Remote Sensing Basics

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An Eye in the Sky – The Basics of Remote Sensing

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Every time a farmer scouts a field, we might say they are employing remote sensing. They are observing the crop health, the signs of disease or insect infestation, the soil moisture status, and are making a visual assessment of plant health.

Remote sensing for precision agriculture is a collection of technologies that attempt to emulate that process. These technologies collect information about the plants in the field from a distance, without being in physical contact. Most often we refer to aerial photography or satellite imaging as remote sensing for precision agriculture.

The premise of remote sensing is that by looking at spatial variations in plant color over a field, we can pick out areas of the crop that are stressed. This may be due to extremes in moisture, fertility stress or pest infestations. Once these areas are identified, they can be assigned a spatial location (latitude-longitude coordinates for our GPS units) and a close-up visual observation of the area will help identify the problem.

Basics of Remote Sensing

Remote sensing technologies measure the energy that is reflected or emitted from plants or soil. Visible (to humans) light is one segment of the energy that can be observed. However, we need to consider visible light as only part of broader spectrum of electromagnetic energy. The electromagnetic spectrum, illustrated in the figure, includes familiar types of electromagnetic energy like ultraviolet rays (those contributing to sunburn), visible light, infrared radiation (like those shop heaters), microwaves and radio waves.

The energy in the electromagnetic spectrum is scientifically defined by the wavelength which is measured in microns (one millionth of a meter). The figure illustrates that visible light has wavelengths of something less than 0.4 microns (violet light) to something more than 0.7 microns (red light). Just beyond the red light is the infrared light (radiation) with wavelengths that stretch to about 100 microns (0.1 mm). Although undetectable by the human eye, near-infrared radiation can be detected by man-made sensors.

Remote sensing technologies currently associated with precision agriculture generally use only a small portion or band of this spectrum. These technologies depend on the energy radiated by the sun, which lies in the band including the ultraviolet through the infrared radiation. The most important bands for current remote sensing technologies are the visible light band and the near-infrared band.

Roger Brook

Abstracted from The Precision-Farming Guide for Agriculturists by John Deere Publ., 1997.


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This page was last updated on 10/08/01.