Measurement Of The Landsat Thematic Mapper Mtf Using A 2-Dimensional Target Array

Abstract

As part of the Landsat Thematic Mapper (TM) engineering evaluation effort, there have been several studies to measure a modulation transfer function (MTF) for the TM. In contrast to work that measured or modeled only the optical and electronic components of the MTF, our goal was to measure the complete imaging system MTF that includes factors such as optics and electronics. Measurements of the TM MTF using targets-of-opportunity have been previously reported, however this paper describes new results using a specially designed target. To arrive at an estimate of the system MTF, the TM point-spread function (PSF) was measured using a two-dimensional array of black squares constructed at the White Sands Missile Range in New Mexico. The target provides relatively good spatial and radiometric control of the scene and thereby reduces the uncertainties introduced by targets-of-opportunity. The clever design of the target allows 1/4 pixel shifts of point sources throughout the instantaneous-field-of-view (TFOV) of the TM. The shifting allows exploitation of sample-scene phasing to effectively resample the PSF at the finer rate. A method for sorting the image data and assembling a PSF and a technique for correction of rotation of the target relative to the sensor scan direction are discussed. Also, a technique for partial elimination of variations in the scene background is presented. The resulting estimates of the TM imaging system PSF and MTF are presented and compared with earlier results.