During this study two models were developed to predict growth of Pinus radiata D.Don plantations in Canterbury, New Zealand. The first, CanSPBL(1.2), is a model for whole rotations of stands owned by Selwyn Plantation Limited in Canterbury. The second model, CanSPBL(water) is a hybrid growth model for the Selwyn estate in Canterbury that incorporates an index of root zone water balance over the simulation period. An existing stand growth and yield model CanSPBL was examined using a validation dataset of PSP measurements that were not used in model fitting. Projection bias was shown for mean top height, basal area per hectare, and residual stand stocking particularly for stands at elevations exceeding 450 metres. The new model, CanSPBL(1.2) showed an increase in precision of 4 - 46% over CanSPBL(1.0) at a stand level. The components of the stand model include mean top height, basal area per hectare, stems per hectare, and diameter distribution. The mortality model was made in conjunction with managers at CanSPBL to exclude catastrophic mortality events from model projections. Data used for model fitting was filtered using a mortality index based on the -3/2 power law. An examination of this model with an independent dataset showed little apparent bias. The new model, CanSPBL(water) was developed to include an index of water balance over the simulation period. Water balance estimates were made using a sub model for root zone water balance included in the hybrid physiological model 3-PG (Landsberg and Waring, 1997). The new model showed an increase in precision of 1 - 4% over CanSPBL(1.2) at a stand level (with the exception of the model for maximum diameter which showed a decrease in precision of 0.78%) using climatic inputs that included yearly variation. However the model showed increases of precision from 0.5 to 8% (with the exception of maximum diameter again, showing a decrease in precision of 0.13%) using long term monthly average climatic inputs. The components of the stand model also include mean top height, basal area per hectare, stems per hectare, and diameter distribution. The mortality model was also fitted with a data set filtered using a mortality severity index based on the -3/2 power law to exclude catastrophic mortality events. An examination of this model with an independent dataset showed little apparent bias. Two models to predict a one sided canopy leaf area index (LAI) of radiata pine stands in the Canterbury Plains of New Zealand were also developed. The models were fitted using non-linear least squares regression of LAI estimates against stem measurements and stand characteristics. LAI estimates were derived from digital analysis of fisheye lens photography. The models were kept simple to avoid computational circularity for physiological modelling applications. This study included an objective comparison and validation of a range of model types. The models CANTY (Goulding, 1995), CanSPBL(1.2) (Pinjuv, 2005), CanSPBL-water (Pinjuv, 2005), and 3-PG (Landsberg and Waring, 1997) were compared and validated with the main criteria for comparison being each model s ability to match actual historical measurements of forest growth in an independent data set. Overall, the models CanSPBL(water), and CanSPBL(1.2) performed the best in terms of basal area and mean top height prediction. Both models CanSPBL(water), and CanSPBL(1.2) showed a slightly worse fit in predictions of stocking than did the model CANTY. The hybrid model 3PG showed a better fit for the prediction of basal area than the statistically based model CANTY, but showed a worse fit for the prediction of final stocking than all other models. In terms of distribution of residuals, CanSPBL(1.2) had overall the lowest skewness, kurtosis, and all model parameters tested significant for normality. 3PG performed the worst on average, in terms of the distribution of residuals, and all models tested positively for the normality of residual distribution.

No description available.

