Component measurement of the MODIS spectral filters

The Moderate Resolution Imaging Spectroradiometer (MODIS) is a space-based sensing instrument currently being built by SBRC for the NASA EOS polar platform. The spectral band separation for the 36 MODIS bands is based on a complex system of dichroic beamsplitters, focal plane masks,and individual bandpass filters. There are four co-registered focal planes separated by three dichroic beamsplitters to cover the VIS (400 nm to 550 nm), NIR (650 nm to 950 nm), SWIR (1200 nm to 2250 nm), MWIR (3600 nm to 4600 nm) and LWIR (6500 nm to 14500 nm). Linear detector arrays, one for each band, are covered by bandpass filters of dimensions as small as 1 mm by 7 mm. The MODIS requirements include relative bandwidths as small as 1%, with tight tolerances on band center, band width, edge slopes, and out-of-band specifications. These requirements must be met for the warm focal planes operating at f/2.15 and for the cold (85 K) focal planes at f/1.58. The spectral separation scheme of MODIS is briefly described. The equipment and procedures assembled by SBRC for measurement of the component band parameters under conditions that simulate the operating thermal, vacuum, and optical environments are described. Measured results are compared with modeled predictions.<
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