Mid-Latitude Snowmelt Onset Detection Via Microwave Remote Sensing

The timing and magnitude of spring snowmelt events are critical for understanding the winter-to-spring transition of the hydrologic cycle and ecosystem processes. Melt timing determination is challenging because snowpack ripening observations are seldom available. Remotely sensed passive microwave observations show promise for determining snowpack wetting and melt onset at global scales. Studies performed in northern latitude regions verify the theoretical concept of microwave snowmelt detection methods under ideal conditions. However, early winter snowmelt events within mid-latitude regions introduce large regional climate differences that add considerable amounts of noise to the microwave observations. Diurnal Amplitude Variation (DAV), Frequency Difference (FD) and Polarization Ratio (PR) are three methods that use remotely sensed passive microwave observations to determine snowpack wetting and melt onset. This study evaluates the performance of these approaches to determine spring melt onset and early winter flood events in mid-latitudes. The suitability of microwave remote sensing techniques to detect snowmelt was found to vary regionally. Physical characteristics including basin latitude, regional air temperatures, snow depth, snow covered area, forest density, and rain intensity were examined to understand how and why the observed microwave signatures associated with snow cover vary over contrasting regions.