Lband radiometric behaviour of pine forests for a variety of surface moisture conditions

TL;DR

This study investigates how L-band radiometry responds to different moisture conditions in pine forests, combining field measurements and laboratory dielectric property analysis to enhance understanding relevant for satellite missions like SMOS.

Contribution

It provides new insights into the L-band radiometric behaviour of pine forests under varying moisture conditions, including the influence of litter layers, through combined field and laboratory experiments.

Findings

L-band emissivity varies with ground moisture levels.

Litter layer significantly influences the L-band signal.

Laboratory dielectric measurements support field observations.

Abstract

From July-December 2004 the experimental campaign 'Bray 2004' was conducted in the coniferous forest of Les Landes near Bordeaux, France, using a multi-angle L-band (1.4 GHz) radiometer to measure upwelling radiation above the forest. At the same time, ground measurements were taken of soil and litter moisture content. This experiment was done in the context of the upcoming SMOS mission in order to improve our understanding of the behaviour of the L-band signal above forested areas. Very little information exists on this subject at the moment, especially for varying hydrological conditions. Furthermore, additional measurements were done at the University of Bordeaux (PIOM laboratory) to determine the dielectric behaviour of a litter layer such as that found at the Bray site. There is some evidence that this layer may have a different influence on the L-band signal than either the soil or the vegetation, however the exact behaviour of the litter layer and the extent of its influence on the L-band signal are as yet unknown. This paper presents 1) results of the Bray experiment describing the behaviour of the above-canopy L-band emissivity for different conditions of ground moisture and 2) the relationship between soil and litter moisture content and results of the laboratory experiments on litter dielectric properties. Together this will give a first insight into the L-band radiometric properties of the different forest layers for varying hydrological conditions.