# Remote Sensing for Irrigation of Horticultural Crops
## 4 Approaches to Precision Irrigation  
Remote sensing has many potential applications in many fields and at different scales. Table 2 lists field applications of remote sensing in agriculture. [PERSON] et al. [28] summarized the important role of remote sensing in site-specific farming. Remote Sensing can provide non-destructive, automatic, and continuous measurements, easily implemented with data transmission systems for the user to have nearly real time access to the collected data from a remote computer, smart phone or similar [30]. Most of these methods and related systems are highly sensitive and capable of working under field conditions for long periods. These characteristics confer great potential for both monitoring water stress and scheduling irrigation [105]. Remote sensing can provide precise information of irrigated crop areas [106] by monitoring the phenological development of crops through multi-temporal image [107]. \begin{table}
\begin{tabular}{l l} \hline \hline \(\bullet\) & Precision farming \\ \(\bullet\) & Surveillance of farms \\ \(\bullet\) & Crop yield potential assessment \\ \(\bullet\) & Sampling procedure (soil and crop) \\ \(\bullet\) & Improving assessment of irrigation water use at regional scale \\ \(\bullet\) & Field-based plant phonemics \\ \(\bullet\) & Plant abiotic stresses (water, heat, nutritional, pollution stress) \\ \(\bullet\) & Plant biotic stress (diseases, weeds) \\ \(\bullet\) & Crop water status \\ \(\bullet\) & Canopy volume/crop biomass detection, crop cover fraction \\ \(\bullet\) & Light penetration of the canopy \\ \(\bullet\) & Application of canopy measurements \\ \(\bullet\) & Soil nutrients and other soil characteristics \\ \(\bullet\) & Visible (VIS)/NIR spectroscopy \\ \(\bullet\) & Mapping soil types \\ \(\bullet\) & Wind and water erosion, flooding \\ \(\bullet\) & Monitoring the extent and type of vegetation \\ \(\bullet\) & Assessing water resources \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Applications of remote sensing in agriculture Crop water status is the crucial biophysical property, used in particular to manage irrigation by remote sensing. It is, in most cases, directly associated to the available soil water content, and in other conditions to soil salt content when salinity is a limiting factor of water uptake. Similarly, plant diseases, which may be obstacles to plant-water flow, may negatively influence crop water status, which becomes an indicator of disease presence and severity [108; 109]. Crop water status can be quantified at the canopy and leaf levels, by monitoring leaf or stem water potential, or leaf water content [110]. Unfortunately, this simplistic view is complicated by several plant factors (root signaling, aerodynamic characteristics of vegetation, genetic control of crop performance, etc. ), which interact in a complicated way with environmental factors, such as solar radiation (intensity and insulation), wind speed and direction, air humidity, and air temperature. Plant species may or may not be highly coupled to the environment [111]. The \(\Omega\) coefficient (or decoupling coefficient) is a measure of the coupling between conditions at the canopy surface and in the free airstream (well above the crop), and can vary between 0 (for perfect coupling) to 1 (for complete isolation). [PERSON] [111] reports \(\Omega\) values of 0.85, 0.7, 0.4, 0.3 for strawberry, tomato, raspberry, and citrus orchards, respectively. In other words, a citrus orchard is more coupled to the environment than more dense horticultural crops. The concept is summarized by [PERSON] [112], who stated that relatively open, tall and aerodynamically rough canopies made of small leaves facilitate turbulence and air movement within the canopy, and therefore, are closely coupled to the air overhead. Conifer forests show a low decoupling factor \(\Omega\). In contrast, dense, smooth and short canopies, with all the leaves packed into the limited vertical space, would obstruct air movement and therefore are nearly uncoupled from the air overhead.