Abstract
Irrigation scheduling is critical as it affects both fruit yield and composition. We examined the potential to use field-measured hyperspectral remote sensing data (reflectance and transmission over the 350–2500 nm wavelength region) to estimate leaf water content, equivalent water thickness (EWT), and leaf water potential (Ψ) in a commercial vineyard of Vitis vinifera cv. Pinot noir. The data allowed us to evaluate a number of reflectance patterns to estimate vine water status through correlations using two spectral approaches: direct measurement of vegetation indexes (VIs) and continuum removal analysis (CRA). Continuum removal analysis was applied to obtain the maximum band depth (MBD) and the band area (BA) of several absorption features sensitive to water content. Correlations were high for EWT at the leaf level using a modification of the Simple Ratio VI (SR2; R2 = 0.916) and for CRA with MBD970 (R2 = 0.917) and BA1160 (R2 = 0.897). Correlations with EWT and water potential at the canopy level for SR2 were nonsignificant, which was characteristic for many VIs. For predawn water potential (ΨPD) and midday stem water potential (Ψstem) at the canopy level, best fits were realized for Modified Triangular VI (MTVI2; R2 = 0.360) and Red/Green VI (RGI, R695/R554; R2 = 0.462), respectively. For canopy level water status, the best results were obtained using the difference between the midday stem water potential and the pre-dawn leaf water potential (Ψstem - ΨPD) with R2 = 0.619 for RGI and R2 = 0.541 for Structure Intensive Pigment Index (SIPI, R800-R445/R800-R680), while for CRA R2 = 0.477 for BA1600 and R2 = 0.509 for MBD970. Results suggest that noninvasive monitoring using hyperspectral data could improve current methods for estimating water status in individual vines. Applications of similar measurements could be produced from airborne hyperspectral imagers to provide spatially resolved estimates of water stress for use in water management of large-scale commercial vineyards.
- Ψleaf, midday leaf water potential (MPa)
- ΨPD, predawn leaf water potential (MPa)
- Ψstem, midday stem water potential (MPa)
- Ψs, osmotic potential (MPa)
- Ψt, turgor pressure (MPa)
- gs, stomatal conductance to water vapor (mmol m−2 s−1)
- E, transpiration rate (mmol H2O m−2 s−1)
- A, net photosynthetic rate (μmol CO2 m−2 s−1)
- LA, leaf area (cm2)
- LAI, leaf area index (m2 m−2)
- Wt, total leaf weight (g)
- Wd: oven dry leaf weight (g)
- RWC, relative water content (%)
- WCd, water content as percent of dry mass (%)
- WCt, water content as percent of total fresh mass (%)
- EWT, equivalent water thickness (g cm−2)
- SLW, specific leaf weight dry mass (kg m−2)
- TSLW, total specific leaf fresh weight (kg m−2)
- CRA, continuum removal analysis
- BA, band area of the absorption feature in CRA
- D, band depth in CRA
- R, measured reflectance
- MBD, maximum band depth of the absorption feature in CRA
- lMBD, wavelength of the maximum band depth of the absorption feature in CRA (nm)
- FWHM, full band width at half maximum (nm)
- REIP, red-edge inflection position (nm)
- REIPv, derivative value of REIP (nm)
- ASD, Analytical Spectral Device (350–2500 nm)
- VIS, visual light spectrum (400–700 nm)
- IR, infrared light (750 nm–1 mm)
- NIR, near-IR (700–1300 nm)
- MIR, mid-IR (1300–2500 nm)
- SWIR, shortwave IR reflectance (1400–3000 nm)
- Rs, reflectance (relative units)
- Is, leaf reflectance (relative units)
- Id, leaf reflectance in the dark (relative units)
- Ir reference reflectance (relative units)
- VI, vegetation index(es) (waveband ratios)
- Received October 2006.
- Revision received December 2006.
- Copyright © 2007 by the American Society for Enology and Viticulture
Sign in for ASEV members
ASEV Members, please sign in at ASEV to access the journal online.
Sign in for Institutional and Non-member Subscribers
Log in using your username and password
Pay Per Article - You may access this article (from the computer you are currently using) for 2 day for US$10.00
Regain Access - You can regain access to a recent Pay per Article purchase if your access period has not yet expired.
Vol 58 Issue 3
Jump to section
Related Articles
Cited By...
More from this TOC section
Similar Articles
