Modeling Forest Emissivity at L-Band and a Comparison With Multitemporal Measurements

Abstract

This letter describes recent advances in modeling forest emissivity at L-band. The formulation is based on a previously developed discrete model and includes a new representation of forest litter. Comparisons with multitemporal radiometric data collected in the framework of the "Bray 2004" experiment, which was carried out within Les Landes forest, are shown and discussed. Input variables are given by using detailed ground measurements. In general, the model reproduces both absolute values and temporal variations of measured brightness temperature. The contribution of the litter to overall emission was found to be important.

Study of multifrequency sensitivity to soil moisture variations in the lower Bermejo basin

“…It is well known that the presence of vegetation reduces the sensitivity of the microwave measurements to the soil moisture but, since vegetation attenuation increases as wavelength decreases, longer wavelengths are preferred for soil moisture studies [Jackson and Schmugge, 1991]. In view of the availability of the ESA Soil Moisture and Ocean Salinity (SMOS) radiometer and dissemination of its data, several works began to prove the effectiveness of L-band radiometry [Ferrazzoli et al, 2002;Della Vecchia et al, 2007;, which has been shown to have a good sensitivity to soil moisture variations. However, ground based experiments at L-band did not give a definite indication about soil moisture sensitivity in forested areas: some works reported low effects , while others showed moderate sensitivity [Santi et al, 2009].…”

Microwave remote sensing for soil moisture monitoring: synergy of active and passive observations and validation of retrieved products

“…As explained in Section 6.2.4, the soil-litter medium is considered a homogenous half-space with a permittivity depending on soil and litter permittivity. However, Della Vecchia et al (2007) found that the resulting soil-litter permittivity is lower than that of the soil and it is less sensitive to soil moisture variations. When the litter effect is removed, the Tor Vergata model simulates a decrease of approximately 13 K from 7 to 12 May in V polarization, similar to what observed by AMSR-E.…”

“…The module was initially developed for forest litter (Della Vecchia et al 2007), but it was adapted to the case of grassland litter in this study. This module represents the litter as a mixture of air and dielectric material overlaying the soil.…”

“…The litter thickness linearly depends on the input litter biomass, and the litter gravimetric moisture content is linearly related to the soil moisture, as proposed by Grant et al (2007). The slope of the empirical relationship between thickness and biomass found for the forest case by Della Vecchia et al (2007) was adapted in order to have more realistic values of thickness for the grassland case. Soil and litter are modelled as a unique homogeneous half-space with an equivalent permittivity, which is computed to produce the same reflectivity as the one due to soil-litter multiple reflections.…”

“…The discrete scattering model developed by the Tor Vergata University (Bracaglia et al 1995;Ferrazzoli and Guerriero 1996) was used for this purpose. Both active and passive versions of the model have been validated over different land covers in several studies (Della Vecchia et al 2006;Della Vecchia et al 2008;Della Vecchia et al 2007;Ferrazzoli et al 2000). In the present study, the model simulations were compared against the observations collected by AMSR-E and by ASCAT (both C-band sensors) over the Maqu region in the north-eastern part of the Tibetan Plateau.…”