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Scatterometer Climate Record Pathfinder
ASCAT Enhanced Resolution Image Product Users Notes

This page is designed as a dynamic repository of relevant information to aid users of ASCAT enhanced resolution image products. Additional information is available here as a pdf document.

Enhanced resolution images made from ASCAT data are created from SZF files using the multi-variate Scatterometer Image Reconstruction (SIR) algorithm with filtering (SIRF). Like previous fan-beam scatterometers, ASCAT collects measurements at multiple incidence angles and up to 6 azimuth angles. The effective image resolution varies depending on region and sampling conditions but is estimated to be 12-15 km in most areas. The SIRF algorithm makes A images at 4.45 km pixel spacing. Multiple passes of the spacecraft are combined to produce a higher spatial resolution (at a cost of reduced temporal resolution).

ASCAT data was obtained the PO.DAAC. No recalibration has been applied.

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 and so are landmasked. However, .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.

Due to its polar orbit, the local-time-of-day of the ASCAT observations varies with latitude and direction of the orbit. At mid- to low-latitudes, most areas are imaged at two different local times-of-day -- one for the ascending (north-bound) pass and one for the descending (south-bound) pass. Thus, by separating the data into ascending and descending passes, images corresponding to two different local times-of-day are created. In the polar regions, particular locations are observed at multiple local times-of-day and so a different method is required. Local time-of-day is considered in more detail in MERS research report.