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Description
This work presents the first results of canopy forest height mapping with L-Band SAOCOM data by means of Polarimetric SAR Interferometry (Pol-InSAR). SAOCOM stands for Satélite Argentino de Observación con Microondas and it is operated by CONAE, the Argentinean space agency. For this study case, a collocated temporal series of SAOCOM full polarimetric images covering the years 2021 and 2022 was acquired, with a temporal baseline of 8 days between acquisitions. The study area corresponds to Corrientes, Argentina, which is one of the main forest production regions in the country, and where field measurements provided by local producers were available in order to validate the obtained results, along with canopy height measurements from the Global Ecosystem Dynamics Investigation (GEDI) mission. The main planted species in Corrientes are Pinus and Eucalyptus, with forest heights ranging from 10 to 35 meters at the age of maturity.
In the first step of this research, we carried out an exploratory assessment of the different decorrelation sources affecting the interferometric pairs. On one side, the temporal decorrelation term was analyzed with support of the different temporal spans between the existing images. On the other hand, the volumetric decorrelation was assessed by analyzing the sensitivity of the interferometric coherence to forest canopy height coming from field inventories and GEDI measurements. The results showed that, provided the shortest temporal span was guaranteed, that is, 8 days, a relationship between canopy height and interferometric coherence could be observed and estimated by models such as the Random Volume over Ground (RVoG).
In a second step, a multi-baseline Pol-InSAR approach was adopted, following the methodology proposed by Denbina and Simard (2018) and Pourshamsi et al (2018) with Land Vegetation and Ice Sensor (LVIS) and UAVSAR data. Field data measurements and GEDI transects acquired over the study periods were used to select the RVoG-inverted maps that best represented the different forest heights present in the study areas. The results show that this multi-baseline selection approach is more appropriate than a single-baseline one, given the high variability that SAOCOM presents in the spatial baseline between acquisitions, and the lack of orbital control over this parameter, unlike other missions such as Sentinel-1 or UAVSAR. This study presents, for the first time, forest canopy height maps of 8-day temporal baselines, L-band, orbital interferograms, along a temporal window of almost two years. The conclusions yielded by this preliminary research are of great importance for the understanding of the Pol-InSAR capabilities of SAOCOM in the field of forest height mapping. The generalization of these results to other types of forests, such as boreal, tropical, or Mediterranean forests, is a foremost task, especially regarding the future L-band SAR missions like ROSE-L and NISAR. It is also important to assess the suitability of the RVoG model to characterize the structure of these forests with L-band data retrieved by the Argentinean constellation.
Summary
This paper presents and analyses the capabilities of the Argentinian SAOCOM system for forest height estimation.
