Airborne Lidar to Verify ICESat-2 Arctic Summer Sea Ice Heights and Melt Pond Depths: Calibration and Validation Campaign, Greenland 2022

In July 2022, the National Aeronautics and Space Administration (NASA) funded an airborne lidar data acquisition campaign over the central Arctic Ocean to evaluate ICESat-2 ATLAS (Ice, Cloud, and Land Elevation Satellite, Advanced Topographic Laser Altimeter System) retrievals of summer sea ice heights and melt pond characteristics. A Leica Chiroptera-4x (CHIR) was mounted on a Gulfstream V aircraft with a glass viewport, alongside NASA's Land, Vegetation, and Ice Sensor (LVIS). Despite the operational constraints—including CHIR's low-altitude, slow-cruise constraints, and other logistical and environmental challenges—measurements nearly coincident with ICESat-2 observations were successfully collected. In total, 138 min of CHIR lidar data and four-band aerial imagery were acquired at 500 m altitude, mapping 11,000 km² of sea ice. Cross-check validation between CHIR and LVIS over a 31-km long swath demonstrated strong agreement (R² > 0.98, RMSE = 0.045 m), confirming both the spatial accuracy and redundancy of the airborne measurements. A novel algorithm was developed to compare lidar data sets in a tide-free system by repositioning CHIR measurements to align with ICESat-2 observed points, accounting for drift speed (m/s) and heading (degrees), which significantly improved consistency. Comparisons between CHIR's near-infrared returns and ATL07 strong-beam products yielded an absolute height difference of 0.015 m with an agreement of R² = 0.73. Additionally, ATL03 photons showed a slight bias of 0.01 m and strong correspondence (R² = 0.84) with CHIR green-wavelength returns for coincident melt pond and lead depths in the height domain.