DSP Analysis of Digital Vector Slope Gauge Data Produced by Ocean Wave Simulation

Transcription

1 DSP Analysis of Digital Vector Slope Gauge Data Produced by Ocean Wave Simulation EECS Introduction to Research Prof. Earl Schweppe,, Instructor Evan L. Bryson

2 Overview Ocean Wave Behavior The Vector Slope Gauge (VSG) VSG History VSG Function Ocean Wave Data Simulation Off-line Processing Future Work

3 Overview Ocean Wave Behavior The Vector Slope Gauge (VSG) VSG History VSG Function Ocean Wave Data Simulation Off-line Processing Future Work

4 Ocean Wave Behavior Spectrum Wavelength, period, and velocity Deep water vs. shallow water waves Sea = linear sum of waves Orbital velocity

5 Ocean Wave Spectrum (From Kampion, 1997)

6 Wave Velocity vs. Wavelength and Period (From Kampion, 1997)

7 Simple Wavefront Description Height of ocean wave at time t and position (x,y): h( x, y, t) = Acos( Ωt + κx cosα + κy sinα + φ) where Ω = κ = L = T = α = φ = 2π = angular frequency (rad/sec) T 2π = wave number (rad/m) L wavelength (m) wave period (sec) wave approach direction phase

8 Superposition of Waves Complex Sea = Superposition of many wavefronts Individual wavefronts are approximately sinusoidal in deep ocean Wavefronts change shape near shore as water depth decreases Single wavefront is rare in nature Wavefronts are initiated by winds over the ocean at other locations (From Bascom, 1964)

9 (From Kampion, 1997)

10 Orbital Velocity (From Kampion, 1997) (From Bascom, 1964)

11 Overview Ocean Wave Behavior The Vector Slope Gauge (VSG) VSG History VSG Function Ocean Wave Data Simulation Off-line Processing Future Work

12 VSG History Version 1 Analog VSG Tested in the North Sea in 1990 Version 2 Improvement of Version 1 Tested at Duck Pier in 1995 Version 3 Digital VSG No ocean surface data available

13 VSG Function VSG z y axis is radar look direction Θ is incidence angle H is height above mean ocean surface H Θ y x

14 Typical VSG Beam Pattern on Ocean Surface Beam 3 Beam 2 Beam 1 ~ 1 meter ~ 1 meter

15 Frequency Format of VSG Radar Signal Sweep Cycle Upsweep Downsweep F Bandwidth Beam 1 Beam 2 Beam 3 T

16 Instantaneous IF Output and Return for Range Measurement Radar Signals Transmitted Signal Returned Signal F Intermediate Frequency Signal (Difference Frequency) T (Adapted from Ulaby, Moore, and Fung, Fig. 7.25, p. 513)

17 Instantaneous IF Output and Return for Range and Doppler Measurement Radar Signals Transmitted Signal Returned Signal F Intermediate Frequency Signal (Difference Frequency) T (Adapted from Ulaby, Moore, and Fung, Fig. 7.25, p. 513)

18 Instantaneous Frequencies for Point Target Magnified View of a Portion of the Signal Transmitted Signal F F Returned Signal T T (Adapted from Ulaby, Moore, and Fung, Fig. 7.25, p. 513)

19 VSG Parameters Range Sweep repetition frequency Single (Up or Down) sweep time Sweep rate Minimum DSP sample rate R f T B = = sweep f t f smin hvsg = cosθ = c fif 4B R = 1 2f B T B sweep = 2 f IF = 10 cos( 45) = 8 3 (3 10 ) (60010 ) µs = 1.0MHz = m 4000Hz = 4.76Mhz/ µ sec

20 Overview Ocean Wave Behavior The Vector Slope Gauge (VSG) VSG History VSG Function Ocean Wave Data Simulation Off-line Processing Future Work

21 Ocean Wave Data Simulation for Digital VSG Characterize simple ocean surfaces Flat surface (calm sea) Single wavefront Multiple wave fronts Add Doppler shift to surfaces Convert ranges + Doppler to frequencies Digital sampling of frequencies Scale and shift Convert to 12-bit unsigned integers Create data files in digital VSG format

22 Ocean Wave Data Simulation WaveSim7.m RangeEst.m slrangemod.m slopepoimod.m Save2Slopes.m VSG Parameters slopeab2.m SlopeOut.txt Wavesim7.m Range IF SampGen.m Sampled IF Ocean Wave Parameters NsPerSweep.m VSGOutput.m VSGOut.bin

23 Digital VSG Data Format MSB LSB not used (always 0) Beam # Up/Down 0 = Up 1 = Down 00 = Beam 1 01 = Beam 2 10 = Beam 3 11 not used Data 12 bit unsigned integer

24 Overview Ocean Wave Behavior The Vector Slope Gauge (VSG) VSG History VSG Function Ocean Wave Data Simulation Off-line Processing Future Work

25 Off-line Processing Current Vector Slope Gauge Concept VSG Raw VSG Data Data Storage Hard Disk Delay Data Preparation Data Processing and Calculations Printer Output of Results

26 DSP Algorithm Ocean Project Data Beam 1 Up Data Beam 1 Down PSD PSD BPF BPF Calculate f eff, u Calculate f eff, d Storage Buffer Storage Buffer Calculate f avg, u Calculate f avg, d + + _ + Scale to Velocity Scale to Range f d1 1 R 1 R 1 R 2 R 3 Calculate Vector Slope Look Angle Data Beam 2 Up Data Beam 2 Down PSD PSD BPF BPF Calculate f eff, u Calculate f eff, d Storage Buffer Storage Buffer Calculate f avg, u Calculate f avg, d + + _ + Scale to Velocity Scale to Range f d2 2 R 2 f d1 f d2 f d3 Calculate f d, avg Data Beam 3 Up Data Beam 3 Down PSD PSD BPF BPF Calculate f eff, u Calculate f eff, d Storage Buffer Storage Buffer Calculate f avg, u Calculate f avg, d + + _ + Scale to Velocity Scale to Range f d3 3 R 3 Adapted from DSP Algorithm for Ocean Radar Project, Gary W. Hamilton II

27 DSP of Stored Ocean Wave Data DSP2.m VSG Parameters VSGOut.bin DSP2.m GetTimeSeries2.m FindPSD.m Upsweep Downsweep Shift and Scale FindEffFreq.m evanslope.m Sum Average Frequency Difference Average Frequency Slopes Sx, Sy Range Doppler

28 Overview Ocean Wave Behavior The Vector Slope Gauge (VSG) VSG History VSG Function Ocean Wave Data Simulation Off-line Processing Future Work

29 Future Work Collect ocean data on digital VSG Comparison to Duck Pier results Orbital velocity measurement Real-time DSP Adaptation to shipboard environment

30 Real-Time Vector Slope Gauge Concept VSG Raw VSG Data DSP Board On-Screen Results DSP Program

31 (Kampion, 1997) University of Kansas