Investigating the Association of Seasonal Dynamics in GEDI Canopy Cover Profiles and Sentinel-1 Backscatter in Temperate Forests

The change in forest vertical structure influences the carbon, energy, and water cycle in terrestrial ecosystems. Light detection and ranging (LiDAR) and synthetic aperture radar (SAR) have been applied for collecting forest vertical structure information. NASA’s global ecosystem dynamics investigation (GEDI) is a spaceborne LiDAR system, which measures the forest vertical structure and its change at a global scale. In comparison with GEDI, ESA’s Sentinel-1 SAR satellites have regular revisit, longer operational lifespan, and larger spatial coverage. On the one hand, detecting seasonal changes in forest vertical structures with GEDI has not been extensively investigated. On the other hand, the relationship between Sentinel-1 backscatter and GEDI canopy cover at given height is not clear yet. In this study, we first generated the time series of GEDI canopy cover profiles at landscape scale for two broadleaved forests and two coniferous forests in Germany. We then extracted the Sentinel-1 backscatter at all available GEDI acquisition dates. A regression analysis was finally performed to quantify the influence of vertical structure on backscatter. The results show layers between 10 and 25 m have stronger seasonal change of canopy cover in broadleaved forests than in coniferous forests. In broadleaved forests, canopy cover time series at 15–20 m layer height shows the strongest correlation with Sentinel-1 VV/VH time series. There is no significant correlation between canopy cover times series and backscatter time series in coniferous forests. This study provides new insights into monitoring the dynamics of forest vertical structure and understanding its influence on SAR backscatter.