ABSTRACT
In the early years of remote sensing the extent of ground checking was usually somewhat limited and statistical tests for accuracy were less demanding than is commonplace today. In the case of aerial photography, effort was expended on the ground surveying necessary to establish ground height control points. These were then used to set up stereoscopic models for photogrammetric mapping. This work is still necessary but the extension of remote sensing techniques into other wavebands and into spectral modelling of surface features has resulted in a new range of in situ data collection procedures which, more recently, has embraced surface remote sensing technology also. The use of remote sensing techniques by airborne and satellite platforms for most present-day purposes demands that there should be some method of calibrating and evaluating the sensors in use. In addition there is a need for checking the accuracy of analysis and interpretations made from the data, i.e. for verifying or validating remote sensing programme results.
