Measurement of weak airglow emissions with a programmable scanning spectrometer

We demonstrate how the radiance response of a wavelength scanning instrument may be improved with a programmable scanning system. A minicomputer with a high level language offers a versatile software package that can be readily modified for any specific problem. We illustrate the technique with the application of the one meter Ebert Fastie spectrophotometer at the Arecibo Observatory's airglow facility to the measurements of the peak spectral emissions of the 5200 Å doublet of N(²D) in the nightglow and the 7320 Å doublet of O⁺(²P) in twilight. Typical measurement errors were ±0.2 R and ±0.5 R, respectively. We have also applied this method to measurements of the OH rotational temperature from the ratio of the P₁(2) and the P₁(5) rotational lines in the Meinel 8-3 band and obtained a precision of ±3 K within a time period of 6 min. The required modifications to the wavelength drive were not extensive, the costs were not high, and the technique may be applied to any wavelength scanning instrument in operation today.