Reflectance Transformation Imaging (RTI) System for Ancient Documentary Artefacts

This tutorial summarises our uses of reflectance transformation imaging in archaeological contexts. It introduces the UK AHRC funded project reflectance Transformation Imaging for Anciant Documentary Artefacts and demonstrates imaging methodologies

Sub-Meter Tree Height Mapping of California using Aerial Images and LiDAR-Informed U-Net Model

Tree canopy height is one of the most important indicators of forest biomass, productivity, and species diversity, but it is challenging to measure accurately from the ground and from space. Here, we used a U-Net model adapted for regression to map the canopy height of all trees in the state of California with very high-resolution aerial imagery (60 cm) from the USDA-NAIP program. The U-Net model was trained using canopy height models computed from aerial LiDAR data as a reference, along with corresponding RGB-NIR NAIP images collected in 2020. We evaluated the performance of the deep-learning model using 42 independent 1 km$^2$ sites across various forest types and landscape variations in California. Our predictions of tree heights exhibited a mean error of 2.9 m and showed relatively low systematic bias across the entire range of tree heights present in California. In 2020, trees taller than 5 m covered ~ 19.3% of California. Our model successfully estimated canopy heights up to 50 m without saturation, outperforming existing canopy height products from global models. The approach we used allowed for the reconstruction of the three-dimensional structure of individual trees as observed from nadir-looking optical airborne imagery, suggesting a relatively robust estimation and mapping capability, even in the presence of image distortion. These findings demonstrate the potential of large-scale mapping and monitoring of tree height, as well as potential biomass estimation, using NAIP imagery.Comment: 29 pages, 9 figures, submitted to Remote Sensing in Ecology and Conservation (RSEC

Flood Assessment for Risk-informed Planning Along the Sirba River, Niger

South of the Sahara flood vulnerability and risk assessments at local level rarely identify the exposed areas according to the probability of flooding, the actions in place, localize the exposed items. They are, therefore, of little use for local development, risk prevention and contingency planning. The aim of this article is to assess the flood risk, providing useful information for local planning and an assessment methodology useful for other case studies. As a result, the first step involves identifying the information required by the local plans most used south of the Sahara. Four rural communities in Niger, frequently flooded by the Sirba River, are then considered. The risk is the product of the probability of a flood multiplied by the potential damage. Local knowledge and knowledge derived from a hydraulic numerical model, digital terrain model, very high resolution multispectral orthoimages and daily precipitation are used. The assessment identifies the probability of fluvial and pluvial flooding, the exposed areas, the position, quantity, type, replacement value of exposed items, and the risk level according to three flooding scenarios. Fifteen actions are suggested to reduce the risk and to turn adversity into opportunity

Mock-3D Web Application: Interactive Lighting, Rendering and Shading for 2D Artwork

In this thesis, we developed a web-based tool to allow artists to create 3D-looking stylized depictions based on 2D artwork with complete visual control. The controls include multiple lights with diffuse reflections and specular highlights, and refraction and mirror reflection with Fresnel control. Our controls do not necessarily correspond to underlying physical phenomena; however, they still provided results that are visually similar to 3D realistic rendering. The core of this approach is using paintable shape maps, which are similar to normal maps. The shape maps do not have to correspond to 3D shapes and, therefore, they can allow the artist to obtain incoherent and impossible 2D shapes with 3D appearance. Another contribution is that we linearized Fresnel Curve so that it can be controlled by two sliders. This allows it to achieve an intuitive blending of the results of refraction and reflection

