The selection of sensors (link) depends on your objectives. I.e., what do you wish to know from the image? Is it a stress level? If so, what type of stress? Below are some common examples of vegetative indices used to monitor crop health. Vegetation indices are crucial for assessing the health and growth of vegetation.
The soil line, in reference to remote sensing analyses, is a plot line of digital number values that typically fall 45° along this line. These values represent red light wavelengths against very-near infrared light (NIR) wavelengths. Generally, soil values fall close to the plot line and vegetation fall away from it. Thus, the vegetation plotting
Soil Adjusted Vegetation Index is sort of a hybrid between ratio-based indices and perpendicular indices. This index recognizes that the isovegetation lines do not run along side one another nor do they necessarily converge to a single point. It is a way to correct for the impact of soil line disparities on two-band vegetation indices