Pierre Dérian

Atomic Energy and Alternative Energies Commission | CEA · DRT/CTREG/DP2L

Instant fields of surface current are retrieved from shore-based and unmanned aerial vehicle videos by an optical flow (OF) method named "Typhoon". This computer vision algorithm estimates dense two-dimensional 2-component velocity fields from the observable motion of foam patterns in the surf zone. Despite challenging image data resolution and qua...

Using a classical example, the Lorenz-63 model, an original stochastic framework is applied to represent large-scale geophysical flow dynamics. Rigorously derived from a reformulated material derivative, the proposed framework encompasses several meaningful mechanisms to model geophysical flows. The slightly compressible set-up, as treated in the B...

A motion estimation algorithm was applied to image sequences produced by a horizontally scanning elastic backscatter lidar. The algorithm, a wavelet-based optical flow estimator named Typhoon, produces dense two-component vector flow fields that correspond to the apparent motion of microscale aerosol features. To validate the efficacy of this appro...

Observations of two or more wind components that resolve turbulent perturbations over large areas remain a challenge in the atmospheric boundary layer community. One successful approach to multi-component flow measurement in the engineering community is particle image velocimetry (PIV). This presentation will report on recent progress in the develo...

Expanding on a wavelet basis the solution of an inverse problem provides several advantages. First of all, wavelet bases yield a natural and efficient multireso-lution analysis which allows defining clear optimization strategies on nested subspaces of the solution space. Be-sides, the continuous representation of the solution with wavelets enables...

We describe an algorithm that can be applied to horizontally scanning atmospheric aerosol LiDAR data to determine canopy wave orientation and wavelength objectively. We applied it to over 1500 images of canopy waves from 53 episodes collected during the Canopy Horizontal Array Turbulence Study (CHATS) that took place in Dixon, California, in 2007....

In this article, a feasibility study has been carried out in order to detect structural faults in the blade by analyzing the tower vibration. A 5-MW onshore wind turbine was modeled using the NREL FAST code. The structural faults were created on the blade, while only the tower was instrumented by accelerometers and displacement meters. The wind gri...

Numerical simulations of industrial and geophysical fluid flows cannot usually solve the exact Navier–Stokes equations. Accordingly, they encompass strong local errors. For some applications—like coupling models and measurements—these errors need to be accurately quantified, and ensemble forecast is a way to achieve this goal. This paper reviews th...

We refute statements in “Zhou, K., et al. Wind gust detection and impact prediction for wind turbines. Remote Sens. 2018, 10, 514.” the impracticality of motion estimation methods to derive two-component vector wind fields from single scanning aerosol lidar data. Our assertion is supported by recently published results on the performance of two ima...

In this paper, we propose a novel optical flow approach for estimating two-dimensional velocity fields from an image sequence, which depicts the evolution of a passive scalar transported by a fluid flow. The Eulerian fluid flow velocity field is decomposed into two components: a large-scale motion field and a small-scale uncertainty component. We d...

In this paper, we propose a novel optical flow formulation for estimating two-dimensional velocity fields from an image sequence depicting the evolution of a passive scalar transported by a fluid flow. This motion estimator relies on a stochastic representation of the flow allowing to incorporate naturally a notion of uncertainty in the flow measur...

Recent progress in observations of wind fields by scanning aerosol lidar and motion estimation algorithms elevates interest in accuracy, precision , and resolution. Toward this, we are using large eddy simulations to advect a passive tracer in the model domain to mimic atmospheric aerosol. A wavelet-based optical flow algorithm is applied to the mo...

The Typhoon motion estimation algorithm retrieves sea surface current near the shore by remotely observing the displacement of the foam. Video data is provided by a basic video surveillance camera. (1) Left panel: visualization of instant surface currents estimated by Typhoon, superimposed on input images. Vectors in black are estimated by Typhoon...

The performance of two direct-detection atmospheric lidar systems with very different methods of generating and detecting laser radiation is compared as the result of a field experi- ment held in March 2015, in Chico, California. During the noncontinuous, 11-day test period, in which the systems operated side by side, the micropulse lidar was opera...

Numerical and field experiments were conducted to test an optimized cross-correlation algorithm (CCA) for the remote sensing of two-component wind vectors from horizontally scanning elastic backscatter lidar data. Each vector is the result of applying the algorithm to a square and contiguous subset of pixels (an interrogation window) in the lidar s...

An overview of recent research results on the performance of two motion estimation algorithms used to deduce two-component horizontal wind fields from ground-based scanning elastic backscatter lidar is presented. One motion estimation algorithm is a traditional cross-correlation method optimized for atmospheric lidar data. The second algorithm is a...

