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In previous studies, P-band synthetic aperture radar (SAR) has shown potential for biomass retrieval in forests. However, while measurements show a general agreement that backscatter increases with increasing biomass, different studies show that the backscatter from stands of similar biomass can significantly vary depending on forest structure, hence making biomass retrieval more challenging. In this letter, we show that, while biomass may be the single most important parameter determining the backscatter from a forest, the number density of trees has also a major impact. This can be explained using simple arguments, leading us to propose the use of the biomass-consolidation index to describe P-band HV-polarized backscatter. This is supported by electromagnetic-modeling studies and by a few measurements from boreal forest made with the AIRSAR system over the BOREAS test site in Canada. [ABSTRACT FROM PUBLISHER]

Multiple VHF-band radar images from the airborne CARABAS-II system, retrieved with varying look direction to the imaged area, are coregistered and combined to improve spatial and radiometric resolution. Combined images over boreal forest in southern Sweden are used to identify and make backscatter measurements of individual trees. A coregistration scheme is proposed, and backscatter is, compared to ground measurements of individual stem volume. It is found that the spatial resolution and radiometric precision could he significantly improved by combining the images coherently. A nearly linear relation between backscattered amplitude and individual stem volume for trees with a stem volume over 0.2 m³ was found, which is in agreement with previous results at stand level. [ABSTRACT FROM AUTHOR]