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Modeling UHF-Band Spectra of Lake Ice Brightness Temperature

Author(s): A. Bringer; K. Jezek; J. Johnson; M. Durand; L. Tsang; S. Tan; T. Wang; G. Macelloni; M. Brogioni

Linked Author(s): Tengfei Wang, John K. Johnson

Keywords: No Keywords

Abstract: Under calm, quiescent conditions, lake ice forms as a homogenous sheet on the surface of the water. Lake ice growth rate depends on several environmental factors. Considering only the surface temperature, ice growth rates for thin ice are several mm per hour for air temperatures well below the freezing point. Over time, lake ice can reach thickness of several m. Lake ice is important because of the insulation the ice layer offers for the underlying ecosystem and can present an important constraint on operational activities. Ice thickness is an important factor influencing many of theses processes; the remote sensing of lake ice thickness is therefore of interest. We are presently developing a novel radiometer for cryospheric and ice sheet studies. The device, called the Ultra Wide Band Software Defined Radiometer (UWBRAD), measures thermal emission over frequencies from 0.5 to 2 GHz in 12 100 MHz bandwidth frequency channels. Because the dielectric contrast between the ice and water is high and because the dielectric loss in lake ice is relatively small, we investigated whether UWBRAD microwave spectra could be used to measure lake-ice thickness at least for the case wherein ice forms in calm conditions. We model the lake ice as a smooth homogeneous ice bounded above by air and below by water. Because the electrical properties are temperature dependent, we adopt a simple, linear model for the temperature profile in the ice. We use a coherent radiative transfer model to calculate the brightness temperature of the slab. We find that the brightness temperature across our band oscillates because of the reverberation of the emitted energy within the slab. The rate of brightness temperature oscillation changes with ice thickness suggesting that wide-band spectra can be a useful tool for measuring lake ice thickness remotely. The interference phenomenon observed in the frequency domain is related to time delayed features in the temporal correlation function of the thermal noise, as the two are related by a Fourier transform.


Year: 2016

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