Navigation of NOAA APT images

The low resolution APT (automatic picture transmission) images from NOAA polar orbiting satellites received and recorded in 4-bit grey scale by a very small low cost receiver are being used to produce daily total global solar radiation maps over an area of approximately 1450 km by 890 km. As the APT image is geometrically transformed onboard the satellite and also after reception in the present receiver the authors have developed a special navigation program which gives the required accuracy and speed in this application working on IBM-AT compatible PC. Root mean squared errors of 1.06 and 2.24 pixels are obtained along and across the nadir track respectively without correction by GCPs. Errors are reduced to 0.5 pixel by a linear transformation using visible land features