Envisat

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• Experiences with Envisat ASAR WM Wave Product
• Harald Johnsen
• Norut IT, Tromsø, Norway

2nd workshop on Coastal Marine Applications of
SAR,Longyearbyen, 8 12 September 2003
 
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Content

• The ASAR Wave Algorithm
• what it does
• what it doesnt
• Experiences with the Wave Product
• validation approach
• validation results
• Summary
• Future work (that needs to be done!)

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The ASAR Wave Algorithmwhat it does
Level 1 Product
Inversion Model
Processing Set-Up File
Look-Up Table
Cross Spectra Estimation
where

Clutter SNR Estimation
Wind Speed Retrieval
Ocean Wave Spectra Retrieval
Level 2 Product Generation
Level 2 Product
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SAR Ocean Image
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what it doesnt

• bathymetry/tidal flow signature
• current shears, atmospheric fronts
• internal waves
• surfactants
• ship wakes
• upwelling
• mesoscale circulation features
• etc..

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Experiences with the Wave Product Validation
Approach, http//www.oceanor.no/projects/enviwave
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Scatter Plot of CMOD-IF2 Intensity Versus ASAR
SLC Intensity
March 2003
April 2003
ECMWF, K-47.80dB, BUOYS, K-47.19dB,
Transponders, K-47.35dB
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Azimuth Cut-Off and Normalized Image Variance
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ASAR versus WAM 1 D- Spectra
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ASAR/WAM/BUOY 1 D- Spectra
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Significant Waveheight March 2003
ASAR
WAM
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Significant Waveheight (Swell) March 2003
WAM
ASAR
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Significant Waveheight April 2003
ASAR
WAM
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Significant Waveheight (Swell) April 2003
ASAR
WAM
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Scatter Plot of WAM Versus ASAR Significant
Waveheight
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Histogram of ASAR/WAM Significant Waveheight
Difference
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ASAR/WAM Waveheight Difference versus Wind Speed
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Mean Wave Period March 2003
WAM
ASAR
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Mean Wave Period April 2003
ASAR
WAM
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Mean Wave Period (Swell) March 2003
WAM
ASAR
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Mean Wave Period (Swell) April 2003
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Histogram of ASAR/WAM Mean Period Difference
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Scatter Plot of WAM versus ASAR Mean Wave Period
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WAM versus ASAR Wave Peak Period
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Scatter plot of WAM versus ASAR Mean Wave
Direction
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Histogram of ASAR/WAM Mean Wave Direction
Difference
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ASAR versus WAM Spectral Peak Direction
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Wind Speed March 2003
ASAR
ECMWF
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Wind Speed April 2003
ASAR
ECMWF
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ASAR Versus ECMWF Wind Speed
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ASAR Level 2 Azimuth Cut-Off
ASAR Cut-Off
ECMWF wind speed
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WAM ASAR Level 2 Summary
Hs (m) RMS Bias Hs12 (m) RMS Bias Tp (s) RMS Bias Tp12 (s) RMS Bias Mean Dir. (rad) RMS Bias Mean Dir.12 (rad) RMS Bias
0.6 -0.2 0.4 0.1 1.6 1.1 1.0 0.7 1.0 0. 1.0 -0.3
Peak Period (s) RMS Bias Peak Dir. (rad) RMS Bias U10 (m/s) RMS Bias Calibration diff. (dB) Buoy ECMWF
3.1 0.5 1.1 0.1 2.2 0.5 0.16 0.45
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Summary

• Conclusions so far
• The ASAR Wave Mode is able to produce independent
  and ambiguity free information on ocean swell
  systems
• Main WAM ASAR Swell difference
• Bias in swell peak period ASAR tends to measure
  longer period
• Bias in swell energy ASAR tends to measure
  higher energy for swell
• BUOY/ASAR/WAM comparison
• Examples shown where ASAR consistently add swell
  information beyond WAM

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Future Work

• Improve the flaging of data that are not within
  the domain of the algorithm model
• Extend the algorithm to work on other swaths and
  polarizations
• Update the look-up table with better resolution
  and dynamic ranges
• Keep on with the validation and long term QA
• Transition to other modes (ex. Wide Swath
  (complex data))