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Assessing variation in the relationships between remotely sensed data and canopy chlorophyll composition

Assessing variation in the relationships between remotely sensed data and canopy chlorophyll composition
Assessing variation in the relationships between remotely sensed data and canopy chlorophyll composition

The chlorophyll composition of a vegetation canopy is an important indicator of productivity, plant stress and a range of ecosystem processes. Strong relationships exist between remotely sensed data and chlorophyll composition of vegetation canopies. There is, however, considerable variability in the relationships observed which cannot be accounted for by our current understanding of radiation-canopy interactions. This thesis examines three potential factors that may cause variability in such relationships at the local scale; namely, view zenith angle, specular reflectance and spatial resolution.

Research was focused initially on variation in remotely sensed data with view zenith angle, for a wheat canopy. It was observed that remotely sensed data, in the form of vegetation indices, varied significantly with view zenith angle, leading to variation in the relationships between vegetation indices and canopy chlorophyll composition. The strongest correlations were observed at view zeniths approaching the 'hot spot' of canopy reflectance, while relationships appeared weaker at extreme view zenith angles. Partial correlation analysis revealed that the most significant factor in determining variability in the relationships observed, was the proportion of vegetation present within the scene.

Light reflected specularly from a leaf surface contains no information on the concentration of pigments within the leaf. It was hypothesised that the removal of the specular component of wheat canopy reflectance would strengthen the relationships between remotely sensed data and canopy chlorophyll composition. The specular component was isolated through measurements of polarized reflectance and found to comprise a large proportion of total canopy reflectance, particularly at wavelengths of strong pigment absorption. When removed, however, the relationships observed were not stronger than when the specular component was included. The hypothesis was, therefore, rejected.

It has been observed that the range in the wavelength position of the red edge of plant reflectance (REP) derived from coarse spatial resolution data is less than for fine spatial resolution data. Estimates of REP from a grassland site, revealed that the range in REP was considerably less in airborne data than in field data, much of which was attributed to the increased spatial resolution of the data, but, was compounded by the choice of method used to estimate REP.

University of Southampton
Cutler, Mark Edward John
Cutler, Mark Edward John

Cutler, Mark Edward John (1997) Assessing variation in the relationships between remotely sensed data and canopy chlorophyll composition. University of Southampton, Doctoral Thesis.

Record type: Thesis (Doctoral)

Abstract

The chlorophyll composition of a vegetation canopy is an important indicator of productivity, plant stress and a range of ecosystem processes. Strong relationships exist between remotely sensed data and chlorophyll composition of vegetation canopies. There is, however, considerable variability in the relationships observed which cannot be accounted for by our current understanding of radiation-canopy interactions. This thesis examines three potential factors that may cause variability in such relationships at the local scale; namely, view zenith angle, specular reflectance and spatial resolution.

Research was focused initially on variation in remotely sensed data with view zenith angle, for a wheat canopy. It was observed that remotely sensed data, in the form of vegetation indices, varied significantly with view zenith angle, leading to variation in the relationships between vegetation indices and canopy chlorophyll composition. The strongest correlations were observed at view zeniths approaching the 'hot spot' of canopy reflectance, while relationships appeared weaker at extreme view zenith angles. Partial correlation analysis revealed that the most significant factor in determining variability in the relationships observed, was the proportion of vegetation present within the scene.

Light reflected specularly from a leaf surface contains no information on the concentration of pigments within the leaf. It was hypothesised that the removal of the specular component of wheat canopy reflectance would strengthen the relationships between remotely sensed data and canopy chlorophyll composition. The specular component was isolated through measurements of polarized reflectance and found to comprise a large proportion of total canopy reflectance, particularly at wavelengths of strong pigment absorption. When removed, however, the relationships observed were not stronger than when the specular component was included. The hypothesis was, therefore, rejected.

It has been observed that the range in the wavelength position of the red edge of plant reflectance (REP) derived from coarse spatial resolution data is less than for fine spatial resolution data. Estimates of REP from a grassland site, revealed that the range in REP was considerably less in airborne data than in field data, much of which was attributed to the increased spatial resolution of the data, but, was compounded by the choice of method used to estimate REP.

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Published date: 1997

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Local EPrints ID: 463233
URI: http://eprints.soton.ac.uk/id/eprint/463233
PURE UUID: 507a6c19-489d-4578-b1af-c9cd2735c242

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Date deposited: 04 Jul 2022 20:47
Last modified: 04 Jul 2022 20:47

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Author: Mark Edward John Cutler

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