Publications (10)0 Total impact
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Conference Proceeding: Contribution of airborne full-waveform lidar and image data for urban scene classification
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ABSTRACT: Airborne lidar systems have become an alternative source for the acquisition of altimeter data. In addition to multi-echo laser scanner systems, full-waveform systems are able to record the whole backscattered signal for each emitted laser pulse. These data provide more information about the structure and the physical properties of the surface. This paper is focused on the classification of full-waveform lidar and airborne image data on urban scenes. Random forests are used since they provide an accurate classification and run efficiently on large datasets. Moreover, they provide measures of variable importance for each class. This is crucial to analyze the relevance of each feature for the classification of urban scenes. Random Forests provide more accurate results than Support Vector Machines with an overall accuracy of 95.75%. The most relevant features show the contribution of lidar waveforms for classifying dense urban scenes and improve the classification accuracy for all classes.Image Processing (ICIP), 2009 16th IEEE International Conference on; 12/2009 -
Conference Proceeding: Lidar waveform modeling using a marked point process
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ABSTRACT: Lidar waveforms are 1D signal consisting of a train of echoes where each of them correspond to a scattering target of the Earth surface. Modeling these echoes with the appropriate parametric function is necessary to retrieve physical information about these objects and characterize their properties. This paper presents a marked point process based model to reconstruct a lidar signal in terms of a set of parametric functions. The model takes into account both a data term which measures the coherence between the models and the waveforms, and a regularizing term which introduces physical knowledge on the reconstructed signal. We search for the best configuration of functions by performing a Reversible Jump Markov Chain Monte Carlo sampler coupled with a simulated annealing. Results are finally presented on different kinds of signals in urban areas.Image Processing (ICIP), 2009 16th IEEE International Conference on; 12/2009 -
Conference Proceeding: Rain rate retrieval by processing the observations of the 85V and 85H GHz channels of the SSM/I and TMI passive microwave sensors
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ABSTRACT: We present a new methodology, which provides the sea surface rain rate by inverting the 85 GHz channel measurements (TB) of the SMM/I and TMI microwave radiometers. This high frequency channel has the advantage of a spatial resolution close to the size of rain cells. We used a neural network whose inputs were the vertical and horizontal polarized 85 GHz TBs, the output being the rain rate. The learning dataset was made of downscale ECMWF atmospheric parameters and the corresponding brightness temperatures computed through the use of the radiative transfer equations. The computed rain rate compared well with the standard SSM/I algorithm both at global and regional scales. The comparison with the rain rates retrieved by TRMM radar, with similar pixel areas, showed a correlation coefficient higher than 0.97. A major difficulty was finding suitable observations to validate our results.Neural Networks, 2009. IJCNN 2009. International Joint Conference on; 07/2009 -
Conference Proceeding: Statistical analysis of the Syracuse 3 satellite EHF propagation experiment
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ABSTRACT: An Earth-to-satellite propagation experiment operating in the EHF band was set up as part of the Syracuse 3 program. The Syracuse 3 satellites are the new generation of French military SATCOM systems. This experiment is a good opportunity to carry out attenuation measurements and increase knowledge about tropospheric propagation effects on EHF links at a low elevation angle (17deg). At these frequencies (20 & 44 GHz), the attenuation due to the troposphere can be very strong. This paper presents yearly statistics of attenuation level, frequency scaling ratio and fade durations. A comparison with ITU models is given.Antennas and Propagation, 2009. EuCAP 2009. 3rd European Conference on; 04/2009 -
Conference Proceeding: Short-term prediction of atmospheric attenuation in Q band from Ka-band measurements on earth-to-satellite links
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ABSTRACT: Fade mitigation techniques on Earth-satellite links require the estimation of channel propagation conditions. This is generally done by using downlink measurements at a lower frequency to derive the channel uplink propagation conditions at higher frequencies. Moreover, when atmospheric conditions are changing, the ground stations have to change their own configuration (increase or decrease transmit power and/or data rates for example). These changes involve estimating the uplink propagation conditions in advance. The proposed algorithm allows the margin to be estimated a few seconds in advance from the downlink so that a given percentage of availability of the uplink is reached. For that purpose, we have used a recently developed prediction method based on an ARMA/GARCH model (de Montera et al., 2008) and scaling frequency models. From the downlink attenuation, first the attenuation is first predicted with a prediction horizon ranging between 2 and 30 seconds. The contributions of gases, clouds and rain are then estimated using a neural network (Barthes et al., 2006) and scaled using specific scaling factors. Finally, the attenuation and its variance for the uplink are estimated and the margin is derived. This algorithm allows an accurate upper-bound of the future attenuation to be estimated in real time, which minimizes the cost of fade mitigation techniques and therefore enables the communication system to reach an appropriate percentage of availability. After a presentation of the method, we describe results obtained from the Syracuse 3 EHF measurements (20/44 GHz). We show that the method gives good results for a prediction horizon in the range 2-30 seconds. We conclude the paper by showing that for a prediction horizon of 10 seconds and for attenuations greater than 5 dB the error due to frequency scaling is larger than the prediction error, so that future improvements should focus on scaling frequency models.Antennas and Propagation, 2009. EuCAP 2009. 3rd European Conference on; 04/2009 -
Article: Rain rate time series as an integrated multiplicative process
