Sensor Placement Algorithm With Range Constraints for Precision Agriculture Figure 3. RS precision farming data. ability to remove water from the surface through evaporation processes and transpiration without water supply limitations. Generally, the crop water need of a field is estimated through NDVI ¼ NIR-RED : NIR+RED (17) cropwaterneed ¼ potentialevapotranspiration À actualevapotranspiration: NDVI has a range from À1 to +1. Negative values of NDVI indicate water bodies and highly positive for vegetated landscapes. An NDVI close to zero indicates lack of water or plants or urban areas. The only source for estimating the AET is remote sensing whose unit is in millimeters. EVI VEGETATION INDICES The EVI was developed as an alternative vegetation index to address some of the limitations of the NDVI. The EVI was specifically developed to be more sensitive to changes in areas having high biomass and reduce the atmospheric conditions' influence on vegetation index values. EVI is calculated as Vegetation indices are mathematical combination or transformation of spectral bands that accentuates the spectral properties of green plants so that they appear distinct from other image features. Indices used in our work are as follows. EVI ¼ 2:5 Â NVDI NDVI quantifies vegetation by measuring the difference between near-infrared (from 0.4 to 0.7 m m) which vegetation strongly reflects and red light (from 0.7 to 1.1 m m) which vegetation absorbs and normalizing it further [54], [55] 10 ððNIR À REDÞ ðNIR þ C1 Â RED À C2 Â BLUE þ LÞ (18) where NIR, RED, and BLUE are atmospherically corrected surface reflectance and C1 , C2 , and L are coefficients for correcting the atmospheric condition. The standard values are L ¼ 1, C1 ¼ 6, and C2 ¼ 7:5. IEEE A&E SYSTEMS MAGAZINE JUNE 2019