To advance crop monitoring techniques in horticultural tree crops, earlier research has examined the relationship between crop vigor (height, canopy den- sity, health) as assessed by remote sensing technologies and aspects such as fruit quality and yield requirements. In recent years, structure-from-motion image pro- cessing techniques have been widely used to generate orthomosaics and 3D point clouds from RGB and multispectral (MS) imagery acquired by unmanned aerial vehicles. However, this process requires a lot of computing power and can be expensive, especially for large commercial orchards. However, studies have been scarce comparing the accuracy of different remote sensing technologies in deter- mining tree height and plant area index. Light detection and ranging (LiDAR) is an alternative method to generate 3D point clouds that requires less compu- tational power. This study assessed the accuracy, processing parameters, and limitations of UAV-based RGB, MS, and LiDAR data for measuring cherry trees’ height and plant area index in a high-density orchard in Malauc`ene, southeastern France. Furthermore, the plant area index changes of 5 different cherry culti- vars were assessed during the growth cycle. Overall, the LIDAR data provided the highest accuracy for tree height measurements around harvest (R² = 0.923, RMSE = 0.215 m) and the beginning of leaf senescence (R² = 0.863, RMSE = 0.218 m). LiDAR-derived plant area index also produced the best accuracy at May (R² = 0.48 and RMSE = 0.42) and October (R² = 0.45 and RMSE = 0.59). Our findings demonstrate that UAV-based LiDAR data provide an effective and rapid means for measuring cherry tree height and plant area index over time. Such information can serve as a general indicator of tree health and aid growers in making informed agricultural crop monitoring and management decisions.

As the cost of unmanned aerial systems (UAS) and their sensing payloads decrease the practical applications for such systems have begun expanding rapidly. Couple the decreased cost of UAS with the need for increased crop yields under minimal applications of agrochemicals, and the immense potential for UAS in commercial agriculture becomes immediately apparent. What the agriculture community needs is a cost effective method for the field-wide monitoring of crops in order to determine the precise application of fertilizers and pesticides to reduce their use and prevent environmental pollution. To that end, this thesis presents an unmanned aerial system aimed at monitoring a crop's status. The system presented uses a Yamaha RMAX unmanned helicopter, operated by Virginia Tech']s Unmanned Systems Lab (USL), as the base platform. Integrated with helicopter is a dual-band multispectral camera that simultaneously captures images in the visible and near-infrared (NIR) spectrums. The UAS is flown over a quarter acre corn crop undergoing a fertilizer rate study of two hybrids. Images gathered by the camera are post-processed to form a Normalized Difference Vegetative Index (NDVI) image. The NDVI images are used to detect the most nutrient deficient corn of the study with a 5% margin of error. Average NDVI calculated from the images correlates well to measured grain yield and accurately identifies when one hybrid reaches its yield plateau. A secondary test flight over a late-season tobacco field illustrates the system's capabilities to identify blocks of highly stressed crops. Finally, a method for segmenting bleached tobacco leaves from green leaves is presented, and the segmentation results are able to provide a reasonable estimation of the bleached tobacco content per image. / Master of Science

Electromagnetic radiation reflectance increases dramatically around 700 nm for vegetation. This increase in reflectance is known as the vegetation red edge. The NDVI (Normalized Difference Vegetation index) is an imaging technique for quantifying red edge contrast for the identification of vegetation. This imaging technique relies on reflectance values for radiation with wavelength equal to 680 nm and 830 nm. The imaging systems required to obtain this precise reflectance data are commonly space-based; limiting the use of this technique due to satellite availability and cost. This thesis presents a robust and inexpensive new terrestrial-based method for identifying the vegetation red edge. This new technique does not rely on precise wavelengths or narrow wavelength bands and instead applies the NDVI to the visible and NIR (near infrared) spectrums in toto. The measurement of vegetation fluorescence has also been explored, as it is indirectly related to the efficiency of photochemistry and heat dissipation and provides a relative method for determining vegetation health. The imaging methods presented in this thesis represent a unique solution for the real time monitoring of vegetation growth and senesces and the determination of qualitative vegetation health. A single, inexpensive system capable of field and greenhouse deployment has been developed. This system allows for the early detection of variations in plant growth and status, which will aid production of high quality horticultural crops. / Master of Science

