Post on 26-Aug-2020
SEASAR 2008 Symposium, 21-25 January 2008, ESA-ESRIN, Frascati, Italy
Global swell wave observation and application for NRT storm swell tracking and swell attenuation estimation.
Fabrice Collard : BOOST TechnologiesBertrand Chapron : IFREMER
Fabrice Ardhuin : SHOM
SEASAR 2008 Symposium, 21-25 January 2008, ESA-ESRIN, Frascati, Italy
Swell partition extraction and validation
• Extraction of swell systems integratedparameters from ENVISAT WAVE MODE level2 products. (based on improved wavespectra algorithm now operational in PFASAR).
• One set of parameters (E,Dir,K) per partition
SEASAR 2008 Symposium, 21-25 January 2008, ESA-ESRIN, Frascati, Italy
1) Static validation against directional BUOYS
• Collection of 50 image mode and 35 wide swath single look complex image.
• Collection of collocated buoy directional spectra over deep and shallow water.
• NDBC buoys : courtesy of NOAA• Datawell buoys in iroise sea and golfe Normand Breton
: courtesy SHOM
SEASAR 2008 Symposium, 21-25 January 2008, ESA-ESRIN, Frascati, Italy
Buoy data preparation
• Maximum Entropy Method estimation• SAR spectrum BUOY spectrum
SEASAR 2008 Symposium, 21-25 January 2008, ESA-ESRIN, Frascati, Italy
Deep water buoy configuration
SEASAR 2008 Symposium, 21-25 January 2008, ESA-ESRIN, Frascati, Italy
Deep water buoy configuration
SEASAR 2008 Symposium, 21-25 January 2008, ESA-ESRIN, Frascati, Italy
Swell height comparison
SEASAR 2008 Symposium, 21-25 January 2008, ESA-ESRIN, Frascati, Italy
Swell wavelength comparison
SEASAR 2008 Symposium, 21-25 January 2008, ESA-ESRIN, Frascati, Italy
Swell direction comparison
SEASAR 2008 Symposium, 21-25 January 2008, ESA-ESRIN, Frascati, Italy
Validation summary
-0.070N/A0.2 0.2 N/A Φ, rad0.760.270.010.940.87 1.1 Tp, s 0.090.190.250.880.280.7Hs, m
Bias WSBias IMBias WMRMSe WSRMSe IMRMSe WM
• Comparison of integrated swell parameters extracted from SAR and BUOY wave spectra for different ASAR modes. RMS error and BIAS are provided for the three usual parameters that are the significant wave height (Hs) the dominant wave period (Tp) and the dominant wave direction (Φ)
SEASAR 2008 Symposium, 21-25 January 2008, ESA-ESRIN, Frascati, Italy
“Dynamic” validation
• basic idea is to verify the coherence of swell observation when propagated in time along great circle rays at group velocity.
SEASAR 2008 Symposium, 21-25 January 2008, ESA-ESRIN, Frascati, Italy
Observed swell at a given location versus time (virtual buoy)
• Time-frequency diagram for one month at position longitude 100 °W and 0°N
color indicates propagation direction.
SEASAR 2008 Symposium, 21-25 January 2008, ESA-ESRIN, Frascati, Italy
Ridge validation
DAYS OF JULY 2004
Wav
efr
eque
ncy
Wav
efr
eque
ncy
SEASAR 2008 Symposium, 21-25 January 2008, ESA-ESRIN, Frascati, Italy
Ridge validation
DAYS OF JULY 2004
Wav
efr
eque
ncy
Wav
efr
eque
ncy
SEASAR 2008 Symposium, 21-25 January 2008, ESA-ESRIN, Frascati, Italy
fireworks
• now implemented in near real time. 3 hourly animated gifs produced every morning for Altantic, Pacific and Indian oceans.
