A critical examination of worldwide guidelines for minimising the disturbance to marine mammals during seismic surveys

Marine seismic exploration has potentially detrimental effects upon marine life and marine mammals in particular. Potential effects range from disturbance that may lead to displacement from feeding or breeding areas, to auditory damage and potential mortality. Nations including the USA, Canada and Brazil have followed the example set by the United Kingdom by introducing guidelines to minimise acoustic disturbance to marine mammals. This paper describes the mitigation measures central to the guidelines currently in place, and identifies the similarities, differences and deficiencies within them. A need for further review by some nations is identified, with a recommendation that an international standard should be produced, benefiting both the geophysical exploration industry and the conservation community.     

Developing self-guided scuba dive routes in the Algarve (Portugal) and analysing visitors' perceptions

Scuba diving allows for underwater visitation of cultural and natural resources. Underwater routes can be used as a tool for guided and supervised underwater visits. Two scuba diving routes were implemented in the Algarve (South of Portugal), the “B24” and “Poço” diving sites. The perceptions of scuba divers regarding several aspects of the routes and the existing support infrastructures were studied following a survey carried out through face-to-face interviews from 2008 to 2012. Divers profile and their perceptions were analysed using 246 valid questionnaires. Divers were mainly Portuguese, over 30 years old and with more than 12 years of formal education. Some of the support infrastructures did not achieve a “good” or “acceptable” grade. This should be carefully considered by diving operators and managers, because perceptions tend to circulate throughout the diving tourists. All features of interpretative slates were graded as highly satisfactory. Overall, diver satisfaction increased slightly after route implementation, with an average ranking of “good”. These findings support the implementation of underwater routes as a way to promote diving activity, and to increase divers' environmental education and awareness.     

Characterization of the solar light field within the ocean mesopelagic zone based on radiative transfer simulations

The solar light field within the ocean from the sea surface to the bottom of the mesopelagic zone was simulated with a radiative transfer model that accounts for the presence of inelastic radiative processes associated with Raman scattering by water molecules, fluorescence of colored dissolved organic matter (CDOM), and fluorescence of chlorophyll-a contained in phytoplankton. The simulation results provide a comprehensive characterization of the ambient light field and apparent optical properties (AOPs) across the entire visible spectral range within the depth range 200–1000 m of the entire mesopelagic zone for varying chlorophyll-a concentration and seawater optical properties in the mixed surface layer of the ocean. With increasing depth in the mesopelagic zone, the solar irradiance is reduced by ~9–10 orders of magnitude and exhibits a major spectral maximum in the blue, typically centered around a light wavelength of 475 nm. In the green and red spectral regions, the light levels are significantly lower but still important owing to local generation of photons via inelastic processes, mostly Raman scattering and to a lesser extent CDOM fluorescence. The Raman scattering produces a distinct secondary maximum in irradiance spectra centered around 565 nm. Comparisons of our results with light produced by the radioactive decay of the unstable potassium isotope contained in sea salt (⁴⁰K) indicates that the solar irradiance dominates over the ⁴⁰K-produced irradiance within the majority of the mesopelagic zone for most scenarios considered in our simulations. The angular distribution of radiance indicates the dominance of downward propagation of light in the blue and approach to uniform distribution in the red throughout the mesopelagic zone. Below the approximate depth range 400–500 m, the shape of the angular distribution is nearly invariant with increasing depth in the green and red and varies weakly in the blue. The AOPs at any light wavelength also assume nearly constant values within the deeper portion of the mesopelagic zone. These results indicate that the mesopelagic light field reaches a nearly-asymptotic regime at depths exceeding ~400–500 m.     

Photogrammetric modeling of the relative orientation in underwater environments

Underwater photogrammetry provides an efficient means for documentation of environments which are complex and have limited accessibility. Yet the establishment of reference control networks in such settings is oftentimes difficult. In this regard, use of the coplanarity condition, which requires neither knowledge of object space coordinates nor setting a reference control network, seems to be an attractive solution. However, the coplanarity relation does not hold in such environments because of the refraction effect, and methods that have been proposed thus far for geometrical modeling of its effect require knowledge of object-space quantities. Thus, this paper proposes a geometrically-driven approach which fulfills the coplanarity condition and thereby requires no knowledge of object space data. Such an approach may prove useful not only for object space reconstruction but also as a preparatory step for application of bundle block adjustment and for outlier detection. All are key features in photogrammetric practices. Results show that no unique setup is needed for estimating the relative orientation parameters using the model and that high levels of accuracy can be achieved.     

