Scatterometer Climate Record Pathfinder
SASS Enhanced Resolution Image Product Users Notes

Enhanced resolution images made from SASS data use the Scatterometer Image Reconstruction with Filtering (SIRF) algorithm. This version of the algorithm incoporates a median filter and a simplified spatial response function in which the spatial response is assumed to be 1 over the footprint and 0 elsewhere. In the processing, a linear model relating sigma-0 and incidence angle is assumed, i.e. sigma-0(db) = A + B (theta - 40) where A is the "incidence angle normalized sigma-0" at 40 deg incidence in dB, B is the effective incidence slope of sigma-0 versus incidence angle in dB/deg, and theta is the incidence angle of the observation. The SIR algorithm makes images of A and B on a 4.5 km pixel grid. The effective resolution varies depending on region and sampling conditions. Multiple passes of the spacecraft are combined to produce a higher spatial resolution (at a cost of reduced temporal resolution) and fill in coverage gaps between the individual measurement footprints. SASS measurement footprints were not contiguous, had irregular six-sided shapes, and varied in size depending on beam and location on the earth.

Capable of dual-pol operation over a single 500 km wide swath, it normally operated in V-pol, dual-sided swath mode over the ocean with the mode frequently switched over land, resulting in very little H-pol coverage during most of the abbrievated mission. SASS operated at 14.6 GHz. In combining the multiple passes, sigma-0 is assumed to be independent of azimuth angle. While true for most areas, some azimuth dependence in sigma-0 has been observed in Antarctic firn, presumably due to sastrugi or snow dunes.

SASS data was obtained from the SASS GDR datasets archived at 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.