1. Introduction
Agricultural irrigation has a major impact on waterresources management as it accounts for more than 80% of total water withdrawn [1-3]. The global extentof irrigated area has expanded during the last 30 years by 1.6% per year [4] leading to a significant increase in freshwater consumption and therefore to water resource degradation and depletion. Further, the emerging concern over climate and land use change impact on agriculture needs accurate monitoring of
crop yield production. Precise use of fresh water resources for irrigation is required for implementation of sustainable water management policies and to monitor high yields in a changing climate and rising water demands. Soil moisture, water content in the root zone, and vegetation indices are critical parameters for crop yield forecasting, irrigation management, and issuing early warning of droughts. Soil moisture data with high spatial and temporal resolution over the agricultural growing season have potential for rational planning of irrigation management and increased crop yields. Temporal monitoring of soil moisture at different growth stages of crop could prevent water stress and improve the crop yield [5]. Soil moisture characteristics influence the availability of nitrogen and water to the crop during the growing season, strongly affecting the availability of soil nitrogen during periods of low water availability [6]. On the other hand, excessive irrigation leads to leaching of fertilizer (N and P), inducing groundwater pollution and soil degradation [7]. Using knowledge of soil moisture to manage insects and plant disease [8] is a potential application that needs more research. Information on spatial
distribution of soil moisture over the field will allow pesticides to be applied selectively to achieve economic and environmental benefits. Currently, various crop monitoring schemes are
used to retrieve crop yield information from visible/near IR remote sensing data. These schemes
could be improved with the addition of microwave based soil moisture information to achieve greater efficiency. Many studies carried out during past three decades have successfully demonstrated the use of active and passive microwave remote sensing techniques to obtain spatial and temporal estimates of soil moisture mapping over large regions [9-12]. In the
case of passive microwave system, the radiometric emission measure as a brightness temperature
decreases with the increasing soil moisture. However, in the case of active microwave system, the stronger radar backscatter signals are observed at higher soil moisture [13].The spatial heterogeneity soil moisture and precipitation make it difficult to estimate soil moisture
at relevant scales from field soil moisture measurements. Lacking accurate information,
farmers/managers often leave irrigation systems