Spatial interferometry is based on the kind of interferometry used for many years by radio astronomers. It uses the property known as coherence to obtain positional information from processing received signals. However, we can now take the method one stage further and can obtain

The way this works is illustrated in the diagram shown above. We collect copies‘ of a radiated signal in at least three different places. We then compare these and determine the relative times of arrival. This tells us the differences in the path-lengths from each collecting point (port) and the signal source. Provided we also know the relative positions of the collecting points we can then use simple trigonometry to work out the direction to (the bearing) and the distance to (the range) of the source. If we use at least four ports, placed so that they are not all on the same straight line, we can make a 3D measurement of the source position.

Unlike radar, this method does not require us to beam power

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Acoustic Imaging and Interferometry.

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