ocean remote sensing using lasers topics: 1.the principles 2.bathymetry 3.water column parameters...

Ocean Remote Sensing Using LasersOcean Remote Sensing Using Lasers

Topics:1. The principles2. Bathymetry3. Water column parameters4. Pollution survey 5. Lidar in space?

European Association of Remote Sensing LaboratoriesAssociation Européenne de Laboratoires de Télédétection

Dubrovnik, Croatia, 27 May 2004

Ocean Remote Sensing Using Lasers

1. The principles

The electromagnetic spectrum

frequencyspectralrange

photonenergy wavelength

wave-number

rays

x rays

UV

VIS

IR

micro-waves

Radar FM

AM

radio waves

Radio detection and ranging

Radar

Light detection and ranging

Lidar

water is transparentorg. matter is absorbing


1. The principles

Range resolution z from

with c speed of light

2

ΔΔ

tcz

What can be measured?

Water depthfrom seabottom reflection

substances at the water surface and underwater

from backscatterand fluorescenceAustralian Antarctic Division

http://www.antdiv.gov.au

Lidar in the atmosphere

Oceanic Lidar

Light sources with short pulses nanosecond pulse lasers

Time-resolved signal detection GHz bandwidth detectors


1. The principles

z

ozzc

emHz

nzP

'd)'(

2~)(

Lidar equation for receiver power P(z):

substances:concentration nefficiency

water:m: refractive indexc=cex+cem attenuation coeff.

tele

sc

op

eopt. filter

detector

laser

seafloor

z = 0

water depth z

flight altitude H

Oceanic Lidar

cH

nP

1~

2

A homogeneous water column: c=const., =const.


2. Bathymetry: water depth sounding

Scanning with laser pulses andregistration of induced signals

Optech Inc., Canada

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

Motivation:



Optech Inc., Canada


Signal echo versus time-of-flightof elastic backscattered light

sea surface: IR laser pulse (=1064 nm)

seafloor: green laser pulse (= 532 nm)

Method:



Optech Inc., Canada

G. Guenther et al., 2000


Signal response function:

Surface return

Bottom return

Signals from the water column



G. Guenther et al., 2000

Chart based on 5 overlapping flight tracks



Solander Island, New Zealand

Optech Inc., Canada

Surveying underwater pinnacles



sunken cargo vessel3 m below sea surface

Baltic Sea,water depth 25 m

Swedish Maritime Administration



Looe Key, Florida

Optech Inc., Canada

Channel through a coral reef


Looe Key, Florida

digital underwater elevation model

Optech Inc., Canada


Channel through a coral reef



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 Associationrequirements for nautical charting


Small object detection 111 m3

Small object detection/identification

Seafloor classification (sand, mud, gravel, stones, vegetation)Land-water discriminationNear-shore applicability (waves, foam)Safe navigation (shoreline, anchorage, wrecks)

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


300 400 500 600 700wavelength /nm

1.00

0.10

0.50

0.05

0.01

H2O Raman scattering

proteinsGelbstoffe

Chlorophyll pu

re w

ater

ab

sorp

tio

n c

oef

fici

ent

/m-1

0.02

0.20

fl

uo

resc

ence

, typ

ical

ly o

f N

ort

h S

ea w

ater ex= 270 nm

Signal echo versus time-of-flightat higher wavelengths

attenuation

Raman scattering

3. Water column parameters

fluorescence

proteins Gelbstoffe plankton pigments

Method:

depth profiles of substances



Fluorescence of molecules

distance of nuclei

ener

gy

singlet state So

singlet state S1

distance of nuclei

ener

gy

singlet state So

singlet state S1

triplet state T1

phosphorescence

> 1 ms

relaxation

: 1 ns ... 10 µs

fluorescenceabsorption absorptionrelaxation

Fluorescence spectra do not depend on excitation wavelength!

intersystem crossing



Molecular scattering

EΔ

1h2h

a

bc

d

1h1h

a

bc

d

1h3h

EΔa

bc

d

elastic Stokes shift anti-Stokes shift

Rayleigh scattering Raman scattering Raman scattering

Ehh Δ12 Ehh Δ12

Raman spectra preserve the vibrational energy E!


arb

. in

ten

sit

y

/nm


Water Raman scattering: O

HHO

HHO

HH-1cm3756~ -1cm3657~

-1cm3400~

-1cm1595~ free molecules:liquid water:

