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A compact 3D ultrasonic sensor for scene analysis is presented in this paper. A centered transmitter emits a broadband ultrasonic impulse which is reflected by obstacles in the environment. Reflected waves, if propagated back to the sensor, are then received by four identical ultrasonic microphones. These signals are used to provide polar- and azimuth information based on time difference of arrival and in addition, by using a novel method presented in this paper, sub wavelength accurate distance measurements are possible as well. The used algorithm does not rely on the actual shape of the signal but only on its statistical properties. This is a great achievement because commercially available broadband ultrasonic transducers are typically piston membrane types which exhibit a strong frequency dependent radiation pattern. If measurements are performed outside of the main lobe, not only the signal amplitude is greatly reduced requiring algorithms capable of dealing with a low SNR but also the phase of the signal is affected yielding simple pulse compression techniques useless. The article includes a description of the problem, a comparison to existing systems, a theoretical treatment of the system configuration and experimental results demonstrating the performance of our sensor.