The representation of high-latitude surface processes and quantifying surface-climate feedbacks are some of the most serious shortcomings of present day Arctic land surface modelling. The energy balance of seasonally snow-covered sparse deciduous forests at high latitudes is poorly understood and inaccurately represented within hydrological and climate models. Snow cover plays an important role in wintertime fluxes of energy, water and carbon, controlling the length of the active growing season and hence the overall carbon balance of Arctic ecosystems. Snow cover is non-uniform and spatially variable, as wind redistributes snow from areas of exposed open tundra to sheltered areas within the forest, where a deeper snowpack develops. Low solar zenith angles, coupled with sparse deciduous leafless trees, cast shadows across the snow surface. The spatial distribution of canopy gaps determines the timing of direct radiation which penetrates down through the canopy to the snow surface. The forest canopy also excludes incoming longwave radiation and yet also emits longwave radiation to the snow surface. Consequently the forest canopy plays a key role in the radiation balance of sparse forests. To improve our knowledge of these complex processes, meteorological and field observations were taken in an area of highly heterogeneous birch Betula pubescens ssp. czerepanovii forest in Abisko, Sweden during the spring of 2008 and 2009. Detailed measurements of short and longwave radiation above and below the canopy, hemispherical photographs, tree temperatures and snow surveys were conducted to quantify the radiation balance of the sparse deciduous forest. An array of below canopy pyranometers found the mean canopy transmissivity to be 74 % in 2008 and 76 % in 2009. Hemispherical photographs taken at the pyranometer locations analysed with Gap Light Analyzer (GLA) showed reasonable agreement with a mean canopy transmissivity of 75 % in 2008 and 74 % in 2009. The canopy transmissivity was found to be independent of the diffuse fraction of radiation as the canopy is very sparse. A series of survey grids and transects were established to scale up from the below canopy pyranometers to the landscape scale. Hemispherical photographs analysed with GLA showed the sparse forest canopy had a mean transmissivity of 78 % and a mean LAI of 0.25, whereas the open tundra had a mean transmissivity of 97 % and a mean LAI of < 0.01. Snow surveys showed the sparse forest snow depth to vary between 0.34 and 0.55 m, whereas the snow depth in the open tundra varied between 0.12 and 0.18 m. Observations of canopy temperatures showed a strong influence of incident shortwave radiation warming the tree branches to temperatures up to 15 °C warmer than ambient air temperature on the south facing sides of the trees, and up to 6 °C on the north facing sides of the trees. To reproduce the observed radiation balance, two canopy models (Homogenous and Clumped) were developed. The Homogeneous canopy model assumes a single tree tile with a uniform sparse canopy. The Clumped canopy model assumes a tree and a grass tile, where the tree tile is permanently in shade from the canopy and the grass tile receives all the incoming radiation. These canopy models identified the need for a parameter that accounts for the spatial and temporal variation of the shaded gaps within the sparse forest. JULES (Joint UK Land Environment Simulator) is the community land surface model used in the UK Hadley Centre GCM suite. Modifications of the land-surface interactions were included in JULES to represent the shaded gaps within the sparse deciduous forest. New parameterisations were developed for the time-varying sunlit fractions of the gap (flit), the sky-view fraction (fv), and the longwave radiation emitted from the canopy (LWtree). These model developments were informed by field observations of the forest canopy and evaluated against the below canopy short and longwave radiation observed data sets. The JULES Shaded gap model output showed a strong positive relationship with the observations of below canopy shortwave and longwave radiation. The JULES Shaded gap model improves the ratio of observed to modelled short and longwave radiation on sunny days compared to the JULES model. The JULES Shaded gap model reduces the time to snow melt by 2 to 4 days compared to the JULES model, making the model output more aligned with in-situ observational data. This shortening of the modelled snow-season directly impacts on the simulated carbon and water balance regionally and has wider relevance at the pan-Arctic scale. When JULES Shaded Gap was evaluated on the global scale, it improved the modelled snowmass across large areas of sparse forest in northern Canada, Scandinavia and Northern Russia with respect to GlobSnow. The performance of the land surface-snow-vegetation interactions of JULES was improved by using the Shaded gap to model the radiation balance of sparse forests in climate-sensitive Arctic regions. Furthermore these observational data can be used to develop and evaluate high latitude land-surface processes and biogeochemical feedbacks in other earth system models.

