Teke K.,Hacettepe University |
Teke K.,Vienna University of Technology |
Nilsson T.,German Research Center for Geosciences |
Bohm J.,Vienna University of Technology |
And 7 more authors.
Journal of Geodesy | Year: 2013
Continuous, very long baseline interferometry (VLBI) campaigns over 2 weeks have been carried out repeatedly, i.e., CONT02 in October 2002, CONT05 in September 2005, CONT08 in August 2008, and CONT11 in September 2011, to demonstrate the highest accuracy the current VLBI was capable at that time. In this study, we have compared zenith total delays (ZTD) and troposphere gradients as consistently estimated from the observations of VLBI, Global Navigation Satellite Systems (GNSS), and Doppler Orbitography and Radiopositioning Integrated by Satellite (DORIS) at VLBI sites participating in the CONT campaigns. We analyzed the CONT campaigns using the state-of-the-art software following common processing strategies as closely as possible. In parallel, ZTD and gradients were derived from numerical weather models, i.e., from the global European Centre for Medium-Range Weather Forecasts (ECMWF) analysis fields, the High Resolution Limited Area Model (European sites), the Japan Meteorological Agency-Operational Meso-Analysis Field (MANAL, over Japan), and the Cloud Resolving Storm Simulator (Tsukuba, Japan). Finally, zenith wet delays were estimated from the observations of water vapor radiometers (WVR) at sites where the WVR observables are available during the CONT sessions. The best ZTD agreement, interpreted as the smallest standard deviation, was found between GNSS and VLBI techniques to be about 5-6 mm at most of the co-located sites and CONT campaigns. We did not detect any significant improvement in the ZTD agreement between various techniques over time, except for DORIS and MANAL. On the other hand, the agreement and thus the accuracy of the troposphere parameters mainly depend on the amount of humidity in the atmosphere. © 2013 Springer-Verlag Berlin Heidelberg.
Charru M.,French National Institute for Agricultural Research |
Seynave I.,French National Institute for Agricultural Research |
Herve J.-C.,Institute National Of Linformation Geographique Et Forestiere |
Bontemps J.-D.,French National Institute for Agricultural Research
Trees - Structure and Function | Year: 2014
Key message: Productivity changes in Norway spruce show important regional and local spatial variations, highlighting their context dependence at different spatial scales. These variations suggest the enhancing role of climate warming, and interplay with local water and nutrient limitations. While forest growth changes have been observed in many places worldwide, their spatial variation and environmental origin remain poorly documented. Analysis of these historical changes in contrasted regional contexts, and their mapping over continuous environmental gradients, may help uncover their environmental causes. The approach was tested on Norway spruce (Picea abies) in three western European mountain contexts (Massif Central, Alps and Jura), using National Forest Inventory (NFI) data. We explored the environmental factors influencing stand basal area increment (BAI) in each context. We then estimated and compared mean regional changes in BAI and related these to the regional environmental limitations evidenced. Within each region, we further mapped local BAI trends using a geographically weighted regression (GWR) approach. In each region, local estimates of BAI changes were finally correlated to environmental indicators. We found an increase in BAI in the three regions over 1980-2005, greater in the Massif Central (+71 %) than in the Alps (+19 %) and the Jura Mountains (+21 %). Inter-regional differences in BAI changes suggested the release of a thermal constraint-found more important in the Massif Central-by the strong temperature increase over the period, and a limitation by water availability in the Jura and the Alps Mountains. Spatial patterns of BAI change revealed significant local variations in the Massif Central and the Alps. From the correlation analysis, these were again found consistent with the hypothesis of an enhancing effect of climate warming in these mountain ranges. They were also related to local soil nutritional status in the two regions, and negatively related to nitrogen deposition level in the Massif Central. As a main outcome, a strong context and spatial scale dependence of productivity changes is emphasized. In addition, the enhancing effect of climate warming on productivity is suggested, with local modulation by climatic and nutritional conditions. © 2013 Springer-Verlag Berlin Heidelberg.
Lebourgeois F.,Agro ParisTech |
Lebourgeois F.,French National Institute for Agricultural Research |
Eberle P.,Agro ParisTech |
Eberle P.,French National Institute for Agricultural Research |
And 3 more authors.
Forest Ecology and Management | Year: 2014
The aim of the study was to assess the effects of competition at both stand and tree levels on climate tree-growth relationships of 414 Abies alba and 243 Fagus sylvatica trees growing in 2 contrasting ecological conditions (north- and south-facing) under mountainous continental climate (mean altitude: 886m). Stand level competition was considered through three stand basal area (SBA) modalities (Low: 32m2/ha, Medium: 41 and High: 49) while tree level competition was assessed through three social statuses (SST, Dominant, Codominant and Suppressed trees). A strong specific response to climate was pointed out with different key periods; growth of Abies being mainly driven by previous and current late summer temperatures, while that of Fagus was controlled by April and June ones. No obvious difference between facing sides was evidenced. Competition at stand level prevailed on competition at tree level. In Low and Medium SBA, trees exhibited similar responses to climate whatever their social statuses. On the opposite, sensitivity to summer drought increased with dominancy in high SBA. Inter-specific differences and consequences for forest management are discussed. © 2014 Elsevier B.V.
