Andrea Crepaz

Monitoring of melting refreezing cycles of snow with microwave radiometers: the Microwave Alpine Snow Melting Experiment (MASMEx 2002-2003)

A study of the melting cycle of snow was carried out by using ground-based microwave radiometers, which operated continuously 24 h/day from late March to mid-May in 2002 and from mid-February to early May in 2003. The experiment took place on the eastern Italian Alps and included micrometeorological and conventional snow measurements as well. The measurements confirmed the high sensitivity of microwave emission at 19 and 37 GHz to the melting-refreezing cycles of snow. Moreover, micrometeorological data made it possible to simulate snow density, temperature, and liquid water content through a hydrological snowpack model and provided additional insight into these processes. Simulations obtained with a two-layer electromagnetic model based on the strong fluctuation theory and driven by the output of the hydrological snowpack model were consistent with experimental data and allowed interpretation of both variation in microwave emission during the melting and refreezing phases and in discerning the contributions of the upper and lower layers of snow as well as of the underlying ground surface.

Ground-Based L-Band Emission Measurements at Dome-C Antarctica: The DOMEX-2 Experiment

In recent years, there has been growing interest on the part of the remote sensing community in using the Antarctic area for calibrating and validating data of low-frequency satellite-borne microwave radiometers. In particular, the East Antarctic Plateau appears to be suited for this purpose. The reasons for this interest are the size, structure, spatial homogeneity, and thermal stability of this area. This is particularly interesting for low-frequency microwave radiometers since, due to the low extinction of dry snow, the upper ice-sheet layer is almost transparent and the brightness temperature variability is therefore extremely small. In the context of calibration and validation activities of the European Space Agencys Soil Moisture and Ocean Salinity (SMOS) satellite, an experiment called DOMEX-2, which included radiometric L-band measurements, was carried out at the Italian-French base of Concordia located at Dome C in the East Antarctic Plateau from December 2008 to December 2010. Ground measurements (i.e., snow temperature at different depths, snow structure, meteorological data, etc.) were also collected during the experiment. This paper presents information on the experimental campaign, the characteristics of the radiometric measurements, and the main results. A comparison with SMOS data is also presented.

Monitoring Snow Characteristics With Ground-Based Multifrequency Microwave Radiometry

Long-term microwave and infrared radiometric measurements of snowpack were carried out with ground-based sensors in winter 2006-2007 and 2007-2008, together with conventional measurements of snow-cover profiles. The first experiment focused on the behavior of snow emission during the destructive and constructive metamorphisms. The second involved a correlation analysis of the small fluctuations related to diurnal solar cycle in order to obtain the time delay of microwave brightness temperatures Tb with respect to the snow surface temperature. From this analysis, it was possible to estimate an effective (weighed average) temperature and the thickness of the layer that mostly contributed to microwave emission at 19 and 37 GHz. The ratio of the brightness temperature to the effective temperature can be assumed to be an equivalent emissivity of the snowpack. Data collected in both years have been compared with simulations carried out using the advanced Institute of Applied Physics (IFAC) Radiative Advanced Dry Snow Emission (IRIDE) model driven by data collected on ground. The model is based on the advanced integral equation method to represent soil, coupled to a layer of dry snow whose electromagnetic properties are described by the dense medium radiative transfer theory with quasi-crystalline approximation applied to a medium (air) filled with sticky particles. Simulations performed by using ground data as inputs to the model have been found to be well in agreement with experimental data. Moreover, the comparison of model simulations with experimental data allowed one to understand some peculiar characteristics of microwave emission from the snowpack related to its physical conditions.

Study of the snow melt–freeze cycle using multi-sensor data and snow modelling

The melt cycle of snow is investigated by combining ground-based microwave radiometric measurements with conventional and meteorological data and by using a hydrological snow model. Measurements at 2000 m a.s.l in the basin of the Cor- devole river in the eastern Italian Alps confirm the high sensitivity of microwave emission at 19 and 37 GHz to the snow melt^freeze cycle, while the brightness at 6.8 GHz is mostly related to underlying soil. Simulations of snowpack changes performed by means of hydrological and electromagnetic models, driven with meteorological and snow data, provide additional insight into these processes and contribute to the interpretation of the experimental data.

