Spire Near-Nadir GNSS-R for Sea Ice Detection: First Results

Global Navigation Satellite System reflectometry (GNSS-R) has emerged as a valuable tool for Earth observations, providing low-cost measurements with high spatiotemporal resolution. This study presents the first application of Spire Global Inc. near-nadir (NN) GNSS-R observations for sea ice detection and sea ice extent (SIE) mapping, covering the Arctic and Antarctic. The delay and Doppler maps (DDMs) of Spire NN GNSS-R show a significant difference over various surfaces. For a test period from February to July 2024, results show that the Arctic’s SIE decreases from 584600 to 333400 km<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup>, and the Antarctic’s SIE increases from 142825 to 584750 km<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup>. Compared to Advanced Microwave Scanning Radiometer 2 (AMSR2) estimates, Spire NN GNSS-R retrievals achieve a probability of detection (Pd) of 94%–96% and the probability of false alarm (Pfa) and probability of error (Pe) below 0.23%. These results demonstrate the high sensitivity, accuracy, and operational potential of Spire NN GNSS-R for sea ice remote sensing.