ICESat‐2 Surface Height and Sea Ice Freeboard Assessed With ATM Lidar Acquisitions From Operation IceBridge

• Published in: Geophysical research letters 2019-10, Vol.46 (20), p.11228-11236
• Main Authors: Kwok, R., Kacimi, S., Markus, T., Kurtz, N. T., Studinger, M., Sonntag, J. G., Manizade, S. S., Boisvert, L. N., Harbeck, J. P.
• Format: Article
• Language: English
• Subjects: Airborne sensing; assessment; Data; Data collection; Deployment; Elevation; Evaluation; Freeboard; freeboard, sea ice; Ground tracks; Height; Ice; ICESat‐2; Instruments; Lidar; Profiles; Roughness; Satellite data; Satellite ground tracks; Satellite surfaces; Satellites; Sea ice; Sea ice data; Sea level; Sea surface; Segments; Slope; Snow and ice; surface height; validation
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2019GL084976

Surface height and total freeboard from the Ice, Cloud, and Land Elevation Satellite‐2 (ICESat‐2, IS‐2) sea ice data products (ATL07/ATL10) are assessed with near‐coincident retrievals from the Airborne Topographic Mapper (ATM) lidar in four dedicated underflights during the 2019 Operation IceBridge Arctic deployment. Over a mix of seasonal and older ice, we find remarkable correlations between the ATM and IS‐2 height profiles and roughness (in ninety‐nine 10‐km segments) that averages to >0.95 and > 0.97, respectively. Regression slopes near unity, between 0.93 and 0.99, indicate close agreement of the height estimates. Larger differences between the surface heights are seen in rougher areas where it is more difficult for the photon heights (used in IS‐2 surface finding) to capture the surface distributions at short length scales. Total freeboard in 10‐km segments, calculated using three different approaches, show variability of 0.02 to 0.04 m. Sources of residual variance, attributable to differences between the two instruments, are discussed. Plain Language Summary NASA's Ice, Cloud, and Land Elevation Satellite‐2 (ICESat‐2) was launched in September of 2018. For sea ice, the topic of focus here, the lidar instrument onboard ICESat‐2 is tasked to measure surface height and freeboard—the vertical height of the floating snow and ice above the sea surface—which will be used to estimate the thickness the Arctic and Southern Ocean ice covers. One of the first steps in the scientific use of data collected by any new satellite mission is an evaluation of data quality from the instrument. In this paper, we compare the ICESat‐2 sea ice data with airborne measurements from Operation IceBridge taken in April of 2019. Operation IceBridge is a NASA airborne mission that has collected data over sea ice since 2009 and served as a bridge between the first ICESat and the new ICESat‐2. For validation of the sea ice data, the airborne platform was tasked to fly the same satellite ground tracks. In our comparisons, we find the quality of the satellite surface height and freeboards to be high: the airborne and satellite data are in agreement with each other. These results will serve as a baseline for evaluation and improvements of future releases of the ICESat‐2 data set. Key Points We present a first assessment of the quality of the surface height and total freeboards from the ICESat‐2 mission Correlations between the airborne and IS‐2 height profiles and roughness are qui