||Diurnal Water Relations of Walnut Trees: Implications for Remote Sensing.
Weber, J. A. ;
Ustin., S. L. ;
||Corvallis Environmental Research Lab., OR. ;California Univ., Davis.
Remote sensing ;
Moisture content ;
Irrigation systems ;
Dielectric constants ;
Diurnal distribution ;
Soil moisture ;
Vegetation establishment ;
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||Leaf water content (LWC), relative water content (RWC) and water potential (LWP) were measured as indicators of diurnal change in tree water status in an experimental walnut orchard receiving two irrigation treatments: 100% and 33% of potential evapotranspiration (PET). LWP had the greatest magnitude of diurnal change throughout the experimental period with minima occurring each day in early to mid-afternoon and maxima between midnight and sunrise. The temporal discrepancy could be caused by cavitation of xylem elements in the vicinity of the DC (Dielectric Constants) probe. Microwave backscatter for L- and X-bands also measured diurnal variation that had local minima in the afternoon, but the pattern among wavelength and polarization signatures was complex. From these data it appears that radar backscatter can respond to diurnal changes in plant water status. Interpretation of diurnal patterns using a satellite sensor will require models that account for multiple sources of canopy and soil variance, including canopy architecture and soil moisture and more precise understanding of the basis of diurnal patterns in backscatter.
||Pub. in IEEE Transactions on Geoscience and Remote Sensing, v29 n6 p864-874 Nov 91. See also N89-18704. Prepared in cooperation with California Univ., Davis.
|NTIS Title Notes
||Reprint: Diurnal Water Relations of Walnut Trees: Implications for Remote Sensing.
||48B; 48D; 48C; 57C
||PC A03/MF A01