Measurement of the MODIS On-Orbit Spatial Response

Several techniques will be used to measure the PS or its Fourier transform, the Optical Transfer Function (OTF), from in-flight imagery(Table 1). The MTF is usually desired.

Table 1. Techniques for measuring the in-flight sensor response
technique	measured characteristic	relation to PSF	relation to OTF
line	Line Spread Function (LSF)	1-D integral of PSF	inverse Fourier transform of OTF
edge	Edge Spread Function (ESF)	integral of LSF	via LSF
comparison to high resolution image	Optical Transfer Function (OTF)	Fourier transform	same

We will be using high contrast line targets and band matching with ASTER. The high contrast line targets should be about 1/5 to 1/3 the GIFOV in width. Our current targets are Lake Tahoe, the All-American Canal, and other geometric features in the Yuma agricultural district on the Arizona/California border.

A close up area of interest of the All-American Canal.

The 3 MODIS GIFOV's

Characteristics that our targets have:

high contrast in all spectral bands
line targets should be on the order of 1/4 EGIFOV wide or less
uniform background on either side of the target for several pixels
at an angle to the cross-track and in-track directions to allow subpixel sampling and avoid aliasing

Lake Tahoe

depth >300m , high contrast boundary in NIR and SWIR bands
well-defined perimeter with variety of shapes
high winter scene contrast
large (18 x 33km), PSF tails may be measurable over several pixels in some MODIS bands
The Landsat-5 orbit passes nearly through the center of the Lake
minimal atmospheric effects at high altitudes

Yuma

Rectangular fields provide high frequency content
Unvegetated and large dune fields provide uniform, bright calibration targets
center pivot irrigation fields provide edge profiles (Fig. (10)).
dry atmosphere minimal atmospheric water vapor absorption

Band Matching

A plot of ASTER, MODIS and ETM+ band ranges is shown for the VIS SWIR and for the LWIR. We are measuring the spatial response of each MODIS focal planes; PSF variation among detectors within a band on a given focal plane is reasonably assumed negligible. The differences between MODIS and ASTER or ETM+ bands are not important if the atmosphere and surface spectral radiances are flat over the range of the widest band. This is a consideration in our selection of bands, targets and sites for the PSF analysis.