The Landsat Sensors´ Spatial Responses

Based on the geometrical characteristics of the Landsat-4 and Landsat-5 Thematic Mapper (TM) and Multispectral Scanner (MSS), functions defining their spatial responses are derived, i. e., transfer functions (TF´s) and line-spread functions (LSF´s). These design LSF´s and TF´s are modified based on prelaunch component and system measurements to provide improved estimates. Prelaunch estimates of LSF/TF´s are compared to in-orbit estimates where available. For the MSS instruments, only limited prelaunch scan direction squarewave response (SWR) measurements were available. Design estimates were modified by including a variable Gaussian blur, adjusted such that the derived LSF/TF´s produced SWR´s comparable to the measurements. The two MSS instruments were comparable at their temperatures of best focus; separate calculations were performed for bands 1 and 3, band 2, and band 4. The presample nadir effective instantaneous fields of view (EIFOV´s), based on the 0.5 modulation transfer function (MTF) criteria, are 70-75 m in the track direction and 79-82 m in the scan direction. For the TM instruments, more extensive prelaunch measurements were available. Bands 1-4, 5 and 7, and 6 were handled separately, as were the two instruments. LSF´s derived from component measurements differed from the limited measured LSF data only in the ringing response/overshoot behavior. Derived MTF´s indicated nadir presample EIFOV´s of 32-33 m in the track direction and 36 m in the scan direction (bands 1-5, 7) and 124 m track and 141 m scan (band 6) for both TM´s.