Chlorophyll Estimation Using Multi-spectral Reflectance and Height Sensing C. L. JonesResearch...

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

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


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


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


Previous Work

No single spectral approach offers an adequate method of estimating pigment (chlorophyll) concentration in all plants.


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


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)


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


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


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)


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


UDS Response


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

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


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)


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


NIR Green or Red

NIR Green or Red

ρ - ρNDVI =

ρ +ρ

Biomass Estimation

PWC = 0.86


WEST = AMS x HUDS

Where: WEST = estimated plant biomass

AMS = surface area estimate from camera (pixels)

HUDS = estimated plant height from UDS (cm)

Biomass Estimation

PWC = 0.86


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

Chlorophyll Content Estimation, r2


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

Chlorophyll Content Estimation, r2



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

Chlorophyll Concentration Estimation


•Estimated chlorophyll content calculated from regression equations for each band or ratio

•CCONC = CCONT / WEST

•Compared to actual Chlorophyll concentration

Chlorophyll Concentration Estimation, r2



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

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


QUESTIONS?

AcknowledgmentsSupport through funding from the USDA Special

Research Grant Number 2003-06134


Chlorophyll Estimation Using Multi-spectral Reflectance and Height Sensing C. L. JonesResearch...

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