Quantifying volumetric scattering bias in ICESat-2 and Operation
IceBridge altimetry over snow-covered surfaces
Abstract
The Ice, Cloud, and Land Elevation Satellite-2 (ICESat-2) mission has
collected global surface elevation measurements for over three years.
ICESat-2 carries the Advanced Topographic Laser Altimeter (ATLAS)
instrument, which emits laser light at 532 nm, and ice and snow absorb
weakly at this wavelength. Previous modeling studies found that melting
snow could induce significant bias to altimetry signals, but there is no
formal assessment on ICESat-2 acquisitions during the Northern
Hemisphere melting season. In this work, we performed two case studies
over the Greenland Ice Sheet to quantify volumetric scattering in
ICESat-2 signals over snow. Elevation data from ICESat-2 was compared to
Airborne Topographic Mapper (ATM) data to quantify bias. We used snow
optical grain sizes derived from ATM and the Next Generation Airborne
Visible/Infrared Imaging Spectrometer (AVIRIS-NG) to attribute altimetry
bias to snowpack properties. For the first case study, the mean optical
grain sizes were 340±65 µm (AVIRIS-NG) and 670±420 µm (ATM), which
corresponded with a mean altimetry bias of 4.81±1.76 cm in ATM. We
observed larger grain sizes for the second case study, with a mean grain
size of 910±381 µm and biases of 6.42±1.77 cm (ICESat-2) and 9.82±0.97
cm (ATM). Although these altimetry biases are within the accuracy
requirements of the ICESat-2 mission, we cannot rule out more
significant errors over coarse-grained snow, particularly during the
Northern Hemisphere melting season.