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Fundamentals of Remote Sensing

2.7 Did You Know?

"...let's take a look at the BIG PICTURE..."

...that the U.S. Space Shuttles have been used to take photographs from space. The astronauts onboard the shuttle have taken many photographs using hand-held cameras, similar to the type you would use for taking family photos. They have also used much larger and more sophisticated cameras mounted in the shuttle's cargo bay, called Large Format Cameras (LFCs). LFCs have long focal lengths (305 mm) and take high quality photographs covering several hundreds of kilometres in both dimensions. The exact dimensions depend (of course) on the height of the shuttle above the Earth. Photos from these passive sensors need to be taken when the Earth's surface is being illuminated by the sun and are subject to cloud cover and other attenuation from the atmosphere. The shuttle has also been used several times to image many regions of the Earth using a special active microwave sensor called a RADAR. The RADAR sensor can collect detailed imagery during the night or day, as it provides its own energy source, and is able to penetrate and "see" through cloud cover due to the long wavelength of the electromagnetic radiation. We will learn more about RADAR in Chapter 3.

... although taking photographs in the UV portion of the spectrum is problematic due to atmospheric scattering and absorption, it can be very useful where other types of photography are not. An interesting example in wildlife research and management has used UV photography for detecting and counting harp seals on snow and ice. Adult harp seals have dark coats while their young have white coats. In normal panchromatic imagery, the dark coats of the adult seals are readily visible against the snow and ice background but the white coats of the young seals are not. However, the coats of both the adult and infant seals are strong absorbers of UV energy. Thus, both adult and young appear very dark in a UV image and can be easily detected. This allows simple and reliable monitoring of seal population changes over very large areas.