Optical EngineeringAnalysis of nodding system requirements for satellite radiometry
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Estimates are made of nodding requirements for a secondary mirror used for radiometry of satellites in the 8- to 12-μm band. The first portion of the analysis determines the fundamental nodding frequency based on atmospheric turbulence and wind measurements taken at the Air Force Maui Optical Station. The temporal power spectral density for sky background fluctuations shows that a 50-Hz frequency will satisfy 50-percentile wind and turbulence conditions. The required frequency for a maximum operating wind condition of 40 mph is above 100 Hz. In addition to the 50-Hz fundamental, the analysis indicates that at least one, and preferably two, higher order harmonics of 150 and 250 Hz, respectively, are required to reconstruct a mirror drive waveform with sufficient duty cycle or integration time for background subtraction. The results are shown to be consistent with the performance of existing nodding systems.