Optimisation of line of sight matching to obtain wind vectors from the SIW satellite

Abstract: SIW, Stratospheric Inferred Winds, is one of the upcoming Swedish research satellites, aiming to study the winds in the middle atmosphere by measuring the Doppler shifts in molecules such as O3 with a limb viewing sub-mm spectrometer. By conducting simulations on the expected observations, the pointing sensitivity requirement of the satellite was investigated to be able to optimise the matching of the wind vectors. The development of SIW is in the early phases and therefore few studies of this topic has been conducted. The Python program AMATERASU (Advanced Model for Atmospheric TeraHertz Radiation Analysis and Simulation) developed by P. Baron has been used to calculate the radiative transfer through the atmosphere with the aim of simulating the satellite observations and the induced pointing errors, both horizontal and vertical. The results indicate that the effects of the horizontal pointing errors are neglectable due to their small contributions to the measurements. If horizontal pointing errors were induced the scan bias could be corrected for in the retrieval to a good degree for all species and the wind. If not corrected for, H2O and O3 were the most affected species and something to take into consideration during further development of the satellite design. The optimisation of the wind vectors showed that the bias of the matching could get decreased by changing the angle between the satellite antennas.