Modeling the MODIS Pre-Flight Spatial Response

MODIS is a complex optical/electronic/mechanical system. A simplified schematic is based on references 2 and 3 and other technical specs. The components that primarily influence thespatial response are the fore-optics, the aft-optics, the FPA detectors and the signal processing electronics. To find the spatial response of a complex system like MODIS, we typically model it at a higher level as three major components 
Our approach is to determine the overall PSF as a convolution of the following PSFs.

• Optical PSF :

The optical PSF is defined as the spatial energy distribution in the image of a point source, such as a star, or in the laboratory, an illuminated pinhole. An optical system is never perfect in the sense of forming a point image of a point source. The energy from the source is spread over a small area in the focal plane. The extent of spreading depends on many factors, including optical diffraction, aberrations and mechanical assembly quality.

• Detector PSF

This is spatial blurring caused by the non-zero spatial area of each detector in the sensor. A separable, uniform square function model will be used.

• Electronics PSF

The signal from the detectors is usually filtered electronically to reduce noise. The electronic components operate in the time domain of the signal as it is scanned and read from the detectors. The time dependence can be converted to an equivalent spatial dependence.

• Image Motion PSF

If the image moves across the detectors during the time it takes to integrate the signal at each pixel.