Microwave remote sensing and hydrological modelling of snow melting cycle

A study of the melting cycle of snow was carried out by combining microwave active and passive measurements with meteorological data and snow modelling. The experiment took place in the eastern Italian Alps from mid February to late May 2003. Brightness temperature at C-, Ku- and Ka- bands (vertical and horizontal polarizations) and backscattering coefficient at Ku-band (VV), were continuously measured (24 h/day) with ground-based sensors. Remote sensing observations were supported by meteorological data, and snow measurements. A continuous simulation of the snow temperature, depth, and liquid water content was performed for the entire monitoring period by means of a physically based distributed snowmelt model. Both hydrological and remote sensing approaches gave useful and coherent results in describing the snow melting and refreezing cycles. Microwave active and passive data were consistent each other. During the melting cycle, the presence of liquid water caused an increase of absorption with a consequent increase of the brightness temperature and a decrease of the backscattering coefficient

Comparison of Cosmo-SkyMed and TerraSAR-X data for the retrieval of land hydrological parameters

The backscattering coefficient variations of Cosmo-SkyMed and TerraSAR-X SAR sensors have been investigated. When possible, the data of the two sensors have been compared and a quantitative analysis was carried out. The comparison of SAR data has been also performed taking into account the temporal variations, in order to quantify potential changes of surface parameters. A series of both Cosmo-SkyMed (CSK) and TerraSAR-X (TSX) images were collected on both mountain and agricultural areas. The potentials of X-band backscattering in estimating hydrological parameters of the surface were investigated.

Combined use of experimental data and a multi-layer model for investigating the sensitivity of microwave indexes to snow parameters

The analysis of the relationships between FI & SPD and SWE/SD was carried out using experimental data and simulations obtained using the DMRT-QCA Multilayer model. The comparison of experimental results and model analyses made it possible to investigate the polarizing effect of snow layering and to better assess the sensitivity of FI and SPD to the snow accumulation.

Sensitivity analysis of microwave backscattering and emission to snow water equivalent: Synergy of dual sensor observations

An accurate sensitivity analysis of microwave emission and scattering to snow water equivalent (SWE) is performed by using a two layer Dense Medium Radiative Transfer Model implemented for both active and passive case. In order to evaluate the potential of the recent Cosmo-Skymed and TerrasarX missions, the study is mainly focussed on X band sensors. Model simulations have shown that an appreciable sensitivity of X-band backscattering and emission to dry snow can be found for Snow Water Equivalent higher than 70–100 mm and relatively high values of snow density and crystal dimensions. These results have been confirmed by experimental data taken from Cosmo Skymed mission and ground based multifrequency radiometers on a test site in the Italian Alps.

The Microwave Alpine Snow Melting Experiment (MASMEx 2002): a contribution to the ENVISNOW project

A study of the melting cycle of snow was carried out by combining microwave radiometric measurements with conventional micrometeorological data and snow modelling. The experiment took place in the eastern Italian Alps. The high sensitivity of microwave emission at 19 and 37 GHz to the melting refreezing-cycles of snow was confirmed. Moreover, micro-meteorological data provided additional insight on the processes. Simulations obtained with electromagnetic and hydrological models were consistent with experimental data.

DOMEX-2 : L-band microwave emission measurements of the Antarctic Plateau

In recent years there is growing interest, on the part of the remote sensing community, in using the Antarctic area, for calibrating and validating data of satellite-borne microwave radiometers. With a view to the launching of the ESAs SMOS satellite, which is a satellite designed to observe soil moisture over the Earth landmasses, salinity over the oceans and to provide observations over regions of ice and snow, an experimental activity called DOMEX-2 was started at Dome-C Antarctica. The main scientific objectives of this activity are to provide microwave data for SMOS satellite calibration and in particular: the continuous acquisition of a calibrated timeseries of microwave (L-band) and thermal Infrared (8–14micron) emission over an entire Austral annual cycle, the acquisition of a long time-series of snow measurements and the acquisition of relevant local atmospheric measurements from the local weather station. This paper is focusing on the preparation and installation of DOMEX-2 experiment and a preliminary analysis of data.