Investigating the Influence of Variable Freshwater Ice Types on Passive and Active Microwave Observations

Abstract

Dual-polarized airborne passive microwave (PM) brightness temperatures (T b ) at 6.9 GHz H/V, 19 GHz H/V and 37 GHz H/V and spaceborne active microwave (AM) X-band (9.65 GHz VV, VH) backscatter (σ 0 ) are observed coincident to in situ snow and lake-ice measurements collected over two lakes near Inuvik, Canada. Lake-ice thickness is found to be positively correlated with 19 GHz V emission (R = 0.67) and negatively with 19 GHz H emission (R = −0.79), indicating surface ice conditions influence microwave interaction. Lake ice types are delineated from TerraSAR-X synthetic aperture radar (SAR) images using the iterative region growing with semantics (IRGS) segmentation algorithm implemented in the MAGIC (MAp Guided Ice Classification) system. The spatial extent of derived ice type classes correspond well to in situ observations. The overall magnitude of emission at 19 GHz H and X-band VH σ 0 increase with the scattering potential of associated ice types (grey/rafted ice). Transects of 6.9 GHz PM and 19 GHz PM exhibit positive relationships with VH σ 0 over freshwater lake ice, with the greatest R coefficients at H-pol (R = 0.64, 0.46). Conversely, 6.9 GHz T b and 19 GHz T b exhibit negative R coefficients in regions of brackish water due to tubular bubble and brine inclusions in the ice. This study identifies congruency between PM and AM scattering mechanisms over lake ice for the purpose of identifying the influence of ice types on overall microwave interaction within the lake-ice system.

Investigating the Effect of Lake Ice Properties on Multifrequency Backscatter Using the Snow Microwave Radiative Transfer Model

“…X-band responds to increases in s, but this response decreases at higher incidence angles and the frequency becomes more responsive to increases in surface bubble radius or other scatterers such as snow. This demonstrates that X-band is useful for identifying surface ice types as noted in past research [72]. Additionally, results show that increases in backscatter are likely not a result of increasing ice thickness but are due to changes that occur in ice properties (i.e., bubble radius and s) throughout the ice season.…”

“…8) demonstrate that X-band is a valuable source for identifying surface ice types and understanding bubble characteristics within ice columns. This is supported by past research that has utilized this frequency for use in classifying surface ice types in the Northwest Territories [72]. Furthermore, co-pol ratios for Xband do show an increase with increasing thickness both with and without snow ice.…”

Community Development of the Snow Microwave Radiative Transfer Model for Passive, Active and Altimetry Observations of the Cryosphere

“…A rough interface between the lake ice and unfrozen water resulted in a 15 K increase in T B . The rough substrate simulations compare well with airborne observations in Figure 6 of [15].…”

“…SMRT was used to simulate brightness temperature at 6 GHz and incidence angle of 53 o for a layer of snow on a layer of lake ice. Snow parameters within the measurements of [15] were ∆z=0.3m, snow sphere radius of 1mm and T=260 K. A sticky hard sphere microstructure model was assumed, with stickiness of 1.0. The sensitivity of brightness temperature to lake ice thickness was simulated, based on spherical air bubbles within the ice with 1mm radius, ice porosity of 1% and T=260 K. The sensitivity study distinguishes between a flat water substrate and a rough ice-water interface with reflectivity given by [16] (rms roughness = 1mm and water temperature of 273 K).…”

Forward modelling of synthetic-aperture radar (SAR) backscatter during lake ice melt conditions using the Snow Microwave Radiative Transfer (SMRT) model

“…Additionally, SAR imagery provides resolutions of < 50 m for most image products, allowing for the delineation of small and medium lakes (Murfitt and Duguay, 2021). The most common frequency for SAR remote sensing of lake ice is the C-band, partially due to the availability of sensors that provide C-band imagery as well as the penetration depth, which is less impacted by upper ice layers and snow cover (Gunn et al, 2017). Observations of lake ice using the L-band and X-band can provide additional information to the C-band; for example the L-band has shown success in monitoring methane ebullition bubbles for lakes in Alaska (Engram et al, 2012).…”