IGARSS2011_GulfOilSpill_CJones.pdf

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IGARSS2011_GulfOilSpill_CJones.pdf

  1. 1. Polarimetric Decomposition Analysis of the Deepwater Horizon Oil Slick using L-band UAVSAR Data Cathleen Jones1 Brent Minchew2 Benjamin Holt1 1Jet Propulsion Laboratory/California Institute of Technology 2California Institute of Technology© 2011. All rights reserved.
  2. 2. NASA UAVSAR GULF OIL SPILL CAMPAIGN 22-23 JUNE 2010 DEPLOYMENT o  2 days, 21 flight hours o  ~5500 km of flight lines with 22 km swath width o  imaged an area of 120,000 km2 L-Band 1217.5 to 1297.5 MHz Frequency (23.8 cm wavelength) Intrinsic Resolution 1.7 m Slant Range, 0.8 m Azimuth DWH rig site, photographed from NASA G3Polarization HH, HV, VH, VV Repeat Track ± 5 meters Accuracy Transmit Power > 3.1 kW Radiometric 1.2 dB absolute, 0.5 dB relative Calibration Noise Floor -47 dB average IGARSS 2011, 25-29 July 2011, Vancouver, Canada Cathleen Jones (Jet Propulsion Laboratory) 2
  3. 3. UAVSAR FLIGHT LINES COVERING MAIN SLICK OF THE DEEPWATER HORIZON SPILL Two UAVSAR lines viewing the main slick from opposite directions were using in our analysis of the polarimetric response of the oil from the DWH spill. gulfco_32010_10054_101_100623 collected 23-June-2010 21:08 UTC gulfco_14010_10054_100_100623 collected 23-June-2010 20:42 UTC Because of the vast extent of the spill, we are able to measure the radar cross section as a function of incidence angle between 26°-65° using this data set. By looking at different portions of the slick, we could also quantify the variability of the returns from oil. UAVSAR data available at:Polarimetric L-band Radar Signatures of Oil from the Deepwater Horizon Spill www.asf.alaska.eduBrent Minchew, Cathleen Jones, Ben Holt, submitted to TGARS uavsar.jpl.nasa.govIGARSS 2011, 25-29 July 2011, Vancouver, Canada Cathleen Jones (Jet Propulsion Laboratory) 3
  4. 4. SURFACE CONDITIONS JUNE 23, 2010 Photographs of the DWH spill site on 6/23/2010Surface conditions:sea state 1.0-1.3 m SWHwinds 2.5-5 m/s from 115°-126° Photos from NOAA RAT-Helo, EPA ASPECT, USFIGARSS 2011, 25-29 July 2011, Vancouver, Canada Cathleen Jones (Jet Propulsion Laboratory) 4
  5. 5. BRAGG SCATTERING THEORY WAVE FACET MODEL Radar backscatter from the ocean surface is dominated by scattering from small scale capillary and gravity-capillary waves that roughen the surface. In Bragg scattering theory, the dominant mechanism is resonant backscatter from surface waves of wave number kBragg where As the incidence angle increases, the wavelength of kBragg = 2k sin(" inc ) the Bragg surface wave decreases to a minimum of k = 2# λradar/2 at grazing angles. $radar L-band (λradar=23.8 cm) : λBragg = 23.8 cm (30°), 13.7 cm (60°) 2 sin($ + % )cos & *2 sin & *2 "HH = 4 #k 4 cos!($ i )W(2k sin($ + % ),2k cos($ + % )sin &) ) 4 , RHH +) , R ( sin $ i + ( sin $ i + VV Ocean wave spectral density at Bragg wavelength 2 sin($ + % )cos & *2 sin & *2 "VV = 4 #k 4 cos 4 ($ i )W(2k sin($ + % ),2k cos($ + % )sin &) ) , RVV + ) , RHH ( sin $ i + ( sin $ i + 2 "HV = 4 #k 4 cos 4 ($ i )W(2k sin($ + % ),2k cos($ + % )sin &) RVV - RHH ! i = cos!1[cos(! + " )cos(# )]! (! r !1)(! r (1+ sin 2 (! i )) ! sin 2 (! i )) ! r !1 RVV = 2 RHH = 2 (! cos(! ) + r i 2 ! r ! sin (! i )) ) (cos(! ) + i 2 ! r ! sin (! i )) ) " =out-of-plane tilt angle IGARSS 2011, 25-29 July 2011, Vancouver, Canada Cathleen Jones (Jet Propulsion Laboratory) 5 !
