Spectral Comparison of UAV-Based Hyper and Multispectral Cameras for Precision Viticulture

• Published in: Remote sensing (Basel, Switzerland) Switzerland), 2022-02, Vol.14 (3), p.449
• Main Authors: Di Gennaro, Salvatore Filippo, Toscano, Piero, Gatti, Matteo, Poni, Stefano, Berton, Andrea, Matese, Alessandro
• Format: Article
• Language: English
• Subjects: Calibration; Cameras; Canopies; Crops; Digital cameras; Drones; Empirical analysis; Grasses; Ground truth; Hyperspectral imaging; Image acquisition; Image segmentation; imaging sensor; Irradiance; Metadata; Optical measuring instruments; Panels; Performance evaluation; Photogrammetry; precision agriculture; Precision farming; Radiation; radiometric calibration; Remote monitoring; Remote sensing; Remote sensors; Sensors; Software; Soils; Spectra; Spectral sensitivity; spectral signature; Spectroradiometers; Stony soils; Unmanned aerial vehicles; Vegetation; vegetation indices; Vineyards; Viticulture
• ISSN: 2072-4292; 2072-4292
• DOI: 10.3390/rs14030449

Analysis of the spectral response of vegetation using optical sensors for non-destructive remote monitoring represents a key element for crop monitoring. Considering the wide presence on the market of unmanned aerial vehicle (UAVs) based commercial solutions, the need emerges for clear information on the performance of these products to guide the end-user in their choice and utilization for precision agriculture applications. This work aims to compare two UAV based commercial products, represented by DJI P4M and SENOP HSC-2 for the acquisition of multispectral and hyperspectral images, respectively, in vineyards. The accuracy of both cameras was evaluated on 6 different targets commonly found in vineyards, represented by bare soil, bare-stony soil, stony soil, soil with dry grass, partially grass covered soil and canopy. Given the importance of the radiometric calibration, four methods for multispectral images correction were evaluated, taking in account the irradiance sensor equipped on the camera (M1–M2) and the use of an empirical line model (ELM) based on reference reflectance panels (M3–M4). In addition, different DJI P4M exposure setups were evaluated. The performance of the cameras was evaluated by means of the calculation of three widely used vegetation indices (VIs), as percentage error (PE) with respect to ground truth spectroradiometer measurements. The results highlighted the importance of reference panels for the radiometric calibration of multispectral images (M1–M2 average PE = 21.8–100.0%; M3–M4 average PE = 11.9–29.5%). Generally, the hyperspectral camera provided the best accuracy with a PE ranging between 1.0% and 13.6%. Both cameras showed higher performance on the pure canopy pixel target, compared to mixed targets. However, this issue can be easily solved by applying widespread segmentation techniques for the row extraction. This work provides insights to assist end-users in the UAV spectral monitoring to obtain reliable information for the analysis of spatio-temporal variability within vineyards.