codes, please see the bad_code.txt document.


  13. (Left-click) on the button to start compiling your query. Then an output like the following will appear:



    If no data matching your selection criteria is found, you will get a message that says: In those cases, you need to go back and modify your query.

    Note that in the example above the data is compiled but no data files are downloaded yet. You still may go back and change your criteria. If you wished to modify this query, pressing the button will allow you to go back and redo it.

    All files are downloaded in zip (PC compressed) file format. The above gives you the number of records that matched your query, and the estimated file size of your data file once it has been unzipped.

  14. To download the file, click on the link to it (on the estimated file size) under "Download." In our example above, you would left-click on .

    A status window, generated by your web browser, will then appear and inform you of the progress of the download. Below is an example window from Netscape, version 7:



  15. Click on the "Save to File" in your browser's download window. Then a window similar to the following will appear, prompting you to choose a folder to download the file to:

    Make certain you have adequate disk space on your computer before you save the file.

  16. Click on the button (or equivalent, depending on your browser) to save the file. Depending on the size of the file to be downloaded, this can take a few minutes or many minutes, depending on your internet connection speed, your computer's speed, and the size of the file.

  17. Use the Data Viewer software provided by the GRS PDS Data Node to quickly peruse the data, or write custom programs in the language of your choice to read and utilize the data. A library of source code that will parse the uncalibrated (EDR) and calibrated (IDR) data product files is included in the folder. This library allows a programmer to build applications that display or manipulate the GRS data. This source is written in the Java language, and requires version 1.4 of the Java Runtime Environment (JRE) or Java Software Development Kit (SDK). For those who wish to use other languages, consult the Labels files to create structures to read in the files for each type of data.