Bontemps J.-D.,Agro ParisTech |
Bontemps J.-D.,French National Institute for Agricultural Research |
Gelhaye P.,Agro ParisTech |
Gelhaye P.,French National Institute for Agricultural Research |
And 3 more authors.
Annals of Forest Science | Year: 2013
• Context: While historical increases in forest growth have been largely documented, investigations on historical wood density changes remain anecdotic. They suggest possible density decreases in softwoods and ring-porous hardwoods, but are lacking for diffuse-porous hardwoods. • Aims: To evaluate the historical change in mean ring density of common beech, in a regional context where a ring-porous hardwood and a softwood have been studied, and assess the additional effect of past historical increases in radial growth (+50 % over 100 years), resulting from the existence of a positive ring size-density relationship in broadleaved species. • Methods: Seventy-four trees in 28 stands were sampled in Northeastern France to accurately separate developmental stage and historical signals in ring attributes. First, the historical change in mean ring density at 1.30 m (X-ray microdensitometry) was estimated statistically, at constant developmental stage and ring width. The effect of past growth increases was then added to assess the net historical change in wood density. • Results: A progressive centennial decrease in mean ring density of -55 kg m-3 (-7.5 %) was identified (-10 % following the most recent decline). The centennial growth increase induced a maximum +25 kg m-3 increase in mean ring density, whose net variation thus remained negative (-30 kg m-3). • Conclusions: This finding of a moderate but significant decrease in wood density that exceeds the effect of the positive growth change extends earlier reports obtained on other wood patterns in a same regional context and elsewhere. Despite their origin not being understood, such decreases hence form an issue for forest carbon accounting. © 2013 INRA and Springer-Verlag France.
Vega C.,Institute Francais Of Pondichery |
Vega C.,Institute National Of Linformation Geographique Et Forestiere |
Hamrouni A.,Institute Francais Of Pondichery |
El Mokhtari A.,Institute Francais Of Pondichery |
And 5 more authors.
International Journal of Applied Earth Observation and Geoinformation | Year: 2014
This paper introduces PTrees, a multi-scale dynamic point cloud segmentation dedicated to forest tree extraction from lidar point clouds. The method process the point data using the raw elevation values (Z) and compute height (H = Z - ground elevation) during post-processing using an innovative procedure allowing to preserve the geometry of crown points. Multiple segmentations are done at different scales. Segmentation criteria are then applied to dynamically select the best set of apices from the tree segment sextracted at the various scales. The selected set of apices is then used to generate a final segmentation. PTrees has been tested in 3 different forest types, allowing to detect 82% of the trees with under 10% of false detection rate. Future development will integrate crown profile estimation during the segmentation process in order to both maximize the detection of suppressed trees and minimize false detections. © 2014 Elsevier B.V.
Cadio C.,Yale University |
Cadio C.,CNRS Paris Institute of Global Physics |
Ballmer M.D.,University of Hawaii at Manoa |
Panet I.,CNRS Paris Institute of Global Physics |
And 3 more authors.
Earth and Planetary Science Letters | Year: 2012
Analyzing the formation mechanism of hotspot swells enhances our understanding of intraplate volcanism and the underlying geodynamical processes. The two main hypotheses for the origin of the archetypal Hawaiian swell are thermal lithospheric thinning, and dynamic support by an ascending plume. Any successful model would have to be able to simultaneously explain the swell topography and the corresponding geoid anomaly. In simple models of isostatic compensation, the geoid-to-topography ratio (GTR) is linearly related to the depth of the compensating mass; therefore it is often considered a fundamental parameter to assess swell support mechanisms. Previous estimates for the geoid-to-topography ratio (GTR) of the Hawaiian swell however are biased towards low values by incomplete removal of the effects of volcanic loading and lithospheric flexure. In order to resolve these issues, we here apply a continuous wavelet transform, which allows resolution of lateral variations of the GTR at various spatial scales. In a series of synthetic tests, the robustness of this approach and its power to identify the origin of hotspot swells are established. With 8. m/km on the youngest part of the chain, the recovered GTR agrees well with the predictions for dynamic support, therefore ruling out thermal rejuvenation as an important mechanism. We also find that the depth of the compensating mass decays by 20. km over a distance of 500. km from Hawaii to Kauai, and identify sublithospheric erosion by small-scale convection in the ponded plume material as a viable mechanism to support this decay. © 2012.
Fadil A.,University of Otago |
Denys P.,University of Otago |
Tenzer R.,Wuhan University |
Grenfell H.R.,Geomarine Research |
And 2 more authors.
