Transcript The use of in situ, laboratory and airborne measurements to

The use of in situ, laboratory and airborne
measurements to estimate the chlorophyll-a
concentration in the St. Lawrence River
Yushan Zhu
Vodacek Anthony
Michael Twiss
Center for Imaging Science
Digital Imaging and Remote Sensing Lab
Rochester Institute of Technology
04/05/2006
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Digital Imaging and Remote Sensing Laboratory
Outline
• In situ measurements: HOBI Labs HydroRad4(RIT), bbe FluoroProbe 2 (Clarkson
University)
• Field collected water sample was analyzed in
lab by spectrophotometer (Cary 500)
• Airborne image was taken at the same time by
MISI
• Summary
• Further studies
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Study Area – St. Lawrence River
• Block section of St. Lawrence
north of Wilson Hill Island:
44°53.425 to 44°54.484
75°06.870 to 75°06.873
• Time: July 21, 2005
• Yellow points: HydroRad-4
• Red points: bbe fluoroprobe
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MISI image after MNF
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HydroRad-4
•HydroRad-4 is a versatile system for in-situ radiometric measurements
constructed from four Ocean Optics spectrometer
•2048 pixels ; wavelength from: 350nm~700nm; spectral resolution 3.0nm
•The four sensors are used as two pairs
•This method of deployment was effective for determine the scalar irradiance,
net irradiance, and average cosine
•Approximately total absorption can also be derived using Gershun’s
equation
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HydroRad-4
A
B
1
1
AOP : A : ( E 01  Ez1 ), C : ( E 02  E z 2 )
2
2
1
1
B : ( E 01  Ez1 ), D : ( E 02  Ez 2 )
2
2
E01  A  B, Ez1  A  B
E02  C  D,
D
C
Ez 2  C  D
average cos ine :   Ez / E0
diffuse attenuation :
1 dEd
downwelling irradiance : K d  
Ed dz
net irradiance : K E  
IOP : a  K E  
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E z1  E z 2
1 dEz
1

Ez dz 2( Ez1  Ez 2 ) z1  z 2
1+cos - collector
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Example of measurements by HydroRad-4
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bbe FluoroProbe 2 (Clarkson University)
• Highly sensitive measuring instrument
for in situ chlorophyll analysis
• Algae differentiation uses 5 LEDs for
fluorescence excitation. (450, 525, 570,
590, 610nm)
• Give the concentration for different
type of algae: green algae, bluegreen
algae, diatoms, and cryptophyta
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Laboratory measured parameters from water
samples
The field collected water samples were
analyzed in lab to get following results
1. Total Suspended Solids (TSS)
2. Colored Dissolved Organic Matter
absorption (CDOM)
3. Particle and pigment absorption
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TSS
TSS
• TSS: 1L water sample
filter through GF/F glassfiber filter (0.2 µm);
weight the difference of
GF/F filter
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Station
Pre Weight
after filtering
Difference
tss(g/m3)
10
0.1339
0.135
0.0011
1.1
9
0.1317
0.1325
0.0008
0.8
8
0.1308
0.1315
0.0007
0.7
7
0.1306
0.1318
0.0012
1.2
6
0.1314
0.1318
0.0004
0.4
5
0.1344
0.135
0.0006
0.6
4
0.1334
0.1341
0.0007
0.7
3
0.1327
0.1337
0.001
1
2
0.132
0.133
0.001
1
1
0.1345
0.1351
0.0006
0.6
Digital Imaging and Remote Sensing Laboratory
Cary spectrometer
• Absorption can be measured by Cary 500
• Typical of high performance laboratory spectrometers
range from UV to NIR
• It has a dual-beam design: The instrument alternately
measures the spectral radiance from a reference
material and from the sample material of interest
• The instrument uses a common light source,
monochromators, and detector for both beams. A
chopper wheel controls which beam the detector is
viewing during the measurement cycle
• The spectral transmission of a material can be
determined by the two measured beams
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CDOM absorption
•
Use two 10cm length cuvettes, one with pure water and the
other with filtered sample water through GF/F and membrane
(0.2um) filter. When the same light beam penetrated two cell,
the difference tells the CDOM absorption
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Digital Imaging and Remote Sensing Laboratory
Particle and pigment absorption
• A pair of filters is used: one is wetted with pure water as a
reference; the other is filtered with sample water. The difference
of the two filters can tell the optical density of concentrated
cultures
• After the sample filter is washed by MeOH, the pigment will
extracted out and the difference now is only about particle
absorption
• Absorption spectra measured for aquatic particles concentrated
onto glass-fiber filters require a correction for increase in path
length caused by multiple scattering in the glass-fiber filter
ODsusp ( )  0.378ODfilt ( )  0.523OD2 filt ( )
 p ( ) 
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2.3ODsusp ( )
(V / A)
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Particle and pigment absorption
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Compare the results of in situ and laboratory
measurements
The absorption obtained from in situ measurements
(HydroRad – 4) can tell the information about the CHL
concentration well
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Modular Imaging Spectrometer Instrument MISI
• MISI is designed by Digital Imaging and Remote
Sensing Group at RIT
• Line scanner: scanner mirror spinning to project
the image of the detector along a line on the
ground perpendicular to the aircraft ground track
• High spatial resolution: 1.0 m GIFOV at 1km of
altitude
• High spectral resolution: two separate 36channel spectrometers to cover the spectrum
from 440nm to 1020nm in 10nm spectral bands.
