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,

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

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