By continuously adjusting the axis of a scanning beam, targets can be localized via amplitude modulations in their reflected echoes.

Extracting angular position from a single modulated echo requires precise knowledge of receiver position during the scan. By contrast, comparing echoes picked-up by 2 receivers scanning at the same speed but in opposite directions only requires knowledge of their overall trajectory.

Below, elevation localization of a small moving target in a cluttered environment. Delay between peaks in the filterbank outputs from left and right receivers scanning through opposing vertical arcs measures elevation angle. (Approx 10ms per degree.)

Target elevation = 0 degr Target elevation = 4 degr