Title: Seasonal snow observations with Wideband Autocorrelation Radiometry during Winter 2018-19
Presenting Author: Roger De Roo
Organization: University of Michigan
Co-Author(s): Mohammad Mousavi; Anthony W. England; Line van Nieuwstadt

Wideband Autocorrelation Radiometry (WiBAR) is a recently developed technique for passively measuring the microwave propagation time of low loss layers. Radiobrightness from below the layer propagates upward toward the sensor through the layer after transiting first the lower and then the upper interfaces. At the same time, some of the radiation reflects from the upper interface, then the lower interface, before transiting the upper interface towards the sensor. This delayed ray is an attenuated and delayed copy of the direct ray, leading to a local maximum in the autocorrelation function of the received waveform. The time lag at which this maximum occurs is the round trip propagation time of the layer. To resolve short time lags, on the order of nanoseconds, large bandwidths, on the order of gigahertz, is needed. This technique has application in Earth Science for the annually regenerated low loss layers of snow pack and lake ice. Lake ice is easier to measure than snow pack, due to the typically smoother surfaces and larger dielectric contrasts at the interfaces. We have used observations of lake ice to validate various expectations of the technique, but measurements of snow pack have been sparse. In the winter of 2018-19, we deployed two independent WiBAR instruments at the University of Michigan Biological Station specifically to observe the passive lag signature of snow on the ground, one operating roughly in L-band and one in S-band. In early March 2019, a snow pack up to 64cm had developed, which is deep enough for the WiBAR observable to be detected by each instrument. We have recently downloaded the data, and see some first hints of the signal, albeit contaminated with considerable radio frequency interference. We will report on on our findings.