Observing Freeze-Thaw Transitions Over Land Using Cygnss Measurements

Measuring freeze-thaw (F/T) changes over land plays a crucial role in various climate, ecological and hydrological processes. Active and passive microwave measurements of land surface have shown a potential to monitor land surface F/T conditions. Especially at L-band, the measurements have previously been shown to be effective in estimating soil freeze-thaw. In this work we plan to look at the GNSS-R reflections over land, captured by the CYGNSS observatories, for this purpose. Though CYGNSS constellation was initially developed for ocean surface roughness measurements, it has shown sensitivity to changes in soil moisture over land, thereby making it a potential candidate for observing freeze-thaw transitions as well. We plan to look for changes in signal SNR during Freeze-thaw transitions due to the changes in the dielectric property of the surface during those events and develop machine learning based empirical regression models to understand the relationship between F/T events and GNSS-R reflections.