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Retrieval of Effective Correlation Length and Snow Water Equivalent from Radar and Passive Microwave Measurements

Finnish Meteorological Institute, Erik Palménin aukio 1, FI-00560 Helsinki, Finland
Institute of Remote Sensing and Digital Earth, Chinese Academy of Sciences, No.9 Dengzhuang South Road, Haidian District, Beijing 100094, China
Environment and Climate Change Canada, 4905 Dufferin Street, Toronto, ON M3H 5T4, Canada
ENVEO IT GmbH, Fürstenweg 176, A-6020 Innsbruck, Austria
Institute of Atmospheric and Cryospheric Sciences, University of Innsbruck, A-6020 Innsbruck, Austria
Institute of Applied Physics “Nello Carrara”, Via Madonna del Piano, 10-50019 Sesto Fiorentino (FI), Italy
WSL Institute for Snow and Avalanche Research SLF, Flüelastrasse 11, CH-7260 Davos Dorf, Switzerland
GAMMA Remote Sensing Research and Consulting AG, Worbstr. 225, CH-3073 Gümligen, Switzerland
Author to whom correspondence should be addressed.
Remote Sens. 2018, 10(2), 170;
Received: 18 January 2018 / Accepted: 21 January 2018 / Published: 25 January 2018
Current methods for retrieving SWE (snow water equivalent) from space rely on passive microwave sensors. Observations are limited by poor spatial resolution, ambiguities related to separation of snow microstructural properties from the total snow mass, and signal saturation when snow is deep (~>80 cm). The use of SAR (Synthetic Aperture Radar) at suitable frequencies has been suggested as a potential observation method to overcome the coarse resolution of passive microwave sensors. Nevertheless, suitable sensors operating from space are, up to now, unavailable. Active microwave retrievals suffer, however, from the same difficulties as the passive case in separating impacts of scattering efficiency from those of snow mass. In this study, we explore the potential of applying active (radar) and passive (radiometer) microwave observations in tandem, by using a dataset of co-incident tower-based active and passive microwave observations and detailed in situ data from a test site in Northern Finland. The dataset spans four winter seasons with daily coverage. In order to quantify the temporal variability of snow microstructure, we derive an effective correlation length for the snowpack (treated as a single layer), which matches the simulated microwave response of a semi-empirical radiative transfer model to observations. This effective parameter is derived from radiometer and radar observations at different frequencies and frequency combinations (10.2, 13.3 and 16.7 GHz for radar; 10.65, 18.7 and 37 GHz for radiometer). Under dry snow conditions, correlations are found between the effective correlation length retrieved from active and passive measurements. Consequently, the derived effective correlation length from passive microwave observations is applied to parameterize the retrieval of SWE using radar, improving retrieval skill compared to a case with no prior knowledge of snow-scattering efficiency. The same concept can be applied to future radar satellite mission concepts focused on retrieving SWE, exploiting existing methods for retrieval of snow microstructural parameters, as employed within the ESA (European Space Agency) GlobSnow SWE product. Using radar alone, a seasonally optimized value of effective correlation length to parameterize retrievals of SWE was sufficient to provide an accuracy of <25 mm (unbiased) Root-Mean Square Error using certain frequency combinations. A temporally dynamic value, derived from e.g., physical snow models, is necessary to further improve retrieval skill, in particular for snow regimes with larger temporal variability in snow microstructure and a more pronounced layered structure. View Full-Text
Keywords: snow water equivalent; passive microwave; radar; snow correlation length snow water equivalent; passive microwave; radar; snow correlation length
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MDPI and ACS Style

Lemmetyinen, J.; Derksen, C.; Rott, H.; Macelloni, G.; King, J.; Schneebeli, M.; Wiesmann, A.; Leppänen, L.; Kontu, A.; Pulliainen, J. Retrieval of Effective Correlation Length and Snow Water Equivalent from Radar and Passive Microwave Measurements. Remote Sens. 2018, 10, 170.

AMA Style

Lemmetyinen J, Derksen C, Rott H, Macelloni G, King J, Schneebeli M, Wiesmann A, Leppänen L, Kontu A, Pulliainen J. Retrieval of Effective Correlation Length and Snow Water Equivalent from Radar and Passive Microwave Measurements. Remote Sensing. 2018; 10(2):170.

Chicago/Turabian Style

Lemmetyinen, Juha, Chris Derksen, Helmut Rott, Giovanni Macelloni, Josh King, Martin Schneebeli, Andreas Wiesmann, Leena Leppänen, Anna Kontu, and Jouni Pulliainen. 2018. "Retrieval of Effective Correlation Length and Snow Water Equivalent from Radar and Passive Microwave Measurements" Remote Sensing 10, no. 2: 170.

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