Cost-effective non-metric photogrammetry from consumer-grade sUAS: implications for direct georeferencing of structure from motion photogrammetry

The declining costs of small Unmanned Aerial Systems (sUAS), in combination with Structure-from-Motion (SfM) photogrammetry have triggered renewed interest in image-based topography reconstruction. However, the potential uptake of sUAS-based topography is limited by the need for ground control acquired with expensive survey equipment. Direct georeferencing (DG) is a workflow that obviates ground control and uses only the camera positions to georeference the SfM results. However, the absence of ground control poses significant challenges in terms of the data quality of the final geospatial outputs. Notably, it is generally accepted that ground control is required to georeference, refine the camera calibration parameters, and remove any artefacts of optical distortion from the topographic model. Here, we present an examination of DG carried out with low-cost consumer-grade sUAS. We begin with a study of surface deformations resulting from systematic perturbations of the radial lens distortion parameters. We then test a number of flight patterns and develop a novel error quantification method to assess the outcomes. Our perturbation analysis shows that there exists families of predictable equifinal solutions of K1-K2 which minimize doming in the output model. The equifinal solutions can be expressed as K2 = f (K1) and they have been observed for both the DJI Inspire 1 and Phantom 3 sUAS platforms. This equifinality relationship can be used as an external reliability check of the self-calibration and allow a DG workflow to produce topography exempt of non-affine deformations and with random errors of 0.1% of the flying height, linear offsets below 10 m and off-vertical tilts below 1°. Whilst not yet of survey-grade quality, these results demonstrate that low-cost sUAS are capable of producing reliable topography products without recourse to expensive survey equipment and we argue that direct georeferencing and low-cost sUAS could transform survey practices in both academic and commercial disciplines

An assessment of airborne lidar for forest growth studies

Accurate and up-to-date information on forest growth rates is important for management purposes. Recent studies indicate that airborne LiDAR offers a rapid and more cost-effective approach that challenges traditional methods of forest inventorying and may have the potential not only to revolutionise forest management but also to provide key data for assessing terrestrial carbon stocks. This study aims to assess the potential of LIDAR to estimate forest growth of the temperate Sitka spruce plantation forests using canopy height distribution models at Kielder Forest, Northumberland. LIDAR data from 2003 and 2006 provides an excellent opportunity to contribute to existing work which has so far been limited in focus, looking primarily at individual tree level growth in the less densely stocked, slow-growing, cold climate forests of Scandinavia. LIDAR point cloud data from the first and last pulse returns are filtered and classified. Ground returns are used to create digital elevation models (DEM), and first returns used to create digital canopy height models (DCHM). Processed LIDAR data from both years are compared to estimate forest growth. In continuation, LIDAR plot height and growth values are extracted. The results are compared with plot level ground-based data. Height correlations are strong and positive. Growth is detected at all plot locations but correlations with ground-based data are weak and mostly negative. Potential explanations for the lack of correlation are presented and discussed. Further study is necessary to quantify and eliminate systematic and random error within both the LiDAR and ground-based data before LIDAR may be used routinely for forest management purposes

Structure de populations de vigne: Analyse des phénomènes de compétition entre plantes

