Speaker
Description
One of the recommendations resulting from previous radar-based earth observation mission concepts for snow parameter retrieval is that high-resolution imagery of the vertical structure of snow is required to gain further insight into the complex electromagnetic interaction within snowpacks.
As part of the ESA SnowLab campaign the SnowScat device, a terrestrial stepped-frequency continuous-wave (SFCW) scatterometer, which supports fully-polarimetric measurements within a frequency band from 9.2 to 17.8 GHz, was operated in tomographic profiling mode to obtain time series of high-resolution vertical snow profiles. (See also the attached collage of images, which, on the left, shows the SnowScat device deployed in tomographic mode.).
In this tomographic profiling mode, the SnowScat device is subsequently displaced in elevation direction to obtain a high resolution not only in range direction but also along elevation. This yields two-dimensional vertical profiles of the snowpack, which means that observables such as radar backscatter, co-polar phase difference, interferometric phase and coherence can be distinguished also along the vertical dimension.
In winter 2014/2015, a first test campaign at a test site hosted by the WSL Institute for Snow and Avalanche Research (SLF), in Davos, Switzerland was carried out yielding a successful proof of concept of the enhanced hardware, the tomographic measurement, and a basic processing concept. First comparisons of tomographic profiles with in-situ snow profiles indicated that melt-freeze crusts/ice layers present within the snowpack could be identified.
As a follow-up to this proof of concept the ESA SnowLab project has been set up to provide an experimental framework to investigate the interaction of microwaves with a snowpack under the varying conditions throughout an entire alpine snow season. One aspect within this 3-year project was to acquire and process time series of tomographic profiles - as well as regular SnowScat measurements - at dedicated test sites in the Swiss alps. During these campaigns, up to three tomographic profiles were acquired per day.
Using this data set it could be shown that various phenomena can be investigated based on this time series of tomographic profiles, such as using
1) the variation of radar backscatter to locate melt-freeze crusts/horizontal layers within the snow pack, 2) using the co-polar (HH-VV) phase difference to characterize potential anisotropy or changes in anisotropy, and 3) using differential (temporal) coherence between tomographic profiles along the time series to measure changes in the propagation delay, spatially resolved in the 2-D vertical profile.
In this talk, we will give a summary and outlook of three years of daily time-series of tomographic measurements of snow obtained within the ESA Snowlab campaign at two different locations in the Swiss Alps.
(1) the measurement and imaging concept of SnowScat in tomographic mode is presented, (2) examples of acquired data products obtained within the ESA SnowLab campaign in the Swiss Alps during three snow seasons are shown,
and (3) approaches to retrieve snow parameters as well as comparisons with in-situ snow measurements are discussed.
