Relating forest biomass to TanDEM-X mean phase height

Journal article, 2025

The Copernicus DEM is derived as a mean of TanDEM-X phase heights. It is known that there is an almost linear - but variable - relationship between phase height and above ground biomass (AGB). This paper investigates the relationship between the mean of TanDEM-X phase heights and AGB. The slope between TanDEM-X phase height and AGB varies across different acquisitions from the same site, influenced by meteorological conditions and the height of ambiguity (HoA), which is the height corresponding to a 2π phase shift. An expression based on the Interferometric Water Cloud Model (IWCM) is introduced to represent an average of meteorological variations. This approach uses an ICESat-based method to describe the relationship between area-fill (canopy cover) and forest height. The product of density and height is shown to be approximately linear with AGB under certain conditions. This enables us to express mean phase height as a function of AGB, provided that either the AGB-height allometry or reference AGB values from field data are known. The results demonstrate a strong resemblance and near-linear relationship between mean phase height, mean forest height, and AGB across a wide range of conditions. The analysis is illustrated with 32 TanDEM-X acquisitions from the Remningstorp and Krycklan sites. Forest height and area-fill are estimated from mean phase height, and AGB is also derived for these sites.