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Fundamentals of Remote Sensing

1.2 Did You Know?

"I've Gone Batty!"

...that remote sensing, in its broadest definition, includes ultrasounds, satellite weather maps, speed radar, graduation photos, and sonar - both for ships and for bats!. Hospitals use imaging technology, including CAT scans, magnetic resonance imaging (3-D imaging of soft tissue), and x-rays for examining our bodies. These are all examples of non-intrusive remote sensing methods.

...you can use an oscilloscope, a special electronic device which displays waves similar to the electromagnetic radiation waves you have seen here, to look at the wavelength and frequency patterns of your voice. High-pitched sounds have short wavelengths and high frequencies. Low sounds are the opposite. Scientists say that the Earth itself vibrates at a very low frequency, making a sound far below the human hearing range.

...that the concept of wavelength and frequency is an important principle behind something called the Doppler Shift, which explains how sound and light waves are perceived to be compressed or expanded if the object producing them is moving relative to the sensor. As a train or race car advances towards us, our ears tend to hear progressively lower sounds or frequencies (shorter wavelengths) until it reaches us, the original frequency of the object when it is broadside, then even lower frequencies as it moves further away. This same principle (applied to light) is used by astronomers to see how quickly stars are moving away from us (the Red shift).