Q. Method of observation by satellite?

The difference between a photographs and imageries needs to be understood first. A photograph covers a specific area within its view and a picture is taken covering the full area at a time. Everybody is familiar with this process. A satellite observes and records the data line by line, which is made up of many points. The point-by-point observations of the intensity of light are taken in digital form. shows the movement of satellite and the process of observation in schematic way. The process can be compared to a scanner where the source of light travels over the document, collects, and stores the data in digital form.

Therefore, a satellite takes certain time to capture the data covering the specific area of interest. The collected digital data can be converted and printed on photographic paper to form a "photograph" called in the technical term as "imagery". This process can be compared to a Xerox machine, where a document is "scanned" and the data is printed on a paper.

Aircrafts and satellites are the other most commonly used methods for data acquisition from the earth surface. Aerial photography, i.e. remote sensing of data using aircrafts, took up shape with the development of aircrafts and its suitable remote sensing cameras. Aerial photography has the advantage of flexibility of operations and higher resolution.