Modelling climate control on cropland and grassland development using phenologically tuned variables

in Geophysical Research Abstracts (2010), 12

Many studies already investigated the impact of climate change and climate variability on vegetation at global and continental scales. Using time series of remote sensing and climate data, Nemani et al ... [more ▼]

Many studies already investigated the impact of climate change and climate variability on vegetation at global and continental scales. Using time series of remote sensing and climate data, Nemani et al. (2003) analyzed trends in Net Primary Production in relation with changes in climate and showed that, between 1982 and 1999, primary productivity increased by 6% globally in response to climate change. This study also stressed the need to take into account the spatial variability of climatic constraints to plant growth when analyzing the climate change impact on vegetation. Others authors described different phenomenon linked with climate change such as increases of seasonal NDVI amplitude and growing season duration in the Northern high latitude or changes in circumpolar photosynthetic activities. Understanding the interactions between climate and vegetation is also a key issue in our PhD research. Our objective is to identify the meteorological factors which limit the development of croplands and grasslands in relation with their geographical localization. For that purpose, we acquired 10-daily time series of the Normalized Difference Vegetation Index, NDVI, derived from SPOT-VEGETATION and 7 meteorological parameters (Tmean, Tmin, Tmax, Rain, Rad, ETP, Rain-ETP) derived from ERA40 re-analyses and the operational ECMWF (European Centre for Medium-Range Weather Forecast) atmospheric model. Cross-correlations between NDVI and each one of the meteorological parameters were analysed for a set of 25 regions over Europe and Africa: 15 agricultural regions and 10 regions covered by grassland or savannas. Unlike others studies, we did not consider the vegetation globally but we focussed on two types of vegetation: croplands and grasslands. This is quite important considering the role of phenology on the vegetation cycle and its relation with climate. Moreover the analysis was not realised using yearly estimates but using 10-daily products. In order to avoid stationarity related issue, a specific methodology was developed taking into account the phenological cycle of the vegetation under consideration. Preliminary results showed that the relation between a meteorological limiting factor, e.g. precipitation, and NDVI can not be considered as linear during the year or even during the growing season. Interactions must to be studied at a smaller time scale than the growing season in order to identify properly the limiting factors to plant growth taking into account its phenology. Moreover the main limiting factors are variable from a region to another. In our analysis we also considered the possibility of a delayed response of the vegetation or a cumulated effect of meteorological events (up to 3 months). Our methodology will be presented during the conference and results will be discussed and illustrated by some test cases. [less ▲]

Limnological variability and pelagic fish abundance (Stolothrissa tanganicae and Lates stappersii) in Lake Tanganyika

in Hydrobiologia (2009), 625(1), 117-134

Characterising urban morphology with spectral unmixing and spatial metrics: a case study on Dublin

in Proceedings of the 24th International Cartographic Conference (ICC 2009), (2009)

In today’s urbanising world, effective urban management and planning strategies are needed to temper the impact of urban change processes on the natural and human environment. To develop and monitor such ... [more ▼]

In today’s urbanising world, effective urban management and planning strategies are needed to temper the impact of urban change processes on the natural and human environment. To develop and monitor such strategies, and to assess their spatial impact, analysing changes in urban structure is essential. Data from earth observation satellites provide regular information on urban development and, as such, may contribute to the mapping and monitoring of cities and the modelling of urban dynamics. Especially images of medium resolution (Landsat, SPOT, …), which are cheap, widely available and often part of extensive historic archives, offer a wealth of information that may be useful for urban monitoring purposes. The lower resolution of this type of imagery, however, hampers the study of urban morphology and change processes at a more detailed, intra-urban level. Spectral unmixing approaches, which allow characterising land-cover distribution at sub-pixel level, may partly compensate for this lack of spatial detail, and may render medium-resolution imagery more useful for urban studies. The main research question addressed in this paper is how medium-resolution imagery could be used to describe urban morphology, by combining spectral unmixing approaches with spatial metrics. Spatial metrics derived from satellite imagery may be useful to quantify structural characteristics of expanding cities, and may provide indications of functional land use. In this study, we develop a set of urban metrics for use on continuous sealed surface data produced by sub-pixel classification of Landsat ETM+ imagery. Two sub-pixel classification approaches are examined for that purpose. In a first approach, we use a linear spectral mixture model with a vegetation and a non-vegetation endmember to deconvolve each pixel’s spectrum into fractional abundances of the two end member spectra, which are determined by visualising mixture space with principal component analysis. In a second approach, we use a linear regression model to estimate the proportion of vegetation cover within each Landsat pixel. In both approaches, an urban mask is used to indicate pixels belonging to urban land cover. Only pixels within the urban mask are subjected to sub-pixel classification. We hereby assume that the urban area does not contain bare soil and that the area of a pixel not covered by vegetation fully consists of sealed surface cover. The resulting sealed surface proportion map is then used to characterise urban morphology and land use by means of the shape of the cumulative frequency distribution of the estimated sealed surface fractions within a building block. A transformed logistic function is fitted to this distribution with a least-squares approach to obtain function parameters that are used as variables in a supervised classification approach, together with spatially explicit metrics (spatial variance and Moran’s I). Our study demonstrates that images from medium resolution sensors can be used to characterise intra-urban morphology, and that the structure of a building block as described by the proposed metrics gives an indication of its membership to certain morphological/functional urban classes. In future research we will incorporate socio-economic data in the metric analysis to further improve the distinction of urban land-use categories. The spatial metrics approach developed in this study will be used in experiments to improve the calibration of the MOLAND urban growth model, which is currently calibrated with historical land-use maps available for approximately 10-year intervals. [less ▲]

