Commercial Off-the-Shelf Digital Cameras on Unmanned Aerial Vehicles for Multitemporal Monitoring of Vegetation Reflectance and NDVI

Abstract

This paper demonstrates the ability to generate quantitative remote sensing products by means of an Unmanned Aerial Vehicle (UAV) equipped with one unaltered and one near infrared-modified Commercial Off-The-Shelf (COTS) camera. Radiometrically calibrated orthomosaics were generated for 17 dates, from which digital numbers (DNs) were corrected to surface reflectance and to Normalized Difference Vegetation Index (NDVI). Validation against ground measurements showed that 84-90% of the variation in the ground reflectance and 95-96% of the variation in the ground NDVI could be explained by the UAV-retrieved reflectance and NDVI respectively. Comparisons against Landsat 8 data showed relationships of 0.73≤R 2 ≥0.84 for reflectance and 0.86≤R 2 ≥0.89 for NDVI. It was not possible to generate a fully consistent time series of reflectance, due to variable illumination conditions during acquisition on some dates. However, the calculation of NDVI resulted in a more stable UAV time series, which was consistent with a Landsat series of NDVI extracted over a deciduous and evergreen woodland. The results confirm that COTS cameras, following calibration, can yield accurate reflectance estimates (under stable within-flight illumination conditions), and that consistent NDVI time series can be acquired in very variable illumination conditions. Such methods have significant potential in providing flexible, low-cost approaches to vegetation monitoring at fine spatial resolution and for usercontrolled revisit periods.

System identification and H∞-based control of quadrotor attitude

“…(6). Finally, for the model identification, the number of poles and zeros are considered in the ranges of [2,5] and [0, 3], respectively. Consequently, for each experiment, fifteen proper transfer functions are obtained, and one of them is selected as the best-fitted model.…”

“…G roll (s) = 2049.8 (s + 6.764) (s 2 + 19.03s + 426. 2) . In order to verify the nominal models, the real experimental data (dashed) and the time-domain response (solid) are depicted in Fig.…”

“…Quadrotors are widely considered due to their remarkable features and applications in a variety of areas such as monitoring [1,2], surveillance [3,4], search and rescue [5,6], agriculture [7,8], and delivery of goods [9,10]. Quadrotors are also of paramount interest owing to the advantages of low cost, maneuverable, small size, simple design structure.…”

Cultural Heritage Through Time: A Case Study at Hadrian’s Wall, United Kingdom

“…These targets comprised four lightweight wood boards each measuring 1.2 x 1.2 x 0.01 m, which were painted black and three different grey tones with matt paint (Berra et al, 2017). Spectral measurements of the targets were acquired with an ASD field spectrometer (FieldSpec Pro, ASD Inc., CO, U.S.), using an 8 degree fore optic accessory positioned at nadir, 1.5 m above the target's surface.…”

“…Spectral measurements of the targets were acquired with an ASD field spectrometer (FieldSpec Pro, ASD Inc., CO, U.S.), using an 8 degree fore optic accessory positioned at nadir, 1.5 m above the target's surface. A 24" white barium sulphate-based panel (LabSphere, Inc. NH, U.S.) was used as a white reference (Berra et al, 2017).…”