Evaluation of GNSS-R Retrieved Sea Ice Surface Height Using ICESat-2 Ice Freeboard Measurements

This paper presents an evaluation of the relative sea ice surface heights retrieved using carrier phase measurements of coherent GNSS reflection signals recorded by Spire Global Inc.'s LEMUR-2 low-Earth orbit (LEO) cubeSats between January to April 2019. Coherent GNSS signal reflection usually occurs at relatively low elevation angles, and sea ice is a good reflector for GNSS signals. As analyzed in [1], most of the uncertainty for GNSS-R relative sea surface height (SSH) retrievals is from the tropospheric delay models, which usually have several centimeters error in the zenith total error (ZTD), and the effects will be significantly amplified at low elevation angles. In this paper, the retrieved sea surface height anomalies (SSHA) using LEMUR-2 GNSS-R data are compared with the monthly averaged ice freeboard measurements from ICESat-2. Overall, the comparison shows good consistency. However, for some reflection events/segments, adjustments of the zenith troposphere delay model of up to 11 cm is required in order to fit the ICESat-2 ice freeboard measurements. Therefore, the tropospehere delay correction may be a challenge for high-precision GNSS-R sea ice altimetry.