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Ocean Remote Sensing Using Lasers

European Association of Remote Sensing Laboratories Association Européenne de Laboratoires de Télédétection. Ocean Remote Sensing Using Lasers. Topics: The principles Bathymetry Water column parameters Pollution survey Lidar in space?. Dubrovnik, Croatia, 27 May 2004. wavelength.

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Ocean Remote Sensing Using Lasers

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  1. European Association of Remote Sensing Laboratories Association Européenne de Laboratoires de Télédétection Ocean Remote Sensing Using Lasers • Topics: • The principles • Bathymetry • Water column parameters • Pollution survey • Lidar in space? Dubrovnik, Croatia, 27 May 2004

  2. wavelength wave-number spectralrange photonenergy frequency The electromagnetic spectrum  rays x rays LightdetectionandrangingLidar UV VIS IR micro-waves water is transparent org. matter is absorbing RadiodetectionandrangingRadar Radar FM AM radio waves 1. The principles

  3. Lidar in the atmosphere • Range resolution zfromwith c speed of light Australian Antarctic Divisionhttp://www.antdiv.gov.au 1. The principles Oceanic Lidar • Light sources with short pulses nanosecond pulse lasers • Time-resolved signal detection GHz bandwidth detectors What can be measured? • Water depth from seabottom reflection • substances at the water surface and underwater from backscatter and fluorescence

  4. Lidar equation for receiver power P(z): opt. filter detector telescope laser flight altitude H • A homogeneous water column: c=const., =const. z = 0 water: substances: m: refractive index concentration n c=cex+cemattenuation coeff. efficiency  water depth z seafloor 1. The principles Oceanic Lidar

  5. Optech Inc., Canada Scanning with laser pulses andregistration of induced signals 2. Bathymetry: water depth sounding Motivation: • Nautical charts are often based on very old data • Until 1997:almost no acoustic data used • Since 2002:approx. 2500 Gbyte/year of acoustic imagery data • Nearshore charting with lidar has become fast and reliable

  6. Optech Inc., Canada Scanning with laser pulses andregistration of induced signals 2. Bathymetry: water depth sounding Method: Signal echo versus time-of-flightof elastic backscattered light sea surface:IR laser pulse(=1064 nm) seafloor: green laser pulse (= 532 nm)

  7. G. Guenther et al., 2000 Optech Inc., Canada Scanning with laser pulses andregistration of induced signals 2. Bathymetry: water depth sounding • Signal response function: • Surface return • Bottom return • Signals from the water column

  8. Chart based on 5 overlapping flight tracks G. Guenther et al., 2000 2. Bathymetry: water depth sounding

  9. Solander Island, New Zealand Surveying underwater pinnacles Optech Inc., Canada 2. Bathymetry: water depth sounding

  10. sunken cargo vessel3 m below sea surface Baltic Sea,water depth 25 m Swedish Maritime Administration 2. Bathymetry: water depth sounding

  11. Looe Key, Florida Channel through a coral reef Optech Inc., Canada 2. Bathymetry: water depth sounding

  12. digital underwater elevation model Looe Key, Florida Optech Inc., Canada 2. Bathymetry: water depth sounding Channel through a coral reef

  13. 2. Bathymetry: water depth sounding Bathymetric Lidar Performance Example: Shoals 1000 Int. Hydrographic Associationrequirements for nautical charting Challenges • Further reading: • http://www.optech.on.ca • G. Guenther et al., EARSeL eProceedings 1, 2001http://las.physik.uni-oldenburg.de/eProceedings/vol01_1/01_1_guenther1.pdf

  14. 1.00 ex= 270 nm 0.50 H2O Raman scattering depth profiles of substances 0.20 • fluorescence fluorescence, typically of North Sea water proteins Gelbstoffe plankton pigments 0.10 pure water absorption coefficient /m-1 0.05 proteins • Raman scattering Gelbstoffe 0.02 attenuation Chlorophyll 0.01 300 400 500 600 700 wavelength /nm 3. Water column parameters Method: Signal echo versus time-of-flightat higher wavelengths

  15. singlet state S1 singlet state S1 triplet state T1 energy energy : 1 ns ... 10 µs  > 1 ms singlet state So singlet state So distance of nuclei distance of nuclei 3. Water column parameters Fluorescence spectra do not depend on excitation wavelength! Fluorescence of molecules fluorescence relaxation absorption phosphorescence intersystem crossing absorption relaxation

  16. 3. Water column parameters Raman spectra preserve the vibrational energy E! Molecular scattering Stokes shift anti-Stokes shift elastic Rayleigh scattering Raman scattering Raman scattering

  17. O O O H H H H H H arb. intensity arb. intensity 3000 3400 3800 /nm 3. Water column parameters Water Raman scattering: free molecules: liquid water: From: Schröder M et al., Applied Optics 42(21), 4244-4260, 2003

  18. water Raman scattering • fluorescence • fluorescence normalised to Raman scattering 3. Water column parameters The lidar equation

