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The plants interact with the sunlight differently based on the observed wavelengths. The incident solar radiation can either be transmitted, absorbed, or reflected. The pattern of transmittance, reflectance and absorbed part of electromagnetic (EM) radiation provides essential insight to acquire information about plant physical and physiological status. Such as the absorbance bands of EM radiation (i.e. short wave infrared – SWIR 1 near 1.5 μ and short wave infrared‐ SWIR 2 near 2.5 μm) suggests the moisture availability in plants and vegetated landscapes. The health of forests or the photosynthesis activity by chlorophyll can be detected by analyzing the photosynthetic active radiation (PAR) range of EM waves where utilization of PAR is manifested as low reflectance of PAR in 0.6–0.7 μm range. Relating to their structural and biomass properties, leaves exhibit high reflectance and transmission in the near‐infrared spectral region (0.7–1.3 μm) (Tucker 1979; Avery and Berlin 1992). The structure of leaf area and plant canopy is also generally related to the reflectance patterns (Rautiainen and Stenberg 2005; Disney et al. 2006) which play a key role in growth monitoring. The absorption of radiation in the shortwave infrared region (1.3–2.5 μm), is mostly dominated by water and some biochemical components present in leaves. The phenological stages of plants and their interaction with different environmental aspects can be translated into unique signal patterns. These patterns or changes in electromagnetic radiation reflectance can then be interpreted and monitored using satellite data (Sharp et al. 1985; Blazquez and Edwards 1986; Curran et al. 1990; Miller et al. 1990; Pen Uelas et al. 1995; Kokaly 2001; Aparicio et al. 2002; Steddom et al. 2005; Disney et al. 2006; Guerif et al. 2007; Chen et al. 2010). The Chlorophyll content in vegetation is linked to the photosynthesis process and can be detected using the remotely sensed signature of selected EM wavelengths. Remote sensing signatures can further be linked to the various levels of stresses a plant may be facing. Thus remote sensing serves as a useful tool for monitoring the global health of vegetation (Gitelson and Merzlyak 1996) to suggest for water content and biomass of a vegetated landscape. This exemplifies the use of spectral signature in monitoring vegetation and its different parameters such as leaf area index, growing season, water stress, chlorophyll content, leaf structure, etc.

Figure 2.5 Applications of geospatial techniques for crop monitoring and management.

Precision agriculture is a site‐specific crop management prescriptions relying on information that can be measured using remote sensing for different crops across varying spatial and temporal scales. This system utilizes the power of modern technologies and information sources, including remote sensing, GIS, and GPS (Figure 2.5). Remote sensing supplements cost‐effective data for developing plans for precision agriculture. At the same time, the geographical information system provides a robust and flexible environment for the storage, processing, manipulation, analysis, and displaying of multiple spatial layers that can be used for the monitoring of agriculture and formulating a decision support system. Satellite imagery can be used for mapping discrete land cover and land use and for estimating other parameters of vegetation using spectral signatures (Steininger 1996).

Agriculture is the primary consumer of water, utilizing more than 70% of the global freshwater. Therefore, the role of irrigation water plays a significant in increasing the productivity of the land. Evapotranspiration (ET) from land surfaces is one of the key components of the water balance responsible for water loss. Evapotranspiration is of prime interest for various environmental applications, like optimization of irrigation water, irrigation system performance, water deficit for crops, etc. Also, poor irrigation timing and insufficient water application are common factors responsible for limiting agriculture production in many arid and semi‐arid agricultural areas. To address these issues, geospatial technology has emerged as a powerful tool to monitor irrigated lands over various climatic conditions and locations over the last few decades. It aids in determining when and how much to irrigate by monitoring the water status of plants. This is done by measuring evapotranspiration rates and by estimating crop coefficients. Efficient use and monitoring of surface water using geospatial techniques have recently attracted the interest of irrigation water policymakers.