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National Snow & Ice Data Center, Boulder, CO
This document is being continually updated. If you have questions, comments, or suggestions regarding the use of these data or this document, please contact NSIDC User Services via this form, send us e-mail (nsidc@nsidc.org), or call us at 303-492-6199.
This file is intended as a quick question and answer reference guide. More detailed information about the data are available from the following data set documents:
- AVHRR Polar Pathfinder Twice-Daily 5 km EASE-Grid Composites
- AVHRR Polar Pathfinder Twice-Daily 25 km EASE-Grid Composites
- DMSP SSM/I Pathfinder Daily EASE-Grid Brightness Temperatures
- Nimbus-7 SMMR Pathfinder Daily EASE-Grid Brightness Temperatures
- Polar Pathfinder Sampler: Combined AVHRR, SMMR-SSM/I, and TOVS Time Series and Samples
- Snow Data Assimilation System (SNODAS) Data Products at NSIDC
- TOVS Pathfinder Path-P Daily Arctic Gridded Atmospheric Parameters
Please note that, as of 02 June 2008, the Polar Spatial Query tool (PSQ) is no longer available. The machine on which PSQ resided has reached its life expectancy and we do not plan to rectify the machine or the PSQ tool. Thus, orders placed after 02 June 2008 will not be fulfilled. Please contact NSIDC User Services if you have questions or concerns regarding the PSQ tool.
There are a number of differences and the relative importance of those differences depends your intended use of the data. We'll summarize here but we recommend you read all the data documentation as well.
Input data: The GISMO is designed to work with gridded input data while the PSQ is designed to work with swath and scene input data. Both GISMO and PSQ produce gridded output data.
Interface: There are two GISMO interfaces (see question #2) and only one PSQ interface. There is a lot of reuse between these interfaces, and they are designed to accomplish similar tasks, so they look quite similar. There are, however, two main differences:
The GISMO allows searches on only one collection at a time, but it can search on one or more parameters within that collection. The PSQ allows searches on any number of collections and any number of parameters.
The user may not select the grid in the geographic screen of the GISMO. The displayed grid is the grid the selected collection is in. PSQ input data, however, are not already in a grid. Consequently, PSQ users can, and should, select their desired output grid in the geographic screen.
Searching: The GISMO only allows searches of one collection at a time, and the geographic coverage of every granule in a given collection is the same. Consequently, the GISMO only searches by temporal range and parameter. The GISMO does not search by spatial extent since every granule in the collection has the same geographic coverage.
The PSQ does search by spatial extent since the spatial coverage of the SSM/I swath data and AVHRR scene data varies significantly. The PSQ uses an orbit search algorithm to search for SSM/I swath data and a slightly more restrictive version of that same algorithm to search for AVHRR scene data. These algorithms depend on orbit and sensor characteristics, so the PSQ runs a slightly different search for each data set. Consequently, searches on a wide variety of data may take a bit longer.
Input data: We currently distribute TOVS, SMMR, SSM/I, AVHRR, and SNODAS data via the GISMO. Only SSM/I and AVHRR are available via the PSQ.
Output data: The GISMO back end processing simply subsets the data by extracting the user's region of interest out of the existing grid. The PSQ back end processing grids the data on the fly. The portion of the swath or scene data that intersects the user's region of interest is gridded to the users chosen grid. This makes the PSQ a bit more versatile, but also a bit more CPU intensive.
For more specific information on the differences between the GISMO and the PSQ see the PSQ FAQ.
The two GISMO interfaces contain different data products. The Pathfinder Interface contains the NASA gridded Polar Pathfinder data sets (SMMR, SSM/I, AVHRR, and TOVS). The SNODAS Interface contains the Snow Data Assimilation System (SNODAS) Data Products at NSIDC data set.
Java applets written in Java2 will not work in most browsers without the plugin, and the GISMO is written in Java2.
Java2 offers additional functionality that is unavailable in Java1. The results panel makes the most use of Java2 and has a number of capabilities that would not have been possible with Java1. These include: results can be sorted by any column, columns can be resized, columns can be moved, and a range of rows can be selected by dragging the mouse. Several other features of the GISMO would have been possible using Java1, but would have been more difficult to implement and more awkward to use.
They are on the next page. The small icons above and below the scrollbar on the right hand side of the results screen are the "Page Up" and "Page Down" buttons. The status message at the top of the results panel tells you what page you are on and what subset of the complete result set you are looking at. There is an upper limit of 20,000 granules returned. For more information see the Results section of the help page.
There is no data from the First Century A.D. available via the GISMO. The temporal coverage of data available via the GISMO starts in late 1978. For more information on the temporal coverage of specific data sets in the GISMO see the data set documentation:
AVHRR Polar
Pathfinder Twice-Daily 5 km EASE-Grid Composites
AVHRR Polar
Pathfinder Twice-Daily 25 km EASE-Grid Composites (derived
from the 5 km grids data)
DMSP
SSM/I Pathfinder Daily EASE-Grid Brightness Temperatures
Nimbus-7 SMMR
Pathfinder Daily EASE-Grid Brightness Temperatures
Snow
Data Assimilation System (SNODAS) at NSIDC
TOVS Pathfinder Path-P
Daily Arctic Gridded Atmospheric Parameters
The latitude and longitude files are binary arrays of 4-byte integers. Divide the values by 100,000 to get the actual latitude or longitude. For ASCII output that division has already been done.
