A Low Frequency Biomass Monitoring Satellite System

By mapping the aboveground woody biomass in northern boreal forests and the distribution and accumulation of secondary regenerating forests in the tropics, along with the vegetation in the savannah, biomass measurements will provide insight into the size of the carbon sink. The carbon fluxes however are related to changes in the carbon sink and to green biomass activity and therefore monitoring of vegetation changes and activity are needed. By monitoring the changes in above ground woody biomass and estimation of total biomass and its temporal variability, such a mission will contribute significantly to the understanding of the carbon cycle. Furthermore biomass information is also very important to the economies of various countries both in the tropics and in boreal climates. Airborne measurements and in-situ ground campaigns cannot provide a homogeneous and frequently updated data set on a global scale, which is collected independent of national interests. Radar backscatter measurements have proven to be positively correlated with aboveground biomass and this correlation increases with the wavelength. Biomass retrieval algorithms have been developed for airborne P-band data collected over both boreal and tropical forests. Radar measurements are insensitive to cloud cover and can be operated during day and night. Hence a spaceborne radar system, operating at low frequency, will permit the measurement, mapping, and understanding of these parameters with a spatial and temporal resolution suitable for modelling ecosystem processes at regional, continental, and global scales. BIOSAR will be a stand-alone mission such that its objective can be met without any additional data, but synergy is expected with using other radar and optical sensors. The main geophysical parameters, which are estimated from the polarimetric radar backscatter measurements performed by this mission, are biomass, flooding condition, and land cover class. Based on experience with airborne campaigns, a polarimetric low frequency SAR has been shown to be the most appropriate instrument to this purpose. The design philosophy behind a P-band spaceborne SAR is based on small size and low-cost, which should be achieved by using available space qualified hardware components. Also a (relative) small antenna is foreseen, for which an adequate performance will be shown. By merging user and scientific requirements with technical constrains the scenario of a SAR instrument has been investigated. It operates as a normal side-looking synthetic aperture radar and images a 50-km swath positioned such that the incidence angle at mid swath is 23 degrees, which also coincide with the ERS AMI SAR swath and the ASAR IS2 swath.