Quantifying the Effect of the Wind on Trees Observed by Synthetic Aperture Radar Systems

Abstract

Forests are an integral component of local ecosystems as well as the global carbon cycle and as a result of the subject of intense human interest and study. Synthetic Aperture Radar (SAR) and Interferometric Synthetic Aperture Radar (InSAR) are proven technologies and have both been used to image forests across weather and daylight conditions. Both SAR and InSAR systems require the formation of at least one synthetic aperture which is not an instantaneous occurrence. Rather, synthetic apertures are formed by coherently combining multiple adjacent radar observations which are collected temporally close but not simultaneously. The time required to collect sufficient measurements to form a synthetic aperture or the time between synthetic aperture collections in the case of an InSAR system are of interest in this study as both delays enable an observation of temporal processes, such as a moving wind field, and their impact on SAR and InSAR measurements. We present an approach to quantify the effect of wind on a SAR system's ability to achieve coherence between adjacent measurements and that of an InSAR system to accurately estimate the canopy height of a tree. We propose to simulate a set of physically realistic trees and to expose each to the same set of incident wind fields. During the exposure, the instantaneous geometry of each tree will be stored and then imaged by a combined SAR and InSAR simulator thereby generating a temporal record of wind-blown tree geometries and their corresponding SAR and InSAR measurements. This collection of tree geometries, wind fields, and electromagnetic simulations will be used to develop a relationship between an incident wind field and the expected impact on SAR and InSAR measurements.