Scatterometer Climate Record Pathfinder
NSCAT Enhanced Resolution Image Product Users Notes

Enhanced resolution images made from NSCAT 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 an 4.5 km pixel grid. The effective resolution varies depending on region and sampling conditions but is estimated to be 8-10 km in most areas. 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. NSCAT measurement footprints are not contiguous and have six-sided shapes with a nominal 25 km resolution.

NSCAT was operated continuously in double-sided mode, collecting measurements over two 600 km wide swaths at both V and H pol. Since only two of the antennas were operated in dual-pol mode, there are significantly fewer H pol measurements than V pol and, in contrast to the V pol measurements, tend to be aligned with each other and thereby reducing the effective resolution enhancement. NSCAT operated at 13.995 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.

NSCAT data was obtained from the NSCAT L1.5 dataset 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.