34003000 3800 1cm/~

arb

. in

ten

sit

y

-1cm400~Δ

From: Schröder M et al., Applied Optics 42(21), 4244-4260, 2003



The lidar equation

cH

nP

RamanRaman

1~

2OH2

water Raman scattering

fluorescence cH

nPfluor

1~

2fluorfluor

fluorescence normalised to Raman scattering fluorfluor~ n

P

P

Raman

fluor

cPRaman

1~



Onboard ship

laser receiver

t ttt

R/V Polarstern

Nd:YAG

keel

hull

valve

quartz window

receiver unit

telescopelaser

pump

From: Ohm K et al., EARSeL Yearbook 1997. Paris, 1998



300 400 500 600 700wavelength /nm

1.00

0.10

0.50

0.05

0.01


proteins

Gelbstoffe

Chlorophyll pu

re w

ater

ab

sorp

tio

n c

oef

fici

ent

/m-1

0.02

0.2

fl

uo

res

ce

nc

e,

typ

ica

lly

of

No

rth

Se

a w

ate

r

ex= 270 nm

Chlorophyll vs. depthin the Antarctic Ocean

arb. units

Onboard ship

From: Ohm K et al., EARSeL Yearbook 1997. Paris, 1998


Depth Profiling Fluorescence Lidar Performance:

Maximum depth:

Open ocean 100 m

Coastal waters 10..20 m

Temperature, salinity

Underwater imaging

Lidar signal deconvolution

Challenges:


Underway measurements

Maximum depth

Chlorophyll 20 m

Gelbstoffe 40 m

Water Raman 40 m

Elastic backscatter 60 m


Onboard ship



Lidar signal deconvolution

)()('d)'()'()( tPtRttPttRtP

Measured signal:

where:

)(tP

)(tR instrument response function

ideal signal

ideal signal measured signal signal with 0.1% noise, Fourier Transformation

signal with 0.1% noise, Richardson-Lucy algorithm

From: Harsdorf & Reuter, EARSeL eProceedings 1, 2001



Airborne

1983

depth profilingat nighttime

depth integratingin daylight


Tidal fronts

UV attenuationex 308 - em 344

VIS attenuation ex 450 - em 533

gelbstoff flu.ex 308 - em 366

chlorophyll flu.ex 450 - em 685


Airborne

From: Reuter R et al., Int J Remote Sensing, 14: 823-848, 1993



Tidal fronts

Airborne

gelb

stof

f flu

ores

cenc

eex

308

– e

m 3

60

From: Reuter R et al., Int J Remote Sensing, 14: 823-848, 1993


red:Gelbstoffe broughtto the sea surface by upwelling


Canary Islands: wind-induced upwelling

trade

win

ds

blue:Gelbstoffe bleached by UV

From: Milchers et al., 3rd Workshop Lidar Remote Sensing of Land and Sea, EARSeL, 1997


4. Pollution monitoring

to do:


300 400 500 600 700wavelength /nm

1.00

0.10

0.50

0.05

0.01


proteinsGelbstoffe

Chlorophyll pu

re w

ater

ab

sorp

tio

n c

oef

fici

ent

/m-1

0.02

0.2

fl

uo

resc

ence

, typ

ical

ly o

f N

ort

h S

ea w

ater ex= 270 nm1. signal loss of

water Raman scatter

Methods:



wavelength /nm300 350 400 450 500 700550 650600

Inte

nsity

crude oils

700

0

50

100

150

200

250

wavelength /nm 300 400 500 600

AgrillAukBrent

Inte

nsity

refined oils

wavelength /nm

0

100

200

300

400

500

600

300 400 500 600 700

DieselGasolineReformat

Inte

nsity

1. signal loss of water Raman scatter

Methods:

2. the fluorescence signature


From: Hengstermann T & R Reuter, EARSeL Adv Rem Sens, 1, 52-60, 1992


Airborne maritime surveillance


approx. 30 litresvery light crude


3+4. Airborne

Depth resolving40 m

Nighttime onlyMaximum depth 20 m

Integrating upper 2-10 m

Parameters

chlorophyll 0.1-100 µg/l

Gelbstoffe coastal conc.

mineral particles 0.1-10 mg/l

attenuation coeff. c < 10 m-1

oil film thickness 0.1-10 µm

oil type 5...10 classes

certain chemicals

Fluorescence Lidar Performance

Challenges Reliable, compact, transportable

Affordable

Data fusion with other sensor data


5. Lidar in space?

v = 7.7 km/slower earth orbit

stratospheric aerosolsand ozone layer

ocean surface with fluorescent substance

Rationale:

Measures Gelbstoff

in the open ocean No ambiguity in

coastal waters Verifies oil spills

in SAR images Possibly an add-onto atmospheric lidars


5. Lidar in space?

Atmospheric lidars: LITE http://www-lite.larc.nasa.gov/

http://www-lite.larc.nasa.gov/


5. Lidar in space?


5. Lidar in space?

Atmospheric lidars: LITE http://www-lite.larc.nasa.gov/

Flight from the Atlantic (left) over the Sahara (centre, right)


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


5. Lidar in space?

Radiative transfer simulation

From: Bartsch B et al, Applied Optics, 32, 6732-6741, 1993


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/

Further reading:

ocean remote sensing using lasers topics: 1.the principles 2.bathymetry 3.water column parameters...

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