COld REgions Hydrology High-resolution Observatory Research Articles

Feasibility of Characterizing Snowpack and the Freeze–Thaw State of Underlying Soil Using Multifrequency Active/Passive Microwave Data

An ensemble-based data assimilation approach is developed to characterize the snow water equivalent (SWE) and underlying soil freeze-thaw state (including the soil surface temperature and both soil ice and liquid water content) using multifrequency passive and active microwave remote-sensing measurements. Its feasibility was examined using a synthetic test where passive microwave (1.4, 18.7, and 36.5 GHz) and active microwave [L-band (1.4 GHz), C-band (5.4 GHz), and Ku-band (12 GHz)] measurements at the point scale were individually and simultaneously assimilated to estimate the SWE and soil freeze-thaw state using an Ensemble Batch Smoother framework. The contribution of each channel in retrieving the true SWE, soil surface temperature, soil liquid water and ice content was investigated at the local-scale observation site of the National Aeronautics and Space Administration Cold Land Processes Experiments Field Campaign in northern Colorado during both the snow accumulation (Fall 2002-Winter 2003) and melt (Spring 2003) periods. All of the utilized passive and active measurements were found to contain valuable and complementary information for characterizing the SWE and freeze-thaw state of the underlying soil. L-band measurements were most effective for soil freeze-thaw state estimation, whereas higher frequencies were more effective at SWE characterization. In addition, results from the simultaneous assimilation of passive and active microwave data were compared to those from a modeling approach without assimilating microwave data (open loop). It was found that assimilating both passive and active microwave data decreased the errors that are associated with the open-loop approach. Finally, passive and active measurements were undersampled as expected from the overpasses of current and future satellite platforms. It was observed that the developed method can reliably estimate the soil freeze-thaw state and SWE, even with measurement sequences anticipated from the temporal frequency of existing and future satellites such as the Special Sensor Microwave/Imager, Soil Moisture Active Passive Mission, and Cold Regions Hydrology High-Resolution Observatory.

Electromagnetic Models of Co/Cross Polarization of Bicontinuous/DMRT in Radar Remote Sensing of Terrestrial Snow at X- and Ku-band for CoReH2O and SCLP Applications

In this paper, we study the scattering properties of the terrestrial dry snow by modeling the snow structure as Bi-continuous media. The model is applied to study the snow scattering characteristics at X-band and Ku-band that are two frequencies in the proposed Cold Regions Hydrology High-resolution Observatory (CoReH2O) mission by ESA and the proposed Snow and Cold Land Process (SCLP) mission by NASA. There are two variables in the Bi-continuous media that can be adjusted to generate various snow microstructures. The different snow structures are illustrated. The extinction properties and phase matrices are studied through the Monte Carlo simulations. For each realization, the Maxwell Equations are solved numerically to take into account the coherent wave interactions among the inhomogeneties. We demonstrated the frequency dependences of scattering coefficients, which can vary depending on the setup parameters of the bicontinuous media. The power law are compared with experiment data of extinction coefficients of terrestrial snow. The calculated extinction and phase matrices are combined in the Dense Media Radiative Transfer theory (DMRT). We obtain the 1st order solution by using the iterative method. The surface scattering from the snow-ground interface is included by searching the look up table of NMM3D. The results of co-polarization and cross polarization are compared with the POLSCAT Ku-band airborne data and X-band TerraSAR-X satellite data in North Slope, Alaska.

Cold Regions Hydrology High-Resolution Observatory for Snow and Cold Land Processes

Snow is a critical component of the global water cycle and climate system, and a major source of water supply in many parts of the world. There is a lack of spatially distributed information on the accumulation of snow on land surfaces, glaciers, lake ice, and sea ice. Satellite missions for systematic and global snow observations will be essential to improve the representation of the cryosphere in climate models and to advance the knowledge and prediction of the water cycle variability and changes that depend on snow and ice resources. This paper describes the scientific drivers and technical approach of the proposed Cold Regions Hydrology High-Resolution Observatory (CoReH <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O) satellite mission for snow and cold land processes. The sensor is a synthetic aperture radar operating at 17.2 and 9.6 GHz, VV and VH polarizations. The dual-frequency and dual-polarization design enables the decomposition of the scattering signal for retrieving snow mass and other physical properties of snow and ice.