Impact of GCP distribution on the rectification accuracy of Landsat TM imagery in a coastal zone

The purpose is to explore the effect of the spatial distribution of ground control points (GCPs) on the accuracy of imagery rectification in a coastal zone.Choosing southern part of the radiative sandy ridge field along the coast of Jiangsu Province, China as the study area, both areadist ributed and linearly distributed GCPs (namely, AGCP and LGCP methods) were used to rectify a coastal Landsat TM image.Rectification accuracy was checked against 99 independent points over the intertidal mudflats of noground control.Results indicated that the root-mean-square error of residuals over these areas is several times larger than its GCPs-measured counterpart in which the rectification accaracy by the two methods was good.From the directivity of spreading error for the image rectification, it was shown that if the GCPs are spatially dispersed over an area, in east ward residuals fluctuate but increase steadily with distance to the source of control (R²=0.827).In northward they fluctuate around 150 muntil 15 km, beyond which they rise steadily at a small range of fluctuation.These residuals are less predictable from distance to the source of control than in east ward (R²=0.517).And if GCPs are distributed along a control line, residuals rise with distance to it linearly and predictably (R²=0.877) in the direction perpendicular to it.In a direction parallel to it, a distance has little impacton rectification residuals.From the value of spreading error, it could be found that the LGCP method could get an accuracy of about 20 m when the distance to a coastal dyke was less than 30 km while at the same time the AGCP method could only afford the accuracy of about 100 mat the similar distance conditions.This conclusion could give a reasonable reference for the error-spreading rule of Landsat TM image rectification in the area of coast or ocean where there existed little or no GCPs