Optical Techniques for Atmospheric Cross-Wind Profiling

Transcription

1 Optical Techniques for Atmospheric Cross-Wind Profiling Dr. Mikhail A. Vorontsov, Army Research Laboratory, CISD, Intelligent Optics Lab. and University of Maryland, College Park, Intelligent Optics , www://iol.umd.edu Dr. Miao Yu, University of Maryland, College Park, Mechanical Eng. Dep. Single-pass propagation Double-pass propagation

2 Wind-profiling Based on Intensity Scintillation Measurements Light source Phase-distorting layer moving with wind velocity v Fast-framing camera v

3 Phase Distorting Layer Location and Intensity Scintillations Light source Phase-distorting layer moving with wind velocity v f v e d c Fast-framing camera a a b ac b Phase screen ad ae af

4 Intensity Scintillation Correlation Technique: Single Turbulence Layer Correlation function C( x = a, y b, Δt) = I( x, y, t) I( x + x a, y + y b, t + Δt) dxdy I Intensity distribution ( x, y, t) L 1 L R ϕ p ϕ v A in I( x, y, t) Intensity distribution at time t Taylor hypothesis: Moving turbulent layers are frozen Intensity at t Correlation between two images (a,b) coordinate of the correlation peak maximum a = v t b = v t x Δ y Δ Intensity at t+δt (a,b) f s = 1/ Δt Sampling frequency Wind velocity: v x = a Δt v y = b Δt

5 Digital Processing of a Set of Short-Exposure Scintillation Patterns Example 1: Sampling frequency 66 fr/sec. DALSA camera (256x256 pixels) receiver aperture diameter D=15 mm v x (m/s) t (s) v y (m/s) t (s) Wind velocity v x 1.35m/s, v y.81m/s 1 pixel shift corresponds to.27m/s Intensity at pupil plane Wind direction

6 Digital Processing of a Set of Short-Exposure Scintillation Patterns Example 2: Sampling frequency 83 Hz, receiver aperture size.42cm Wind velocity v x m/s, v y m/s 1 pixel shift/step=.42cm 83Hz=.34m/s Intensity at pupil plane Wind velocity v x Wind velocity v y Wind velocity

7 Multiple Turbulent Layers: Numerical Simulations Image of cross-correlation Multiple phase-distorting layers L=.25 ka Finding peaks of the correlation function corresponding to each phase-distorting layer The size of the peak corresponding to the distance of phase-distorting layer Sensitive to wind velocity difference between different phase-distorting layers and strength of turbulence dz 1 =.4 dz 2 =.45 dz 1 =.5 dz 2 =

8 Correlation Peak Enhancement Via Moving Camera Two phase-distorting layers Scanning receiver image plane Enhance peaks of correlation function C s ( x, y) L = C( x, y, z) dz D/r =1 V d = a 1 b D/r =4 2 V d =.1

9 Correlation Peak Enhancement Via Phase-Image Diffraction Two distant phase distorting layers Use pupil-plane intensity as input of the wavefront corrector Propagate beam to the matched distance (.1 and.5) to get output intensity 1 & 2 Perform the same process as single phase-distorting layer case to get wind velocity for both phase screens

10 Correlation Peak Enhancement Via Phase-Image Diffraction Two distant phase-distorting layers Example: simulation results Input wind velocity: v = sin( nδt / 2 ) v 2 = 5 1 π Pupil-plane intensity Wind velocity for phase screen 1 Wind velocity for phase screen 2

11 Wind Profiling Based on Intensity Scintillations Analysis: Atmospheric Experiment Telescope and wind sensor 2.3 km Intelligent Optics Laboratory Water Tower

12 Wind Profiling Based on Intensity Scintillations Analysis: Experimental Results Telescope laser Experimental Parameters: Telescope aperture size:15cm CCD camera sampling rate: 25 Hz t t+δt Correlation Receiver aperture size resolution: Wind sensor located at the pupil plane NovaLynx Corporation Weather Monitoring Instruments and Systems

13 Wind speed (mph) Wind speed(mph) wind speed from intensity scintillations wind sensor data 1:37:55 1:4:48 1:43:41 1:46:34 1:49:26 1:52:19 Time Wind Profiling Based on Intensity Scintillations Analysis: Experimental Results Wind data acquired from 1:38am to 1:52am on July 5 25: Wind data acquired from 11:5am to 12:24pm on July 15 25: wind sensor data wind speed from intensity scintillations 11:48:29 11:55:41 12:2:53 12:1:5 12:17:17 12:24:29 Time Negative wind data corresponding to east wind and positive wind data corresponding to west wind Wind direction: south west to south east Wind direction: east

14 Wind Profiling Using Differential Nonlinear Zernike Filter Correlation of intensity I dif + ( r) = I ( r) I ( r) = 8πF I ( r) I () sin[ ϕ( r) Δ] zer zer F D/r =1 V d =.2 DNZF Visualized screen Visualized screen scanning and visualizing the image plane of each distant phasedistorting layer the dominant correlation peak corresponds to the visualized phase-distorting layer Comparison of correlation function using DNZF and without DNZF for two phase screens