The best way to reduce data from passive ranging is suggested
Electromagnetic waves and sound waves are widely used for the
determination of the location of objects. Familiar examples are
radar, sonar, GPS positioning, Polaroid cameras, police speed
meters, and many others. Most are echo devices, generating a
wave and interpreting its echo from the object of interest. GPS
is a cooperative system, in which the receiver observes timing
signals from sources of known location, and locates itself in
reference to them. In what follows, we will consider systems
based on sound waves in water, locating in two dimensions only,
and in the simple case of a uniform, isotropic speed of
propagation. This will allow us to clarify the fundamentals free
of unnecessary complication. For any practical system, all the
complicating factors must be taken into consideration. The
problem of determining the location of an object will be called
ranging here. There are three kinds of ranging systems, which we
will call echo, cooperative