chlorophyll estimation using multi-spectral reflectance and height sensing c. l. jonesresearch...
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![Page 1: Chlorophyll Estimation Using Multi-spectral Reflectance and Height Sensing C. L. JonesResearch Engineer N. O. Maness Professor M. L. Stone Regents’ Professor](https://reader038.vdocument.in/reader038/viewer/2022110320/56649ca45503460f94965067/html5/thumbnails/1.jpg)
Chlorophyll Estimation Using Multi-spectral
Reflectance and Height Sensing
C. L. Jones Research Engineer N. O. Maness Professor M. L. Stone Regents’ ProfessorR. Jayasekara Research Engineer
2004 ASAE/CSAE Annual International Meeting
Paper Number: 043081
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Objectives
• Select “best” wavelength or indices for estimating chlorophyll content and concentration in spinach• Non-destructively quantify chlorophyll content and concentration by combining biomass estimates
with multi-spectral imaging system reflectance data.• Assess the feasibility of reflectance-based sensing in estimating chlorophyll concentration in
spinach
Paper Number: 043081
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Let’s Talk Chlorophyll…(Content vs. Concentration)
• Content: related to nitrogen concentration in green vegetation
• Chlorophyll mass per unit ground surface area or per plant (mg/ha or mg/plant)
• Indicator of photosynthetic capacity: productivity of the plant canopy
Paper Number: 043081
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Let’s Talk Chlorophyll…(Content vs. Concentration)
• Concentration: estimate of pigment concentration – chlorophyll a and b
• Chlorophyll mass per unit mass of plant material (mg/kg)
• Indicator of plant physiological status: level of stress
Paper Number: 043081
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Previous Work
No single spectral approach offers an adequate method of estimating pigment (chlorophyll) concentration in all plants.
Paper Number: 043081
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Experimental Plan• Consider spinach plants at the single plant level
• Use chlorophyll content estimates to determine chlorophyll concentration (implies a need for biomass estimate)
• Ccontent (mg) = Cconcentration (mg/kg) x biomass (kg)
• Use ultrasound and digital imagery for biomass estimate
Paper Number: 043081
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Experimental PlanEstimators used for chlorophyll content investigation:
– Rgreen : Reflectance at 550 nm ±10 nm
– Rred : Reflectance at 670 nm ±10 nm
– RNIR : Reflectance at 780 nm ±10 nm
– NIR/RED : Ratio of reflectance at 780 and 670 nm ±10 nm
– NIR/GREEN : Ratio of reflectance at 780 and 550 ±10 nm
– NDVI670 = (R780 – R670)/(R780 + R670)
– NDVI550 = (R780 – R550)/(R780 + R550)
Paper Number: 043081
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Plant SamplesTwo flats- no fertilizer
Two flats adequate fertilizer
Two flats 2x adequate fertilizer amount
Provided varying biomass and chlorophyll levels
Sampled at six weeks post plant
Paper Number: 043081
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Data Gathering Overview
• Plants removed from flats
• Individually placed on turntable (0.91 m diameter) 1.04 m below ultrasonic distance sensor (UDS) for height estimation
• Turntable rotating at 1.06 rpm
Paper Number: 043081
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Data Gathering Overview• Plants placed under multispectral
camera mounted on tripod for reflectance data and top view surface area estimate
• Vegetative portion harvested, weighed, and packed on ice for transport to lab
• Chlorophyll analysis per Inskeep and Bloom (1985)
Paper Number: 043081
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Ultrasonic Distance Sensor (UDS)
Senix™ Ultra-SPA.(Senix, Bristol, Virginia)• 50 kHz, piezoelectric• 12 degree angle view, signal > 3db• Accuracy: better than 1% of target