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ABSTRACT: High resolution rain rate time series derived from disdrometer measurements are analyzed on an event-by-event basis. The rain rate process is found to be an integrated non-stationary cascade (H=0.53 in the framework of Universal Multifractals). This result is in contradiction with the usual modeling of rain rate time series as pure stationary multiplicative cascades (H=0) based on daily or hourly measurements. In order to resolve this apparent difficulty, we show that, at these low resolutions, multifractal analysis techniques are profoundly biased by rain on-off intermittency. Therefore a new model for rain rate time series is proposed. The latter is based on an integrated multiplicative cascade thresholded in order to reproduce rain on-off intermittency. These synthetic time series are able to reproduce correctly the fractal dimension of rain periods, the non-stationarity of rain rate at high resolution and the artificial stationary multiplicative cascade when only low resolutions are considered. Finally, the analysis of non-intermittent radar rain maps leads to the same conclusion in space, although the value H is lower, which could be explain by the uncertainty of the relation between rain rates and radar reflectivities.03/2009; 11:7356. -
Conference Proceeding: EHF Propagation Experiment with Syracuse 3 Satellite: First Results
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ABSTRACT: An Earth-to-satellite propagation experiment operating at EHF band was set up within the framework of the Syracuse 3 program. Syracuse 3 satellites are the new generation of French military SATCOM system. This experiment is a good opportunity to make attenuation measurements and increase our knowledge of tropospheric propagation effects on EHF links at a low elevation angle (17deg). At these frequencies (20 & 44 GHz), the attenuation due to the troposphere can be very strong. Although rain is the major contributor, clouds and gases are no longer negligible, and contribute in a significant way to attenuation, especially above 40 GHz. Among the various fade mitigation techniques, we will focus in a second part on an Up-Link Power Control technique. This technique consists in a real-time uplink adjustment of transmitted power according to the channel attenuation conditions. The channel propagation conditions are generally estimated at a lower frequency, using the downlink (20 GHz). Due to the delay of the control loop, the power margin has to be estimated a few seconds in advance, typically 10 seconds. A new prediction method based on an ARMA/GARCH model is proposed. This non-linear model originally proposed for financial studies is shown to be accurate to describe the attenuation process, which exhibits volatility clusters (periods with sudden and strong variations). Comparisons with other existing models are presented.Antennas and Propagation, 2007. EuCAP 2007. The Second European Conference on; 12/2007 -
Article: A passive scalar-like model for rain applicable up to storm scale
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ABSTRACT: Analysis of the data collected during the AMMA (African Monsoon Multidisciplinary Analyses) campaign shows that rain storms typical of the African monsoon have multifractal properties, and can be modelled by fractionally integrated multiplicative cascades. The originality of the present study lies in the application of a constraint, which results in the interior only of storms being investigated, such that the multifractal analysis is not affected by the presence of numerous zero values. The model is validated in the time domain by means of disdrometer measurements, and in the spatial domain with co-localized meteorological radar rain maps. The non-conservation parameter obtained in the spatial domain is found to be consistent with the assumption that the rain rate follows a passive scalar-like scaling law up to the scale of storms, including corrections due to fluxes intermittencies. Comparison of the value of this parameter with that obtained in the temporal domain indicates the presence of a space–time anisotropy, which could be explained by turbulent advection.Atmospheric Research. -
Article: Analysis of full-waveform lidar data for classification of urban areas
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ABSTRACT: In contrast to conventional airborne multi-echo laser scanner systems, full-waveform (FW) lidar systems are able to record the entire emitted and backscattered signal of each laser pulse. Instead of clouds of individual 3D points, FW devices provide connected 1D profiles of the 3D scene, which contain more detailed and additional information about the structure of the illuminated surfaces. This paper is focused on the analysis of FW data in urban areas. The problem of modelling FW lidar signals is first tackled. The standard method assumes the waveform to be the superposition of signal contributions of each scattering object in such a laser beam, which are approximated by Gaussian distributions. This model is suitable in many cases, especially in vegetated terrain. However, since it is not tailored to urban waveforms, the Generalized Gaussian model is selected instead here. Then, a pattern recognition method for urban area classification is proposed. A supervised method using Support Vector Machines is performed on the FW point cloud based on the parameters extracted from the post-processing step. Results show that it is possible to partition urban areas in building, vegetation, natural ground and artificial ground regions with high accuracy using only lidar waveforms. -
Article: Multifractal analysis of African monsoon rain fields, taking into account the zero rain-rate problem
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ABSTRACT: Nonlinear rain dynamics, due to strong coupling with turbulence, can be described by stochastic scale invariant (such as multifractal) models. In this study, attention is focused on the three-parameter fractionally integrated flux (FIF), based on the universal multifractal (UM) model developed by Schertzer and Lovejoy (1987). Multifractal analysis techniques were applied to experimental radar data measured during the African monsoon multidisciplinary analysis (AMMA) campaign, during the summer of 2006. The non-conservation parameter H, which has often been estimated at 0, was found to be more likely close to 0.4, meaning that rain is not a conserved cascade. Moreover, it is shown that the presence of numerous zero values in the data has an influence, which has until now been underestimated, but should in fact be accounted for. UM parameters are therefore estimated from the full dataset, and then only from maps in which almost all pixels have a non-zero value. Significant differences were found, attributed to on–off intermittency, and their role was checked by means of simulations. Finally, these results are compared with those previously based on time series, and collected by a co-localized disdrometer. The sets of parameters obtained in the spatial and time domains are found to be quite close to each other, contrary to most results published in the literature. This generally reported incoherency is believed to result mainly from the influence of on–off intermittency, whose effects are stronger for time series than for selected radar maps.Journal of Hydrology.
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Institutions
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2009
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Université de Versailles Saint-Quentin
Versailles, Ile-de-France, France
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