Processing full-waveform lidar data in an alpine coniferous forest: assessing terrain and tree height quality

International audienceSmall footprint full-waveform airborne lidar systems hold large opportunities for improved forest characterisation. To take advantage of full-waveform information, this paper presents a new processing method based on the decomposition of waveforms into a sum of parametric functions. The method consists of an enhanced peak detection algorithm combined with an advanced echo modelling including Gaussian and generalized Gaussian models. The study focussed on the qualication of the extracted geometric information. Resulting 3D point clouds were compared to the point cloud provided by the operator. 40 to 60 % additional points were detected mainly in the lower part of the canopy and in the low vegetation. Their contribution to Digital Terrain Models (DTMs), Canopy Height Models (CHMs) was then analysed. The quality of DTMs and CHM-based heights was assessed using eld measurements on black pine plots under various topographic and stand characteristics. Results showed only slight improvements, up to 5 cm bias and standard deviation reduction. However both tree crowns and undergrowth were more densely sampled thanks to the detection of weak and overlapping echoes, opening up opportunities to study the detailed structure of forest stands

Spatial quantification of vegetation density from terrestrial laser scanner data for characterization of 3D forest structure at plot level

International audiencePrecise description of forest 3D structure at plot level is required for sustainable ecosystem management. However, a detailed structure description from traditional field measurements is tedious. We propose an innovative method to quantify in 3D the spatial distribution of forest structure from terrestrial lidar data. The method rests on the hypothesis that the normalized number of laser returns within a given volume element is proportional to the density of vegetation material inside this volume. The developed model is based on analysis made inside Svoxels (spherical voxels) to compute a spatialized vegetation density index. The model was tested on two different scans of the same plot. The resulting vegetation density index well represents the vegetation structure as observed within the lidar point cloud. Quantitative analyses confirmed a global consistency of the results within and between scans. However, we observed a slight bias in the computed density indexes. It might be mainly explained by occlusions, which cause 1) a slight decrease of the density index with distance and 2) local differences in density index between scans.. Future work will focus on improving our algorithm and correcting biases. These results are promising for the development of quantitative measures of the 3D forest structure

Utilisation conjointe de trains d'ondes LiDAR vert et infrarouge pour la bathymétrie des eaux de très faible profondeurs

La bathymétrie et la topographie des surfaces immergées sont des connaissances essentielles pour la gestion durable des rivières et des espaces littoraux. Parmi les techniques permettant de les obtenir, le LiDAR bathymétrique apparaît prometteur par sa capacité à relever de grandes surfaces en un temps limité, avec une forte résolution spatiale et de manière continue entre zones émergées et immergées. Bien que certaines études aient porté sur la précision de cette technique dans les zones côtières de profondeur modérée, peu se sont intéressées aux eaux très peu profondes (<3m). Dans cette étude, une nouvelle méthode de traitement de formes d'ondes LiDAR pour les très faibles profondeurs est proposée. Cet algorithme s'appuie sur le traitement conjoint des trains d'ondes vert et proche-infrarouge (PIR). La densité et la précision des données résultantes sur les eaux côtières très peu profondes sont ensuite analysées. Les résultats de ces développements et analyses sont présentés sur des données acquises sur le Golfe du Morbihan (France) par le Service Hydrographique et Océanographique de la Marine (SHOM) en 2005 avec un système SHOALS qui fournit les formes d'ondes Raman, PIR et vert. Ce travail met l'accent sur la comparaison de la qualité entre les données bathymétriques livrées issues du traitement des signaux par l'opérateur et celles issues de l'algorithme de traitement proposé. Pour la validation des résultats, une méthode spécifique est utilisée ici afin de faciliter la comparaison de mesures altimétriques réalisées entre des points GPS de référence et des empreintes LiDAR (diamètre de l'ordre de 2m). Dans les très faibles profondeurs d'eau, l'algorithme proposé extrait 41% de mesures supplémentaires par rapport aux données livrées, avec un biais de mesure comparable (environ 5cm) et un écart-type des erreurs plus faible (26,1cm contre 41,1cm). 55% de ces mesures supplémentaires sont situés à une profondeur comprise entre 1,5m et 2m. De plus, l'algorithme proposé améliore la profondeur minimale détectable de 80cm par rapport aux données livrées (1m contre 1,8m)

Temperature profile in a reverse flow reactor for catalytic partial oxidation of methane by fast IR imaging

Catalytic partial oxidation of methane with air was investigated in a reverse flow reactor with commercial Rh/A1(2)O(3) catalyst in pellets. Temperature profile of the catalyst bed was measured by fast IR thermography and product composition was measured with a continuous gas analyzer. The effect of internal heat recovery on reactor performance and catalyst thermal stress is presented and compared with steady state operation. Feed direction switching time, total flow rate, and methane to oxygen ratio were investigated as process operating parameters. Data of catalyst bed temperature evolution during the flow cycle are presented and discussed. Comparison of dynamic heat integration with external feed preheating in terms of product composition and catalyst temperature profile is also presented. (C) 2008 American Institute of Chemical Engineers

High velocity infrared thermography and numerical trajectories of solid particles in compressible gas flow

The use of High Velocity Infrared Thermography as a valuable alternative to other existing techniques for the visualization and tracking of solid particles transported by a gas jet has been assessed by considering different situations in terms of problem characteristic numbers (jet Reynolds and Mach numbers and Particle Stokes and gravitational Froude numbers). Particles paths have also been calculated by means of a hybrid Eulerian-Lagrangian technique under the intent to cross-validate the two (experimental and numerical) approaches. The results indicate that such a strategy is robust and sufficiently flexible to be used in relatively wide regions of the space of parameters. Experiments have clearly demonstrated that thermography can properly capture particle dynamics with a level of detail comparable to that provided by simulations. Computations have proved to be valuable on their own by allowing the explorations of regions of the parameters space otherwise out of reach. Different tests have been conducted considering both isolated particles and "swarms". We show that the observed dynamics are induced by the delicate interplay of different effects, including inertial, gravitational and eventually "lift" contributions produced by a non-perfect horizontal orientation of the jet or other uncertainties (such as those due to a non mono-sized set of particles). (C) 2018 Elsevier B.V. All rights reserved

