A solar infrared photometer for space flight application

Abstract

Solar radiation at wavelengths longward of 1.6 μm can be used to great advantage as a probe of the thermal state of the solar photosphere. We describe a photometer concept which is capable of nearly simultaneous measurements of solar radiation from 1.6 to 200 μm in seven wavelength bands. This range of wavelengths can probe the solar photosphere from below the level of unit optical depth in the visible to the temperature minimum, ≈ 500 km above it. An instrument package including a 20-cm Gregorian telescope and a filter wheel photometer utilizing non-cryogenic pyroelectric infrared detectors is described. Approaches to the rejection of the visible solar spectrum in the instrument, the availability of optical and mechanical components, and the expected instrumental sensitivity are discussed. For wavelengths below 35 μm the projected instrumental sensitivity is adequate to detect the intensity signature of solar p-mode oscillations in a single 5 minutes of integration. For longer wavelengths clear detection is expected using Fourier analysis of modest data sets. The size, mass and power requirements of the photometer are well within constraints imposed by space missions, including those by the NASA Small Explorer program.