Precision agriculture allows farmers to efficiently use their resources with site-specific applications. The current work looks to computer vision for the data collection method necessary for such a smart field, including cameras sensitive to visual (430-650~nm), near infrared (NIR,750-900~nm), shortwave infrared (SWIR,950-1700~nm), and longwave infrared (LWIR,7500-16000~nm) light. Three areas are considered in the study: image segmentation, multispectral image registration, and the feature tracking of a stressed plant. The accuracy of several image segmentation methods are compared. Basic thresholding on pixel intensities and vegetation indices result in accuracies below 75% . Neural networks (NNs) and support vector machines (SVMs) label correctly at 89% and 79%, respectively, when given only visual information, and final accuracies of 97% when the near infrared is added. The point matching methods of Scale Invariant Feature Transform (SIFT) and Edge Orient Histogram (EOH) are compared for accuracy. EOH improves the matching accuracy, but ultimately not enough for the current work. In order to track the image features of a stressed plant, a set of basil and catmint seedlings are grown and placed under drought and hypoxia conditions. Trends are shown in the average pixel values over the lives of the plants and with the vegetation indices, especially that of Marchant and NIR. Lastly, trends are seen in the image textures of the plants through use of textons. / Master of Science

Cette thèse a pour objet l'étude des surfaces sélectives en fréquence comme filtres pour l'imagerie multispectrale infrarouge. Les surfaces sélectives en fréquence en transmission sont composées d'une couche métallique percée d'ouvertures périodiques résonantes. La longueur d'onde de résonance et le gabarit du filtre (transmission, largeur à mi-hauteur) dépendent de paramètres géométriques latéraux, ce qui permet d'envisager la conception de matrices multispectrales de pixels. Un modèle théorique utilisant la théorie temporelle des modes couplés sera utilisé pour mettre en évidence les mécanismes du fonctionnement de ces structures dans le domaine de l'infrarouge (λ=1-12 µm), où les métaux sont absorbants. Dans le cadre de cette théorie, des taux de pertes radiatifs et par absorption métallique seront calculés et commentés. Des simulations en FDTD (Finite Difference Time Domain) seront effectuées pour comparaison avec le modèle. De plus, des empilements prenant en compte les contraintes technologiques seront simulés et analysés et permettront de définir les composantes d'un empilement optimal en terme de géométrie et de paramètres matériau (choix des indices optiques). La tolérance à l'angle d'incidence de ces filtres sera également étudiée. / This thesis investigates frequency selective surfaces as filters for infrared multispectral imaging. Frequency selective surfaces for the transmission of light are made of a metallic layer etched with periodic resonant apertures. The resonance wavelength and the filter's parameters (transmission, full width at half maximum) depend on lateral geometrical parameters, facilitating the design and integration of filters on the focal plane array of the detector. A theoretical model using the temporal coupled mode theory will be used to highlight key parameters of the physics of these structures at infrared wavelengths (λ=1-12 µm), where metals are absorbing. Radiative and absorptive loss rates will be calculated and commented. FDTD (Finite Difference Time Domain) simulations will be made and compared with the model. Furthermore, optical stacks taking into account technological constraints will be simulated and analyzed and will allow us to define an optimal optical stack, considering geometrical and material parameters (choice of optical indexes). The filters' angular tolerance will be considered.

