Determination of Snow Emission on Lake Ice from Airborne Passive Microwave Measurements
ABSTRACT The study focuses on the microwave emission properties of snow-covered lake ice. Lakes typically differ from their surrounding terrain regarding snowpack structure, and thus microwave emission. Ice and water layers beneath the snow also influence the result when compared to frozen ground, decreasing brightness temperatures especially on low frequencies. Estimates of snowpack properties from low-resolution microwave data, such as snow depth or snow water equivalent, are susceptible to these effects. In order to correct for the resulting underestimation, the lake fraction over the area of study as well as the emission properties of those lakes should be known. This could potentially be achieved through the assimilation of modeled estimates of snow-covered lake emissions to satellite data. In this study, a modified HUT snow emission model, including modeled influence from the ice and water layers, is applied to model emission over several lakes in Finland during two winter periods. Input parameters to the model are derived from a large quantity of available ground data. Airborne radiometer data are applied to investigate the quality of the emission estimates. Finally, emissions over several AMSR-E pixels are modeled using fractional lake coverage and available ground data.
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ABSTRACT: A multilayer formulation of snow hydrological processes implemented in an existing snow hydrology-emission model (MLSHM-ML) was applied in observing system simulation mode (OSS) to two very different climatic and physiographic regions (Valdai, Russia and Colorado, USA) for both wet and dry snow regimes, and over multiple years. The results were evaluated against ground-based observations of snowpack physical properties and microwave radiometric observations from the Scanning Multichannel Microwave Radiometer (SMMR), Special Sensor Microwave/Imager (SSM/I), and Advanced Microwave Scanning Radiometer–EOS (AMSR-E) observations at 18–19-, 22–23-, and 36–37-GHz vertical and horizontal polarizations (V-pol and H-pol, respectively). Whereas snow water equivalent (SWE) results are similar to the results obtained with single-layer physics when the snow is dry, the multilayer physics have a better skill at capturing the overall temporal evolution of bulk density, snow temperature, and snow depth during the accumulation season, and at the onset and throughout the melting season. However, snow density profiles overestimate density at the bottom of the snowpack, consistent with the lack of an explicit representation of depth hoar in the rearrangement of mass and grain size distribution in the snowpack. Regarding the radiometric behavior, the multilayer SMMR OSS for Valdai shows improved results for nighttime simulations (descending SMMR paths, 11 p.m. LST) and H-pol ( $sim$ 3–5 K decrease in error statistics), particularly at 37 GHz. For daytime simulations (ascending SMMR paths, 11 a.m. LST), there are modest improvements at 18 ( $sim$ 1 K) and 37 GHz ( $sim$ 2–3 K) for H-pol, and generally loss of skill for V-pol at all frequencies. Systematic improvements at nighttime but not during daytime suggest that surface heterogeneities, including- - subgrid scale variability of transient melting, play an important role on surface emissivity. This is the case for cold land process experiment in Colorado, where spatial variability in fractional forest cover, geology, and complex topography explains the modest differences between the single and multilayer SSM/I OSS for H-pol, whereas significant gains ( $sim$ 4–8 K decrease in error statistics) were attained for V-pol at 37 GHz only. For AMSR-E, the multilayer OSS looses skill for H-pol, and only bias and mean absolute error improve for V-pol at all frequencies. These somewhat mixed results suggest that representation of snow stratigraphy alone is not sufficient to improve the OSS ability to describe the nonlinear interactions among hydrologic and electromagnetic processes. Chief among these are the temporal evolution of snow correlation length with depth and the representation of subgrid scale variability constrained by the spatial resolution and inherent uncertainty of the meteorological forcing. Nevertheless, the multilayer OSS improved performance at 37 GHz is an important finding toward reducing ambiguity in the sensitivity of 37-GHz H-pol brightness temperature to SWE in retrieval models.IEEE Transactions on Geoscience and Remote Sensing 05/2012; 50(99-PP):1 - 15. DOI:10.1109/TGRS.2011.2169074 · 2.93 Impact Factor
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ABSTRACT: In this work we chose the Helsinki University of Technology (HUT) snow emission model to character the emission behavior for a snowpack-ice-water system with the ground microwave radiometer observation. This snow and lake ice surveys was conducted in Songhua River, Songyuan city, Jilin Province, on Jan. 21- 22, 2010. Compared to the ground measurements over shallow snow-covered lake ice surface, the simulated brightness temperature at horizontal polarization was better than that at vertical polarizations. The R2 of the HUT simulation and measured value was 0.9304 at H-pol, and 0.9194 at V-pol, respectively. Further, we investigated the impact of lake on snow retrieval using passive microwave remote sensing using these ground-based observations. The snow depth in our ground snow survey was almost 5~8cm, ,the brightness temperature difference at the frequencies of 18.7 GHz and 36.5 GHz at V-pol and H-pol was up to -21.4K, -31.9K, respectively. These negative brightness temperature difference (18.7 GHz-36.5 GHz) over lakes caused errors in current SWE retrieval algorithms. Finally, we took sensitivity analysis of ice thickness and snow depth using HUT model on the show that the current brightness temperature difference snow retrieval algorithm was very sensitive to ice thickness, especially in the case of thinner ice. It needed us to make more study in the lake-rich area to improve the snow estimation accuracy.
Conference Paper: Microwave emission signature of snow-covered lake ice.[Show abstract] [Hide abstract]
ABSTRACT: Airborne microwave radiometer measurements of lake ice have been performed in 2004, 2007, and 2011 in southern Finland. The HUTRAD radiometer system provided data in the 6.9 to 36.5 GHz range using an incidence angle of 50 degrees off nadir. In 2011 also the interferometric HUT-2D radiometer was used to provide 1.4 GHz imagery of lake ice. Index Terms—Microwave radiometry, HUTRAD2011 IEEE International Geoscience and Remote Sensing Symposium, IGARSS 2011, Vancouver, BC, Canada, July 24-29, 2011; 01/2011