AS2GT: AMSR-E Swath-to-Grid Toolkit
The AMSR-E Swath-to-Grid Toolkit (AS2GT) is a suite of software tools to subset and grid Levels 1B and 2A AMSR-E swath data. AS2GT makes it possible to quickly and easily work with the AMSR-E data in ways that may not be available in the Level 3 gridded data sets. This toolkit allows you to process data into custom grids with whatever temporal or spatial resolution you require. AS2GT maintains the highest data quality for your application by giving you control over map projection, number of samples per day, input resolution and interpolation method.
Gridding options in AS2GT include:
- Map projection
- Resolution and grid dimensions
- Resampling method
- How to handle overlapping swaths
- Subsetting by time or region
AS2GT is a suite of software tools distributed with NSIDC's Passive Microwave Swath Data Tools (PMSDT), shown in the following flow chart. (PMSDT also handles some forms of SSM/I and SMMR data. Please refer to the manual (man) pages for the utilities distributed with PMSDT for information).
Current formats supported by AS2GT include the reprocessed Level 1B SMMR Pathfinder Brightness Temperatures available from NSIDC. These two sources of data combined with the AMSR-E form a continuous time series of freely available passive microwave observations from 1979 to the present.
Documentation for AS2GT utilities is in the man pages included with the tools download.
AS2GT and the MODIS Swath-to-Grid Toolbox (MS2GT) use the same configuration files to describe their output grids. This makes it easy to compare overlapping AMSR-E and MODIS data, as shown in the following images.
How Does AS2GT Aid Science?
AS2GT provides some important benefits over NASA's Earth Observing System (EOS) AMSR-E Level 3 products. It allows you to choose between the different resolutions of Level 2A data or the unsmoothed Level 1B data. You can use it to grid data at any spatial resolution and map projection and choose the best interpolation method for your application. And it allows you to increase the temporal resolution of a time series by gridding all the available samples rather than just the two selected overpasses provided by the Level 3 products.
For example, if you wanted to study the diurnal cycle of some process at high latitude, the AMSR-E Level 3 grids provide two observations per day, but the swath data might provide up to eight observations. AS2GT lets you grid each of the swaths separately. The Level 3 gridded products would give only the first and last data samples for this point.
The following requirements apply to AS2GT and the larger PMSDT package.
- AS2GT runs on Unix and Linux systems.
- Some converters, like hdftogs, get_smmr_tbs, and AMSR_E_L2A_togs, depend on the Hierarchical Data Format (HDF) Version 4 available from NCSA.
- A special version of the Mapx library is required to run gsgrid.
- gsgrid stores 2 floating point grids per channel in memory, so you will need 2*Nbands*Width*Height*4 bytes of RAM.
- You´ll need a C compiler and the "make" utility to build it.
- Each AMSR-E L2A half orbit takes up about 80 megabytes of disk space and there are up to 30 half orbit files per day.
- Users experiencing installation problems should bear in mind the following known installation issues for PMSDT Verison 0.5:
- A special edition of Mapx is required. Please make sure to download and install the version of Mapx included in the directory with the PMSDT toolkit.
- Users should remove the ssmidriver reference on line 102 of the top-level Makefile.
- Users with a newer version of the GCC compiler may receive an error referencing libg2c. Newer versions of GCC no longer include libg2c. Using GCC version 3.x and older is a known solution to this error.
How to Download the Toolkit
Please register as a user before you download the tools. When you register, NSIDC can send you notification of updates to this toolkit.
To bypass the registration form, download the software and updates directly from: ftp://sidads.colorado.edu/pub/tools/pmsdt/
Documentation for the AS2GT utilities is located in the manual (man) pages included with the tools download.