TABLE OF CONTENTS Techniques for determining PF estimates of targets based on measuring the TOA, TDOA, differential frequency [otherwise known as differential Doppler (DD)], and RD are discussed in this chapter.
When the TOA or the time difference of arrival (denoted here by ?) measured at two or more widely dispersed sensors are used to geolocate emitters, then quadratic LOPs result. Generally, the intersection of these LOP curves is taken as the estimated emitter location. Calculation of this intersection can be tedious and complicated, requiring a search over a large parameter space.
The principal advantages of these forms of processing are the following:
Frequently a single antenna per sensor is required as opposed to an array for interferometric and similar processing methods that rely on the intersection of LOBs to determine the PF.
Normally, higher precision and more accuracy can be obtained with quadratic processing.
On the other hand, there is one primary drawback:
Typically, preprocessed data samples are required for nonpulsed modulations. This requires interlinking data links with considerable bandwidth between sensor platforms or the sensor platform and some processing site. This is not normally a problem in pulsed signal environments where signal events can be identified (for example, the leading edge of a pulse), such as radar geolocation or digital data signals.
A technique that yields the PF in closed form using TDOA measurements was presented in [1]. Presented here are some alternative algorithms. Two of these algorithms would be expected to perform better with noisy or erroneous measurements...