  6. 6. EFFECT OF SURFACE LAYER OF OIL ON RADAR BACKSCATTER FROM WATEROil damps the small-scale capillary and gravity-capillary waves on the ocean surface mainlythrough a reduction in the surface tension at the gas-liquid interface. gravity is the restoring force Dispersion relationship for waves at the interface between air and a liquid of density ρ with surface tension σ: " 2 = gk + (# $ )k 3 surface tension and inertia are ρoil/ρwater ≈ 0.8 - 0.9 the restoring forces σoil/σwater ≈ 0.25 - 0.5 g " ! v phase = + k for a given velocity, k k # increases when the surface tension decreasesOcean waves are excited by resonant forcing in aturbulent wind field. The wavelength of capillary waves !resonantly excited in the presence of oil is smaller thanfor a clean water-air interface, hence the damping of thesmaller wavelengths. This affects the roughness scale ofthe water surface. In a real slick, the surfacecharacteristics will vary between pure H20 and pure oil,depending upon layer thickness, oil type, and arealcoverage.Also, in viscoelastic fluids gravity waves with shortwavelength are damped by restoring forces arising fromgradients in the surface tension (Marongoni effect).IGARSS 2011, 25-29 July 2011, Vancouver, Canada Cathleen Jones (Jet Propulsion Laboratory) 6
  7. 7. POLARIMETRIC DECOMPOSITION ENTROPY/ANISOTROPY/ALPHAWe have applied two polarimetric decompositions to the oil spill data, the Cloude-Pottierdecomposition and the Shannon decomposition.Cloude-Pottier:Scattering Matrix is expressed in the Pauli basis:" SHH SHV % Pauli 1 T$ ( ( () k = [SHH + SVV SHH * SVV 2SHV ]# SVH SVV & 2Diagonalization of the coherency matrix T=kk* gives 3 eigenvalues, , and eigenvectors, u.Consider 4 variables derived from the eigenvalues and eigenvectors: 3# & # & "i "i Entropy: H = )% (Log3% ( 0 * H *1 $ "1 + "2 + "3 $ "1 + "2 + "3 i=1 " + "3 Anisotropy: A = 2 0 * A *1 "2 + "3 Mean angle: , (u) 3# "2i & Averaged intensity: - = )% ( % "1 + "2 + "3 ( i=1$ IGARSS 2011, 25-29 July 2011, Vancouver, Canada Cathleen Jones (Jet Propulsion Laboratory) 7 !
  8. 8. POLARIMETRIC DECOMPOSITION SHANNON ENTROPYShannon Entropy:We derived the Shannon entropy parameters from the Pauli basis vectors and the coherencymatrix: 1 T k= 2 [SHH + SVV SHH " SVV 2SHV ] T = kk * ! SE = # PDF(k) = log(PDF(k)dk $ SE intensity + SE polarization & %eTrace(T) ) SE intensity = 3log( + 3 * & 27Det(T) ) SE polarization = log( + Trace(T) *This decomposition is significantly less computationally intensive than the H/A/ /decomposition since it requires calculation of only the trace and determinant of the coherencymatrix. !C.E. Shannon, Bell Systems Technical Journal, 27, 1948; Refregier and Morio, J. Opt. Soc. of America A, 23(12), 2006IGARSS 2011, 25-29 July 2011, Vancouver, Canada Cathleen Jones (Jet Propulsion Laboratory) 8
  9. 9. AVERAGED INTENSITY OVER THE DWH SLICK Averaged Intensity Images 320° Heading 140° Heading In the following slides, for each UAVSAR line the parameters are averaged in the Clean Water along track direction and plotted as a wind function of incidence angle for a clean water region and for three strips within the slick. scene overlap common point Oil 1 MAIN SLICK Oil 4 Oil 2 Oil 5 Oil 6 Oil 3 Clean Water + rig site 5 kmIGARSS 2011, 25-29 July 2011, Vancouver, Canada Cathleen Jones (Jet Propulsion Laboratory) 9
  10. 10. RADAR BACKSCATTER POLARIZATION-DEPENDENCE 320° Heading 140° Heading Polarimetric Returns vs. Incidence Angle 320° Heading 140° Heading |SVV| HH VV HVIGARSS 2011, 25-29 July 2011, Vancouver, Canada Cathleen Jones (Jet Propulsion Laboratory) 10
  11. 11. CLOUD-POTTIER POLARIMETRIC DECOMPOSITION ENTROPY, ANISOTROPY 320° Heading 140° Heading 140° Heading Anisotropy Entropy entropy anisotropy alpha avg intensityIGARSS 2011, 25-29 July 2011, Vancouver, Canada Cathleen Jones (Jet Propulsion Laboratory) 11
