Processing steps used to prepare the imagery in the URI/GSO AVHRR image archive

Each of the Advanced Very High Resolution Radiometer (AVHRR) images in the archive were produced either using archived raw satellite data from our extensive off-line and near-line archives or new data transmitted from the University of Miami Rosensteil School for Marine and Atmospheric Studies (RSMAS). Some processing steps were (and are) performed at RSMAS and some at GSO. Each satellite pass is first copied to a disk file and its calibration information retrieved during the `INGEST' processing step. The data read during ingestion is a complete AVHRR high resolution picture transmission (HRPT) pass downlinked from a satellite platform by a ground receiving station.

Processing produces either corrected temperature, for the 5 channel instruments (NOAA-7, NOAA-9, and NOAA-11) or sensor radiances for the 4 channel instruments (TIROS-N, NOAA-6, NOAA-8 and NOAA-10). Accurate sea surface temperature values that take into account atmospheric attenuation are obtained using two channel split window method with channels 4 and 5. (McClain et al 1983, McMillin and Crosby 1984). For the 4 channel TIROS-N, NOAA-6, NOAA-8 and NOAA-10 sensors radiances are computed directly from channel 4 of the the data. While it is not possible to remove the atmospheric attenuation from single channel data, images generated using sensor radiance values contain detailed information on the thermal structure the surface waters and features.

Once ingested, the data is subsampled within each 4 by 4 pixel square so that only the warmest of those pixels is retained. This reduces the resolution of the data from ~1.1 km/pixel to ~5.5 km/pixel. Following this subsampling step the NOAA/NESDIS two-channel atmospheric correction algorithm and then a scan angle correction algorithm designed at GSO are applied to the image data (See Cornillon, Gilman et al. ``Processing and Analysis of Large Volumes of Satellite-Derived Thermal Infrared Data'', Journal of Geophysical Research, Vol 92:c12, 1987. pp.12,993-13,002.

Following the ingest, subsampling and atmospheric correction steps, the image data is remapped so that each image in the archive covers the same area.

The historical data in the archive were derived from satellite passes archived at GSO. The archive is updated automatically every day using partially processed data from RSMAS. The data is processed through the atmospheric correction step and moved over the Internet to GSO. At GSO the remainder of the processing steps are performed and the images are written to magnetic disk.

The AVHRR Archive Home

James Gallagher
jimg@dcz.gso.uri.edu