FABSOAR—An Instrument for Measurement of Solar Shortwave Forcing

Steven Watchorn Scientific Solutions, Inc.
John Noto Scientific Solutions, Inc.

Category: Instruments

Working Group: Cloud-Aerosol-Precipitation Interaction

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Scaled conceptual representation of the FABSOAR instrument, with a double Fabry-Perot represented.

Many atmospheric processes are driven by the infusion and dispersion of solar energy. The amount of shortwave (SW) solar radiation absorbed is of particular interest, regarding the terrestrial climate and atmospheric photochemistry. Some recent estimates of the SW budget, inferred from measurements, suggest that there are still major uncertainties in the levels predicted by atmospheric models in cloudy sky conditions, by up to 100 W/m2 for instantaneous measurements and 35 W/m2 in the diurnal mean. The problem may lie in radiative transfer models that, for relative ease of computation, treat the clouds as plane-parallel entities, ignoring three-dimensional cloud effects. While some sophisticated models—such as independent pixel and Monte Carlo simulations—have been developed, there have only been a few measurements of path lengths (or direct absorption measurements) with which to test them. The FABSOAR instrument will provide many more such measurements and probe the question of which situations are amenable to a simple plane-parallel cloud model. FABSOAR—a FABry-Perot Spectrometer for Oxygen A-band Research—is a high-throughput, high-resolving power, imaging, tandem Fabry-Perot spectrometer targeted particularly for the oxygen A-band (760–780 nm), though other nearby emissions can also be studied if they are also useful for the scientific goals. Designed for ground and airborne use, it gives high resolution in a much more compact package than a grating spectrometer, and combines that with high throughput, giving the performance of a refrigerator-sized grating spectrometer in a shoebox package. It also requires no moving parts for scanning, making it much more robust than conventional grating spectrometers. Development of FABSOAR has begun via a U.S. DOE SBIR Phase I grant. Under this contract, Scientific Solutions has developed a mechanical and optical design for the FABSOAR etalons, obtained and analyzed test images of a Helium-Neon laser source with an etalon with equivalent gap spacing, and begun work on a forward model to use FABSOAR data to obtain PDF-GP values for Solar shortwave. All of these results will be presented, along with a look ahead to projected work for a soon-to-be-proposed Phase II.

This poster will be displayed at ASR Science Team Meeting.