Seeing with microwaves
A radar device emits bundled electromagnetic waves in the form a primary signal. It then receives the »echoes« that are reflected from objects as a secondary signal and evaluates these according to various criteria. The term »radar« is actually an abbreviation for Radio Detection and Ranging.
The following are examples of information that can be gathered from echoes:
- the angle or direction of an object
- the distance to the object (derived from the time lapse between the transmission and reception of the respective signals)
- the relative movement between the transmitter and the object – this can be calculated using the Doppler effect from the frequency shift of the reflected signal
- the distance covered and the absolute speed of the object can be determined by stringing together individual measurements (pulses)
- if the radar has a good resolution, the contours of the object can be identified (e.g. the airplane type) or it is even possible to generate images (Earth and planetary research).