Quality assessment of synthetic aperture sonar images based on a single ping reference

Abstract

The formation of high resolution Synthetic Aperture Sonar (SAS) images requires precise position information of sensors over the whole synthetic aperture in order to coherently combine the reverberated signals. Due to an insufficient accuracy of the on-board navigation system additional means are necessitated. The state-of-the-art approach is to exploit the correlation structure of received echoes of overlapping phase centers between succeeding pings. This is well-known as the Displaced Phase Center Antenna (DPCA) or Redundant Phase Center (RPC) algorithm. We propose to use a quality metric to recursively assess the reconstructed images against a single ping reference image. This approach obtains a focused image with the maximum resolution by automatically selecting the maximum number of consecutive pings for which unwanted motion has completely been compensated.

A Correction Approach for the Inclined Array of Hydrophones in Synthetic Aperture Sonar

“…Considering that most of work reported is based on the assumption that only yaw angle has an impact on the image quality [ 8 , 12 , 13 , 14 , 15 , 16 , 17 , 18 ], we perform the correction in three cases: only pitch angle correction, only yaw angle correction, and both pitch angle and yaw angle correction. It is important to note that the proposed approach in this paper is the case of both pitch angle and yaw angle correction.…”

“…Thus, roll is not a significant defocusing factor, and only yaw and pitch need to be taken into account. At present, most of work reported is based on the assumption that only yaw has an impact on the image quality [ 8 , 12 , 13 , 14 , 15 , 16 , 17 , 18 ], and there is little research reported that yaw and pitch both have an impact on the image quality. The approaches of the yaw-only correction can be classified into three categories: time-domain beamforming method [ 19 , 20 , 21 ], preprocessing correction method [ 12 ], and imaging autofocus method [ 3 ].…”

Moderate squint imaging algorithm for the multiple‐hydrophone SAS with receiving hydrophone dependence

“…Currently, there are two methods of equivalent azimuth sampling used in motion compensation, which can be applied to squint. The first method is to take the projection position of hydrophones on the trajectory as the equivalent azimuth sampling position [10, 11], referred as PANT. The second method is to take the ideal azimuth sampling position as the equivalent azimuth sampling position [12, 13].…”

Sequential focus evaluation of synthetic aperture sonar images

“…In contrast to the speed of electromagnetic waves in air, the limited speed of sound in water requires an SAS system to consist of an array of hydrophones to achieve reasonable coverage rates [6]. Simultaneously, it provides the capability of constructing low resolution images, which can be exploited to successively evaluate the cross-range focusing of the synthetic aperture and therefore the quality of the resulting images [7]. Besides assessing the reliability of the input for automatic detection and classification, image quality evaluation is also important for adaptive mission planing [8].…”

“…This is in contrast to [1,8], who relate image quality to the peak correlation between successive pings and therefore, work in the raw data domain. Moreover, the proposed approach facilitates an evaluation based on the theoretical resolution, while this is not feasible with the energy ratio proposed in [7].…”