Power cycle analysis of two-phase underwater ramjet

To predict the cycle and propulsive performance, and further instruct the integral engine design, an ideal power cycle model for a two-phase underwater ramjet is established. Four performance parameters are defined to evaluate overall performance of the two-phase underwater ramjet systems: transmission efficiency, propulsive efficiency, overall efficiency and specific impulse. Then, a scaled-down experimental ramjet engine was tested in a direct-connect ground testing system to validate the present model, and the predictions with present model compare favorably with experimental results. Subsequently, the influences of cruise velocity, air/water mass ratio and cruising depth on the theoretical performance of the two-phase underwater ramjet are discussed. The results indicate that one of the most outstanding advantages of two-phase underwater ramjet is its high propulsive efficiency with the order of 50–95%. As a result, the overall efficiency magnitude are as high as 30% at cruise speed of 100 m/s. Furthermore, regarding rules of specific impulse vs cruise velocity under a certain air/water mass ratio, the occurrence of peak specific impulse of order 400 s is observed.     

Pseudo long base line navigation algorithm for underwater vehicles with inertial sensors and two acoustic range measurements

This paper presents an integrated navigational algorithm for unmanned underwater vehicles (UUV) using two acoustic range transducers and strap-down inertial measurement unit (SD-IMU). A range measurement model is derived for a UUV having one acoustic transducer and cruising around two reference transponders at sea floor or surface. The proposed algorithm, called pseudo long base line (PLBL), estimates the position of the vehicle integrating the SD-IMU signals corrected with the two range measurements. Extended Kalman filter was applied to propagate error covariance, to update measurement errors and to correct state equation whenever the external measurements are available. Simulations were conducted to illustrate the effectiveness of the PLBL using the 6-d.o.f. nonlinear numerical model of a UUV at current flow, excluding bottom-fixed DVL. This paper also shows the error convergence of the vehicle's initial position by the additional range measurements without velocity information.     

水下差分GPS定位系统差自修正迭代算法研究

在水下差分GPS定位中，星形空间网具有良好的图形强度，可以快速得到一定精度的初始坐标解。本文研究了水下差分GPS定位模型及其算法，并提出了一种系统差自修正迭代算法，以提高水下定位的可靠性。     

A bottom-up methodology for integrating underwater video and acoustic mapping for seafloor substrate classification

A method that links acoustic mapping data to underwater video observations of seafloor substrate is described for use in defining fish habitat. Three study areas in the Aleutian Islands were acoustically mapped using sidescan and multibeam sonar. The sidescan sonar data were used to compute average reflectivity (hardness) and seafloor complexity. The multibeam depth data were used to determine local slope, rugosity (seafloor roughness) and relative height. Underwater video was collected from three to four transects in each of the three study areas. The underwater video was used to classify the seafloor into nine observed primary and secondary substrate classes. A statistical relationship between the observed (video) and the remotely sensed (acoustic) seafloor characteristics was estimated using a classification tree. The best classification tree utilized rugosity, reflectivity and complexity data and produced misclassification rates of less than 25% overall. Mean grain size of sediment samples was not strongly related to the acoustic data. Error rates were highest for those substrate classes with the smallest number of data points. The results highlight the need for adequate sample sizes and coverage of all potential substrate types when groundtruthing acoustic maps.     

Laboratory experiments evaluating sedimentation and mound formation of obliquely discharged sand particles in stagnant water

Many parameters are involved in the deposition of a known mass of sand particles discharge from oblique pipes used in a range of engineering applications. Existing knowledge is not sufficient to accurately predict sediment mound dimensions and development from vertical and horizontal pipes. To better understand deposition patterns, laboratory experiments were done to investigate the development of subaqueous sand deposits from oblique pipes in stagnant water. Factors including nozzle diameter, release angle, release height, and sand mass were evaluated. It was found that nozzle size plays the most important role in shape formation and mound development. Release angle and release height were secondarily important. Five different shape patterns were observed and denoted as circular, ellipse, circular-ring, ellipse-ring, and pear-shaped. The scour hole diameter in the middle of the sediment mound was predicted using engineering assumptions and available semi-empirical correlations from the literature. It was found that the existing formulations can accurately predict the size of the scour hole for large release angles (θ = 60°). An aspect ratio of L/d_o was defined to combine the effect of nozzle size, d_o, and sand mass where L is the equivalent length of sand particles in a pipe. It was found that the mass balance equation can predict the deposition for L/d_o < 100. For higher aspect ratios, semi-empirical formulations were developed to predict the deposition length, width, height, and area with ±10% error.     

水下爆破对大坝影响的离心模拟试验研究

由于离心机能够在原型应力条件下模拟爆破对大坝的影响。本文使用中国水利水电科学研究院研制的离心模拟爆破系统,在不同重力加速度之下研究了在不同水深,距坝面不同距离的情况下雷管爆破对于大坝的影响。