To use SO and LNO data, firstly we suggest that you read both Neefs et al. 2015 and Liuzzi et al. 2019 to understand how the AOTF and diffraction grating work to select the desired spectral region (diffraction order). For calibration of the SO channel, we suggest you additionally read Villanueva et al. 2022 (particularly the appendix); for LNO you should read Thomas et al. 2022; for UVIS you should read Willame et al. 2022.
SO Solar Occultation
Calibration of solar occultation spectra is relatively simple, as during each solar occultation, spectra are taken of the Sun above the atmosphere, which can then be divided by the spectra of the Sun measured through the atmosphere to convert the data to transmittance.
The SO and LNO channel spectrometers have three critical components: an Acousto-Optic Tunable Filter (AOTF), a diffraction grating, and a 256x320 pixel detector. To correctly interpret transmittance spectra, all these must be taken into account.
AOTF
The SO and LNO channels are set up to measure high diffraction orders between ~100-200, where each order is
The AOTF acts as an order sorting filter, preventing unwanted wavelengths from far away diffraction orders to reach the grating.
To run retrievals on the SO data, it is essential that the Instrument Line Shape, AOTF shape, blaze function and temperature-dependent spectral calibration are correctly accounted for within the retrieval code. The latest model presented in the appendix in Villanueva et al. 2022; for more information on the AOTF and blaze, please see Liuzzi et al. 2019.