Development of an Acousto-Optic Tunable Filter Based Imaging Radiometer for Solar Spectral Measurement

70104S02-II Existing devices for collecting atmospheric radiation measurements have many limitations to the performance and accuracy of information derived from the acquired data. For example, some devices can obtain information only at certain fixed wavelengths, some have low spectral resolution, and some have moving components, subject to vibration or shock, that require frequent calibration. This project will develop an acousto-optic tunable filter (AOTF), as the dispersive element in the radiometer, which will reduce contamination error, provide higher resolution, and perform instantaneous measurement at any wavelength¿all in a device with no moving parts. Phase I designed and fabricated two dual-channel AOTFs that operated over the wavelength range from 360nm to 2500nm; demonstrated apodization techniques to minimize the sidelobes of the AOTF; and measured the diffraction efficiency and spectral resolution at various wavelengths. Preliminary imaging, including solar imaging, in the visible and infrared regions (360nm to 1100nm) was demonstrated. Phase II will focus on developing two radiometer systems: a complete imaging radiometer system that uses silicon CCD arrays in the wavelength range from 360¿1100nm, and a radiometer that uses a dual wavelength detector in the wavelength range from 360¿2500nm. Performance will be optimized by increasing the spectral resolution, increasing out-of-band rejection, and optimizing the apodization techniques. Commercial Applications and Other Benefits as described by awardee: The device should increase our understanding of meteorological, chemical, physical, and thermodynamic processes and phenomena in the atmosphere.