Conference Agenda

The ESA BIOMASS mission is a single platform, fully polarimetric P-band SAR launched in April 2025 with the task of monitoring world forest and Above Ground Biomass distribution.

Besides supporting the generation of primary mission products, i.e. above ground biomass, forest height, the interferometric acquisitions can also be used to estimate the ground topography.

The estimation of a DTM over forested areas requires to separate the response of the ground from the one of the overlying volume, and to accurately estimate the elevation from which it originates. TomoSAR is a natural solution to this problem as it allows spatial discrimination in the vertical direction to identify the different scattering sources [1-3].

The small bandwidth of the signals measured by the BIOMASS sensor limits the vertical resolution to coarse values in the tomographic mode and to extremely coarse ones in the dual-baseline case. The resulting lack of accuracy and a limited contrast between the responses of the ground and of the canopy may seriously affect the performance of DTM retrieval using classical tomographic imaging techniques or phase center estimation [5].

High-Resolution (HR) spectral analysis techniques represent an alternative to Fourier-based approaches, characterized by significantly improved resolution values. Whereas Fourier-based techniques discriminate sources from reconstructed intensity profiles, HR techniques separate sources by associating the response to low-rank models whose simplicity guarantees both identifiability and robustness [4,5].

In the BIOMASS ground phase estimation processor, the HR spectral analysis is applied after compensating the image stack for low-pass phase screens, mainly caused by tropospheric disturbances. This compensation can be performed using a Phase linking approach (PL) or SKP decomposition.

In BIOMASS processor, the outputs of the HR spectral analysis and the low-pass phase screen calibration are combined to estimate the ground phase, defined as the interferometric phase corresponding to the ground scattering, necessary for ground steering.

This contribution evaluates the performance of HR methods for the estimation of ground phases in the context of the BIOMASS mission, and addresses the following points:

1) association with the SKP and PL methods.

2) assessment of the robustness of the proposed method with respect to residual phase screens.

Performance evaluation is carried out using data from ESA’s TropiSAR, AfriSAR, and TomoSense campaigns, analyzing the influence of polarization choice and calibration methods. Results derived from the BIOMASS ground processor will also be presented.

[1] Soja, M.J., Quegan, S., d’Alessandro, M.M. et al. (2021) Mapping above-ground biomass in tropical forests with ground-cancelled P-band SAR and limited reference data. Remote Sensing of Environment, 253. 112153. ISSN 0034-4257

[2] Y. Huang, L. Ferro-Famil and A. Reigber, "Under-Foliage Object Imaging Using SAR Tomography and Polarimetric Spectral Estimators," in IEEE Transactions on Geoscience and Remote Sensing, vol. 50, no. 6, pp. 2213-2225, June 2012.

[3] Y. Huang and L. Ferro-Famil, "3-D Characterization of Urban Areas Using High-Resolution Polarimetric SAR Tomographic Techniques and a Minimal Number of Acquisitions," in IEEE Transactions on Geoscience and Remote Sensing, vol. 59, no. 11, pp. 9086-9103, Nov. 2021.

[4] Y. Huang, Q. Zhang, and L. Ferro-Famil, “Forest Height Estimation Using a Single-Pass Airborne L-Band Polarimetric and Interferometric SAR System and Tomographic Techniques,” Remote Sensing, vol. 13, no. 3, p. 487, Jan. 2021

[5] P. -A. Bou, L. Ferro-Famil, F. Brigui and Y. Huang, "Tropical forest characterisation using parametric SAR tomography at P band and low-dimensional models," in IEEE Geoscience and Remote Sensing Letters