Abstract
The CryoSat-2 radar altimeter and ICESat-2 laser altimeter can provide complementary measurements of the freeboard and thickness of Arctic sea ice. However, both sensors face significant challenges for accurately measuring the ice freeboard when the sea ice is melting in summer months. Here, we used crossover points between CryoSat-2 and ICESat-2 to compare elevation retrievals over summer sea ice between 2018–2021. We focused on the electromagnetic (EM) bias documented in CryoSat-2 measurements, associated with surface melt ponds over summer sea ice which cause the radar altimeter to underestimate elevation. The laser altimeter of ICESat-2 is not susceptible to this bias but has other biases associated with melt ponds. So, we compared the elevation difference and reflectance statistics between the two satellites. We found that CryoSat-2 underestimated elevation compared to ICESat-2 by a median difference of 2.4 cm and by a median absolute deviation of 5.3 cm, while the differences between individual ICESat-2 beams and CryoSat-2 ranged between 1–3.5 cm. Spatial and temporal patterns of the bias were compared to surface roughness information derived from the ICESat-2 elevation data, the ICESat-2 photon rate (surface reflectivity), the CryoSat-2 backscatter, and the melt pond fraction derived from Sentinel-3 Ocean and Land Color Instrument (OLCI) data. We found good agreement between theoretical predictions of the CryoSat-2 EM melt pond bias and our new observations; however, at typical roughness <0.1 m the experimentally measured bias was larger (5–10 cm) compared to biases resulting from the theoretical simulations (0–5 cm). This intercomparison will be valuable for interpreting and improving the summer sea ice freeboard retrievals from both altimeters.
| Original language | English |
|---|---|
| Pages (from-to) | 4165-4178 |
| Number of pages | 14 |
| Journal | The Cryosphere |
| Volume | 17 |
| Issue number | 9 |
| DOIs | |
| Publication status | Published - 27 Sept 2023 |
Bibliographical note
Funding Information:Geoffrey J. Dawson acknowledges support from the European Space Agency project “CryoSat ThEMatic PrOducts” (Cryo-TEMPO), grant no. ESA AO/1-10244/2-/I-NS. Jack C. Landy was supported by the European Space Agency project “EXPRO Polar+ Snow on Sea Ice” under grant no. ESA AO/1-10061/19/I-EF and by the Research Council of Norway (RCN) projects CIRFA (Centre for Integrated Remote Sensing and Forecasting for Arctic Operations) under grant no. 237906 and INTERAAC (air-snow-ice-ocean INTERactions transforming Atlantic) under grant no. 328957. The authors thank the SARvatore (SAR Versatile Altimetric Toolkit for Ocean Research & Exploitation) service available through ESA Grid Processing on Demand (G-POD) for providing level 2 CryoSat-2 observation.
Funding Information:
Geoffrey J. Dawson received support from the European Space Agency project “CryoSat ThEMatic PrOducts” (Cryo-TEMPO) (grant no. ESA AO/1-10244/2-/I-NS). Jack C. Landy was supported by the European Space Agency project “EXPRO Polar+ Snow on Sea Ice” (grant no. ESA AO/1-10061/19/I-EF) and by the Research Council of Norway (RCN) projects CIRFA (grant no. 237906) and INTERAAC (grant no. 328957).
Publisher Copyright:
© 2023 Geoffrey J. Dawson.