Evaluation of underwater acoustic images obtained by the early stage monotone pulse-echo Synthetic Aperture Sonar

Abstract

Synthetic Aperture Sonar (SAS) is a side-looking underwater acoustic imaging sonar that can obtain higher resolution images than those by the conventional Side Scan Sonar (SSS). Due to its high resolution images, it can be applied to various fields of studies from military to civilian purposes. Republic of Korea recently has launched a research project developing the prototypes of SAS being operated in a few hundreds kHz of acoustic signals. This project adopted the towfish as the SAS platform that are to be towed under a few tens of water depth, which has a price advantage over Autonomous Underwater Vehicle (AUV), but gives unstable motion. It also adopted the monotone pulse-echo mode as transceiver method of the prototypes that gives relatively simpler implementation of the data acquisition module although it gives inferior SNR to the chirp mode. In the current study, the underwater acoustic images of the protype SAS taken both in the fresh water and offshore of Korea are to be shown. Current study also shows the evaluation method of image resolutions using test targets simulating point scatterers. Resulting images are to be compared with the images by the conventional SSS through the evaluation of the resolution. As is well known, although SAS generated clearer underwater images than SSS images, phase uncertainty of the array is critical factor determining the image resolution of SAS that is heavily degradated by the unwanted motion of the SAS platform.Synthetic Aperture Sonar (SAS) is a side-looking underwater acoustic imaging sonar that can obtain higher resolution images than those by the conventional Side Scan Sonar (SSS). Due to its high resolution images, it can be applied to various fields of studies from military to civilian purposes. Republic of Korea recently has launched a research project developing the prototypes of SAS being operated in a few hundreds kHz of acoustic signals. This project adopted the towfish as the SAS platform that are to be towed under a few tens of water depth, which has a price advantage over Autonomous Underwater Vehicle (AUV), but gives unstable motion. It also adopted the monotone pulse-echo mode as transceiver method of the prototypes that gives relatively simpler implementation of the data acquisition module although it gives inferior SNR to the chirp mode. In the current study, the underwater acoustic images of the protype SAS taken both in the fresh water and offshore of Korea are to be shown. Current study also...