  12. 12. SHANNON POLARIMETRIC DECOMPOSITION SHANNON ENTROPY Shannon 140° Heading Shannon Intensity Polarization 320° Heading 140° Heading total entropy intensity polarizationIGARSS 2011, 25-29 July 2011, Vancouver, Canada Cathleen Jones (Jet Propulsion Laboratory) 12
  13. 13. DETAILS OF THE OIL SLICK VARIATIONS IN THE AVERAGED INTENSITYNOT ONLY IS THE OIL SLICK CLEARLY DIFFERENTIATED FROM THE SURROUNDING WATER (DARK BLUE IN THE UAVSARIMAGE), BUT THE LOW NOISE UAVSAR RADAR BACKSCATTER CAN DIFFERENTIATE SOME OIL CHARACTERISTICS WITHINTHE SLICK. 16 km N (iii) (i) (i) (iii) (ii) DWH rig site wind (iv) (ii) (iv) C. Jones, B. Holt, S. Hensley (JPL/Caltech) Photos taken over the slick on 6/23/2010 B. Minchew (Caltech), Studies of the Deepwater N between 16:00 and 20:00 UTC (NOAA Horizon Oil Spill with the UAVSAR Radar, RAT-Helo and EPA/ASPECT) submitted to AGU monographs windIGARSS 2011, 25-29 July 2011, Vancouver, Canada Cathleen Jones (Jet Propulsion Laboratory) 13
  14. 14. CLOUDE-POTTIER DECOMPOSITION WEATHERED OIL IN BARATARIA BAY 22 km Large amounts of oil moved far into Barataria Bay in SE Louisiana on 16-17 June 2010, with oil remaining in the area until after the UAVSAR over- flight. Weathered oil in the interior of Barataria Bay shows a significantly higher entropy than oil around the rig site or in the Gulf of Mexico approaching the Louisiana shoreline.C. Jones, B. Holt, S. Hensley (JPL/Caltech), B. Minchew (Caltech), Studies of the Deepwater Horizon Oil Spill with the UAVSAR Radar, submitted to AGU monographsIGARSS 2011, 25-29 July 2011, Vancouver, Canada Cathleen Jones (Jet Propulsion Laboratory) 14
  15. 15. CONCLUSIONS•  Radar returns of all polarizations discriminate oil in the DWH slick from clean water in an adjacent area, for incidence angles from 26° to 65°.•  The HV returns showed greatest sensitivity to variations in the oil within the slick, although low signal level limited its usefulness to incidence angles <~60° for UAVSAR.•  Both the CP and Shannon polarimetric decompositions can be used to discriminate oil from clean water.•  The CP averaged intensity and Shannon intensity are the best discriminators across the entire incidence angle range, but the other polarimetric parameters also have regions where they show a statistically significant difference between oil and clean water and between different areas of oil with the slick itself.•  The Shannon entropy decomposition is a useful, computationally efficient algorithm for oil slick detection.•  The entropy of relatively fresh oil-on-water within the main DWH slick is significantly lower than for the weathered oil in Barataria Bay.•  UAVSAR results indicate that it could be possible to discriminate varying oil properties within slicks under all-weather conditions given a sufficiently low noise radar instrument.IGARSS 2011, 25-29 July 2011, Vancouver, Canada Cathleen Jones (Jet Propulsion Laboratory) 15
  16. 16. Back-up SlidesCathleen Jones1, Brent Minchew2, Benjamin Holt11JetPropulsion Laboratory/California Institute of Technology 2California Institute of Technology
  17. 17. UAVSAR INSTRUMENT NOISE FLOOR Comparison with other RADAR instruments UAVSAR NOISE FLOOR noise equivalent σ0 (dB) The low noise floor of the UAVSAR instrument makes it possible to measure the radar cross section from water with an L-band radar, even with oil damping the surface waves. We find that the instrument noise floor is reached only at the far edge of the swath for the HV returns from oil.C. Jones, B. Holt, S. Hensley (JPL/Caltech), B. Minchew (Caltech), Studies of the Deepwater Horizon Oil Spill with the UAVSAR Radar, submitted to AGU monographsIGARSS 2011, 25-29 July 2011, Vancouver, Canada Cathleen Jones (Jet Propulsion Laboratory) 17

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