Surface Appearance Estimation from Video Sequences

The realistic virtual reproduction of real world objects using Computer Graphics techniques requires the accurate acquisition and reconstruction of both 3D geometry and surface appearance. Unfortunately, in several application contexts, such as Cultural Heritage (CH), the reflectance acquisition can be very challenging due to the type of object to acquire and the digitization conditions. Although several methods have been proposed for the acquisition of object reflectance, some intrinsic limitations still make its acquisition a complex task for CH artworks: the use of specialized instruments (dome, special setup for camera and light source, etc.); the need of highly controlled acquisition environments, such as a dark room; the difficulty to extend to objects of arbitrary shape and size; the high level of expertise required to assess the quality of the acquisition. The Ph.D. thesis proposes novel solutions for the acquisition and the estimation of the surface appearance in fixed and uncontrolled lighting conditions with several degree of approximations (from a perceived near diffuse color to a SVBRDF), taking advantage of the main features that differentiate a video sequences from an unordered photos collections: the temporal coherence; the data redundancy; the easy of the acquisition, which allows acquisition of many views of the object in a short time. Finally, Reflectance Transformation Imaging (RTI) is an example of widely used technology for the acquisition of the surface appearance in the CH field, even if limited to single view Reflectance Fields of nearly flat objects. In this context, the thesis addresses also two important issues in RTI usage: how to provide better and more flexible virtual inspection capabilities with a set of operators that improve the perception of details, features and overall shape of the artwork; how to increase the possibility to disseminate this data and to support remote visual inspection of both scholar and ordinary public

Tidal marsh restoration for flood risk mitigation: The effectiveness of managed realignment at Freiston Shore, Lincolnshire, UK

The ecosystem services delivered by coastal wetlands are among the most valuable onthe planet, including the mitigation of climate related risks by sequestering carbon at rates several orders of magnitudes faster than tropical rainforests as well as the provision of natural coastal protection. Despite their ecological and socio-economic importance, coastal wetlands have been lost on a large scale in the past centuries, mostly due to human induced stress factors. The projected acceleration of Sea-Level Rise (SLR) may exacerbate the vulnerability of wetlands in the coming centuries, particularly in case of limited accommodation space due to the presence of anthropogenic infrastructure. Increasing flood risk for low lying coasts and the continued reliance on traditional engineered solutions that have become economically and ecologically unsustainable in many locations require the development of new measures to mitigate these risks. In the last decades, Managed Realignment (MR) has been implemented with the aim to provide a cost effective and ecologically sustainable alternative to conventional coastal defence schemes. MR constitutes one of several Nature-Based Solutions (NBS) making use of the natural wave and surge attenuating capacity of coastal wetlands and their ability to build up vertically at rates often higher than historical SLR. MR involves the realignment of river, estuary or coastal defences to (re-)establish tidal exchange, supporting the formation of coastal wetlands such as mudflats and saltmarshes. Yet, an important knowledge gap constitutes lacking evidence on the true protective value of MR, which fosters political and societal opposition, ultimately counteracting large scale coastal restoration efforts. This thesis tackles the above knowledge gap in a combined approach, including field measurements and hydrodynamic modelling, to study the effectiveness of High Water Level (HWL) attenuation across one of the earliest and, at time of establishment, largest coastal MR schemes of the United Kingdom: Freiston Shore, located in Lincolnshire on the east coast of England. Between August and October 2017, a series of 16 water level loggers was deployed across the MR site and the adjacent natural saltmarsh to measure the reduction of peak water levels during the highest tides of the year. Subsequently, these data were used to calibrate and validate a hydrodynamic model of the study area, which enabled studying the effects of MR scheme design on the site’s HWL attenuation capacity during these tides. In a last step, the model was implemented to investigate HWL attenuation rates inside the MR site under the influence of very high storm surge levels, by additionally identifying MR width thresholds for HWL attenuation in relation to surge height and vegetation cover. The main findings of this thesis are: 1) The MR site of Freiston Shore does not provide effective HWL attenuation under all measured conditions. 2) At the open coast of Freiston Shore, only large and wide MR sites can effectively attenuate very high tides, and the reduction of storm surges with return periods of more than ten years requires MR widths of >1148 m (measured perpendicular to the coastline). 3) Increased vegetation cover and larger MR widths enable the attenuation of even higher surges. 4) Breaching dikes should be preferred over complete dike removal when coastal protection is the target of MR implementation. Three priority areas for future research are recommended: 1) Generating more in situ data on MR internal water level dynamics and HWL attenuations, particularly under storm surge conditions. 2) Freiston Shore’s HWL attenuation function is particularly effective when tidal exchange is restricted through narrow dike breaches, which could also be achieved by applying sluices or culverts (i.e. Regulated Tidal Exchange (RTE)). However, this should be balanced against reduced sedimentation rates, limited MR drainage and vegetation establishment, and the potential erosion and widening of dike breaches, which may all result from breaches being designed too narrow or RTE. 3) Investigating the effectiveness and applicability of several MR schemes and other NBS to mitigate flood risks on a regional scale