3D Forest Structure Mapping Using BIOMASS Tomography: Challenges, Potentials and Ways Forward

Abstract

Since November 2025 the ESA BIOMASS Synthetic Aperture Radar (SAR) mission is acquiring multi-baseline full-pol P-band data in a 3 day repeat pass mode enabling the reconstruction of the full 3D distribution of the backscattered radar power (reflectivity) by means of tomographic (TomoSAR) techniques. In this context, BIOMASS TomoSAR reconstructions provide for the first time the unique possibility of characterizing 3D forest structure (linked to the 3D size, location and arrangement of trees, trunks and branches in a stand) at global scales. The interpretation of TomoSAR reconstructions in terms of 3D forest structure has been addressed so far only at airborne spatial / temporal resolution and coverage in correspondence of lidar and ground measurements [1]. However, real data experiments have shown that the BIOMASS instrument and mission implementation make conventional multi-baseline TomoSAR reconstructions different from airborne ones. In particular, two factors become critical: the coarse BIOMASS range resolution and the 3-day repeat-pass interferometric implementation. Both of them limit the lateral (> 50 m) and vertical resolution (in the order of 20 m) of the TomoSAR reconstructions, and in turn of structure indices (> 4 ha). At the same time, the 3-day revisit-time introduces a non-stationary change of the underlying reflectivity profile due to changes of water content in the vegetation on ground. While experiments so far show that the separation of scattering contributions seems achievable within the resolution limits, their reconstructed reflectivity loses significance. In this context, this work addresses the challenges and discusses the potentials for 3D forest structure mapping using BIOMASS measurements, based on experimental analyses performed in a variety of in relevant forest sites / types. The ecological significance of currently available structure metrics [1] at the BIOMASS resolution will be discussed over relevant (known) large scale structure gradients. In this, the use of single-baseline reflectivity reconstruction algorithms (as Polarization Coherence Tomography, PCT) will be considered not only for limiting the effects of a changing reflectivity profile in the TomoSAR reconstruction, but also to characterize such temporal change. Finally, Possible possible directions for increasing the significance and resolution of structure mapping will be will be addressed and discussed. as well. References: [1] M. Tello, V. Cazcarra-Bes, M. Pardini and K. Papathanassiou, “Forest Structure Characterization From SAR Tomography at L-Band,” IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing, vol. 11, no. 10, pp. 3402-3414, Oct. 2018. [2] S. R. Cloude, "Polarization coherence tomography," Radio Science, vol. 41, no. 04, pp. 1-27, Aug. 2006.