Calibration and Processing of AVHRR Images
Geometric correction
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.)
Radiometric correction
- 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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