Introduction to Remote Sensing


Remote sensing is defined as the technique of obtaining information about objects through the analysis of data collected by special instruments that are not in physical contact with the objects of investigation. This allows us to make decisions, predictions, and to model environments and situations quickly and efficiently without ever having to visit the area to be studied. Remote sensing allows us to ``see'' things we normally could not with the naked eye.

The first use of remote sensing was in military operations. One could fly a spy plane and take reconnaisance photos of the enemy's territory and thus gather information about it without ever being on the ground. When it became apparent that information was being gathered from above, camoflage methods were used. However, with the invention and use of thermal infrared and ultraviolet films, identification of ``hot'' and inorganic items became easily attainable.

Remote sensing then evolved into the use of space satellites to obtain images of the ground. These images could be recorded in different portions of the electromagnetic or ``light'' spectrum. Humans view objects in the visible portion of the spectrum. That is, with our own eyes, we see green plants as having a green color, or a red sweater as looking red. In different portions of the electromagnetic spectrum, pictures of objects do not always appear to be their ``normal'' color. In the infrared portion of the spectrum, the colors appear shifted so that green plants appear red, and a red sweater appears yellow. Parts of the visible spectrum are broken into different regions. At the highest energy level are the gamma rays and x-rays. The middle energy levels are the ultraviolet, the visible, and the infrared. Microwaves and radio waves are at the low end of the spectrum. Remote sensing allows us to take advantage of the entire electromagnetic spectrum as a method of detecting objects.

Today, many countries have many satellites that orbit the earth. Data is recorded in pixels. The word pixel was formed as a word by combining picture and element. The pixels are then put together in a rectangular array to form a picture. The smallest detail of data obtained from these remote sensing satellites that is presently available to the public is a square 30 feet by 30 feet. So, using a satellite that has a resolution of 30 feet square within each pixel, the human eye can recognize on the picture generated by remote sensing data objects that are longer and wider than 30 feet. The military is currently working with resolutions that are 3 feet square or less. This will allow you to recognize not only a car on the ground but also its license plate from data gathered by an orbiting satellite.

Acquiring Information about Bees from Remotely Sensed Data

Remote sensing allows us to map the vegetation on the ground from a satellite which is orbiting the earth at an altitude over 500 miles above the surface of the earth. This allows us to gather information on a large area without having to visit each and every square inch of it. As far as mapping the movement of honey bees outside of the hive, we can use satellites to examine the types and densities of vegetation, the riparian or water areas, and the elevation. Using what is called a false color composite map, we make a map in which healthy and dense vegetation appears dark red and water appears black. Using overlay analysis, we can then map elevation in relation to vegetation and locate the areas which have the most favorable conditions for honey bee migration.

Here, in Arizona, we can match this information with information from known Africanized honey bee sightings. These sightings are records collected from the public and from scientists who have discovered bees in swarm traps. So far, we see that the bees have been following riparian areas at low elevation having low laying desert vegetation. Africanized honey bees tend not to migrate into colder areas at higher elevation. Instead, they are moving into Arizona's southwest deserts. The Africanized honey bees have also been found in areas where water is used for irrigation and agriculture.

Where the Africanized honey bees will go next and at what rate is a topic of research. Since the first Africanized bee swarm was detected in Hildalgo, Texas in October, 1990, their rate of spread has increased to more than 375 miles per year in the southwestern United States. Some researchers suggest that the Africanized honey bee will disperse almost as far north as Canada; others say that they will go no farther than the southwestern and southeastern corners of the United States. What is known is that the Africanized honey bee is in the United States to stay and will continue to have some impact on its native plants and animals.