Microwave radiometric measurements of soil moisture in Italy

Abstract

Within the framework of the MAP and RAPHAEL projects, airborne experimental campaigns were carried out by the IFAC group in 1999 and 2000, using a multifrequency microwave radiometer at L, C and X bands (1.4, 6.8 and 10 GHz). The aim of the experiments was to collect soil moisture and vegetation biomass information on agricultural areas to give reliable inputs to the hydrological models. It is well known that microwave emission from soil, mainly at L-band (1.4 GHz), is very well correlated to its moisture content. Two experimental areas in Italy were selected for this project: one was the Toce Valley, Domodossola, in 1999, and the other, the agricultural area of Cerbaia, close to Florence, where flights were performed in 2000. Measurements were carried out on bare soils, corn and wheat fields at different growth stages and on meadows. Ground data of soil moisture (SMC) were collected by other research teams involved in the experiments. From the analysis of the data sets, it has been confirmed that L-band is well related to the SMC of a rather deep soil layer, whereas C-band is sensitive to the surface SMC and is more affected by the presence of surface roughness and vegetation, especially at high incidence angles. An algorithm for the retrieval of soil moisture, based on the sensitivity to moisture of the brightness temperature at C-band, has been tested using the collected data set. The results of the algorithm, which is able to correct for the effect of vegetation by means of the polarisation index at X-band, have been compared with soil moisture measurements in the ground. Finally, the sensitivity of emission at different frequencies to the soil moisture profile was investigated. Experimental data sets were interpreted by using the Integral Equation Model (IEM) and the outputs of the model were used to train an artificial neural network to reproduce the soil moisture content at different depths.

Hydrological aspects of the Mesoscale Alpine Programme: findings from field experiments and simulations

“…During the SOP, soil moisture was sampled on a continuous time basis at five sites with time domain 873 reflectometer (TDR) probes and at nine sites during the four missions of a helicopter-borne microwave radiometer in the C, X and L bands and different polarizations. Macelloni et al (2003) showed how the sensitivity of the radiometer to different surface types and roughness confirmed previous literature data (Wang et al, 1983), although electromagnetic interference prevented a completely successful use of the microwave antennae for soil moisture monitoring in the investigated area. The recent literature also confirms that active microwave sensors, although promising, are still far from being effective for soil moisture monitoring in mountain areas because the effect of surface roughness, vegetation and topography overcomes the influence of soil moisture on the backscattered signal.…”

Measuring Soil Water Content: A Review

“…Indeed, modeling techniques are very important for supporting data interpretation and for addressing the many unresolved issues that still limit applications of SWC measurement at this scale (such as down-and upscaling techniques and analysis of spatial heterogeneities). Determination of SWC from airplanes and helicopters using microwave remote sensing was presented by Macelloni et al (2002Macelloni et al ( , 2003, with scattering coefficients used to determine soil moisture. Santi et al (2009) presented a study where an airborne campaign with multifrequency microwave radiometers at L, C, and X bands was carried out on a flat alluvial area in northern Italy, in the Po Valley, with the aim of improving the estimation of airborne soil moisture and vegetation biomass maps, using both active and passive sensors.…”

On the prediction of the Toce alpine basin floods with distributed hydrologic models

“…The Toce basin was a case study of the RAPHAEL (Runoff and atmospheric processes for flood hazard forecasting and control) European Union research project, whose objective was to improve flood forecasting in complex mountain watershed Ranzi, 2000, 2003;Montaldo et al, 2002Montaldo et al, , 2004Bach et al, 2003;Grossi and Falappi, 2003;Macelloni et al, 2003;Richard et al, 2003). Montaldo et al (2002Montaldo et al ( , 2004 demonstrated that the FEST98 model cited above is able to simulate adequately three recent flood events in the Toce basin (in 1993, 1994 and 1997).…”