Stability considerations for a solar spectral intensity monitor (SIM)

George M. Lawrence; Jerald W. Harder; Gary J. Rottman; Thomas N. Woods; Jeremy Richardson; George Mount

doi:10.1117/12.328519

27 October 1998 Stability considerations for a solar spectral intensity monitor (SIM)

George M. Lawrence, Jerald W. Harder, Gary J. Rottman, Thomas N. Woods, Jeremy Richardson, George Mount

Proceedings Volume 3427, Optical Systems Contamination and Degradation; (1998) https://doi.org/10.1117/12.328519
Event: SPIE's International Symposium on Optical Science, Engineering, and Instrumentation, 1998, San Diego, CA, United States

Abstract

A spaceborne spectral irradiance Monitor (SIM) is being developed at the Laboratory for Atmospheric and Space Physics, University of Colorado, to measure solar spectral irradiance and its variation over a 5 year period with a precision of 0.02 percent. The SIM consists of two independent and identical prism spectrometers. Each channel is equipped with an electrical substitution radiometer and ancillary photodiodes to prove spectral coverage from 0.3 to 2.0 micrometers with (lambda) /(Delta) (lambda) > 30. To meet this irradiance specification, the entrance slit must be characterized to give the effective slit width. Additional work is being performed to characterize how the space environment changes the diffractive properties of the slit over the course of the mission. The slit edges skim off the wavefront and then the broken edges diffract, losing energy at angle wider than the prism. The net effect at the detector is to reduce the effective slit width. Calculations using the Fraunhofer approximation show that most of the percentage slit area reduction is due to diffraction from the slit width. For a sharp cut-off at the edge of the slit the effective slit width decreases as 3.242(lambda) , where (lambda) is the wavelength of the incoming radiation. An experimental apparatus was constructed to test this calculation and to study the effects of heating and annealing on etched stainless steel entrance slit edges.

Citation Download Citation

George M. Lawrence, Jerald W. Harder, Gary J. Rottman, Thomas N. Woods, Jeremy Richardson, and George Mount "Stability considerations for a solar spectral intensity monitor (SIM)", Proc. SPIE 3427, Optical Systems Contamination and Degradation, (27 October 1998); https://doi.org/10.1117/12.328519

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