Skip to main content
ARS Home » Pacific West Area » Corvallis, Oregon » Horticultural Crops Research » Research » Publications at this Location » Publication #229078

Title: Simple Linear Regression and Reflectance Sensitivity Analysis Used to Determine the Optimum Wavelength for Nondestructive Assessment of Chlorophyll in Fresh Leaves Using Spectral Reflectance

Author
item Ding, Pinghai
item Scagel, Carolyn
item Fuchigami, Leslie

Submitted to: Journal of the American Society for Horticultural Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/5/2008
Publication Date: 1/1/2009
Citation: Ding, P., Scagel, C.F., Fuchigami, L.H. 2009. Simple linear regression and reflectance sensitivity analysis used to determine the optimum wavelength for nondestructive assessment of chlorophyll in fresh leaves using spectral reflectance. Journal of the American Society for Horticultural Science. 134(1):48-57.

Interpretive Summary: The accuracy of nondestructive optical methods for chlorophyll (Chl) assessment based on leaf spectral characteristics depends on the wavelengths used for Chl assessment. We compared three different methods of estimating optimum wavelengths for Chl assessment (OWChl) (1) the coefficient of determination (R2) from simple linear regression, (2) reflectance sensitivity analysis, and (3) the 1st spectral derivative. Reflectance sensitivity analysis was more accurate than the 1st derivative method because it accounted for differences in spectral reflectance caused by differences in Chl concentration. The 1st derivative could not distinguish whether spectral differences were the result of differences in Chl concentration or other factors. Neither method alone accurately identified the actual OWChl. The use of R2 was was found to be more valuable for verifying the accuracy of OWChl selection when used with reflectance sensitivity analyses.

Technical Abstract: The accuracy of nondestructive optical methods for chlorophyll (Chl) assessment based on leaf spectral characteristics depends on the wavelengths used for Chl assessment. Using spectroscopy, the optimum wavelengths for Chl assessment (OWChl) were determined for almond, poplar, and apple trees grown at different rates of nitrogen (N) fertilization to produce leaves with different Chl concentrations. Spectral reflectance of leaf discs was measured using a spectroradiometer (300 nm to 1100 nm at 1 nm intervals), and total Chl concentration in was determined. The OWChl for nondestructive Chl assessment by reflectance spectroscopy was estimated using (1) the coefficient of determination (R2) from simple linear regression, (2) reflectance sensitivity analysis, and (3) the 1st spectral derivative method. Our results indicated that the 1st derivative method can be used to estimate OWChl in the red edge region of the spectrum and reflectance sensitivity analysis can be used to estimate the OWChl in both the red edge and visible regions. Reflectance sensitivity analysis was more accurate than the 1st derivative method when used for OWChl selection because it ensures differences in the spectral reflectance are caused by differences in Chl concentration. The 1st derivative method could not distinguish whether spectral differences were the result of differences in Chl concentration or caused by other factors (e.g. leaf texture and water status). Neither the 1st derivative method nor reflectance sensitivity analysis alone could accurately identify the actual OWChl. We found that R2 was a valuable indicator for verifying the accuracy of OWChl selection. Higher R2 values were usually associated with lower root mean square errors (RMSE) and higher reflectance sensitivity; therefore, the wavelengths with the highest R2 and highest reflectance sensitivity were selected as the OWChl. Our results indicate that using simple linear R2 in combination with reflectance sensitivity analysis is the more reliable method for determining OWChl in leaves.