Can Commercial Digital Cameras Be Used as Multispectral Sensors? A Crop Monitoring Test

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.

Acquisition of NIR-Green-Blue Digital Photographs from Unmanned Aircraft for Crop Monitoring

“…Digital photography uses either silicon-based charge-coupled detectors or complementary metal-oxide-semiconductors, both of which have a spectral sensitivity from about 350 nm to about 1,100 nm wavelength [18,19]. Most digital cameras use a Bayer pattern array of filters to obtain red, green and blue bands for a digital image [18,19]; however, the chemical basis for making these filters is proprietary and there is variation in filter spectral transmittances among various digital cameras.…”

“…Most digital cameras use a Bayer pattern array of filters to obtain red, green and blue bands for a digital image [18,19]; however, the chemical basis for making these filters is proprietary and there is variation in filter spectral transmittances among various digital cameras. Typically, Bayer-pattern filters transmit at least some near-infrared (NIR) light through either the blue, green or red channels, so almost all commercially-available digital cameras have an internal hot-mirror filter blocking NIR light.…”

“…Typically, Bayer-pattern filters transmit at least some near-infrared (NIR) light through either the blue, green or red channels, so almost all commercially-available digital cameras have an internal hot-mirror filter blocking NIR light. This filter can be removed allowing detection of reflected NIR radiation from vegetation [18,19].…”

Untitled

“…The only modification made to the off-the-shelf version was removal of the NIR blocking filter. This modification increases the camera's sensitivity to red light and hence allows a better use of the spectral sensitivity of the image sensor (Lebourgeois et al 2008). The Canon 1000D camera has an optical resolution of 10.1 million effective pixels (3888 ¥ 2592) and a sensor size of 22.2 ¥ 14.8 mm.…”

An Airborne Multispectral Imaging System Based on Two Consumer-Grade Cameras for Agricultural Remote Sensing

“…Although pixel interpolation lowers the effective spatial resolution of the band images, there is no need to align the three band images. Consequently, consumer-grade digital color cameras have been increasingly used by researchers for agricultural applications [16][17][18][19].…”