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ASCAT Enhanced Resolution Image Products

The fan-beam ASCAT scatterometer provides radar backscatter measurements at 6 azimuth angles and a diversity of incidence angles. The wide swath and frequent overflights permit generation of a wide variety of ASCAT Image products. For highest possible spatial resolution, multiple orbit passes are combined. These are the 'all pass' images. Since generally orbit passes of a given point on the Earth occur at nearly the same time of day, time-of-day studies are facilitated by computing images from ascending (morning) passes only, and descending (evening) passes only. For improved temporal resolution in the polar regions, daily local-time-of-day images have been generated. In non-polar regions ascending/descending images are produced. To ensure adequate spatial coverage and overlap to enable B image estimation, except at the poles, generally multiple days are combined.

Images are made from ASCAT L1B SZF files which are analogous to SeaWinds "slice" measurements.

Further information is available in the ASCAT Enhanced Resolution Image Users Notes.

Images are produced in the BYU .SIR file format using the standard naming scheme. The files are gzipped to minimize storage and transfer requirements. The standard images are designed for land and ice observation. Data over the ocean is generally not useful. However the distributed images are not land masked. .SIR format land mask files (containing 0 for ocean and 1 for land) are available for each standard region. .SIR format images containing "images" of the latitude and longitude of each pixel for each region are also available.

Available Image Classes
SZF-based Images
  V Pol
all passes msfa
ascending passes only+ mafa
descending passes only+ mdfa
morning passes** mmfa
mid-day passes*** mnfa
evening passes** mefa

+ Non-polar regions only
* Only Ant, Arc, and Grn regions
** Only Ant region
*** Only Arc and Grn regions


NOTE: ASCAT image grid and region definitions are identical to QuikSCAT "egg" images. Local-time-of-day boundaries have been altered to match the ASCAT orbit. Both type A and type B images are produced for ASCAT with A being sigma-0 in dB normalized to a 0 deg incidence angle and B being the slope of sigma-0 in dB versus incidence angle. The nominal image pixel resolution is 4.45 km/pixel. Click here for specific details on the map projection used for each image product.