# Remote Sensing for Irrigation of Horticultural Crops
## 2 Scope of the Review  
The applications of remote sensing to irrigation monitoring and management are reviewed herein. The assessment of the ideal crop water requirement is indispensable for several objectives linked to agronomic, economic, and environmental issues: (i) maximize crop yield (the 'yield gap'); (ii) stabilize production by adopting a safeguard against the vagaries of weather; (iii) ameliorate crop quality; (iv) save water; (v) limit onset of diseases; and (vi) limit groundwater pollution caused by N leaching losses. A seventh (vii) crucial point is the 'yield gap' of the environment under study. This means defining the potential and constraints of the field environment (sub optimal management, inappropriate technology, and/or lack of training of farmers). This is possible when water constraints on crop production are removed by using appropriate irrigation scheduling for getting more crop yield per drop of water [9; 29], contributing to social growth of the irrigated area.  
In 2008, [PERSON] [8] called for a more efficient and sustainable irrigation than in the past, at a time when the rate of irrigation was expected to slow down, and when the investments in irrigation and drainage were on the decline. [PERSON] also emphasized challenges in irrigated agriculture due to modernization of irrigation networks and management, the improvement of water institutions, and the responses to periodic droughts. The last point has imposed the introduction of new water saving technologies in horticulture.  
A holistic approach is necessary for moving from a traditional approach to precision irrigation, defined as site-specific irrigation management that relies on the variable application of water according to soil and crop variability. It is a potential solution for increasing productivity and reducing the environmental impact of irrigated agriculture. A holistic approach needs a deep and precise knowledge of the crop water requirements and the cultivated environment. The innovative deficit irrigation and partial root drying management strategies [29] have encouraged the development of new methods for monitoring water stress (abiotic). [PERSON] [30] focused on plant-based methods that integrate the soil and atmospheric water status and the plant response to the surrounding conditions.  
The present review describes the role of remote sensing with respect to crop water status, its surface energy balance, the relationship between surface temperature and remotely sensed vegetation indices, and WUE and evapotranspiration. This review is limited to field-key studies, and presents applications of remote sensing for managing irrigation and water resources for meeting the current and future challenges of agricultural water resources management. A list of references is presented as a good resource for any who are interested in remote sensing applied to irrigation studies. The review is organized into the following main sections: (1) Sensors and platforms applied to irrigation studies; (2) Remote sensing approaches for precision irrigation for estimating crop water status, evapotranspiration, infrared thermography, and soil and crop characteristics.