Correlation Radiometry to Remotely Measure the Freshwater Lake Icepack Thickness

As lakes provide one of the most important freshwater resources, there is an immediate need to monitor the lake ice formed during winter seasons. In addition, lake icepack puts pressure on off-shore structures, such as wind farms. Lake icepack thickness is also an important safety parameter for ice fishing and ice skating activities. The current method of ice thickness measurement, which is by drilling holes through the pack, is not only laborious but also unsafe and hazardous. Altimeters and ground penetrating radars (GPRs) have also been used to measure the ice thickness, but these active techniques are not well-suited to stand-off operation.

As an alternative way of microwave remote sensing of lake icepack, we developed a new, robust, and low-cost passive microwave remote sensing technique, known as wideband autocorrelation radiometry (WiBAR). It is a passive microwave remote sensing method that can directly measure the microwave propagation time of multipath microwave emission from low-loss layered surfaces such as freshwater lake icepack. The microwave propagation time difference through the pack returns a measure of its thickness. It is also a low-power microwave remote sensing technique since there is no transmitter as opposed to active techniques. An X-band instrument fabricated from commercial-off-the-shelf (COTS) components is used to measure the thickness of freshwater lake icepack at different lakes, such as South Sturgeon and Side Lakes in northern Minnesota and Douglas Lake in northern Michigan. The ice thicknesses are in the range of about 30 cm to 60 cm. Ice thickness retrieval is demonstrated from nadir to about 60 degrees of incidence angle. The WiBAR was able to directly measure the lake icepack thickness with an accuracy of about 2 cm over this range of incidence angles.