Penetration Mapping of Forest Cover Using Spaceborne P-band SAR: A Review of the European Space Agency’s BIOMASS Mission

Forest systems are the largest carbon sink in the terrestrial biosphere and play an irreplaceable role in achieving the goal of carbon neutrality. Forest BIOMASS is a critical indicator for measuring the carbon sequestration capacity of forest ecosystems and plays a decisive role in terrestrial carbon sink estimation and carbon budgeting. However, the largescale BIOMASS maps generated by existing techniques, such as optical remote sensing, still exhibit significant uncertainties, particularly in tropical regions. As the 7th mission in the European Space Agency's "Earth Explorer" program, the BIOMASS will carry the world's first fully polarimetric P-band synthetic aperture radar (SAR) payload to perform primarily global forest mapping and earth observation missions. This will provide robust scientific support for global carbon cycle modeling and "penetrative mapping" of surface cover layers. This paper first introduces the system design and data acquisition overview of the BIOMASS mission, which includes the tomographic mode and the polarimetric SAR interferometry mode. The BIOMASS’s three primary missions are above-ground BIOMASS mapping, forest height mapping, and forest disturbances detection, while its secondary missions are sub-surface geology surveying, sub-canopy topography mapping and measurement of glacier and ice sheet velocities. The corresponding underlying principles and methodologies are elaborated on following each primary mission. Then, the paper analyzes the potential challenges faced by the BIOMASS mission. These challenges include limitations from the low-bandwidth design, the impact of the space objects tracking radar (SOTR), and difficulties in low-vegetation/low-BIOMASS mapping. Finally, this paper discusses the application of BIOMASS within the context of China's national conditions and actual needs. Future research on Chinese civilian P-band SAR satellites is also explored, focusing mainly on improving range resolution within the constraints of limited bandwidth, designing and optimizing lightweight high-efficiency antenna systems, and balancing high vertical resolution with high interferometric coherence (short baseline) in the tomographic mode.