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To support international climate change mitigation efforts, the United Nations REDD+ initiative (Reducing Emissions from\udDeforestation and Degradation) seeks to reduce land use induced greenhouse gas emissions to the atmosphere. It requires\udindependent monitoring of forest cover and forest biomass information in a spatially explicit form. It is widely recognised that\udremote sensing is required to deliver this information. Synthetic Aperture Radar interferometry (InSAR) techniques have gained\udtraction in the last decade as a viable technology from which vegetation canopy height and bare earth elevations can be derived. The\udviewing geometry of a SAR sensor is side-looking where the radar pulse is transmitted out to one side of the aircraft or satellite,\uddefining an incidence angle (θ) range. The incidence angle will change from near-range (NR) to far-range (FR) across of the track of\udthe SAR platform. InSAR uses image pairs and thus, contain two set of incidence angles. Changes in the InSAR incidence angles can\udalter the relative contributions from the vegetation canopy and the ground surface and thus, affect the retrieved vegetation canopy\udheight. Incidence angle change is less pronounced in spaceborne data than in airborne data and mitigated somewhat when multiple\udInSAR-data takes are combined. This study uses NEXTMap® single- and multi-pass X-band HH polarized InSAR to derive\udvegetation canopy height from the scattering phase centre height (hspc). Comparisons with in situ vegetation canopy height over three\udtest sites (Arizona-1, Minnesota-2); the effect of incidence angle changes across swath on the X-HH InSAR hspc was examined.\udResults indicate at steep incidence angles (θ = 35º), more exposure of lower vegetation canopy structure (e.g. tree trunks) led to\udgreater lower canopy double bounce, increased ground scattering, and decreased volume scattering. This resulted in a lower\udscattering phase centre height (hspc) or a greater underestimation of vegetation canopy height given by the single-pass X-HH InSAR\uddata. The opposite effect occurs in the far range (θ = 55º), an increase in volume scattering resulted in more accurate vegetation\udcanopy heights when compared to in situ measurements. These findings indicate that incidence angle corrections should be applied\udto airborne X-HH single-pass InSAR. In contrast, NEXTMap X-HH (multi-pass data) hspc data experienced little or no effect of\udincidence angle, possibly because NEXTMap is an aggregation of multi-pass flight line strips, which averages data over several\udincidence angles. These results may aid in the understanding of potential incidence angle effects in Astrium spaceborne Tandem-X\uddata, which will have global digital surface elevation coverage by 2015

the international archives of the photogrammetry, remote sensing and spatial information sciences/international archives of the photogrammetry, remote sensing and spatial information sciences

AIRBORNE X-HH INCIDENCE ANGLE IMPACT ON CANOPY HEIGHT RETREIVAL: IMPLICATIONS FOR SPACEBORNE X-HH TANDEM-X GLOBAL CANOPY HEIGHT MODEL