Use of commercial off-the-shelf digital cameras for scientific data acquisition and scene-specific color calibration

Akkaynak, Derya; Treibitz, Tali; Xiao, Bei; Gürkan, Umut A.; Allen, Justine J.; Demirci, Utkan; Hanlon, Roger T.

doi:10.1364/josaa.31.000312

Cited by 88 publications

(75 citation statements)

References 28 publications

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“…(6) We used a consumer-grade RGB camera mounted on a UAV to capture images in JPEG format, that provided simple digital number intensity values. Note that such data have an unknown relationship to scene radiance [53], and would be impacted by any changes in solar illumination during a survey. While we found that such imagery is suitable for separating broad and distinct classes, such as green vegetation and charred surface, more detailed vegetation characterization could benefit from using miniaturized multi-or hyper-spectral instruments that provide additional spectral information, and where radiance is normalized based on incident light sensors.…”

Section: Discussionmentioning

confidence: 99%

Calibrating Satellite-Based Indices of Burn Severity from UAV-Derived Metrics of a Burned Boreal Forest in NWT, Canada

2017

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Abstract:Wildfires are a dominant disturbance to boreal forests, and in North America, they typically cause widespread tree mortality. Forest fire burn severity is often measured at a plot scale using the Composite Burn Index (CBI), which was originally developed as a means of assigning severity levels to the Normalized Burn Ratio (NBR) computed from Landsat satellite imagery. Our study investigated the potential to map biophysical indicators of burn severity (residual green vegetation and charred organic surface) at very high (3 cm) resolution, using color orthomosaics and vegetation height models derived from UAV-based photographic surveys and Structure from Motion methods. These indicators were scaled to 30 m resolution Landsat pixel footprints and compared to the post-burn NBR (post-NBR) and differenced NBR (dNBR) ratios computed from pre-and post-fire Landsat imagery. The post-NBR showed the strongest relationship to both the fraction of charred surface (exponential R 2 = 0.79) and the fraction of green crown vegetation above 5 m (exponential R 2 = 0.81), while the dNBR was more closely related to the total green vegetation fraction (exponential R 2 = 0.69). Additionally, the UAV green fraction and Landsat indices could individually explain more than 50% of the variance in the overall CBI measured in 39 plots. These results provide a proof-of-concept for using low-cost UAV photogrammetric mapping to quantify key measures of boreal burn severity at landscape scales, which could be used to calibrate and assign a biophysical meaning to Landsat spectral indices for mapping severity at regional scales.

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Section: Discussionmentioning

confidence: 99%

Calibrating Satellite-Based Indices of Burn Severity from UAV-Derived Metrics of a Burned Boreal Forest in NWT, Canada

2017

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“…Following photography, each image was linearized with regards to light intensity based on camera responses to a set of eight Spectralon gray standards with reflectance values ranging from 2 to 99% (in custom programs written in Image J), because many cameras show non-linear responses in image value to changes in light levels that need to be corrected before accurate data can be obtained (see Westland and Ripamonti, 2004;Stevens et al, 2007a;Garcia et al, 2013). We also equalized the image values (Stevens et al, 2007a;Akkaynak et al, 2014) by removing the effects of varying light conditions with regards to the gray standard, and scaled each image channel (LW, MW, SW, and UV) to reflectance (where an image value of 255 on an 8-bit scale equals 100% reflectance). This gave us four images corresponding to the reflectance of each crab across the visible and UV spectrum, and provides the basis for color analysis independent of any specific visual system or predator group (Stevens, 2011), allowing us to analyze color change in terms of the physical properties of the crabs.…”

Section: Color and Brightness Quantificationmentioning

confidence: 99%

Color change and camouflage in juvenile shore crabs Carcinus maenas

2014

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Camouflage is perhaps the most widespread anti-predator defense in nature, with many different types thought to exist. Of these, resembling the general color and pattern of the background (background matching) is likely to be the most common. Background matching can be achieved by adaptation of individual appearance to different habitats or substrates, behavioral choice, and color change. Although the ability to change coloration for camouflage over a period of hours or days is likely to be widely found among animals, few studies have quantified this against different backgrounds. Here, we test whether juvenile shore crabs (Carcinus maenas) are capable of color change for camouflage by placing them on either black or white (experiment 1) or red and green (experiment 2) backgrounds. We find that crabs are capable of significant changes in brightness, becoming lighter on white backgrounds and darker on black backgrounds. Using models of predator (avian) vision, we show that these differences are large enough in many individuals to lead to perceptible changes in appearance. Furthermore, comparisons of crabs with the backgrounds show that changes are likely to lead to significant improvements in camouflage and potentially reduced detection probabilities. Crabs underwent some changes on the red and green backgrounds, but visual modeling indicated that these changes were very small and unlikely to be detectable. Our experiment shows that crabs are able to adjust their camouflage by changes in brightness over a period of hours, and that this could influence detection probability by predators.

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“…The raw digital counts can then be converted to reflectance values based on the regression equations between the actual reflectance measured from the tarpaulins and the digital counts extracted from the tarpaulins on each band image. Consumer-grade cameras can be used for scientific data acquisition if the image maintains a linear relationship to scene radiance [26] or if camera parameters (i.e., shutter speed, f-stop, and ISO-sensitivity) measuring scene radiance are used in conjunction with a camera calibration procedure [19].…”

Section: Image Acquisition Visualization and Preprocessingmentioning

confidence: 99%

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

et al. 2014

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This paper describes the design and evaluation of an airborne multispectral imaging system based on two identical consumer-grade cameras for agricultural remote sensing. The cameras are equipped with a full-frame complementary metal oxide semiconductor (CMOS) sensor with 5616 × 3744 pixels. One camera captures normal color images, while the other is modified to obtain near-infrared (NIR) images. The color camera is also equipped with a GPS receiver to allow geotagged images. A remote control is used to trigger both cameras simultaneously. Images are stored in 14-bit RAW and 8-bit JPEG files in CompactFlash cards. The second-order transformation was used to align the color and NIR images to achieve subpixel alignment in four-band images. The imaging system was tested under various flight and land cover conditions and optimal camera settings were determined for airborne image acquisition. Images were captured at altitudes of 305-3050 m (1000-10,000 ft) and pixel sizes of 0.1-1.0 m were achieved. Four practical application examples are presented to illustrate how the imaging system was used to estimate cotton canopy cover, detect cotton root rot, and map henbit and giant OPEN ACCESSRemote Sens. 2014, 6 5258 reed infestations. Preliminary analysis of example images has shown that this system has potential for crop condition assessment, pest detection, and other agricultural applications.

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Use of commercial off-the-shelf digital cameras for scientific data acquisition and scene-specific color calibration

Cited by 88 publications

References 28 publications

Calibrating Satellite-Based Indices of Burn Severity from UAV-Derived Metrics of a Burned Boreal Forest in NWT, Canada

Calibrating Satellite-Based Indices of Burn Severity from UAV-Derived Metrics of a Burned Boreal Forest in NWT, Canada

Color change and camouflage in juvenile shore crabs Carcinus maenas

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

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