High-resolution 2-D imaging using narrowband MIMO sonar

For an underwater 2-D imaging sonar system, to discriminate echoes reflected back in the 3-D space, a rectangular array is necessary. However, to obtain a high cross-range resolution, the physical size and the sensor number of the array will become inevitably large. To avoid this, a high-resolution 2-D imaging approach based on a multiple-input multiple-output (MIMO) sonar is proposed in this paper. The MIMO sonar is composed of four uniform linear arrays (ULAs) located on four sides of a rectangle. And narrowband waveforms coded with orthogonal polyphase sequences are employed as transmitting waveforms. By matched filtering the outputs at each receiving sensor, the MIMO sonar is equivalent to a virtual rectangular array with a twice big aperture. With theoretical analysis and computer simulations, we show that the MIMO sonar can save a great number of sensors and double the cross-range resolution simultaneously, when compared to a conventional rectangular array with the same physical size.