Validation for Ice Flow Velocity Variations of Shirase Glacier Derived From PALSAR-2 Offset Tracking

Abstract

We have shown that the flow velocity of Shirase Glacier can be estimated by applying the offset tracking method to the amplitude images derived from the phased array type L-band synthetic aperture radar type-2 (PALSAR-2) onboard the Advanced Land Observing Satellite-2. Although the offset tracking is widely used, the method is sometimes not applicable effectively and the reason is not always clear. Here, we consider a possibility of ionospheric contamination and show the validation results of the estimated flow velocity applied the offset tracking method to the PALSAR-2 data, based on <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">in-situ</i> measurement of the flow velocity from the GNSS receiver on the autonomous phase-sensitive radio echo sounder simultaneously with the PALSAR-2 observation. As a result, the ionospheric contamination can yield a spurious error of ±0.2 km a <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−1</sup> . After statistically removing the erroneous pairs, the RMSE was 0.049 km a <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−1</sup> derived from the flow velocity error between the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">in-situ</i> measurement results and estimated from satellite, and the estimated flow velocity obtained using PALSAR-2 data is proved to be in good agreement with the ground truth. Obtained spatial and temporal variations reveal signature of glacier dynamics, which prove the efficacy of the offset tracking method. The obtained ice-flow velocity increases rapidly from the upstream region to the coast, but its velocity is roughly constant over a region, 10-km long about the grounding line (GL), then gradually tends to increase again downstream from the GL. This trend has continued largely unchanged over24 years since 1996.