Home Projects Information Roadmap

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:
  1. Fit coastline to image; yields mapping from pixel x,y to lon, lat

  2. Grid image, using “nearest neighbor” algorithm.

  3. 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

  1. Compute pixel temperatures from AVHRR channel 4 data using onboard calibration and standard NOAA coefficients.

  2. 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.

  3. Determine an adjustment offset, which is the mean of the temperature differences between each ground truth point and its corresponding image pixel.

  4. Adjust the entire image by adding adjustment offset to each pixel value.

Back to Introduction

 Last Updated: Friday, June 23, 2000