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Vegetation modeled as a water cloud
Author(s) -
Attema E. P. W.,
Ulaby Fawwaz T.
Publication year - 1978
Publication title -
radio science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.371
H-Index - 84
eISSN - 1944-799X
pISSN - 0048-6604
DOI - 10.1029/rs013i002p00357
Subject(s) - canopy , environmental science , water content , attenuation , scattering , volume (thermodynamics) , microwave , atmospheric sciences , polarization (electrochemistry) , dielectric , remote sensing , correlation coefficient , vegetation (pathology) , soil science , materials science , computational physics , hydrology (agriculture) , optics , physics , mathematics , geology , chemistry , geography , medicine , geotechnical engineering , optoelectronics , archaeology , statistics , quantum mechanics , pathology
Because the microwave dielectric constant of dry vegetative matter is much smaller (by an order of magnitude or more) than the dielectric constant of water, and because a vegetation canopy is usually composed of more than 99% air by volume, it is proposed that the canopy can be modeled as a water cloud whose droplets are held in place by the vegetative matter. Such a model was developed assuming that the canopy “cloud” contains identical water droplets randomly distributed within the canopy. By integrating the scattering and attenuation cross‐section contributions of N droplets per unit volume over the signal pathlength through the canopy, an expression was derived for the backscattering coefficient as a function of three target parameters: volumetric moisture content of the soil, volumetric water content of the vegetation, and plant height. Regression analysis of the model predictions against scattering data acquired over a period of four months at several angles of incidence (0°–70°) and frequencies (8–18 GHz) for HH and VV polarizations yields correlation coefficients that range from .7 to .99 depending on frequency, polarization, and crop type. The corresponding standard errors of estimate range from 1.1 to 2.6 dB.