Extraneous variables and their influence on reflectance-based measurements of leaf water content
- 237 Downloads
Leaf water indices based on leaf reflectance may depend not only on the variable of interest, leaf water content, but may also be influenced by a variety of extraneous variables, leading to considerable data variability if such extraneous variables are not eliminated or taken into account. Here, we examined the nature of three potential extraneous variables: homogeneity of the leaf target area, the distance between a primary reflecting leaf and background material, and measurement sensitivity at various wavelengths. Although leaf water indices appear to be homogeneously distributed between major leaf veins, they may fluctuate substantially in areas where major veins are present. Leaf water indices may also depend to some extent on the distance between a primary reflecting leaf and any reflecting background material, at least for small distances. Leaf water indices utilizing the 970 or 1200 nm water absorption bands have been shown to be rather insensitive to changes in leaf water content, potentially resulting in low signal-to-noise ratios, an additional source of data variability.
KeywordsLeaf Water Extraneous Variable Background Material Data Variability Water Deficit Stress
H.-D.S. gratefully acknowledges financial assistance from BioServe Space Technologies (NASA NCC8-242) at the University of Colorado.
- Gausman HW (1974) Leaf reflectance of near-infrared. Photogramm Eng 40:183–191Google Scholar
- Gausman HW, Allen WA, Cardenas R, Richardson AJ (1970) Relation of light reflectance to histological and physical evaluations of cotton leaf maturity. Appl Opt 9:545–552Google Scholar
- Hopkins WG (1999) Introduction to plant physiology, 2nd ed. Wiley, New YorkGoogle Scholar
- Kou L, Labrie D, Chylek P (1993) Refractive indices of water and ice in the 0.65 to 2.5 μm spectral range. Appl Opt 32:3531–3540Google Scholar
- Pierce LL, Running SW, Riggs GA (1990) Remote detection of canopy water stress in conferous forests using the NS001 thematic mapper simulator and the thermal infrared multispectral scenner. Photogramm Eng Remote Sens 56:579–586Google Scholar
- Ripple WJ (1986) Spectral reflectance relationships to leaf water stress. Photogramm Eng Remote Sens 52:1669–1675Google Scholar
- Sinclair TR (1968) Pathway of solar radiation through leaves. M.S. Thesis. Purdue University, LafayetteGoogle Scholar
- Thomas JR, Namken LN, Oerther GG, Brown RG (1971) Estimating leaf water content by reflectance measurements. Agron J 63:845–847Google Scholar