Le travail de cette thèse porte sur l’étude de la télédétection de la fluorescence chlorophyllienne avec un instrument imageur passif depuis une orbite géostationnaire pour le suivi de l’état physiologique de la végétation. Le concept instrumental est étudié théoriquement pour aboutir à la création d’uninstrument et à sa validation. La possibilité de mesurer des cycles diurnes de la fluorescence végétale depuis une orbite géostationnaire est évaluée à l’aide de simulations qui permettent de dresser les spécifications d’un instrument spatial.L’instrument imageur passif mesure dans la bande O 2 -A d’absorption atmosphérique. Il utilise une roue à filtres interférentiels dont la fonction de transmittance varie avec l’angle d’incidence des rayons les traversant. L’étude théorique a permis d’optimiser le placement spectral des filtres en vuede minimiser l’incertitude liée à la mesure de fluorescence.Grâce à la comparaison des mesures de l’instrument imageur avec d’autres instrument de mesure de la fluorescence, l’instrument et son concept instrumental ont été validés. Néanmoins, à cause d’effets de structure de la végétation intervenant sur le transfert radiatif de la fluorescence et de la lumière solaire au sein du couvert végétal, ces mesures ont confirmé la difficulté d’estimer le rendement de fluorescence de la végétation à partir des flux de fluorescence mesurés.Une étude théorique menée grâce à une modélisation du transfert radiatif de la fluorescence dans le couvert végétal jusqu’au capteur a permis d’expliquer la difficulté à retrouver le rendement de fluorescence à partir des flux. Cette étude a mis en avant l’accessibilité du rendement pour des couverts à fortedensité de feuilles et lorsque la distribution de l’orientation des feuilles est centrée sur l’horizontale.Cette modélisation a été étendue pour simuler des mesures spatiales dans le but d’étudier la possibilité de mesurer la fluorescence depuis une orbite géostationnaire dans les bandes O 2 -A et O 2 -B. Les résultats de ces simulations montrent la possibilité de mesurer préférentiellement dans la bandeO 2 -A avec une faible incertitude sur les flux de fluorescence et une bonne répétabilité temporelle pour le suivi des cycles diurnes de la fluorescence de la végétation. / Le travail de cette thèse porte sur l’étude de la télédétection de la fluorescence chlorophyllienne avec un instrument imageur passif depuis une orbite géostationnaire pour le suivi de l’état physiologique de la végétation. Le concept instrumental est étudié théoriquement pour aboutir à la création d’uninstrument et à sa validation. La possibilité de mesurer des cycles diurnes de la fluorescence végétale depuis une orbite géostationnaire est évaluée à l’aide de simulations qui permettent de dresser les spécifications d’un instrument spatial.L’instrument imageur passif mesure dans la bande O 2 -A d’absorption atmosphérique. Il utilise une roue à filtres interférentiels dont la fonction de transmittance varie avec l’angle d’incidence des rayons les traversant. L’étude théorique a permis d’optimiser le placement spectral des filtres en vuede minimiser l’incertitude liée à la mesure de fluorescence.Grâce à la comparaison des mesures de l’instrument imageur avec d’autres instrument de mesure de la fluorescence, l’instrument et son concept instrumental ont été validés. Néanmoins, à cause d’effets de structure de la végétation intervenant sur le transfert radiatif de la fluorescence et de la lumière solaire au sein du couvert végétal, ces mesures ont confirmé la difficulté d’estimer le rendement de fluorescence de la végétation à partir des flux de fluorescence mesurés.Une étude théorique menée grâce à une modélisation du transfert radiatif de la fluorescence dans le couvert végétal jusqu’au capteur a permis d’expliquer la difficulté à retrouver le rendement de fluorescence à partir des flux. Cette étude a mis en avant l’accessibilité du rendement pour des couverts à fortedensité de feuilles et lorsque la distribution de l’orientation des feuilles est centrée sur l’horizontale.Cette modélisation a été étendue pour simuler des mesures spatiales dans le but d’étudier la possibilité de mesurer la fluorescence depuis une orbite géostationnaire dans les bandes O 2 -A et O 2 -B. Les résultats de ces simulations montrent la possibilité de mesurer préférentiellement dans la bandeO 2 -A avec une faible incertitude sur les flux de fluorescence et une bonne répétabilité temporelle pour le suivi des cycles diurnes de la fluorescence de la végétation.

