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Ocean Surface Roughness and Remote Sensing

Ocean Surface Roughness and Remote Sensing. Paul Hwang Remote Sensing Division Naval Research Laboratory. Microwave. Ocean Surface Roughness and Remote Sensing. Modification of ocean surface roughness by. Wind, Wave, Current, Bathymetry (SEASAT, 1978). Paul Hwang

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Ocean Surface Roughness and Remote Sensing

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  1. Ocean Surface Roughness and Remote Sensing Paul Hwang Remote Sensing Division Naval Research Laboratory

  2. Microwave Ocean Surface Roughness and Remote Sensing Modification of ocean surface roughness by Wind, Wave, Current, Bathymetry (SEASAT, 1978) Paul Hwang Remote Sensing Division Naval Research Laboratory

  3. Surface roughness and ocean wind sensing Active Radar backscatter from the ocean surface NRCS (0)  roughness  wind velocity Polarimetric returns (VV, HH; VH=HV), high wind speed and breaking wave measurements from radar backscatter Passive Radiometer brightness temperature of the ocean surface (difference from flat surface)Tb roughness/foam wind velocity, breaking

  4. Improving surface roughness spectrum and understanding of physical processes Cubic wind speed dependence of short wave spectrum (linear in equilibrium spectrum) Source functions Sin (wind), Sds (breaking), Snl (4-wave) for long scale waves (energetic region up to the equilibrium range) Sin (wind, breaking), Sds (vis.,?), Snl (3-wave, parasitic) for short scale waves (roughness) Breakingas a source term: impulses of breaking water jets, surface disturbances and bubble plumes propagating downward from the wave crest and the subsequent rising of the entrained bubble clouds to the water surface Hwang 2011 (JAOT)

  5. Ocean short wave spectrum measured by free- drifting wave gauge array (Hwang and Wang 2004) Banner et al. 1989 Stereo photo ( =0.2~1.6 m) 5.5–13.3 m/s a0=0.18 Toba 1978; Phillips 1985; Hwang et al. 2000

  6. H spectrum Radar backscatter power-law wind speed exponent (Masuko et al., 1986; Phillips, 1988; Weissman et al., 1994; Colton et al., 1995; summarized in Hwang 1997 and Trokhimovski and Irisov 2000) Hwang (2005, 2008, 2011)

  7. Phillips 1984 , Source function balance equilibrium range (0.04)(1) [Snl ~10-4 near spectral peak] |Snl|<<|Sin|,|Sds| For short waves [several times (~10) shorter than the peak wavelength] 0.02<<6 m k > ~2 kp u*/c: 0.3 - 3

  8. Altimeter (LP-Filtered roughness) According to the 2θ deviation, the phase shift causes constructive (left figure) or destructive (right figure) interferences (Wikipedia) Scatterometer (Bragg roughness)

  9. Altimeter mode: filtered roughness Optical 36 GHz 14 GHz 5.5 GHz Vandemark et al. 2004 Walsh et al. 1998 Cox & Munk 1954 Jackson et al. 1992 Hauser et al. 2004

  10. Scatterometer mode: spectrometer Old Old: Hwang: 2008 New: Hwang 2011 201, 293, 377, 449, 508 rad/m

  11. RADARSAT-2 polarimetric data VH VV HH Decreasing sensitivity with wind Saturation/dampening Increasing sensitivity with wind: Linear: low wind Cubic: high wind R2 >> CB Breaking contribution missing in CB computation R2 and CB in good agreement Hwang et al. (2010)

  12. rms 1.65 rms 1.50 rms 1.67 rms 1.62 Hwang et al. 2010

  13. Wind field retrieved with VH Wind field retrieved with VV

  14. Hwang & Sletten 2008

  15. Hwang & Sletten 2008 Measure energy dissipation rate from space Hwang et al. 2010

  16. Emissivity  =0 30 60 SPM/SSA Johnson and Zhang (1999) Flat surface -- Wind/roughness modified Wave spectrum · Weighting function Weighting function

  17. Hwang et al. 2011

  18. Foam Passive Microwave Brightness Temperature WindSat data (Meissner and Wentz 2009) 50~55 deg polar angle SSS=35psu, SST=290K, average of 50 and 55 deg polar angle

  19. Radiometer and scatterometer: global wind retrieval Ocean surface roughness (short surface waves): key role Empirical parameterizations so far, need better understanding of physics: breaking Polarization carries breaking wave information for measurement from space Improving global wind product, improving driving force of wave modelsRoughness may fall between cracks (air-sea interaction, wave dynamics, remote sensing, …)but it is NOT someone else’s problem

  20. 76, 111, 143, 170, 192 rad/m

  21. Scatterometer mode: spectrometer 14 GHz 5 – 6 GHz Hwang & Plant 2010

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