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

• Published in: Remote Sensing
• Main Authors: Juha Lemmetyinen, Chris Derksen, Helmut Rott, Giovanni Macelloni, Josh King, Martin Schneebeli, Andreas Wiesmann, Leena Leppänen, Anna Kontu, Jouni Pulliainen
• Format: Article in Journal/Newspaper
• Language: English
• Published: MDPI AG 2018
• Subjects: snow water equivalent; passive microwave; radar; snow correlation length; Science; Q; Northern Finland
• Online Access: https://doi.org/10.3390/rs10020170; https://doaj.org/article/01719e1cb6af487eb5577e9d6494b5cc

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 ...