• available at following address :
• www.boost-technologies.com/esa/images/nrt_pac.gif• www.boost-technologies.com/esa/images/nrt_atl.gif• www.boost-technologies.com/esa/images/nrt_ind.gif
SEASAR 2008 Symposium, 21-25 January 2008, ESA-ESRIN, Frascati, Italy
SEASAR 2008 Symposium, 21-25 January 2008, ESA-ESRIN, Frascati, Italy
SEASAR 2008 Symposium, 21-25 January 2008, ESA-ESRIN, Frascati, Italy
Observed propagation of 17s swell from July 8 to July 20, 2004
SEASAR 2008 Symposium, 21-25 January 2008, ESA-ESRIN, Frascati, Italy
SEASAR 2008 Symposium, 21-25 January 2008, ESA-ESRIN, Frascati, Italy
SEASAR 2008 Symposium, 21-25 January 2008, ESA-ESRIN, Frascati, Italy
Observed propagation of 13s to 17s swell from July 8 to July 20, 2004
• 6 hour time step• Wavelength from
300 to 450m • Wave period from
13 to 17 seconds
SEASAR 2008 Symposium, 21-25 January 2008, ESA-ESRIN, Frascati, Italy
Observed propagation of 17s swell from Aug.10 to Aug. 21, 2004
SEASAR 2008 Symposium, 21-25 January 2008, ESA-ESRIN, Frascati, Italy
Observed propagation of 13s to 17s swell from Aug. 3 to Aug. 21, 2004
• 6 hour time step• Wavelength from
300 to 450m • Wave period from
13 to 17 seconds
SEASAR 2008 Symposium, 21-25 January 2008, ESA-ESRIN, Frascati, Italy
• Focusing of 17s swell observed from July 8 to July 20, 2004
Identification of swell origin
SEASAR 2008 Symposium, 21-25 January 2008, ESA-ESRIN, Frascati, Italy
Application : Analysis of swell attenuation
Bias up to 30% of obs. !
SEASAR 2008 Symposium, 21-25 January 2008, ESA-ESRIN, Frascati, Italy
Data mining . .. 13Sec
17Sec
SEASAR 2008 Symposium, 21-25 January 2008, ESA-ESRIN, Frascati, Italy
Swell attenuation estimation
• Comparison with theoretical direction spreading and dispersion related attenuation -> dissipation ?
• Color dots and black line SAR data
• Red : model with dissipation• Purple model without
dissipation• Green : theoretical model
(geo+dispersion)
SEASAR 2008 Symposium, 21-25 January 2008, ESA-ESRIN, Frascati, Italy
Swell attenuation estimation
• 16 Sec
SEASAR 2008 Symposium, 21-25 January 2008, ESA-ESRIN, Frascati, Italy
Swell attenuation estimation
• 15 Sec
SEASAR 2008 Symposium, 21-25 January 2008, ESA-ESRIN, Frascati, Italy
Swell attenuation estimation
• 14 Sec
SEASAR 2008 Symposium, 21-25 January 2008, ESA-ESRIN, Frascati, Italy
Swell attenuation estimation
• 13 Sec
SEASAR 2008 Symposium, 21-25 January 2008, ESA-ESRIN, Frascati, Italy
Swell attenuation estimation
• 12 Sec
SEASAR 2008 Symposium, 21-25 January 2008, ESA-ESRIN, Frascati, Italy
Dissipation coefficient estimation
• Estimation of the vTcoefficient
1( ) sinT
TE e ν ϕϕ ϕ ϕ−
,
SEASAR 2008 Symposium, 21-25 January 2008, ESA-ESRIN, Frascati, Italy
Conclusion
• Coherence of SAR swell observation to build a level 3 product
• Swell attenuation compared well with early Snodgrass et al. estimates but previous scatter from event to event can now be explained by the initial wave steepness condition.
• Swell attenuation is at first order governed by simple dispersion and geometrical spreading and at second order non linear in orbital velocity driven dissipation.
• Next step will be to combine with in situ directional buoy network to derive global scale swell analysis for ocean nowcasting.