Search results for " geomatics"
showing 10 items of 479 documents
First Retrievals of ASCAT-IB VOD (Vegetation Optical Depth) at Global Scale
2021
Global and long-term vegetation optical depth (VOD) dataset are very useful to monitor the dynamics of the vegetation features, climate and environmental changes. In this study, the radar-based global ASCAT (Advanced SCATterometer) IB (INRAE-BORDEAUX) VOD was retrieved using a model which was recently calibrated over Africa. In order to assess the performance of IB VOD, the Saatchi biomass and three other VOD datasets (ASCAT V16, AMSR2 LPRM V5 and VODCA LPRM V6) derived from C-band observations were used in the comparison. The preliminary results show that IB VOD has a promising ability to predict biomass $(\mathrm{R}=0.74,\ \text{RMSE} =44.82\ \text{Mg}\ \text{ha}^{-1})$ , which is better …
A combined optical-microwave method to retrieve soil moisture over vegetated areas
2011
A simple approach for correcting for the effect of vegetation in the estimation of the surface soil moisture (wS) from L-band passive microwave observations is presented in this study. The approach is based on semi-empirical relationships between soil moisture and the polarized reflectivity including the effect of the vegetation optical depth which is parameterized as a function of the normalized vegetation difference index (NDVI). The method was tested against in situ measurements collected over a grass site from 2004 to 2007 (SMOSREX experiment). Two polarizations (horizontal/vertical) and five incidence angles (20◦, 30◦, 40◦, 50◦, and 60◦) were considered in the analysis. The best wS est…
Full-Waveform Terrestrial Laser Scanning for Extracting a High-Resolution 3D Topographic Model: a Case Study on an Area of Archaeological Significance
2014
AbstractThis paper describes a method, which uses full-waveform terrestrial laser scanning to survey the surface of the slope below the Temple of Juno, located in the Valley of the Temples in Agrigento (Sicily, Southern Italy). The surface is characterized by the presence of large rock blocks, which have fallen down from the upper side; possible further detachments of rock blocks would cause a situation of general instability, with a very high risk to the archaeological structures in the near future. The methodology was designed to evaluate the potential of full-waveform laser scanning technology for the production of a very high resolution 3D topographic model of the slope, to be used as a…
Using very high resolution (VHR) imagery within a GEOBIA framework for gully mapping: an application to the Calhoun Critical Zone Observatory
2019
AbstractGully erosion is a form of accelerated erosion that may affect soil productivity, restrict land use, and lead to an increase of risk to infrastructure. An accurate mapping of these landforms can be difficult because of the presence of dense canopy and/or the wide spatial extent of some gullies. Even where possible, mapping of gullies through conventional field surveying can be an intensive and expensive activity. The recent widespread availability of very high resolution (VHR) imagery has led to a remarkable growth in the availability of terrain information, thus providing a basis for the development of new methodologies for analyzing Earth's surfaces. This work aims to develop a ge…
LST retrieval algorithm adapted to the Amazon evergreen forests using MODIS data
2018
Abstract Amazonian tropical forests play a significant role in global water, carbon and energy cycles. Considering the importance of this biome and climate change projections, the monitoring of vegetation status of these rainforests becomes of significant importance. In this context vegetation temperature is presented as a key variable linked with plant physiology. In particular some studies showed the relationship between this variable and the CO2 absorption capacity and biomass loss of these tropical forests proving the potential use of vegetation temperature in the monitoring of the vegetation status. Nevertheless, the use of thermal remote sensing data over tropical forests still has so…
An optical classification tool for global lake waters
2017
Shallow and deep lakes receive and recycle organic and inorganic substances from within the confines of these lakes, their watershed and beyond. Hence, a large range in absorption and scattering and extreme differences in optical variability can be found between and within global lakes. This poses a challenge for atmospheric correction and bio-optical algorithms applied to optical remote sensing for water quality monitoring applications. To optimize these applications for the wide variety of lake optical conditions, we adapted a spectral classification scheme based on the concept of optical water types. The optical water types were defined through a cluster analysis of in situ hyperspectral…
Active heave compensation of floating wind turbine installation using a catamaran construction vessel
2021
Abstract The application of floating wind turbines is limited by the high cost that increases with the water depth. Offshore installation and maintenance continue to consume a high percentage of the project budget. To improve the installation efficiency of the floating offshore wind turbine, a novel concept is proposed by the SFI MOVE project. Several wind turbine superstructure components are preassembled onshore and carried to the installation site by a catamaran construction vessel. Each assembly can then be installed using only one lift, and the concept is less sensitive to weather conditions. In this paper, a control algorithm of the proposed hydraulic active heave compensator system i…
Thermo-mechanical volume change behaviour of Opalinus Clay
2016
The paper examines the thermo-mechanical volume change behaviour of Opalinus Clay in relation to different stress conditions and overconsolidation ratio (OCR) values and evaluates the impact of temperature on some hydro-mechanical properties of this material. To this aim, a focused experimental campaign consisting in high-temperature/high-pressure oedometric tests has been carried out. The results show that the thermo-mechanical volume change behaviour of Opalinus Clay is heavily affected by the OCR: thermal expansion is found when the heating is carried out at high OCR, whereas irreversible thermal compaction is observed when heat is applied at a vertical effective stress that is sufficien…
SMAP Multi-Temporal vegetation optical depth retrieval as an indicator of crop yield trends and crop composition
2017
Vegetation Optical Depth (VOD) is related to Vegetation Water Content (VWC). This provides new and highly valuable information for ecological and agricultural studies. In this work, VOD from the Soil Moisture Active-Passive (SMAP) satellite has been retrieved with the new Multi-Temporal Dual-Channel Algorithm (MT-DCA). Then, it has been applied to the study of crop yield trends and crop composition. The increase on VOD (¿VOD) during crop development has been compared to yield data in two selected regions located in the United States. The first region presents a heterogeneous crop composition and weak ¿VOD-yield relationship (r2=0.21). The second region presents a highly homogenous cover and…
A Constrained Band Selection Method Based on Information Measures for Spectral Image Color Visualization
2011
International audience; We present a new method for the visualization of spectral images, based on a selection of three relevant spectral channels to build a Red-Green-Blue composite. Band selection is achieved by means of information measures at the first, second and third orders. Irrelevant channels are preliminarily removed by means of a center-surround entropy comparison. A visualization-oriented spectrum segmentation based on the use of color matching functions allows for computational ease and adjustment of the natural rendering. Results from the proposed method are presented and objectively compared to four other dimensionality reduction techniques in terms of naturalness and informa…