Calibration and Processing of AVHRR Images
The images were acquired at a variety of
viewing geometries, from 3 different satellites. The following steps
were carried out:
- Fit coastline to image; yields mapping from pixel x,y to lon, lat
- Grid image, using “nearest neighbor” algorithm.
- Reproject image to Mercator.
(Steps 2 and 3 were performed using the
Generic Mapping Tools
software package. See Wessel, P., and W. H. F. Smith, 1991, "Free software
helps map and display data", EOS Trans. AGU, 72, 441.)
- Compute pixel temperatures from AVHRR channel 4 data using
onboard calibration and standard NOAA coefficients.
- Get independent SST measurement at several cloud-free
"ground truth" locations visible in image; these include MBARI
moorings M1 and M2, NOAA buoys 46042 and 46028,
MBARI Drifter #4, and RV Point Sur.
- Determine an adjustment offset, which is the mean of the
temperature differences between each ground truth point and its
corresponding image pixel.
- Adjust the entire image by adding adjustment offset to each pixel value.
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