Mapping the bathymetry of shallow tundra lakes using INSAR techniques

There are thousands of shallow lakes on the North Slope of Alaska. They are one of the most obvious manifestations of the hydrological system at work, and they play an important role in physical, biological and biogeochemical processes in the tundra environment. The depth of the lakes is a key determinant of these processes, yet few bathymetric data are available. The authors conducted a pilot study to investigate the ability of interferometric synthetic aperture radar (INSAR) to derive bathymetry of the shallow lakes on the Alaskan North Slope. Because lake ice is transparent in the microwave region, they hypothesize that INSAR can see through the lake ice and reveal the topography beneath the grounded lake ice. The analytical result of a sensitivity analysis indicates that interferometric phase is more sensitive to lake bathymetry under grounded lake ice than to the land surface topography. A series of interferograms are derived for the area near Point Barrow, Alaska, from pairs of ERS-1 3-day repeat SAR images acquired in January through March 1994. Floating ice is identified by the noisy phase pattern and low coherence, which are due to the increase of the ice thickness in the interim. Grounded ice is identified by the clean phase pattern and relatively high coherence, because no further growth occurs once the lake has frozen to the bottom. The phase difference between the grounded ice and the surrounding land reflects the lake bottom topography. The final usefulness of this new INSAR application needs to be verified and validated.