Imaging Fabry–Perot spectrometer for twilight observations

An imaging Fabry-Perot spectrometer specifically designed for ground-based studies of thermospheric photochemistry in twilight has been built, tested, and successfully applied to the measurement of the atomic-oxygen O I 844.6-nm emission. It employs a narrow-band interference filter in series with a stabilized étalon with fixed-plate separation and a 512 × 512 pixel bare CCD, and it achieves a bandpass of 0.02 nm. A least-squares data-reduction technique is shown to be effective in extracting the target feature from the surrounding background continuum. Data from one evening show slant column emission rates of 600 to 130 R.