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:
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.
- The Small Detector (SD), with an energy range of 0.4 eV to 1 keV
- The Medium Detector (MD), with an energy range of 10 eV to 100 keV
- The Large Detector (LD), with an energy range of 10 eV to 1 MeV
- The Inner Scintillator (IN_SC_LOW), with a neutron pulse height of
1 MeV to 2.5 MeV, and
- The High Inner Scintillator (IN_SC_HIGH), with a neutron pulse height of
greater than 2.5 MeV.
For more information, see the
Both of the above documents are in the
section of the
AHD Data Interface pages.
AHD Data Set Description
HEND Data Processing Document.
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:
Once you have performed the above four steps, you are ready to begin downloading data.
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.
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.
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
Decide on the geographical area of interest, delimited by Martian
latitude and longitude, if applicable.
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)
Left-click) once on
. All the calibrated
products available will appear as a clickable list:
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.
- 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.
- 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.
- 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
Click on the link to
activate the Latitude-Longitude Chooser. The following new
window will appear:
Now you may enter the latitude and longitude in one of two ways:
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.
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.
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.
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
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.
(Left-click) on the year, date and degrees of
under the UTC
Start Time and choose the desired value:
(Left-click) on the year, date and degrees of
under the UTC
Stop Time and choose the desired value:
Check the range value. (Left-click) on the range pull-down menu and make any
Note that the range may be viewed by the number of days or angle of the Martian
- 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
For an explanation of bad codes, please see the
- (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
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.
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:
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.
- 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.
- 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.