Altimeter Retrievals of Sea Ice, Lake Ice and Snow Properties

  • Author / Creator
    Beckers, Justin F.
  • Lake and sea ice and their snow covers are major components of Earth’s cryosphere and act to strongly modify climatic and biological systems. Both ice types serve as an important habitat for micro-fauna and support macro-fauna and strongly modify the exchange of energy, gases, and momentum between the atmosphere and the underlying water. Observations of areal properties of ice and snow have been widely available for the past 40 years, allowing for monitoring of the long term decreases in e.g. ice extent, duration and age. Unfortunately, observations of other ice properties remain limited, due to reductions in monitoring programs, operational and logistical limitations such as cost and remoteness and technological limitations such as the absorption of EM radiation by water. Laser and radar altimeters can provide measurements of the surface properties of the ice cover and snow covers such as roughness and thickness but have traditionally suffered from the same issues of poor spatial resolution or coverage. In 2010, The European Space Agency launched CryoSat-2 carrying SIRAL, a pulse-limited Delay-Doppler Synthetic Aperture and Interferometric radar altimeter with improved spatial coverage and along-track resolution and across-track position information using dual antennae. We provide several analyses of CryoSat-2 radar altimeter data over sea ice and lake ice using on-ice manual and autonomous measurements, airborne laser and radar altimetry and electromagnetic sounding and satellite radar imagery. First, a method to produce airborne roughness from a laser scanner without complicated inertial navigation data is presented and shown to better represent the roughness of sea ice and to better highlight differences in roughness between different types of ice, smooth first-year ice (FYI) north of Svalbard, rough drifting multi-year ice (MYI) and FYI in Fram Strait and very rough landfast ice off the eastern coast of Greenland than a single-beam laser altimeter. Second, the first retrievals of lake ice thickness using CryoSat-2, or any radar altimeter, are presented. The retrievals are able to reproduce the seasonal development in ice thickness observed by drill holes and model data (r > 0.65) and with low uncertainty (RMSE < 0.33 m) given that the minimum thickness that can be sensed is 0.26 m. Three studies into the response of CryoSat-2 over sea ice are presented using comparisons with ground and airborne data in the Arctic and Antarctica. The first of these studies highlighted errors with the early versions of CryoSat-2 data. The modal laser and radar freeboards and their latitudinal gradients were found to be the same despite the fact that the CryoSat-2 radar freeboard is assumed to come from the ice surface and the laser freeboard is representative of the snow surface. The agreement between the two freeboard measures may indicate incomplete radar penetration into the snow and the complicating issue of surface roughness and differences in spatial coverage. The second CryoSat-2 study highlighted the influence of snow depth on the retracking of CryoSat-2 radar echoes and the resulting freeboard results over sea ice with thick and thin snow covers. Lastly, the third study compares all available coincident CryoSat-2 and airborne laser and radar altimeter, and EM sounding data collected between 2010 and 2014. Results show low correlations (<0.3) between CryoSat-2 and airborne data at the scale of individual CryoSat-2 footprints but higher correlations (0.3 < r < 0.6) when averaged along 50km sections of the orbit. Higher correlations are observed between modal airborne freeboard and CryoSat-2 freeboard than between mean airborne freeboard and CryoSat-2 freeboard, possibly indicating that CryoSat-2 is more sensitive to modal freeboard than mean freeboard. The three CryoSat-2 and airborne data comparison studies show that CryoSat-2 can accurately capture large areal averages of sea ice freeboard. This study contributes to the understanding of altimeter data over sea ice and lake ice and identifies the need for improved data on snow thickness on sea ice as a major challenge to improve altimetric sea ice products.

  • Subjects / Keywords
  • Graduation date
    Spring 2018
  • Type of Item
  • Degree
    Doctor of Philosophy
  • DOI
  • License
    This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.