Title: Measurement Concept Demonstration: Wideband Autocorrelation Radiometry for Deterministic Passive Microwave Measurement of Lake Ice and Snow Depth
Presenting Author: Roger De Roo
Organization: University of Michigan
Co-Author(s): Seyedmohammad Mousavi, Anthony W. England, Line van Nieuwstadt, Steven Rogacki

Abstract:
Wideband Autocorrelation Radiometry (WiBAR) is a microwave technique for passively measuring the vertical extent of low loss layered media such as the seasonal terrestrial snow pack. The upper and lower interfaces of the low loss medium cause the upwelling Planck radiation from below to experience the coherent effects of constructive and destructive interference. This interference produces a correlation in the thermal noise that propagates upward from surface: this noise contains a an attenuated and delayed copy of itself. The delay corresponds to twice the microwave propagation time through this medium, and so the emission contains information about the depth of the layer. This presentation reports on the results of the observations made with a portable instrument manufactured by the University of Michigan under an ESTO Instrument Concept and Demonstration project. The target of this instrument is another cyrospheric layered low loss medium: lake ice. The instrument uses a broad bandwidth of 3GHz to observe delays as short as 1ns, corresponding to a minimum ice thickness of 10cm. The instrument's center frequency of 8.5GHz is chosen to render the ice surfaces electromagnetically smooth. We have been able to confirm theoretical predictions that measurements can be made relatively quickly at nadir and at grazing, compared to measurements at the more traditional radiometric observing angles near 45 degrees. While larger reflection coefficients for H-pol make it superior to V-pol at most incidence angles, at grazing V-pol can outperform H-pol and appears to provide complementary information about the target. Snow on top of the ice pack can be observed if it is sufficiently thick, 'tho the presence of liquid water destroys the signal. We will conclude with a description of a longer wavelength version of the instrument that is intended to demonstrate measurement of terrestrial snow.