SIMULATION OF X-BAND RADAR FOR THE ASSESMENT OF EDDY DISSIPATION RATE

ON A CONVECTIVE BOUNDARY LAYER Pereira, C. (1), Vanhoenacker-Janvier, D.(1), Barbaresco F. (2) ,

1) ICTEAM, UCL, Louvain-la-Neuve, Belgium, carlos.pereira@uclouvain.be, danielle.vanhoenacker@uclouvain.be (2) Surface Radar Domain,Technical directorate,Thales Air system SA,

France, frederic.barbaresco@thalesgroup.com

SESAR project

Outline

• Introduction

• Background

• Detection of turbulences

• Example of results

• Conclusion and Perspective

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INTRODUCTION

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Introduction • Problematic:

– Real-time monitoring of wind hazards. – Design of sensors for the assessment of wind shear

(Radar, Lidar). • Use of X-Band Radar for air turbulence

monitoring . • Radar simulation for support of measurement

campaigns: – Electromagnetic calculation. – Atmospheric data. – Focus on clear air turbulence in the boundary layer.

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BACKGROUND

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Wake vortices detection

• SESAR SESAR P12.2.2: Simulations of Aircraft Wake Vortices detection by X-band Radar.

• Fluid mechanics 2D model: simulates the movement and evolution of atmosphere parameters (air pressure, air temperature and humidity) in presence of wake vortices.

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Procedure: vortex age detection

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Electromagnetic modeling: computes the power backscattered to the radar by the wake vortices, evolving in function of dielectric permittivity.

dx Xmax

Volume

Slice modulation

Slice

y

z

𝑟𝑟 = distance vector (x, y, z) between the receiver and the volume element [m]; 𝜀𝜀𝑟𝑟 𝑦𝑦,𝑧𝑧 = dielectric permittivity of the atmosphere (evolving in y and z in our case); 𝑓𝑓 𝑥𝑥 = modulation function used to extend the slice in the x dimension (takes into account the antenna radiation pattern); Calculation of Radar Cross Section allows to distinguish Radar cells with and without

presence of vortices.

𝐼𝐼𝐼𝐼𝐼𝐼𝑝𝑝 = � 𝜀𝜀𝑟𝑟 𝑦𝑦,𝑧𝑧 − 1 𝑓𝑓 𝑥𝑥 𝑒𝑒−𝑖𝑖𝑖𝑖𝑖.𝑟𝑟 𝑑𝑑𝑟𝑟𝑟𝑟/𝑖

−𝑟𝑟/𝑖

DETECTION OF TURBULENCES

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Context

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FP7 UFO (Ultra Fast wind sensOrs) Project: (http://www.ufo-wind-sensors.eu) • Goal WP2000:

• Deliver a X-band Radar simulator. • Use a fluid mechanics model to generate representative atmospheric

data.

• Use of a atmospheric simulator for the convective boundary layer: • Large Eddy Simulation.

• Pressure • Temperature • Humidity • Wind

• Parameters in 3D + Time evolution

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Turbulent spectrum

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Turbulent spectrum Input range: energy is introduced into the turbulence (ex: wind shear). Inertial range: energy decreases as eddies size reduces progressively. Dissipation range: energy is converted into heat and absorbed at molecular level.

Φ𝑛𝑛 𝜅𝜅 = 0.033 𝐶𝐶𝑛𝑛𝑖 𝜅𝜅𝑖 + 𝜅𝜅𝐿𝐿𝑖 −11/6𝑒𝑒−𝜅𝜅𝜅𝜅𝑚𝑚

2

– 𝜅𝜅 : wave number [rad/m] – 𝜅𝜅𝐿𝐿: outer wave number – 𝜅𝜅𝑚𝑚: inner wave number

𝚽𝚽𝐧𝐧 𝛋𝛋 = 𝟎𝟎.𝟎𝟎𝟎𝟎𝟎𝟎 𝐂𝐂𝐧𝐧𝟐𝟐𝛋𝛋−𝟏𝟏𝟏𝟏/𝟎𝟎

Position of our study: Inertial range.

Atmospheric simulation

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The turbulence intensity is evaluated by 𝐶𝐶𝑛𝑛𝑖 :

𝐶𝐶𝑛𝑛𝑖 = 𝐼𝐼(𝑟𝑟+�) − 𝐼𝐼(𝑟𝑟)

𝑖

δ 𝑖/3 [𝑚𝑚−𝑖/3]

With: 𝐼𝐼 : is the refractive index 𝑟𝑟 : is the spatial vector position [m] 𝛿𝛿: is the spatial separation [m] <>: represent is average operator

Pressure

Temperature

Humidity

Refractivity

Computes the power backscattered to the radar by use of refractive index structure constant 𝐶𝐶𝑛𝑛𝑖 [1]. [1] Muschinski, A., P.P. Sullivan, D.B. Wuertz, R.J. Hill, S.A. Cohn, D.H. Lenschow, and R.J. Doviak, 1999: First synthesis of wind-profiler signals on the basis of large-eddy simulation data. Radio Science, 34, 1437-1459

EXAMPLE OF RESULTS

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Context

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• Atmosphere data: – Generated by LES model from

Institut franco-allemand de recherches de Saint-Louis

– Environment: Boundary Layer – Place: Virtual flat ground – Weather: Summer day, no cloud, no

rain, no mean wind – Duration: 1 hour with time step of 20

s – Dimension: 6 km horizontally and 1.5

km in height – Spatial resolution: 30 m

Context

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• Turbulences: • Height: 1100 m • Width: 350 m • Significant turbulence

intensity (0 < 𝐶𝐶𝑛𝑛𝑖 < 2 10−11)

Configuration radar

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Scenario: • Elevation angle: 90 deg • Frequency: 9.3 GHz • Pulse length: 40 m • Fixed position • Radar Cross section in

function of altitude and atmosphere time evolution.

Turbulent layer

LES volume

6 km

1.5 km

Radiation Pattern

Radar Cross Section

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Detection: • Turbulence detected around

1000 m of altitude. • Dynamic ~ 20dB • RCS intensity at turbulent

level is regular.

Radar Cross Section

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Turbulence seen from Radar: • Cn² on radar radiation pattern. • Issues with time sampling. • Cause problems on analysis for EDR

retrieval. • + 20 Gb of atmospheric data..

CONCLUSION AND PERSPECTIVE

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Conclusion • Conclusion:

– An early results of X-band simulation using atmospheric data is presented for the turbulence detection in the boundary layer.

• Combination of a Large Eddy Simulation data with an electromagnetic calculation. • Evaluation of Radar Cross Section versus time. • Use of refractive index structure constant 𝐶𝐶𝑛𝑛𝑖 for Radar Cross Section.

– The atmospheric turbulence influence is visible on the Radar Cross Section along

the propagation path. – Issues with time resolution: apparition of jumps due to fast evolution of

atmosphere. – Use of full time resolution to overcome this drawback (1s) in smaller areas.

• Perspective: – Extend the electromagnetic model to other parameters as:

• Doppler shifts; • Eddy Dissipation Rate.

– Use of LES from UCL to investigate the Radar sensitivity to rain.

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THANK YOU FOR YOUR ATTENTION

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