Non-Photographic Remote Sensing

Most remote sensing data are displayed as photographs, or "images." When we think of looking at the data collected by remote sensors we usually think "picture," don't we? Some of the data we use in remote sensing is just that: an analog photograph taken by a camera. Indeed, photos are the mainstay of remote sensing because they are very economical, quite versatile, and record tremendous amounts of information. But photos acquired by aircraft and spacecraft are qualitative. We can say one object is brighter or greener than another, but we can't really say by how much. Wouldn't it be useful if we could measure these differences? Well, measurement implies numbers and that means digital data.

We know that certain Earth materials reflect solar energy differently than other materials; that is to say, they have different spectral characteristics. In fact, we can often identify the object by its spectral signature - a unique reflectance value in a specific part of the spectrum. How can we measure these?

Spectral reflectance of various Earth materials.

There are two basic methods for acquiring digital remotely sensed data: we can "digitize" a photo or we can use a sensor that collects the original data digitally.

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