La connaissance de la structure de diverses populations de vigne mesurées dans des parcelles expérimentales du Domaine de Latresne (INRA, Bordeaux) depuis 1960, nous a permis de trouver des méthodes aptes à diminuer la variation entre ceps et par suite d'améliorer la précision des essais.La vigueur d'un plant greffé-soudé sorti de pépinière ne se transmet pas après la plantation en plein champ; les conditions liées au terrain, au niveau du développement des racines, l'emportent sur les caractères acquis par le plant. La nouvelle structure de la population, souvent unimodale pour les fortes densités et bimodales pour les faibles, est stable au cours des années.On peut déceler une certaine compétition entre ceps voisins le long d'un rang de vigne palissée sur fils de fer, à partir de la 3ème ou 4ème année après plantation. Lorsque cette compétition existe significativement on doit en tenir compte dans les protocoles expérimentaux car les données cep par cep ne sont pas indépendantes.Le phénomène de compétition est lié à la fois aux fluctuations microclimatiques de la partie aérienne ainsi qu'à la concurrence au niveau des racines, ce qui est mis en évidence dans un essai de mode de conduite où sont en particulier comparés deux systèmes très différents: une vigne étroite palissée sur un plan vertical rognée non irriguée et une vigne large semi ouverte en «V» irriguée.A l'intérieur des populations, le coefficient de variation apparaît dépendant des essais et du matériel végétal employé. Il est bon d'utiliser la taille équilibrée proportionnant la charge à la vigueur ainsi que du matériel végétal cloné en choisissant les clones les plus homogènes.De nouveaux essais sont mis en place pour approfondir les méthodes d'expérimentation viticole et quelques idées de nouveaux dispositifs concernant la parcelle élémentaire sont suggérées.Structure of grapevine populations:Analysis of competition phenomenons between vinesThe knowledge of the structure of different grapevine populations analysed in experimental plots of Latresne estate (INRA, Bordeaux) since 1960 has allowed to find suitable methods to minimize the variation between vines, and hence to improve the precision of trials.The vigour of a one-year-old grafted vine plant leaving the nursery is not transferred after planting into the vineyard; the soll conditions affecting the root development surpass the characteristics acquired by the plant before.The new structure of the population, often unimodal for high densities of planting and bimodal for low ones, is stable through the years.It is possible to reveal a certain competition between ad)acent vines within the row of a trellised vineyard 3 or 4 years after planting. If this competition significantly exists, it is necessary to take it lnto account in experimental designs because the data of the single vines are not independent from each other.The competition phenomenon is bound both to microclimatic fluctuations inside the canopy and to a competition between the roots; this has been demonstrated in a training system experiment, particularly comparing two very different systems: vines with narrow rows, trained on one vertical plane, summer pruned, non irrigated annd vines with wide rows and a half-divided canopy in a "V" shape, irrigated.Within the populations the variation coefficient appears to be bound to the experiments and to the employed plant material. It is recommended to utilize balanced pruning adjusting the number of nodes to the vigour, and also to use clones chosen among the most homogeneous ones.New trials are settled in order to study more closely the methods of experimentation in viticulture and some ideas of the new experimental designs conceming the elementary plot are suggested

Quantifying Fluvial Topography Using UAS Imagery and SfM-Photogrammetry.

The measurement and monitoring of fluvial topography at high spatial and temporal resolutions is in increasing demand for a range of river science and management applications, including change detection, hydraulic models, habitat assessments, river restorations and sediment budgets. Existing approaches are yet to provide a single technique for rapidly quantifying fluvial topography in both exposed and submerged areas, with high spatial resolution, reach-scale continuous coverage, high accuracy and reasonable cost. In this paper, we explore the potential of using imagery acquired from a small unmanned aerial system (UAS) and processed using Structure-from-Motion (SfM) photogrammetry for filling this gap. We use a rotary winged hexacopter known as the Draganflyer X6, a consumer grade digital camera (Panasonic Lumix DMC-LX3) and the commercially available PhotoScan Pro SfM software (Agisoft LLC). We test the approach on three contrasting river systems; a shallow margin of the San Pedro River in the Valdivia region of south-central Chile, the lowland River Arrow in Warwickshire, UK, and the upland Coledale Beck in Cumbria, UK. Digital elevation models (DEMs) and orthophotos of hyperspatial resolution (0.01-0.02m) are produced. Mean elevation errors are found to vary somewhat between sites, dependent on vegetation coverage and the spatial arrangement of ground control points (GCPs) used to georeference the data. Mean errors are in the range 4-44mm for exposed areas and 17-89mm for submerged areas. Errors in submerged areas can be improved to 4-56mm with the application of a simple refraction correction procedure. Multiple surveys of the River Arrow site show consistently high quality results, indicating the repeatability of the approach. This work therefore demonstrates the potential of a UAS-SfM approach for quantifying fluvial topography

The accuracy and reliability of traditional surface flow type mapping: Is it time for a new method of characterizing physical river habitat?

Surface flow types (SFTs) are advocated as ecologically relevant hydraulic units, often mapped visually from the bankside to characterize rapidly the physical habitat of rivers. SFT mapping is simple, non-invasive and cost-efficient. However, it is also qualitative, subjective and plagued by difficulties in recording accurately the spatial extent of SFT units. Quantitative validation of the underlying physical habitat parameters is often lacking and does not consistently differentiate between SFTs. Here, we investigate explicitly the accuracy, reliability and statistical separability of traditionally mapped SFTs as indicators of physical habitat, using independent, hydraulic and topographic data collected during three surveys of a c. 50 m reach of the River Arrow, Warwickshire, England. We also explore the potential of a novel remote sensing approach, comprising a small unmanned aerial system (sUAS) and structure-from-motion photogrammetry (SfM), as an alternative method of physical habitat characterization. Our key findings indicate that SFT mapping accuracy is highly variable, with overall mapping accuracy not exceeding 74%. Results from analysis of similarity tests found that strong differences did not exist between all SFT pairs. This leads us to question the suitability of SFTs for characterizing physical habitat for river science and management applications. In contrast, the sUAS–SfM approach provided high resolution, spatially continuous, spatially explicit, quantitative measurements of water depth and point cloud roughness at the microscale (spatial scales ≤1 m). Such data are acquired rapidly, inexpensively and provide new opportunities for examining the heterogeneity of physical habitat over a range of spatial and temporal scales. Whilst continued refinement of the sUAS–SfM approach is required, we propose that this method offers an opportunity to move away from broad, mesoscale classifications of physical habitat (spatial scales 10–100 m) and towards continuous, quantitative measurements of the continuum of hydraulic and geomorphic conditions, which actually exists at the microscale

