A Remote Sensing model for wheat drought monitoring
Yang Xihua Tian Guoliang
Institute of Remote Sensing Application, Chinese
Academy of Sciences, Beiling 100101, P.R. Chian
Abstract
This paper presents a remote sensing approach for wheat drought monitoring and modeling, which based on the principles of soil water balance and energy balance. The initial soil water content ( Wo) was obtained from the relationship between the apparent thermal inertia and soil moisture which was established through the experiments conducted over nearly bare fields on the North China Plain. The evapotranspiration (Et) of the wheat field was estimated using the remotely sensed reflected solar radiation and surface temperature extracted from the NOAA-AVHRR digital image as well as the meteorological data such as incoming solar radiation, air temperature, wind speed and vapor pressure from ground meteorological station. Then the solid water content ( Wt) in a certain period of time ( 10 days ) can be calculated using the equation of soil water balance., At last, a drought index model was developed by concerning the available soil water content and the wheat water requirement. This model has been proved to be practicable in monitoring the wheat drought in parts of the North China Plain.
Introduction
Drought, a worldwide problem, is one is the most critical restrictive factors in plant survival and development. In China, especially in the North China Plain, drought is the most serious natural disaster and it accounts for half of the total agricultural loss. Therefore, the research the practicable methods for plant drought monitoring in order to take immediate measures and strategies of prevention is very important and meaningful.
However, its very difficult to monitor the crop drought due to its dynamic nature and regional variation. Although a lot of researches have been done in this field, there are still many difficulties in methodology left unsolved.
The traditional methods, such as meteorological methods and soil hydrological methods, can in some extend display the plant water status. But they have no exact agricultural meanings be caused they have no relation with crop water requirement. In the meantime, the traditional methods for determining drought are essentially point measurements. It’s difficult to acquire the numerous samples to present the characterize fields and impracticable to apply to a large area. Whereas, remote sensing techniques provide large area coverage and can obtain the surface information rapidly and multitemporally. The means of remote measurement could open a new way for drought monitoring and bring it into practicable service.
The most important factors related to drought are the soil moisture and evapotranspiration. Many researchers have contributed excellent articles on the acquiring of those parameters by remote sensing means. Sherwood B.Idso (1975) and John C. Price (1977 and 1980) have developed the thermal inertia approach for remote sensing of near – surface soil moisture. Although the model was based on simplifying assumptions, it’s useful in application on the bare or low-cover soils.
Presented at the 12th Asian Conference on Remote Sensing, at Eegional English Language Center, International House of the South Asian Ministers of Education Organisation ( SEAMEO ) , 30, Grange Grove Road, Singapore from October 30 to November 5, 1991.
Toby N. Carlson, etc. ( 1980), G. Russell ( 1980) and R.D. Jackson ( 1981 and 1982) suggested that the plant temperature ( or leaf-air-temperature ) may be an indicator of soil moisture. They developed a range of methods to estimate evapotranspiration using plant canopy temperature and net radiation derived from energy balance and converted it into a crop water stress index 9 CWSI), which closely parallel to the extractable soil water content within the root zone. A comprehensive review of research on remote sensing of surface soil water content within the root zone. A comprehensive review of research on remote sensing of surface soil moisture has been presented by T. schmugge ( 1978), It’s instructive to our research.
In this paper, we’ll apply the principles of energy balance and soil water balance to develop a remote sensing model for wheat drought monitoring. This model concerns the wheat water requirement and the available soil water content as a whole, and most of the parameters involved in this model can be derived from NOAA-AVHRR. It’s expected to be practicable to apply to the North China Plain.
