Quantifying kelp canopy traits with airborne imaging spectroscopyNovel Approaches

Katherine Cavanaugh¹, Tom Bell², Kyle Cavanaugh¹

¹University of California, USA - ²Woods Hole Oceanographic Institution, USA

Advances in the remote sensing of giant kelp (Macrocystis pyrifera) forests have provided spatially continuous time series of canopy area and biomass in several global regions. However, spatial and temporal information on other valuable canopy traits (i.e., photosynthetic pigments, nitrogen content, age) are lacking, which would provide insights into the timing and magnitude of physiological responses to changing climatic processes across environmental gradients. In terrestrial forests, canopy chemical patterns are commonly estimated using imaging spectroscopy, as many traits exhibit unique spectral absorption features. Here, we combined field-collected blade spectra and trait data to develop quantitative models for estimating kelp canopy pigments. These models were applied to imagery captured by a VNIR Headwall Nano-Hyperspec sensor mounted on a Matrice 600 drone, as well as 5-meter resolution imagery from the Airborne Visible/Infrared Imaging Spectrometer-Next Generation (AVIRIS-NG), collected from late February to May 2022. Preliminary findings reveal a strong correlation between regional-scale kelp dynamics and nutrient availability, particularly surface nitrogen levels. Additionally, we observed localized senescence patterns that appear to be linked to the age of canopy emergence. Our results demonstrate the extensive utility of imaging spectroscopy in monitoring giant kelp population dynamics, offering the ability to detect declines in physiological condition before full canopy senescence occurs. Additionally, the developed methods inform the Surface Biology and Geology (SBG) designed observable, which is a future NASA spaceborne mission that will provide global imaging spectroscopy data.