The impacts of climate change on temperate forests are predicted to accelerate, with widespread implications for forest biodiversity and function. Remote sensing has provided insights into regional patterns of vegetation dynamics, and experimental studies have demonstrated impacts of specific changes on individual species. However, forests are diverse and complex ecosystems. To understand how different species in different forests respond to interacting environmental pressures, widespread ground-based monitoring is needed. The only practical way to achieve this is through the involvement of non-professional researchers, i.e., with citizen science. However, many techniques used to identify subtle changes in forests require expensive equipment and professional expertise. This thesis aimed to identify practical methods for citizen scientists to collect useful data on forest ecosystem dynamics in relation to climate change. Methods for monitoring tree phenology and canopy-understorey interactions were the main focus, as tree phenology exerts strong control on understorey light and forest biodiversity, and is already responding to climate change. The response of understorey vegetation to canopy closure in four woodlands from a single region of England (Devon) was examined in detail. These geographically close woodlands differed considerably in their composition and seasonal dynamics. The spring period was particularly important for herb-layer development, and small variations in canopy openness had important effects on herb-layer cover and composition. This work highlights the need to monitor a range of different woodlands at the regional scale, with sufficient resolution to pick up small but crucial differences through time. Citizen scientists could help to collect such data by monitoring herb-layer cover and changes in the abundance of key species, alongside monitoring the overstorey canopy. The spring leaf phenology of four canopy trees (ash, beech, oak and sycamore) were monitored intensively in one woodland using a range of methods: counts, percentage estimates and photography. First budburst and leaf expansion dates were compared with estimates of leaf expansion timing and rate, derived from time-series data using logistic growth models. Frequently used first-event dates were potentially misleading due to high variation in leaf development rates within and between species. Percentage estimates and counts produced similar estimates of leaf expansion timing and rate. A photo-derived greenness index produced similar estimates of timing, but not rate, and was compromised by practical issues of photographing individual crowns in closed canopy woodland. Citizen science should collect time-series data instead of frequently-used first event dates―visual observations offer the most practical way to do this, but further work is needed to test reliability with citizen scientists. Given high intra- and inter-species variation in tree phenology, whole forest canopies need to be monitored to infer canopy closure timing. Canopy openness was assessed using sophisticated hemispherical photography and a range of low-cost alternatives, across four Devon woodlands over a year. Visual estimates and ordinary photography were too coarse to identify fine-scale variation in canopies. Smartphone fisheye photography analysed with free software was identified as a reliable surrogate for estimating relative, though not absolute, canopy openness. The method has high potential as a citizen science tool, as different phone models and users gave similar canopy openness estimates. In a detailed follow-up study, smartphone fisheye photography, hemispherical photography and visual observations of leaf expansion were used every other day to characterise spring canopy development. Logistic growth models estimated canopy closure timing and rate. Visual observations identified much earlier canopy development than either photographic method. Smartphone fisheye photography performed comparably to hemispherical photography. There is good potential for practical application of smartphone fisheye photography, as similar canopy closure estimates were gained from photos taken once every two weeks. The research in this thesis identifies a range of methods suitable for widespread monitoring of forest ecosystem dynamics in relation to climate change. Developing a smartphone app for automatic analysis and submission of canopy images will be an important next step to enabling widespread use. A pilot project is underway to begin testing methods with citizen scientists. Further research into data quality with citizen scientists is needed before the methods can be rolled out widely with confidence.

This thesis proposes a concept of sampling, especially for path tracing like algorithms, for faster convergence of the scene, using a local radiance approximation in the scene with hemispherical harmonics, which allows more effective way of ray casting on the given surface. In the first part, the basics of photorealistic rendering are introduced together with commonly used algorithms for image synthesis. The mathematical apparatus used in this thesis is defined in the second part of the thesis. Subsequently, existing solutions in this area are presented. The following chapter summarizes state-of-the-art methods in this branch. The rest of this thesis is focused on proposal and implementation of already mentioned extension.

Fabrication of hemispherical structures for application in hemispherical resonator gyro-scopes (HRG) is an integral part of modern sensing systems, especially in relation to space navigation. First, it is important for these structures to be as symmetric as possible in order to accurately track both in-plane and out-of-plane acceleration that occurs in fast moving satellites and space crafts. Next, they need to be larger for easier application in current mm scale systems and to maintain a lower noise floor and high quality factor. The work in this paper introduces a methodology for the analyzation of the micromachining process for larger symmetric hemispherical shell resonators (HSR). This is in order to increase their size while maintaining symmetry through isotropic etching using HNA and the pop-up ring mask design. The implementation of the pop-up ring mask allows for symmetric etching of<111> silicon and larger MEMS structures at a low cost while giving more design control to the user in comparison to alternative designs such as the pinhole. The investigation of how hemispheric structures are affected based on the adjustment of the pop-up ring design serves to both create larger symmetric HSRs and create a better model for future designs and applications. During this investigation, a range of design tests were done to create the hemispherical resonator molds in order to gauge the effectiveness of the pop-up ring changes. These results were then used to develop a method for achieving the desired larger symmetric HSRs.

Snow interception is one of the most important process of the hydrological balance of river basins. Measuring of snow interception is a very complex activity, therefore, models are frequently used to calculated snow interception from the vegetation structure and measured meteorological variables. A field research has been carried out in the Ptačí Brook basin in the Sumava Mts. to describe the canopy structure of the spruce forest using hemispherical images taken in the winter season 2020/21. The vegetation characteristics are essential for modelling of the snow interception. The mean Leaf area index calculated from the hemispherical images at the study plot reached 2.34 with the respective canopy closure equal to 86.16%. These values were further used as input values for the calculation of seasonal cumulative snow interception at the study plot for the winter season 2020/21. The original, more complex model was compared with two, less complex equations. Consequently, the model was applied to four consecutive winter seasons 2017-2021. The efficiency of the snow interception (a proportion of the intercepted snow to total snowfall water equivalent) ranged from 36.85% to 45.81% depending on the study season. The snow interception efficiency was considerably higher in the last winter season compared to...

