ISHS Acta Horticulturae 278: Symposium on Scheduling of Irrigation for Vegetable Crops under Field Condition
MONITORING OF SOIL AND VEGETATION WATER CONTENT BY MEANS OF PASSIVE MICROWAVE SYSTEMS |
| Authors: | S. Paloscia, P. Coppo |
| Abstract:
The knowledge of soil moisture availability is important to evaluate the plant water requirement and to identify the best schedule of irrigation. This parameter, together with some others concerning the plant water status, such as leaf temperature, leaf water potential and so on, can give useful information about the real evapotranspiration of the crops. Microwave emission, since it is strongly affected by the water content of the surfaces, can be correlated, using the most suitable wavelength, to the soil and plant moisture content. Several years of in-field experiments have pointed out that brightness temperature (i.e. the surface temperature corrected by an emissivity factor) depends on the type of surface and on its physical characteristics. If the brightness temperatures at two different frequencies (10 GHz and 36 GHz) are combined and a new parameter, that is the ratio between the brightness temperature and the infrared temperature, is introduced, bare from vegetated soil can be separated. Moreover, some types of vegetation can also be singled out in different clusters; in each cluster a progressive plant water stress conditions has been identified. After this preliminar analysis, a simplified model based on the radiative transfer theory has been used to go deeper into the mechanism which relates microwave parameters to vegetation features. Thus, a relationship between a microwave index and the plant water content first and then between the former and the leaf area index of corn and alfalfa has been established. Finally, using a lower frequency (1.4 GHz) a strong correlation between microwave emission and soil water content has been found. | |
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