A.W. England
Among the relatively volatile materials that might appear as ground ice in the solar system, water is unique. It has a permanent electric dipole moment, expands upon freezing, and acts as a solvent for ionic materials. These properties contribute to characteristic dielectric and thermal signatures that can be used to detect ground ice in many situations with either radar or with microwave radiometry. Microwave radiometry relative to radar has some advantages in that it is an intrinsically simpler sensor, and some advantages in detecting ground ice in that it is relatively more sensitive to temperature and permittivity, and relatively less sensitive to the geometric features of size, shape, orientation, and roughness. With the new technologies of Synthetic Thinned Array Radiometry (STAR) or with the possibility of large inflatable reflectors, microwave radiometry overcomes some of its disadvantage with respect to radar of requiring larger physical apertures to achieve acceptable spatial resolutions. This tutorial is a review of our experience detecting water ice in soil with microwave radiometry.
The key to interpreting any remote sensing signature is to have adequate models of expected behavior. For ground ice, there are two types of model: Radiobrightness models which are inherently static, and Thermal models which must be dynamic. For radiobrightness models, I will use intrinsic brightness, apparent brightness, penetration, coherence, and polarization as tools to explain the differences we observe in the brightness of frozen and thawed soils. Our thermal models are one-dimensional, coupled heat and moisture transport models forced by downwelling solar and thermal infrared radiance and by atmospheric temperature, humidity, and winds. I will show examples from models for moist bare soil, prairie grassland, and prairie snowpack. We have validated these models with a series of extended Radiobrightness Energy Balance Experiments (REBEX) in northern prairie. We have also collected one year of REBEX data in tussock tundra near Toolik Lake on Alaska's North Slope. The model for this terrain is being developed.
Contact Information:
A. W. (Tony) England
Departments of Atmospheric, Oceanic and Space Science, and of Electrical Engineering and Computer Science
University of Michigan
Ann Arbor, MI 48109-2122
Telephone: (313) 764-8221
email: england@umich.edu