Data can be output to binary format (easily imported into GIS software) or ASCII format. Binary data are subsetted grids in the same format as the original data. ASCII data are the values of the binary data in a tab-delimited ASCII table. See the following data set documents for information on original data formats:
The AVHRR Polar Pathfinder Twice-Daily 5 km EASE-Grid Composites and the AVHRR Polar Pathfinder Twice-Daily 25 km EASE-Grid Composites data obtained via the GISMO are just subsets of the standard products.
The file naming convention for the AVHRR data obtained via the GISMO is the same as the standard product, except that "subset_" is prefixed to the front of the file name if the data are a subset of the original.
DMSP SSM/I Pathfinder Daily EASE-Grid Brightness Temperatures data obtained via the GISMO are just subsets of the the standard SSM/I EASE-Grid products. SSM/I data produced by the GISMO prior to August 2005 are in big-endian byte order. Data produced by the GISMO after August 2005, and the standard product delivered on CD-ROM, are in little-endian byte order.
The file naming convention for SSM/I data distributed on CD-ROM is 8.3 format as described in the data set documentation. The file naming convention for SSM/I data distributed via ftp and subsets distributed via the GISMO is as follows:
EASE-Fss-ggyyyydddp.ccc
where:
| Fss: | Satellite number | {F08, F11, F13} |
| gg: | Grid. | NL indicates Northern Hemisphere azimuthal, 25 km resolution.
NH indicates Northern Hemisphere azimuthal, 12.5 km resolution. SL indicates Southern Hemisphere azimuthal, 25 km resolution. SH indicates Southern Hemisphere azimuthal, 12.5 km resolution. ML indicates full global cylindrical, 25 km resolution. MH indicates full global cylindrical, 12.5 km resolution. |
| yyyy: | 4-digit year | |
| ddd: | 3-digit day of year | (including leading zeros) |
| p: | Direction of pass | A indicates ascending pass
D indicates descending pass |
| ccc: | Channel | { 19H, 19V, 22V, 37H, 37V, 85H, 85V, TIM } |
If the data are a subset of the original, "subset_" is prefixed to the front of the file name. Gzipped files will end with ".gz" and unix compressed files will end with ".Z".
Nimbus-7 SMMR Pathfinder Daily EASE-Grid Brightness Temperatures data obtained via the GISMO are just subsets of the standard SMMR EASE-Grid product, but the SMMR data from GISMO are in big-endian byte order.
The file naming convention for SMMR data distributed on 8MM tape and via the GISMO is as follows:
EASE-SMMR-ggyyyydddp.ccc
where:
| gg: | Grid. | NL indicates Northern Hemisphere azimuthal, 25 km resolution.
SL indicates Southern Hemisphere azimuthal, 25 km resolution. ML indicates full global cylindrical, 25 km resolution. |
| yyyy: | 4-digit year | |
| ddd: | 3-digit day of year | (including leading zeros) |
| p: | Direction of pass | A indicates ascending pass
D indicates descending pass |
| ccc: | Channel | { 06H, 06V, 10H, 10V, 18H, 18V, 21H, 21V, 37H, 37V, TIM } |
If the data are a subset of the original, "subset_" is prefixed to the front of the file name. Gzipped files will end with ".gz" and unix compressed files will end with ".Z".
The TOVS Pathfinder Path-P Daily Arctic Gridded Atmospheric Parameters data available via ftp are stored in Hierarchical Data Format (HDF), and each daily file includes all the parameters. Daily files are, in turn, packaged into annual tar files.
TOVS data obtained via the GISMO are binary grids with one file per day per parameter.
The file naming convention for the TOVS data obtained via the GISMO is the same as the standard product, except that "subset_" is prefixed to the front of the file name if the data are a subset of the original and filenames end with an extension that reflects the parameter. Gzipped files will end with ".gz" and unix compressed files will end with ".Z".
The Snow Data Assimilation System (SNODAS) Data Products at NSIDC data obtained via the GISMO are subsets of the standard products.
The file naming convention for the SNODAS data obtained via the GISMO is the same as the standard product, except that "subset_" is appended to the front of the file name and the ".grz" file extensions are removed from the subsetted file names. Gzipped files will end with ".gz" and unix compressed files will end with ".Z".
If you have any questions or need additional information, please contact NSIDC User Services:
NSIDC User Services
National Snow and Ice Data Center
CIRES, 449 UCB
University of Colorado
Boulder, CO 80309-0449 USA
phone: +1 303.492.6199
fax: +1 303.492.2468
form: Contact NSIDC User Services
e-mail: nsidc@nsidc.org
