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Ocean Remote Sensing Using Lasers

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1 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

2 Light detection and ranging Lidar
1. The principles water is transparent org. matter is absorbing The electromagnetic spectrum frequency spectral range photon energy wavelength wave- number  rays x rays UV VIS IR micro- waves Radar FM AM radio waves Light detection and ranging Lidar Radio detection and ranging Radar

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

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

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

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

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

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

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

10 2. Bathymetry: water depth sounding
sunken cargo vessel 3 m below sea surface Baltic Sea, water depth 25 m Swedish Maritime Administration

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

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

13 2. Bathymetry: water depth sounding
Maximum depth 60 m Vertical accuracy ± 0.15 m Horizontal accuracy ±3 m (DGPS) Pixel distance 8 m Operating altitude 400 m Scan swath width 220 m Operating speed 70 m/s Bathymetric Lidar Performance Example: Shoals 1000 Int. Hydrographic Association requirements for nautical charting Vertical accuracy ± 0.25 m Small object detection 111 m3 Small object detection/identification Seafloor classification (sand, mud, gravel, stones, vegetation) Land-water discrimination Near-shore applicability (waves, foam) Safe navigation (shoreline, anchorage, wrecks) Challenges Further reading: G. Guenther et al., EARSeL eProceedings 1, 2001

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

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

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

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

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

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

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

21 3. Water column parameters
Onboard ship Depth Profiling Fluorescence Lidar Performance: Underway measurements Maximum depth Chlorophyll 20 m Gelbstoffe 40 m Water Raman Elastic backscatter 60 m Vertical accuracy ± 0.15 m Challenges: Maximum depth: Open ocean 100 m Coastal waters m Temperature, salinity Underwater imaging Lidar signal deconvolution

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

23 3. Water column parameters
Airborne 1983 depth profiling at nighttime depth integrating in daylight

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

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

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

27 4. Pollution monitoring to do:

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

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

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

31 3+4. Airborne Depth resolving 40 m Nighttime only Maximum depth 20 m
Integrating upper 2-10 m Parameters chlorophyll µg/l Gelbstoffe coastal conc. mineral particles mg/l attenuation coeff. c < 10 m-1 oil film thickness µm oil type classes certain chemicals Fluorescence Lidar Performance Challenges Reliable, compact, transportable Affordable Data fusion with other sensor data

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

33 5. Lidar in space? Atmospheric lidars: LITE

34

35 5. Lidar in space?

36 5. Lidar in space? Atmospheric lidars: LITE Flight from the Atlantic (left) over the Sahara (centre, right)

37 5. Lidar in space? Atmospheric lidars: WALES (Water vApour Lidar Experiment in Space) ESA Living Planet Programme,

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

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

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

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

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

43 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 Academic Press (1978) Andrews LC & RL Phillips: Laser beam propagation through random media. SPIE (1998) Various papers from many lidar research groups in EARSeL eProceedings


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