Recent remote sensing applications for hydro and morphodynamic monitoring and modelling

It is not new to recognise that data from remote sensing platforms is transforming the way we characterise and analyse our environment. The ability to collect continuous data spanning spatial scales now allows geomorphological research in a data rich environment and this special issue (coming just 7 years after the 2010 special issue of ESPL associated with the remote sensing of rivers) highlights the considerable research effort being made to exploit this information, into new understanding of geomorphic form and process. The 2010 special issue on the remote sensing of rivers noted that fluvial remote sensing papers made up some 14% of the total river related papers in ESPL. A similar review of the papers up to 2017 reveals that this figure has increased to around 25% with a recent proliferation of articles utilising satellite based data and structure from motion derived data. It is interesting to note, however that many studies published to date are proof of concept, concentrating on confirming the accuracy of the remotely sensed data at the expense of generating new insights and ideas on fluvial form and function. Data is becoming ever more accurate and researchers should now be concentrating on analysing these early data sets to develop increased geomorphic insight challenging paradigms and moving the science forward. The prospect of this occurring is increased by the fact that many of the new remote sensed platforms allow accurate spatial data to be collected cheaply and efficiently. This is providing the individual researcher or small research grouping with tremendous opportunity to move the science of fluvial geomorphology forward unconstrained to a large degree of the need to secure substantial research funding. Fluvial geomorphologists have never before been in such a liberated position! As techniques and analytical skills continue to improve it is inevitable that Marcus and Fondstad's (2010) prediction that remotely sensed data will revolutionising our understanding of geomorphological form and process will prove true, altering our ideas on the very nature of system functioning in the process

A new facility for hypersonic flow simulation driven by a high velocity oxygen fuel gun

The paper reports on the development of a new Vacuum High Velocity Oxy Fueled Facility (V-HVOF) for Aerothermodynamic and Propulsion applications. The related setup comprises unique equipment designed to test candidate materials for thermal protection systems and mimic experimentally conditions corresponding to hypersonic sustained flow. We illustrate critically the underlying principles, along with a focused description of the various facility subsystems, their interconnections and the specific procedures to be used to overcome some of the inherent complexities embedded in the overall theoretical and technical architecture on which the facility relies. Its performances are finally presented in relation to some prototype applications, together with the indication of the related limits, advantages and possible directions for future improvements

A combustion-driven facility for hypersonic sustained flight simulation

This study reports on the development of a new Blowdown-Induction Facility driven by two different Oxygen-Fueled Guns. The facility has been conceived and realized to simulate different flow conditions in the context of hypersonic sustained flight. Here the underlying principles are illustrated critically, along with a focused description of the various facility subsystems, their interconnections and the procedures specifically conceived to overcome some of the technical complexities on which this facility relies. The facility performances are finally presented in relation to some prototype applications, together with an indication of the related limits, advantages and possible directions for future improvements

On the Formation and Accumulation of Solid Carbon Particles in High-Enthalpy Flows Mimicking Re-Entry in the Titan Atmosphere

The problem relating to the formation of solid particles enabled by hypersonic re-entry in methane-containing atmospheres (such as that of Titan) has been tackled in the framework of a combined experimental-numerical approach implemented via a three-level analysis hierarchy. First experimental tests have been conducted using a wind tunnel driven by an industrial arc-heated facility operating with nitrogen as working gas (the SPES, i.e., the Small Planetary Entry Simulator). The formation of solid phases as a result of the complex chemical reactions established in such conditions has been detected and quantitatively measured with high accuracy. In a second stage of the study, insights into the related formation process have been obtained by using multispecies models relying on the NASA CEA code and the Direct Simulation Monte Carlo (DSMC) method. Through this approach the range of flow enthalpies in which carbonaceous deposits can be formed has been identified, obtaining good agreement with the experimental findings. Finally, the deposited substance has been analyzed by means of a set of complementary diagnostic techniques, i.e., SEM, spectroscopy (Raman, FTIR, UV-visible absorption and fluorescence), GC-MS and TGA. It has been found that carbon produced by the interaction of the simulated Titan atmosphere with a solid probe at very high temperatures can be separated into two chemically different fractions, which also include "tholins"

Sample Fetch Rover: Enabling Technologies for Planetary Mobility

The Sample Fetch Rover (SFR) is a novel surface vehicle studied for Mars Sample Return (MSR). The rover is designed as a multi-mission transportation system with no scientific payloads on board and the only objective of acquiring sample tubes previously deposited on the surface and delivering them to a lander in a strict timeframe. Its mission imposes demanding requirements, such as traverse distance, timeline, mass, volume and energy, which necessitate the development of new technologies or the augmentation of existing ones. Following the decision not to implement SFR in the MSR Campaign, these technologies are becoming attractive for future rover missions to Mars and to the Moon. This paper summarizes the development of these technologies and their applicability to future use cases. The SFR mission profile and design drivers are described herein, along with the system architecture established in response to them. What follows is an overview of the key technologies studied for SFR, focusing on the most critical or innovative ones, such as locomotion, navigation and sample tube acquisition. The summary includes the other significant aspects of the design: structure, thermal control, mechanisms, control electronics, power, avionics and communications. For each of these, the main technological advancements and their relevance to forthcoming rover missions are discussed