Conference Agenda

This work is dedicated to a starting Biomass Cal/Val project focused on temporal variability of P-band backscatter. In spite of an important literature on the subject, a comprehensive characterization of temporal variability remains challenging, especially from few observations (as for Biomass mission revisit) and when changes magnitude due to forest growth or loss can be easily confused with vegetation or soil moisture variations.

To address this question, the originality of our approach relies on the use of in-situ radar and flux data, respectively from the TropiScat-2 experiment and the Guyaflux tower located in the Paracou research area (French Guiana). The former consists in multifrequency (P, L and C bands) and quasi continuous (every 15 min) radar acquisitions from the top of the Guyaflux tower (ca 55m high), which enables to mimic satellite based acquisitions but with a much higher revisit.

The Guyaflux tower (labelled by ICOS as GF-Guy) has been generating meteorological and CO2, H2O and energy fluxes data since 2003, in order to determine the drivers of ecosystem CO2 source or sink strengths and evapotranspiration.

The TropiScat-2 instrumentation has been operating since 2018, making possible the development of data-driven and semi-empirical models of the radar backscatter variability with respect to a rather diverse range of meteorological conditions (especially for what concerns the intensity of dry and rainy periods in this tropical environment). These time-series models are mainly dedicated to backscattering intensity and temporal decorrelation, which can both serve to parameterize retrieval methods dedicated to the forest (dry) biomass and height estimation, contributing thereby to Biomass external calibration activities for this type of forest. Several examples of parameterization based on such time-series modeling will be presented, whether with fast and simple analytical formulations or with more complex microwave interaction models such as MIPERS-4D (a fully coherent model based on 3D forest representation).

For what concerns validation, the main objective is to compare the Net Primary Production (NPP) derived from the in-situ flux measurements with the forest biomass change estimates from the L3 products. Several observation periods will be tackled as the products delivery will follow, from which we should be able to gain in spatial resolution and better fit the Guyaflux footprint. This task will be also supported by the cross analysis between temporal variations of BIOMASS higher products (esp. L1) and TropiScat-2 radar data, together with the analysis of meteorological conditions and the closest in-situ forest biomass and height estimates. Given the first product delivery for French Guiana in 2027, our methodology will will be mainly illustrated with Sentinel-1, ALOS Scansar and simulated P-band data.