  19. R/V Polarstern 3. Water column parameters Onboard ship From: Ohm K et al., EARSeL Yearbook 1997. Paris, 1998

  20. Chlorophyll vs. depthin the Antarctic Ocean 1.00 ex= 270 nm 0.50 H2O Raman scattering 0.2 pure water absorption coefficient /m-1 0.10 fluorescence, typically of North Sea water 0.05 proteins arb. units Gelbstoffe 0.02 Chlorophyll 0.01 300 400 500 600 700 wavelength /nm 3. Water column parameters Onboard ship From: Ohm K et al., EARSeL Yearbook 1997. Paris, 1998

  21. 3. Water column parameters Onboard ship Depth Profiling Fluorescence Lidar Performance: Challenges:

  22. Measured signal: instrument response function where: ideal signal ideal signal signal with 0.1% noise, Richardson-Lucy algorithm measured signal signal with 0.1% noise, Fourier Transformation 3. Water column parameters Lidar signal deconvolution From: Harsdorf & Reuter, EARSeL eProceedings 1, 2001

  23. 1983 3. Water column parameters Airborne • depth profilingat nighttime • depth integratingin daylight

  24. Tidal fronts UV attenuationex 308 - em 344 VIS attenuationex 450 - em 533 gelbstoff flu.ex 308 - em 366 chlorophyll flu.ex 450 - em 685 3. Water column parameters Airborne From: Reuter R et al., Int J Remote Sensing, 14: 823-848, 1993

  25. Tidal fronts gelbstoff fluorescenceex 308 – em 360 3. Water column parameters Airborne From: Reuter R et al., Int J Remote Sensing, 14: 823-848, 1993

  26. Canary Islands: wind-induced upwelling trade winds 3. Water column parameters blue:Gelbstoffe bleached by UV red:Gelbstoffe broughtto the sea surface by upwelling From: Milchers et al., 3rd Workshop Lidar Remote Sensing of Land and Sea, EARSeL, 1997

  27. to do: 4. Pollution monitoring

  28. 1.00 ex= 270 nm 0.50 H2O Raman scattering 0.2 fluorescence, typically of North Sea water 0.10 pure water absorption coefficient /m-1 0.05 proteins Gelbstoffe 0.02 Chlorophyll 0.01 300 400 500 600 700 wavelength /nm 4. Pollution monitoring Methods: 1. signal loss of water Raman scatter

  29. Intensity Diesel Agrill Gasoline Reformat Auk 300 350 400 450 500 550 600 650 700 Brent wavelength /nm crude oils refined oils 250 600 500 200 400 150 Intensity Intensity 300 100 200 50 100 0 0 300 400 500 600 700 300 400 500 600 700 wavelength /nm wavelength /nm 4. Pollution monitoring Methods: 1. signal loss of water Raman scatter 2. the fluorescence signature From: Hengstermann T & R Reuter, EARSeL Adv Rem Sens, 1, 52-60, 1992

  30. Airborne maritime surveillance 4. Pollution monitoring approx. 30 litres very light crude

  31. 3+4. Airborne Fluorescence Lidar Performance Challenges

  32. 5. Lidar in space? Rationale: • Measures Gelbstoff in the open ocean • No ambiguity in coastal waters • Verifies oil spillsin SAR images Possibly an add-onto atmospheric lidars

  33. 5. Lidar in space? Atmospheric lidars: LITE http://www-lite.larc.nasa.gov/ http://www-lite.larc.nasa.gov/

  34. 5. Lidar in space?

  35. Flight from the Atlantic (left) over the Sahara (centre, right) 5. Lidar in space? Atmospheric lidars: LITE http://www-lite.larc.nasa.gov/

  36. 5. Lidar in space? Atmospheric lidars: WALES (Water vApour Lidar Experiment in Space) ESA Living Planet Programme, 2008-2010 http://www.esa.int/esaLP/ASE77YNW9SC_wales_0.html

  37. 5. Lidar in space? Radiative transfer simulation From: Bartsch B et al, Applied Optics, 32, 6732-6741, 1993

  38. 5. Lidar in space? Radiative transfer simulation From: Bartsch B et al, Applied Optics, 32, 6732-6741, 1993

  39. 5. Lidar in space? Radiative transfer simulation From: Bartsch B et al, Applied Optics, 32, 6732-6741, 1993

  40. 5. Lidar in space? Radiative transfer simulation From: Bartsch B et al, Applied Optics, 32, 6732-6741, 1993

  41. 5. Lidar in space? Radiative transfer simulation From: Bartsch B et al, Applied Optics, 32, 6732-6741, 1993

  42. Further reading: • Measures RM: Laser remote sensing.John Wiley & Sons, New York (1984) • Kirk JTO: Light and photosynthesis in aquatic ecosystems.Cambridge University Press, 2nd ed. (1994) • Mobley CD: Light and water.Academic Press (1994) • Ishimaru A: Wave propagation and scattering in random media.Vol. 1 +2. Academic Press (1978) • Andrews LC & RL Phillips: Laser beam propagation throughrandom media. SPIE (1998) • Various papers from many lidar research groups in EARSeL eProceedingshttp://las.physik.uni-oldenburg.de/eProceedings/

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