First Performance Results Of A New Field-Widened Spatial Heterodyne Spectrometer For Geocoronal H-Alpha Research

A new, high-resolution field-widened spatial heterodyne spectrometer (FW-SHS) designed to observe geocoronal Balmer alpha (H-alpha, 6563 angstrom) emission was installed at Pine Bluff Observatory (PBO) near Madison, Wisconsin. FW-SHS observations were compared with an already well-characterized dual-etalon Fabry-Perot Interferometer (PBO FPI) optimized for H-alpha, also at PBO. The FW-SHS is a robust Fourier transform instrument that combines a large throughput advantage with high spectral resolution and a relatively long spectral baseline (similar to 10 times that of the PBO FPI) in a compact, versatile instrument with no moving parts. Coincident H-alpha observations by FW-SHS and PBO FPI were obtained over similar integration times, resolving powers (similar to 67,000 and 80,000 at H-alpha) and fields of view (1.8 degrees and 1.4 degrees, respectively). First light FW-SHS observations of H-alpha intensity and temperature (Doppler width) versus viewing geometry (shadow altitude) show excellent relative agreement with the geocoronal observations previously obtained at PBO by FPI. The FW-SHS has a 640 km/s (14 angstrom) spectral band pass and is capable of determining geocoronal H-alpha Doppler shifts on the order of 100m/s with a temporal resolution on the order of minutes. These characteristics make the FW-SHS well suited for spectroscopic studies of relatively faint (similar to 12-2R), diffuse-source geocoronal H emission from Earth's upper thermosphere and exosphere and the interstellar medium in our Galaxy. Current and future FW-SHS observations extend long-term geocoronal hydrogen observation data sets already spanning three solar minima. This paper describes the FW-SHS first light performance and H-alpha observational results collected from observing nights across 2013 and 2014.