No description available.

L’objectif de la thèse est d'évaluer l’apport des données satellites dans le suivi saisonnier de la végétation forestière (sous-bois et strate arborée). L'étude a été conduite sur la forêt landaise. Elle est basée sur une série de sept ans d'observations satellitaires décadaires d’un indice de végétation (PVI) et de mesures in situ de la surface foliaire (LAI) du sous-bois et des arbres. Tout d’abord, les observations in-situ ont été analysées. Elles montrent que le sous-bois est le déterminant majeur de la trajectoire saisonnière du LAI de l’ensemble du couvert végétal. Puis, ces informations ont été comparées aux données satellitaires. Il apparaît que la phénologie printanière du PVI renseigne sur celle du LAI du sous-bois. Enfin, ces résultats été exploités à l’échelle régionale et une carte régionale des types de landes a pu être produite. Cette étude ouvre des perspectives en matière d'intégration et de spatialisation des bilans d'eau et de carbone des écosystèmes forestiers à l'échelle régionale. / The aim of this thesis is to assess the potential of the remote sensing data to monitor the seasonal dynamic of the forest vegetation (understory and tree canopy). The study has been carried out on the maritime pine forest in the Southwest of France. It is based on a 7-year time-series of the 10-day vegetation index PVI composite derived from satellite and on in situ leaf area measurements (LAI) of understory and tree story.At first, the in situ observations have been analysed. It shows that the understory vegetation is the main driver of the seasonal dynamic of the whole forest LAI (understory+tree story). Then, these informations have been compared with the time-series of remote sensed PVI . It appears that the spring phenology of the PVI informs directly about the LAI understory one.Finally, these results have been used at the regional scale and a regional map of the lande types has been produced. This study opens some new prospects about integration and spatialisation of water and carbon balance of forest ecosystems at regional scale.

La résolution d'un problème d'estimation de l'état d'un système nécessite de disposer d'un modèle régissant l'évolution des variables d'état et de mesurer de manière directe ou indirecte l'ensemble ou une partie de ces variables d'état. Les travaux exposés dans ce mémoire de thèse portent sur la problématique d'estimation en présence de méconnaissances de modèle et de pertes de capteurs. La première partie de ce travail constitue la synthèse d'un dispositif d'estimation d'état pour systèmes non linéaires. Cela consiste à sélectionner un estimateur d'état et convenablement le régler, puis à concevoir algorithmiquement, à partir d'un critère introduit pour la circonstance, une redondance matérielle visant à compenser la perte de certains capteurs. La seconde partie de ce travail porte sur la conception, à l'aide de la variance d'Allan, d'un sous-modèle permettant de compenser les incertitudes d'un modèle d'état, ce sous-modèle étant utilisable par un filtre de Kalman. Ce travail a été exploité pour tenir compte de dérives gyroscopiques dans le cadre d'une navigation inertielle hybridée avec des mesures GPS par un filtre de Kalman contraint. Les résultats obtenus, issus d'expériences sur deux trajectoires d'avion, ont montré un comportement sain et robuste de l'approche proposée / To solve the problem of estimating the state of a system, it is necessary to have at one's disposal a model governing the dynamic of the state variables and to measure directly or indirectly all or a part of these variables. The work presented in this thesis deals with the estimation issue in the presence of model uncertainties and sensor losses. The first part of this work represents the synthesis of a state estimation device for nonlinear systems. It consists in selecting a state estimator and properly tuning it. Then, thanks to a criterion introduced for the occasion, it consists in algorithmically designing a hardware redundancy aiming at compensating for some sensor losses. The second part of this work deals with the conception of a sub-model compensating for some model uncertainties. This sub-model, designed by using the Allan variance, is usable by a Kalman filter. This work has been used to take into account some gyroscopical drifts in a GPS-INS integrated navigation based on a constrained Kalman filter. The results obtained, coming from experiments on two plane trajectories, showed a safe and robust behaviour of the proposed method