• Procedure: Raw Data -> oversampling
correction, roll compensation -> glint remove ->
spectral, radiometric calibration -> atmosphere
calibration
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MISI Images (before and after deglint)
• The reflection of solar
radiation on non-flat water
surfaces is a serious
problem for the image.
• The wave and glint patterns
can clearly see from the left
image
• In order to eliminate most of
the glint patterns, deglint
algorithm is applied
• After deglint, the image is
more smooth, eliminate most
of the information from sun
glint, and get more
information about water itself
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Sun glint remove algorithm
• Since water is relatively opaque to
NIR wavelength, which mean it has
maximum absorption and minimal
water leaving radiance
• The amount of sun glint in the
visible bands is linearly related to
the brightness in the NIR band
because the real index of
refraction is nearly equal for NIR
and visible wavelength
• The amount of light reflected from
the water surface in the NIR is
good indicator of the amount of
light that will be reflected in visible
wavelengths
• Regions of the image are selected
where a range of sun glint is
Ri 
evident
• Algorithm by J.D.Hedley
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Ri  S i ( RNIR  MinNIR )
Digital Imaging and Remote Sensing Laboratory
Different TSS, CDOM, CHL concentration
simulated by HydroLight
4.00E-02
3.50E-02
3.00E-02
2.50E-02
2.00E-02
1.50E-02
1.00E-02
5.00E-03
0.00E+00
400
chl=1
chl=10
chl=40
500
600
700
800
Wavelength,nm
Rsr with different CHL, CDOM, TSS (Case II)
4.00E-02
Remote Sensing Reflectance
• Hydrolight: radiative
transfer numerical model
that computes radiance
distributions and derived
quantities for natural
water bodies.
• The Chl-a has strong
absorption of blue light
between 400nm and
500nm and red light at
approximately 680nm
Reflectance
Rsr with different CHL, CDOM, TSS (Case I)
3.50E-02
3.00E-02
chl=1 low CDOM,tss
2.50E-02
2.00E-02
chl=10 low CDOM,tss
chl=50 low CDOM,tss
1.50E-02
chl=10 high CDOM,tss
1.00E-02
chl = 1 high CDOM,tss
5.00E-03
0.00E+00
-5.00E-03400
500
600
700
800
Wavelength
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Summary
• The apparent and inherent optical properties
of the St. Lawrence river were obtained using
in situ and laboratory measurements
• The average concentrations of Chl-a and TSS
are 1ug/l and 1mg/l. CDOM absorption is only
about 0.1 at 440nm
• Chl-a concentration can’t be mapped by
airborne image for now because of the less
variance of Chl-a, TSS, and CDOM
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Further studies
• Continue field studies in this summer, more
measurements will be done for different water
samples which have more concentration
ranges for Chl, TSS, and CDOM
• Suitable Chl concentration estimation
algorithms for coastal and inland waters need
to develop using MISI data
• Then algal growth model output can be
compared with these chlorophyll map derived
from MISI to validate and calibrate the models.
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?
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