Tracking landslide displacements by multi-temporal DTMs: A combined aerial stereophotogrammetric and LIDAR approach in western Belgium

in Engineering Geology (2008), 99(1-2), 11-22

Distribution and decline of an endangered amphibian species (Triturus cristatus): Effect of pond characteristics and landscape matrix

Poster (2008)

Spatial aggregation of low resolution satellite data for the monitoring of vegetation response to climatic stresses : analysis of the spatial heterogeneity of aggregated entities.

in Proceedings Envisat Symposium (2007, July)

Our PhD research consists in analysing and modelling the vegetation response or sensitivity to climatic stresses with low satellite imagery. In that framework, the selection of optimal calibration sites ... [more ▼]

Our PhD research consists in analysing and modelling the vegetation response or sensitivity to climatic stresses with low satellite imagery. In that framework, the selection of optimal calibration sites is very important. These sites should be characterised by a stable and homogenous land cover over large area. Here we analyse the spatial heterogeneity of the aggregation entities (EU-NUTS 2) used by the MARSFOOD programme for the extraction of regional NDVI-means. [less ▲]

Measuring and Modeling Urban Dynamics: Impact on Quality of Life and Hydrology. Objectives and methodology

(2007)

Strategies to estimate ground susceptibility to landslide reactivation. A probabilistic application in W Belgium (Oudenaarde)

(2007)

In the hilly region of the Flemish Ardennes in western Belgium, no new big deep-seated landslides have occurred for decades, whereas several reactivation episodes were recently observed in ancient ... [more ▼]

In the hilly region of the Flemish Ardennes in western Belgium, no new big deep-seated landslides have occurred for decades, whereas several reactivation episodes were recently observed in ancient landslides. We selected a test area comprised of 13 rotational landslides located close to the town of Oudenaarde in order to predict the susceptibility of their main scarp to retreat. We propose here two probabilistic models based on a fuzzy set approach. The models use empirical distribution functions (EDFs) as favourability values to build membership values and combine them by using the fuzzy Gamma operator. Based on Kolmogorov-Smirnov tests applied to these EDFs to select the most relevant data, a first model was obtained bases on a combination of 5 quantitative variables: slope angle, distance from cultivation located upstream of the main scarp, slope aspect, elevation and profile curvature. Another, more empirical approach based on the a posteriori analysis of the prediction-rate curves was applied to select the 4 variables of a second model: slope aspect, plan curvature, vegetation index and focal flow. According to the prediction-rate curves and the resulting susceptibility maps, the empirical model appears more efficient in locating the main scarp areas most prone to reactivation. [less ▲]

Activity patterns, home-range size, and habitat utilization of Sarpa salpa (Teleostei : Sparidae) in the Mediterranean Sea

in Ices Journal of Marine Science (2006), 63(1), 128-139

Acoustic telemetry was used to record diel movement and habitat utilization of the salema (Sarpa salpa) (Teleostei: Sparidae) during three consecutive summers from 2000 to 2002 in the Calvi and Achiarina ... [more ▼]

Acoustic telemetry was used to record diel movement and habitat utilization of the salema (Sarpa salpa) (Teleostei: Sparidae) during three consecutive summers from 2000 to 2002 in the Calvi and Achiarina bays of Corsica in the Mediterranean Sea. A total of 18 fish was equipped with acoustic transmitters inserted in the body cavity, 13 were tracked in the Bay of Calvi (275 mm +/- 26.9 L-F), and 5 in Achiarina Bay (260 mm +/- 33.6 LF). Two different systems were used to track the fish. The one used in the Bay of Calvi was a manual receiver and a directional hydrophone. The second system, used in Achiarina Bay, was a radioacoustic-positioning (RAP) system that continuously monitored the movements of the fish. Fish positions were put in a geographic information system (GIS) with information on the substratum and depth. Two patterns of behaviour could be identified in the three years. Either the fish had clearly defined daytime as opposed to night-time areas of residency, characterized by different depths and substrata or the fish persistently occupied the same sites during both day and night. In the Bay of Calvi, six fish were released I km from the capture site. All of them showed homing ability and returned to the site within 48 h. [less ▲]

The usefulness of VHR images for public administrations in an urban hilly region

in Marçal, André (Ed.) "Global Developments in Environmental Earth Observation from Space" (2006)

This paper presents some results of the SPIDER project currently achieved in and around the city of Liège located in a hilly landscape. A Quick Bird image bundle product acquired on the 26th September ... [more ▼]

This paper presents some results of the SPIDER project currently achieved in and around the city of Liège located in a hilly landscape. A Quick Bird image bundle product acquired on the 26th September 2003 is used. Digital spatial data like Very High Resolution (VHR) satellite images could be provided to the public authorities of the Walloon region thanks to the Walloon cartographic gateway. In urban context and especially in hilly region, such images must be orthorectified using a Digital Surface Model (DSM). A 1 m resolution DSM was elaborated by exploiting all the 3D data available in the study area. Firstly, a TIN was generated from vector data (points, lines and polygons) selected, on the one hand, from the 1:50 000 (DTED-WGS) and the 1:10 000 (DTM- 10000, Top10v-GIS) cartographic database provided by the Belgian NGI and, on the other hand, from the 1:1 000 3D topographic database of the Walloon region (PICC). Then the TIN was rasterised and the DSM airborne LIDAR acquired along the main river-valleys is superimposed on the result. The ortho-image was then produced. The public authorities consider it as an end-product by itself which could be used in the place of the obsolete aerial orthophotos in the fast changing urban areas. Normally, the ortho-image of Liège should be available on the map server of the Walloon region in 2005, in order to check its usefulness for local and regional authorities. Moreover the local planning agency wish to take the opportunity of this study to update the spatial databases covering industrial and business development areas delineated on the urban plan. [less ▲]