A number of tests were conducted to determine the realizable accuracies of the Global Positioning System for natural resource conditions. The effects of terrain, forest canopy, number of consecutive position fixes, and PDOP on accuracy were evaluated. Position accuracies were determined for a total of 27 sites: three replicate sites selected for each of nine distinct conditions: three canopy (deciduous, coniferous, open) and three terrain (ridge, slope, valley) in all possible combinations. Each site was visited ten times over a span of eight months to collect position data, for ten replicates of 60, 100, 200, 300, and 500 position fixes. The mean differentially corrected positional accuracy for all sites was 4.35 meters with 95 percent of the positions estimated within 10.2 meters of the true value. The least accurate differential position data were observed at coniferous sites. Positional accuracy was higher for deciduous sites and the most accurate differential position data was collected at open sites. Accuracy increased with increasing number of position fixes. When the number of position fixes increased from 60 to 500, mean accuracy increased 46.7% at deciduous sites, 32.8% at coniferous sites, and 44.5% at open sites. The average time required by the GPS receiver to lock onto four satellites and begin collecting positions varied from one to two minutes. The most time was spent collecting position fixes at coniferous sites. No correlation was found between accuracy and the receiver's distance from the base-station. Nine replicates of 300 position fixes were averaged for six sites, which ranged from 43 kilometers to 247 kilometers from a Virginia Tech base-station. Mean accuracy ranged from 1.48 meters to 2.43 meters. GPS position data were evaluated for ease of conversion to GIS formats. Conversion was accomplished without problems. / Master of Science

ITC/USA 2010 Conference Proceedings / The Forty-Sixth Annual International Telemetering Conference and Technical Exhibition / October 25-28, 2010 / Town and Country Resort & Convention Center, San Diego, California / The purpose of the NASA Remote Imaging System Acquisition space camera prototype is to integrate multiple optical instruments into a small wireless system using radiation tolerant components. This stage of prototyping was the development of a broadband variable-focus camera that can transmit data wirelessly. A liquid lens in conjunction with a cerium doped double gauss eliminates traditional focusing mechanisms.

ITC/USA 2011 Conference Proceedings / The Forty-Seventh Annual International Telemetering Conference and Technical Exhibition / October 24-27, 2011 / Bally's Las Vegas, Las Vegas, Nevada / The National Aeronautics and Space Administration's (NASA) Remote Imaging System Acquisition (RISA) camera will integrate the functionalities of existing space cameras. The system operates between 350nm and 1050nm wavelengths, with a MATLAB user interface, uses a CS-mount standard with a CMOS detector, and has a fixed focal plane. The implementation of a liquid lens uses electrical focus adjustments to image from infinity down to one foot. This will allow wireless operation and reduces mechanical failure. All images and video captured will be transmitted wirelessly to a MATLAB program. This data is then processed and stored, allowing for remote imaging.

A fiber filter spectrometer (FFS) is a novel imaging spectrometer design concept which uses the proximity filter method to create small, lightweight, and cost effective instruments with no detectable spectral crosstalk. An FFS sensor is created by coating the ends of a fiber optic image guide (FIG) with a spectral filter, the FIG is then coupled to a detector array. Using the FIG as the spectral filter substrate reduces the optical crosstalk to the point that it is inconsequential. This work describes the modeling, fabrication, and calibration of a hyperspectral FFS sensor. The image and spectral quality performance metrics are successfully predicted by the FFS model. The laboratory calibration of the instrument validates that the FIG has no substantial impact on the instrument image quality and spectral performance. The FFS concept eliminates the potential for spectral crosstalk and provides the advantages of a less complex imaging spectrometer instrument design with low mass and volume.