Observation and Modeling of X- and Ku-Band Backscatter of Snow-Covered Freshwater Lake Ice

This study is the first assessment of winter season backscatter ( $\boldsymbol{\sigma}^\circ $ ) evolution for snow-covered lake ice observed by X- (9.6 GHz) and Ku-band (17.2 GHz) ground-based scatterometers (UW-SCAT), collected during the Canadian Snow and Ice Experiment in 2010–2011. The $\boldsymbol{\sigma}{^\circ}$ evolution of three ice cover scenarios is observed and simulated using a bubbled ice $\boldsymbol{\sigma}{^\circ }$ model. The range resolution of UW-SCAT provides separation of interaction at the snow–ice interface (P1), and within the ice volume and ice–water interface (P2). Ice cores extracted at the end of the observation period indicate a P2 $\boldsymbol{\sigma}{^\circ}$ increase of approximately 10–12 decibels (dB) (HH & VV) at X- and Ku-band coincident to tubular bubble development. Similarly, complexity of the ice surface (gray ice) results in increased P1 $\boldsymbol{\sigma}{^\circ}$ $({\sim}\mathbf{7}\;\mathbf{dB})$ . P1 observations indicate that Ku-band is sensitive to snowpack overlying lake ice, with $\boldsymbol{\sigma}{^\circ}$ exhibiting a 5 (6) dB drop for VV (HH) when 0.235 m snow is removed. X-band is insensitive to changes in overlying snowpack. A bubbled ice $\boldsymbol{\sigma}{^\circ}$ model is presented using dense medium-radiative transfer theory under the quasi-crystalline approximation (DMRT-QCA), which treats bubbles as spherical inclusions within an ice volume. Model runs demonstrate the capability of DMRT to produce observed $\boldsymbol{\sigma}{^\circ}$ magnitude using snow and ice observations as input. This study improves the understanding of microwave interaction with bubbled ice near the surface or within the volume. Results from this study indicate that further model development involves bubble shape modification within the ice from spherical to tubular.