Assessment of Penetration Bias of ICESat-2 over Snow and Ice-covered Terrain, Western Canada

Abstract:

The ICESat-2 mission has already yielded key information about recent mass change for the Greenland and Antarctic ice sheets. With a repeat cycle of 91 days, ICESat-2 will also provide insight into seasonal-to-annual elevation change for Earth’s mountain glaciers. One source of uncertainty of ICESat-2 to measure elevation change, however, is the degree to which the 532 nm photons emitted by the ATLAS sensor penetrates snow and ice surfaces leading to delayed return times of emitted photons. Previous work showed that this delay could bias surface elevation measurements by up to -0.5 m. We assess the magnitude of this potential bias using coincident airborne surveys over snow and ice surfaces employing an infrared (1024 nm) laser. Our laser altimeter is a Riegl VQ-780 with dedicated Applanix POSAV GNSS-IMU. Positional and vertical uncertainties of post-processed laser shots are typically below 25 cm. Four of our airborne surveys occurred within 1 to 4 days of ICESat-2 data acquisition. For coincident surveys, we observe biases between ATLAS/ICESat-2 L3A surface elevation and those processed from the airborne surveys of -0.06 m to 0.06 m. The magnitude and sign of these differences can be attributed to differences in acquisition dates (1-4 days) between the air- and spaceborne measurements. One survey where air- and spaceborne acquisition were separated by about one day yielded a bias of 0.025 m. Several additional coincident surveys are planned over the next two months to further confirm the lack of penetration bias for snow and ice covered surfaces.