Remote Sensing Upside Down: Exploring the Potential of Ground-Based Multispectral Cameras for Tree Crown Monitoring

Abstract. Recent advancements in remote sensing have enabled increasingly detailed analysis of forest canopies using a range of platforms, from satellites to ground-based systems. This study focuses on zenith multispectral imaging beneath deciduous tree crowns to assess canopy openness and vegetation activity. We conducted two experiments: First, we evaluated the spectral similarity between a 10-lens multispectral camera and a spectrometer in a controlled environment. Using Spectral AngleMapping (SAM) and common Vegetation Indices (VIs), we found that reflectance data acquired at 0.5 m distance under diffuse light closely matched spectrometer measurements. Second, we monitored seasonal foliage development between February and July 2025, capturing ground-based reflectance from 400–850 nm. The inclusion of near-infrared (NIR) bands significantly improved the detection of vegetation activity throughout the growth season. Our results indicate that absolute reflectance values from images captured at greater zenith distance are uncertain due to angular and illumination effects, but relative changes between bands remain informative. Among the tested indices, the Green Normalised Difference Vegetation Index (GNDVI) aligned well with reference data and remained unsaturated during peak foliage months.