Journal of Geophysical Research: Oceans | Year: 2013
Investigations in long-term instrumental tidal records reveal that 20th century sea level along the coast of New Zealand is rising at 1.46 ± 0.10 mm/yr in agreement with the regional rates from southern Australia and Tasmania. We extend the advanced altimeter-gauge approach of combining satellite altimetry and tide gauge data with constraint equations from long-term adjacent tide gauge records to assess its performance in open seas and to explore the impact of vertical land motion on the observed relative sea level. This approach has again proven to be a robust method with an accuracy of 0.4 mm/yr. While no clear sea level rise pattern can be inferred once the tide gauge apparent sea level trends are corrected for vertical land motions from GPS, the advanced altimeter-gauge and geological vertical rates are completely consistent and reveal three temporal phases of sea level rise marked by an increase from 1.46 ± 0.10 mm/yr to 1.72 ± 0.10 mm/yr during the period (1900-1936), followed by a decrease to 1.48 ± 0.10 mm/yr during the period (1936-1956), and a substantial increase to 2.60 ± 0.10 mm/yr during the period (1956-1975). In contrast, the 20th century microfossil proxy records of absolute sea level rise display twice the tide gauge sea level rise rate of 3.17 ± 0.30 mm/yr and 3.28 ± 0.45 mm/yr, respectively, once salt-marsh records are corrected using GPS and geological vertical rates. Differential autocompaction and transfer functions are possible factors, which need further investigation. Key Points Vertical motion at tide gauge using GPS, altimeter-gauge, and geological data New Zealand 20th century sea level rise instrumental and proxy 20th century sea level rise difference ©2013. American Geophysical Union. All Rights Reserved.
Vega C.,Institute National Of Linformation Geographique Et Forestiere |
Renaud J.-P.,Office National des Forets |
Durrieu S.,IRSTEA |
Remote Sensing of Environment | Year: 2016
We proposed a new area-based approach to process Lidar point clouds and develop new sets of metrics to improve models dedicated to predict forest parameters. First, we introduced point normalization based on penetration depth below the outer canopy layer to avoid biases introduced by ground normalization and canopy surface heterogeneity during metric computation. Second, we proposed computation of area and volume metrics from canopy surface models computed from both first and last returns to better characterize the 3D plot heterogeneity. The set of proposed metrics were combined with traditional ones, based on point height above ground level, to measure their contribution to models of basal area (BA) and aboveground volume (AGV). The modeling framework included a wide range of forest types, canopy structures and Lidar characteristics. Models were developed for all sites grouped together or separately. In each case, the set of metrics was submitted to a hierarchical clustering process to select the best variables to be included in the models that were further established using a best-subset method. Overall, the introduction of the proposed metrics allowed a reduction in models root mean squared error from - 0.06% to 19.58% according to forest types and target forest parameters. Best improvements were achieved for broadleaved forests, showing the potential of the proposed metrics to efficiently characterize the structure of such porous forest canopies. © 2015 Elsevier Inc.
Saunier J.,Institute National Of Linformation Geographique Et Forestiere
Advances in Space Research | Year: 2016
Stability of the monumentation is essential for precise positioning applications to minimize velocity uncertainties and noises in the position data. In charge of the DORIS global tracking network deployment since the beginning, IGN, in consultation with CNES, designed three standard monuments compliant with the DORIS system requirements and general geodetic specifications, and suitable for various site configurations: building roofs, concrete pedestals or pillars. This paper describes the monument types in use in the DORIS network according to the current required specifications and provides a comparative assessment of the stability of the monuments over the network based on three methods: a theoretical study of the mechanical behavior of the metallic structures, a misclosure analysis taken during ground surveys and a qualitative approach taking into account different factors. This overview of the network monumentation gives new key numbers following the previous network assessment performed by Fagard (2006). Significant improvements have been made following the continuous efforts to renovate the network monumentation. These results are relevant for the Global Geodetic Observing System (GGOS) goals of measurement stability for the geodetic techniques. Today, two-thirds of the DORIS network monuments are compliant with the standards aiming at stability of 0.1. mm/y. This stability result has been measured for 16 of the 58 stations more than 10. y after its installation while monuments with more than 1. mm antenna tilts are over 10. y old when specifications were less stringent. The grading and scoring grid drawn up for each monument led to the mapping of the stability of the current DORIS network. Finally, we present a number of further actions to monitor the monument stability and provide new elements for the network monumentation assessment, exploring two different approaches: analysis of the time series and direct measurements using devices placed on each monument. © 2016 COSPAR.
Nguyen Q.-D.,Institute National Of Linformation Geographique Et Forestiere |
Benard M.,Institute National Of Linformation Geographique Et Forestiere |
Devaux A.,Institute National Of Linformation Geographique Et Forestiere |
Paparoditis N.,Institute National Of Linformation Geographique Et Forestiere
GIS: Proceedings of the ACM International Symposium on Advances in Geographic Information Systems | Year: 2013
This paper introduces a novel implementation of an online spatial registration service for the 3D GIS web-based street viewer which allows end-users to interact with different spatial data (panoramic image, laser, and open data) for accessibility diagnostics and street mobility services, and to navigate an immersive and superposed multilayer urban scene in 3D. To the best of our knowledge, there are no GIS web-based open street-view systems that propose an online spatial registration for either public or professional use. We have developed an online registration service inside the 3D GIS web-based street viewer which offers an interface to integrate many available open spatial data sources, to create superposed scenes combining different data, and to helps users to interact, measure and update 3D urban maps. © 2013 Authors.