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Some frequently asked questions:

How do scatterometers work?
Why scatterometers for climate studies?
Data from what instruments are available from this site?
What is the BYU .SIR file format?


How do scatterometers work?

Radar scatterometers are satellite instruments designed to measure winds over the ocean from space. They can also be used for land and ice studies. A scatterometer transmits pulses of microwave energy and measures the returned echo. The energy in the echo depends on the electrical properties and roughness of the surface. Over the ocean the roughness is a function of the near-surface vector wind which generates ocean waves. With measurements made from multiple azimuth directions, the wind can be estimated from the radar measurements. Over land, the return echo is a function of the land cover.

Why scatterometers for climate studies?

Radar scatterometers make frequent, very precise measurements of the globe. A variety of studies have shown that scatterometer measurements are very sensitive to key climate variables such as snowfall and melting in the polar regions and vegetation cover in the tropics, among others. A long time series of scatterometer data (dating intermittently back to 1978) has been collected. This long time series can thus be used to support climate change studies.

Data from what instruments are available from this site?

Processed data from the Seasat Scatterometer (SASS), the NASA Scatterometer (NSCAT), the ERS-1 and ERS-2 AMI (scatterometer mode), and the SeaWinds on QuikSCAT scatterometer data is available on this site. While the site emphasizes enhanced resolution image data, other data products are available.

What is the BYU .SIR file format?

The BYU .SIR image file format was developed by the Brigham Young University (BYU) Microwave Earth Remote Sensing (MERS) laboratory to store images of the earth along with the information required to earth-locate the image pixels. A "sir" file consists of one or more 512-byte headers containing all the information required to read the remainder of the file, including projection information to map pixels to lat/lon on the Earth's surface. Image pixel values are generally stored as 2 byte (high order byte first) integers. Scale factors to convert the integer or byte pixel values to native floating point units are stored in the file header. The origin of the images is in the lower left corner of the displayed image. The earth location of a pixel is identified with its lower-left corner. The standard sir format supports a variety of image projections including: Rectangular array (no projection); A rectangular lat/lon array; Lambert equal-area; Polar stereographic; and EASE with various resolutions.