Derived Neutron Data (DND)
The DND product contains normalized neutron counting rates for
all four of the Neutron Spectrometer (NS) prisms, from which thermal
and epithermal neutron count rates are determined.
Thermal and epithermal count rates are included in the data set.
Background-corrected and normalized fast counting data are also
provided for the nadir-looking prism (Prism 1). The data is
presented in a table format with one row of data for each NS
collection interval within a 24 Earth hour period. The DND
data can be used along with models and calibration procedures
described in the literature [Feldman et al., 2003; Prettyman
et al., 2004] to study the composition and structure of the
surface and atmosphere of Mars on sub-seasonal time scales.
The Mars Odyssey Gamma-Ray Spectrometer returns several neutron
spectra and a gamma spectrum about every 19.7 seconds, which is
the collection interval. This interval is the approximate
equivalent of one degree of motion or 59 kilometers over the
surface of Mars.
Derived neutron data follow a naming convention that begins with
the string "deriv_neutron_data_" followed by an eight-digit date field
in the format YYYYMMDD, e.g., deriv_neutron_data_20021001.dat
for data beginning on October 1, 2002.
GRS Product Revisions
It is important to note that DND and other GRS products may be
revised during the course of the mission. A product's revision
status is shown in its PDS label using the keyword
PRODUCT_VERSION_ID. The value of this keyword follows standard
practices of using "1.0" as the first version of a product. The
value on the left side of the decimal point refers to the major
revision, and the number(s) to the right of the decimal point
refer to minor updates. The value is incremented with each
product revision. The label keyword PRODUCT_CREATION_TIME
is also updated with each product revision.
For Further Information...
For more information, see the
section of the
GRS Data Interface pages.
Obtaining Derived Neutron 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 Derived Neutron Data (DND).
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 Corrected
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 Derived Neutron Data (DND)
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 Derived Neutron Data (DND)
button in the left menu. Then the DND 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.
For example, if you wished to obtain
Corrected Gamma Spectra starting on May 2, 2002 at 09:00:18 GMT
you would (Left-click) on the year, month, date, and time fields in the UTC
Start Time and choose the correct
values. Submenus will appear when you Left-click on a column value. For example, if you
(Left-Click) on the Year, the following submenu will appear:
Simply pull down the mouse to "2002" or the value that you have chosen. Then (Left-click)
again on the desired value. (Note: Your browser and mouse may work slightly differently,
but the submenus will still appear.)
Now you will enter the end date and
time (or second set of spatial constraints). If you wish to
collect 10 days of data from the start time entered above, you may enter "10" in the
range box: and press (Enter). The query
tool will automatically enter the correct end date.
You may enter the end date and time under UTC Stop Time by
(Left-Clicking) as above and choosing the correct values. An example end time would be
May 4, 2002, at 00:00:00 GMT. The image below shows how your query tool would look after
entering these example values:
- 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.