Overview of MWP-1.1:
F.W. Chen

We have been having reasonable success with our use of the millimeter-wave channels of AMSU-A/B on NOAA-15/16/17 for retrieving global precipitation rates with ~15-km resolution, and are now willing to share the code with others who may wish to test its capabilities. The primary publication documenting the algorithm and its performance is:

F.W. Chen and D.H. Staelin, "AIRS/AMSU/HSB Precipitation Estimates," IEEE Transactions on Geoscience and Remote Sensing, Vol. 41, No. 2, pp. 410-417, Feb. 2003.

In addition some snapshots of precipitation events and monthly-average maps of precipitation frequency and precipitation rate have been posted on our website, as discussed below. The same website provides links to other relevant papers. These images and maps clearly have meteorological significance, although final calibration and validation remain to be done. Two of these images have been attached to this email for reference.

The primary systematic errors of which we are aware involve a tendency to underestimate detected winter snowfall-rate water equivalents by up to an order of magnitude, and to overestimate summer polar snowfall rates. We are currently attempting to quantify these effects so they can be compensated. There is also the risk that we sometimes detect precipitation that does not reach the ground, and that we miss warm rain in the lowest few kilometers. We hope to quantify these effects too.

The algorithm operates on L1-B data one orbit at a time, ingesting one data set of up to 1000 AMSU-A scan lines at a time. The outputs include the estimated rain rate (mm/h) in each 15- and 50-km pixel, together with a 4-state flag that suggests the reliability of the result (See the comments at the beginning of precip_swath.c for an explanation of the flag). The same algorithm is used for all locations and seasons, but these generally exclude regions between 60° N and 60° S lying above ~2-km altitude, regions between 60° N and 70° N above 1.5 km, and regions above 500 m in the remaining polar regions.

The execution time using a Linux machine with a clock speed of 2.53 GHz, frontside bus speed of 533 MHz, 512 KB of cache, and 1 GB of RAM is approximately 46 minutes per month of AMSU data. The required RAM is ~500 MB. The code is written in MATLAB with imbedded C-code for critical portions; it is provided as an m-file. The MATLAB image processing and mapping toolboxes are also required. Approximately 200 KB are required for the code, plus about 37 MB for associated data files.

Description of the code:

The program is executed by running the MATLAB script samplerain.m. The necessary code and associated files are accessible by going to <rseg.mit.edu> and accessing the MWP file from our home page. The same file also includes links to various references.

The compressed archive file (precipcode.tar.gz) contains the following files:

This package requires MATLAB toolboxes for: 1) Image Processing, and 2) Mapping. The files in this package should be placed in a directory that is in your MATLAB path.

Several steps have to be taken before samplerain.m can be run:

1. Using a text editor, change amsudir in samplerain.m to the directory containing the files in this package.

2. Start MATLAB, and run this command: "cd <directory with files in this package>"

3. Compile the C-code in this package using the following commands:

4. Run the following command: cd ..

5. You are now ready to run the script samplerain.m


Additional References: (click on numbers to link to document)

1) F.W. Chen, A.M. Leckman, and D.H. Staelin, "Passive Microwave Signatures of Arctic Snowstorms Observed by Satellites," Proceedings of the 2003 IEEE International Geoscience and Remote Sensing Symposium, Toulouse, France, July 2003.

2) F.W. Chen, A.M. Leckman, and D.H. Staelin, "Satellite Observations of Polar Precipitation Using Aqua," 7th Conference on Polar Meteorology and Oceanography and Joint Symposium on High-Latitude Climate Variations (American Meteorological Society), Hyannis, MA, May 2003.

3) F.W. Chen and D.H. Staelin, "Global Millimeter-Wave Observations of Precipitation Using AMSU on the NOAA-15 Satellite," Proceedings of the 2002 IEEE International Geoscience and Remote Sensing Symposium, Toronto, Canada, June 2002.

4) F.W. Chen and D.H. Staelin, "Precipitation-Rate Retrievals at 15- and 50-km Resolution Using AMSU Passive Microwave Data," National Radio Science Meeting, Boulder, Colorado, January 2002.

5) F.W. Chen and D.H. Staelin, "Millimeter-Wave Observations of Precipitation Using AMSU on the NOAA-15 Satellite," Proceedings of the 2001 IEEE International Geoscience and Remote Sensing Symposium, Sydney, Australia, Volume 3, pp. 1044-1045, 2001.

6) D.H. Staelin and F.W. Chen, "Precipitation Observations Near 54 and 183 GHz Using the NOAA-15 Satellite," IEEE Transactions on Geoscience and Remote Sensing, vol. 38, no. 5, pp. 2322-2332, Sept. 2000.

7) F.W. Chen and D.H. Staelin, "Precipitation Retrieval and Particle Size Sensing Using AMSU Data," American Geophysical Union Spring 2000 Meeting, Washington, D.C., May 2000.

8) D.H. Staelin, F.W. Chen, and A. Fuentes-Loyola, "Precipitation Measurements Using 183-GHz AMSU Satellite Observations," Proceedings of the 1999 IEEE International Geoscience and Remote Sensing Sympsosium, Hamburg, Germany, July 1999.

9) F.W. Chen, J.W. Barrett, W.J. Blackwell, P.W. Rosenkranz, M.J. Schwartz, and D.H. Staelin, "Millimeter-Wave Spectral Observations of Clouds and Precipitation from Aircraft and Spacecraft," National Radio Science Meeting, Boulder, Colorado, January 1999.