distance• Laptop computer• SoftSpan© software
Paper Number: 043081
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UDS Response
Paper Number: 043081
Spinach Height Profile - Ultrasound
0 2 4 6 8
10 12 14 16 18
1.37 2.74 4.11 5.49 6.86 8.23 9.6 11 12.3 13.7 15.1 16.5 17.8 19.2 Range, cm
He
igh
t,cm
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Multispectral Camera• DuncanTech MS3100• 550, 670, 780 nm ±10 nm FWHM• Resolution: 1392 x 1040 x 3 sensors• Pixel size: 4.65 x 4.65 microns• 14mm focal length lens• RS232 interface with National Instrument’s
PCI-1424 frame grabber• Dolch ruggedized laptop
Paper Number: 043081
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Multispectral Camera
• Mounted on tripod 1 m above target• Target illuminated with incandescent lighting• Labsphere Reflectance Calibration Standard
targets: 10%, 50%, 75%, and 99% (Weckler, et al. 2002)
Paper Number: 043081
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Multispectral Camera• Images processed with Matlab©
• NIR, green, and red reflectance pixel values identified
• > 0 : plant material, < 0 : background, nonplant material, NDVI averaged
• Image binarized• “bwarea” command to calculate vegetation area
Paper Number: 043081
NIR Green or Red
NIR Green or Red
ρ - ρNDVI =
ρ +ρ
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Biomass Estimation
PWC = 0.86
Paper Number: 043081
WEST = AMS x HUDS
Where: WEST = estimated plant biomass
AMS = surface area estimate from camera (pixels)
HUDS = estimated plant height from UDS (cm)
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Biomass Estimation
PWC = 0.86
Paper Number: 043081
W = 3E-05W EST + 2.0958
r 2 = 0.884
0
5
10
15
20
25
30
35
0.00E+00 2.00E+05 4.00E+05 6.00E+05 8.00E+05 1.00E+06 1.20E+06 Estimated Biomass (WEST), H UDS * A MS
Act
ual
Bio
mas
s (W
), g
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Chlorophyll Content Estimation, r2
Paper Number: 043081
Estimator Ccontent vs. estimator
Rgreen0.21
Rred 0.10
RNIR 0.58
NIR/RED 0.15
NIR/GREEN 0.05
NDVI670 0.75
NDVI550 0.40
C CONT = 1364.5NDVI - 370.41
r 2 = 0.75
0
50
100
150
200
250
300
0 0.1 0.2 0.3 0.4 0.5 NDVI
Ch
l. C
on
ten
t, m
g/p
lan
t
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Chlorophyll Content Estimation, r2
Paper Number: 043081
Estimator Ccontent vs. estimator
Ccontent vs. estimator * WEST
Rgreen0.21 0.87
Rred 0.10 0.86
RNIR 0.58 0.90
NIR/RED 0.15 0.90
NIR/GREEN 0.05 0.89
NDVI670 0.75 0.91
NDVI550 0.40 0.89
C
CONT(Estimate) = 17.478(NDVI)(W EST ) + 22.82 r 2 = 0.910
0
50
100
150
200
250
300
350
0.00 2.00 4.00 6.00 8.00 10.00 12.00 14.00 16.00 NDVI*W EST
Chl
. C
onte
nt, m
g/pl
ant
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Chlorophyll Concentration Estimation
Paper Number: 043081
•Estimated chlorophyll content calculated from regression equations for each band or ratio
•CCONC = CCONT / WEST
•Compared to actual Chlorophyll concentration
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Chlorophyll Concentration Estimation, r2
Paper Number: 043081
Estimator Ccontent vs. estimator
Ccontent vs. estimator *
WEST
Actual Cconc
vs. Cconc
estimate
Rgreen0.21 0.87 0.22
Rred 0.10 0.86 0.30
RNIR 0.58 0.90 0.05
NIR/RED 0.15 0.90 0.04
NIR/GREEN 0.05 0.89 0.03
NDVI670 0.75 0.91 0.08
NDVI550 0.40 0.89 0.000004
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Conclusions• Of the indices tested in this study, NDVI670
multiplied by estimated biomass appears to provide best estimate of chlorophyll content in spinach
• Multiplying reflectance ratios and indices by estimated biomass improved chlorophyll content estimations
• Reflectance-based remote sensing may not be the best method for estimating plant pigment concentrations (chl. a and b): RRED best, r2 = 0.30
Paper Number: 043081
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QUESTIONS?
AcknowledgmentsSupport through funding from the USDA Special
Research Grant Number 2003-06134
Paper Number: 043081