Abstract
The use of consumer digital cameras or webcams to characterize and monitor different features has become prevalent in various domains, especially in environmental applications. Despite some promising results, such digital camera systems generally suffer from signal aberrations due to the on-board image processing systems and thus offer limited quantitative data acquisition capability. The objective of this study was to test a series of radiometric corrections having the potential to reduce radiometric distortions linked to camera optics and environmental conditions, and to quantify the effects of these corrections on our ability to monitor crop variables. In 2007, we conducted a five-month experiment on sugarcane trial plots using original RGB and modified RGB (Red-Edge and NIR) cameras fitted onto a light aircraft. The camera settings were kept unchanged throughout the acquisition period and the images were recorded in JPEG and RAW formats. These images were corrected to eliminate the vignetting effect, and normalized between acquisition dates. Our results suggest that 1) the use of unprocessed image data did not improve the results of image analyses; 2) vignetting had a significant effect, especially for the modified camera, and 3) normalized vegetation indices calculated with vignetting-corrected images were sufficient to correct for scene illumination conditions. These results are discussed in the light of the experimental protocol and recommendations are made for the use of these versatile systems for quantitative remote sensing of terrestrial surfaces.
Highlights
Recent developments in sensor technologies have made consumer digital cameras more and more efficient and affordable
The use of consumer digital cameras or webcams is increasingly prevalent in environmental applications
The acquisitions are generally performed with automatic settings and the images are saved in JPEG or TIFF formats
Summary
Recent developments in sensor technologies have made consumer digital cameras more and more efficient and affordable. The main advantage of digital photography lies in simplified image processing. The use of digital cameras or webcams has appeared across multiple different domains, including colorimetric applications [1,2,3] and environmental applications by characterizing and monitoring features [4,5]. Agricultural applications benefit significantly from the use of digital cameras in plant phenology monitoring [6,7,8], precision farming [8,9,10], production assessment [9, 1112], and vegetation structure characterization using hemispherical lenses [13,14]. The digital photographs are recorded in JPEG or TIFF formats, and the Red, Green and Blue (RGB) channels are obtained through simple image processing. The RGB channels are either used for image classification, or combined in spectral indices to be correlated with the surface parameters of interest
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