Although operating at the same near-infrared 1.5- m wavelength, the Raman-shifted Eye-safe Aerosol Lidar (REAL) and the Scanning Aerosol Micro-Pulse Lidar-Eye-safe (SAMPLE) are very different in how they generate and detect laser radiation. We present results from an experiment where the REAL and the SAMPLE were operated side-by-side in Chico, Cali...

This poster presents the latest progress on the recovery of two-dimensional, two-component wind fields derived from horizontally scanning aerosol backscatter lidar data by a new wavelet-based optical flow algorithm named "Typhoon". Optical flow is a family of computer-vision methods dedicated to motion estimation; its various implementations play c...

The Raman-shifted Eye-safe Aerosol Lidar (REAL) and a compact Doppler lidar were operated nearly-continuously for over 7 months at the CSU Chico farm. The experiment was conducted to evaluate the ability of the REAL to remotely sense the wind by applying motion estimation algorithms to elastic backscatter aerosol imagery. The Doppler lidar was used...

We report on the development of a wavelet-based optical flow algorithm to extract two-component 2D wind fields from lidar backscatter imagery. Such computer-vision methods are commonly used in experimental fluid dynamics (Particle Image Velocimetry, PIV): the apparent displacement of small particles advected by the flow is used to infer the underl...

The cross-correlation algorithm [1] is a numerical method used to estimate the motion of features between two frames in image sequences. Prior to this research, it was applied to real aerosol lidar for wind measurements [2, 3]. However, an evaluation of the cross-correlation algorithm involving precise control of aerosol features and flow fields ha...

Interactive visualization framework for low-atmosphere wind fields estimated from aerosol lidar imagery.

We report on the development of a wavelet-based optical flow algorithm to extract two-component 2D wind fields from lidar backscatter imagery. Such computer-vision methods are commonly used in experimental fluid dynamics (Particle Image Velocimetry, PIV): the apparent displacement of small particles advected by the flow is used to infer the underl...

We report on the implementation and testing of a new wavelet-based motion estimation algorithm to estimate horizontal vector wind fields in real-time from horizontally-scanning elastic backscatter lidar data, and new experimental results from field work conducted in Chico, California, during the summer of 2013. We also highlight some limitations of...

This work falls within the general problematic of designing measurement tools adapted to the specificities of fluid flows. The development of digital imaging, combined with visualization techniques commonly employed in experimental fluid dynamics, enables to extract the apparent flow motion from image sequences, thanks to computer vision methods. T...

Results of the application of optical flow methods to eye-safe aerosol lidar images leading to dense velocity field estimations are presented. A fluid motion dedicated for-mulation is employed, taking into account the deform-ing shapes and changing brightness of flow visualization. The optical flow technique has the advantage of provid-ing a vector...

This article describes the implementation of a simple wavelet-based optical-flow motion estimator dedicated to continuous motions such as fluid flows. The wavelet representation of the unknown velocity field is considered. This scale-space represen-tation, associated to a simple gradient-based optimization algorithm, sets up a well-defined multires...

In the context of turbulent fluid motion measure-ment from image sequences, we propose in this paper to reverse the traditional point of view of wavelets per-ceived as an analyzing tool: wavelets and their proper-ties are now considered as prior regularization models for the motion estimation problem, in order to exhibit some well-known turbulence...

Based on a wavelet expansion of the velocity field, we present a novel optical flow algorithm dedicated to the estimation of continuous motion fields such as fluid flows. This scale-space representation, associated to a simple gradient-based optimization algorithm, naturally sets up a well-defined multi-resolution analysis framework for the optical...

We consider a novel optic flow estimation algorithm based on a wavelet expansion of the velocity field. In particular, we propose an efficient gradient-based estimation algorithm which naturally encompasses the estimation process into a multiresolution framework while avoiding most of the drawbacks common to this kind of hierarchical methods. We th...

A combined experimental and numerical investigation of transonic shock wave/boundary layer interaction over a wall-mounted bump has been undertaken looking at the details of the flow and the capability of CFD in predicting such complex, yet fundamental, aerodynamic interactions. The transonic wind tunnel of the Queens University of Belfast (QUB) ha...

The overall energy efficiency of a pulp and paper mill is directly influenced by the design of both the water system and the heat transfer network. In this industry, energy and water systems are linked through the water tank network, and consequently, the production of warm and hot water should be carefully evaluated to identify design improvements...