Marine magnetic method is widely used for detecting and locating the submarine pipeline. In this paper, the theoretical calculation model of total-field magnetic anomalies (TMAs) of submarine pipeline was derived based on Poisson's equation. Taking a submarine gas pipeline for example, the TMA theoretical calculation and the verification sea test were carried out. Based on the calculation, the influences that the geomagnetic parameters, pipeline parameters, and measuring plane height had on the TMA characteristics of pipeline were analyzed. The TMA shape changed slightly with geomagnetic declination D and was significantly influenced by the azimuth θ of the pipeline. The corresponded location of the pipeline on the TMA profile varied with D seemed to be symmetrical with D = 0° as the center, but within 1.0 m, and changed greatly with θwith an offset distance of upping to 4.4 m. The TMA amplitude was linearly positively correlated with geomagnetic intensity T₀, quadratic difference of outer and inner diameters of pipeline d₁²-d₂², and susceptibility κ, respectively, and was inversely proportional to the square of measuring plane height R, and changed greatly with D, I, and θ but without obvious correlation. The TMA width changed greatly with I and θ, respectively, but without obvious correlation, and was approximately positively correlated with R. On the TMA profile that was perpendicular to the pipeline, there would be an obvious ``pulse'' anomaly on the smooth profile, and the location of pipeline corresponded a specific point near the TMA maximum point depending on D and θ, so that the accurate location of the pipeline needed to be corrected according to these two parameters, not just the TMA maximum point.

Marine geophysical and geological investigations are crucial for evaluating the construction suitability of artificial fish reefs (AFRs). Key factors such as seabed topography, geomorphology, sub-bottom structure, and sediment type significantly influence AFR design and site selection. Challenges such as material sinking, sediment instability, and scouring effects should be critically considered and addressed in the construction of AFR, particularly in areas with soft mud or dynamic environments. In this study, detailed investigations were conducted approximately seven months after the deployment of reef materials in the AFR experimental zones around Xiaoguan Island, located in the western South Yellow Sea, China. Based on morphological factors, using data from multibeam echosounders and side-scan sonar, the study area was divided into three geomorphic zones, namely, the tidal flat (TF), underwater erosion-accumulation slope (UEABS), and inclined erosion-accumulation shelf plain (IEASP) zones. The focus of this study was on the UEABS and IEASP experimental zones, where reef materials (concrete or stone blocks) were deployed seven months earlier. The comprehensive interpretation results of multi-source high-resolution acoustic images showed that the average settlement of individual reefs in the UEABS experimental zone was 0.49 m, and their surrounding seabed experienced little to no scouring. This suggested the formation of an effective range and height, making the zone suitable for AFR construction. However, in the IEASP experimental zone, the seabed sediment consisted of soft mud, causing the reef materials to sink into the seabed after deployment, preventing the formation of an effective range and height, and rendering the area unsuitable for AFR construction. These findings provided valuable scientific guidance for AFR construction in the study area and other similar coastal regions.

The topographic features of the seafloor can be observed clearly via high-resolution side-scan sonar imagery. However, the faithful interpretation of a sonar image depends strongly on the accuracy with which the location of the sea bottom line can be tracked within the image, and current tracking methods function poorly under high sonar signal noise or suffer from high complexity. The present work addresses this issue by applying the characteristics of simple sonar waterfall maps in conjunction with robust edge detection and multi-scale analysis based on wavelet transform modulus maxima. The proposed tracking method is demonstrated to provide superior effectiveness and accuracy in comparison with existing baseline methods based on the results of experiments conducted with a representative side-scan sonar image with and without applied speckle noise. This superiority can be attributed to the good localization characteristics and multi-scale detection features of wavelet transform analysis, which can suppress the impact of noise in the sonar image on the accurate extraction of edge information.