Quantifying submerged fluvial topography using hyperspatial resolution UAS imagery and structure from motion photogrammetry

Quantifying the topography of rivers and their associated bedforms has been a fundamental concern of fluvial geomorphology for decades. Such data, acquired at high temporal and spatial resolutions, are increasingly in demand for process oriented investigations of flow hydraulics, sediment dynamics and in-stream habitat. In these riverine environments, the most challenging region for topographic measurement is the wetted, submerged channel. Generally, dry bed topography and submerged bathymetry are measured using different methods and technology. This adds to the costs, logistical challenges and data processing requirements of comprehensive river surveys. However, some technologies are capable of measuring the submerged topography. Through-water photogrammetry and bathymetric LiDAR are capable of reasonably accurate measurements of channel beds in clear water. Whilst the cost of bathymetric LiDAR remains high and its resolution relatively coarse, the recent developments in photogrammetry using Structure from Motion (SfM) algorithms promise a fundamental shift in the accessibility of topographic data for a wide range of settings. Here we present results demonstrating the potential of so called SfM-photogrammetry for quantifying both exposed and submerged fluvial topography at the mesohabitat scale. We show that imagery acquired from a rotary-winged Unmanned Aerial System (UAS) can be processed in order to produce digital elevation models (DEMs) with hyperspatial resolutions (c. 0.02m) for two different river systems over channel lengths of 50- 100m. Errors in submerged areas range from 0.016m to 0.089m, which can be reduced to between 0.008m and 0.053m with the application of a simple refraction correction. This work therefore demonstrates the potential of UAS platforms and SfM-photogrammetry as a single technique for surveying fluvial topography at the mesoscale (defined as lengths of channel from c.10m to a few hundred metres)

On Passion and Sports Fans:A Look at Football

The purpose of the present research was to test the applicability of the Dualistic Model of Passion (Vallerand et al., 2003) to being a sport (football) fan. The model posits that passion is a strong inclination toward an activity that individuals like (or even love), that they value, and in which they invest time and energy. Furthermore, two types of passion are proposed: harmonious and obsessive passion. While obsessive passion entails an uncontrollable urge to engage in the passionate activity, harmonious passion entails a sense of volition while engaging in the activity. Finally, the model posits that harmonious passion leads to more adaptive outcomes than obsessive passion. Three studies provided support for this dualistic conceptualization of passion. Study 1 showed that harmonious passion was positively associated with adaptive behaviours (e.g., celebrate the team’s victory), while obsessive passion was rather positively associated with maladaptive behaviours (e.g., to risk losing one’s employment to go to the team’s game). Study 2 used a short Passion Scale and showed that harmonious passion was positively related to the positive affective life of fans during the 2006 FIFA World Cup, psychological health (self-esteem and life satisfaction), and public displays of adaptive behaviours (e.g., celebrating one’s team victory in the streets), while obsessive passion was predictive of maladaptive affective life (e.g., hating opposing team’s fans) and behaviours (e.g., mocking the opposing team’s fans). Finally, Study 3 examined the role of obsessive passion as a predictor of partner’s conflict that in turn undermined partner’s relationship satisfaction. Overall, the present results provided support for the Dualistic Model of Passion. The conceptual and applied implications of the findings are discussed

Back pressure effects on variable geometry turbine performances

Paper presented at the 6th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, South Africa, 30 June - 2 July, 2008.Turbochargers are widely used in applications to increase specific power and decrease fuel consumption. However, recent anti-pollution regulations have became stricter and pressed automotive engineers to find new solutions to reduce Nox emissions. Two of these solutions are the catalytic converter and the intercooler system. All these modifications will change the initial matching of the turbocharger performance characteristics to the engine requirements. In this paper, several compressor wheel sizes are investigated to evaluate the turbine/compressor matching. The intercooler and catalytic converter back pressure induced are respectively modeled by a lower duct section downstream the compressor stage and a variable valve downstream the turbine stage. The influences of the different modifications are identified through the loading and the flow coefficients and also on classical turbine performance maps. First, an analogy between compressor wheel size and back pressure effects is underlined. Second, it is shown that initial control settings of turbine nozzle vanes are no longer appropriate with a catalytic converter.vk201