THE ARCTIC WEATHER SATELLITE: RADIOMETRIC CALIBRATION CONSIDERATIONS ON SCAN DEPENDENT BIAS

C. Medina¹, R. Albers¹, A. Murk¹

¹University of Bern

The Arctic Weather Satellite (AWS) [1] is the prototype flight model for the future meteorological constellation EPS-Sterna. The satellite carries a cross-track scanning microwave radiometer built by AAC Omnisys operating in the 54, 89, 183 and 325 GHz bands. The satellite development followed a “New space” approach, focusing on rapid construction with a compact, low-cost design. AWS was launched in August 2024, and operational data is already available.

To achieve a compact design, the optics of the instrument consist of a feed cluster that directly illuminates a scanning reflector, without additional focusing elements. The individual beams are not co-aligned and are offset from the boresight of the main reflector, leading to scan-dependent performance variations. Although the antenna design minimizes total spillover variation, the antenna patterns for each frequency continue to exhibit contributions from far sidelobes, which vary in shape and distribution as a function of the scanning angle. This introduces additional challenges for accurate radiometric calibration, requiring antenna pattern corrections to compensate for scan-dependent bias.

The University of Bern was responsible for the optical design of the AWS antenna and for the on-board calibration system. The antenna simulations were performed using the Method of Moments (MOM) of the Ticra Tools software for multiple scanning angles. Using this method, it is possible to account for multiple reflections from the structure of the satellite and their contribution to the antenna pattern far sidelobes and spillover.

In this work we assess the radiometric calibration of AWS including antenna pattern corrections to account for scan dependent spillover variations. We perform radiometric calibrations to the satellite operational data for multiple clear-sky orbits and compare the results to radiative transfer simulations using RTTOV software and ECMWF atmospheric profiles, showing improvements in scan-dependent bias.

1. Eriksson et al.(2025). “The Arctic Weather Satellite radiometer.” EGUsphere,pp.1–32. DOI: 10.5194/egusphere-2025-1769