The Cloud and Surface Parameter Retrieval (CASPR) system is a toolkit for the analysis of data from the Advanced Very High Resolution Radiometer (AVHRR) satellite sensor carried on NOAA polar-orbiting satellites. The toolkit is a collection of algorithms that can be used to retrieve a variety of surface and cloud parameters. These algorithms are integrated into a user-friendly, flexible environment that includes on-line help and a multitude of options for displaying and printing results. CASPR can compute any or all of the following:
|Surface and Clouds:||Radiation:||Cryosphere:|
CASPR is research code. It does a lot of things well but doesn't do anything perfectly. Many of the algorithms have been validated, some have not. They are all detailed in the Reference Guide. There are three broad problems worth mentioning at the outset. First, everything depends on cloud detection, which sometimes borders on being as much an art as a science when working in the polar regions with the AVHRR. We are, indeed, trying to squeeze water from a stone. We do not claim to have solved the cloud detection problem, but rather provide methods that work reasonably well most of the time. Second, there are fundamental difficulties in estimating some parameters at extreme viewing and illumination geometries common to the high latitudes. We're venturing into territory that is difficult to model so beware. Third, the retrieval of cloudy sky parameters requires temperature and reflectance values underneath the clouds. CASPR interpolates clear sky values to cloudy areas for some parameters. This generally works but can result in large uncertainties in very cloudy areas. Cautionary notes are given throughout the Reference Guide. Please do not ignore them!
Version 5.0.1 has many significant changes. Polar stratospheric cloud (PSC) detection was added, cloud type classsification algorithm was implemented, sun glint mask parameter was added, NOAA-16 AVHRR post-launch channel degradations were calibrated and corrected for time series, cloud detection procedures were revised, some of cryosphere products were added (ice extent, ice concentration, ice thickness, ice age), and plotting procedures were enhanced. See the revision history for a detailed list of changes.