The importance of sound velocity determination for bathymetric survey

Bathymetric surveys are carried out whenever there is a need to know the exact morphological trend of the seabed. For a correct operation of the echo sounder, which uses the principle of acoustic waves to scan the bottom and determine the depth, it is important to accurately determine the sound velocity in water, as it varies according to specific parameters (Density, Temperature, and Pressure). In this work, we want to analyse the role of sound velocity determination in bathymetric survey and its impact on the accuracy of depth measurement. The experiments are conducted on data set provided by “Istituto Idrografico della Marina Militare Italiana” (IIM), the official Hydrographic Office for Italy, and acquired in the Ligurian sea. In our case, the formulas of Chen & Millero (UNESCO), Medwin, and Mackenzie were applied. The introduction of errors on chemical-physical parameters of the water column (Temperature, Pressure, Salinity, Depth) simulating inaccurate measurements, produces considerable impacts on sound velocity determination and subsequently a decrease of the depth value accuracy. The results remark the need to use precise probes and accurate procedures to obtain reliable depth data.

Pemodelan 3D Lapisan Dasar Laut Dan Identifikasi Ketebalan Sedimen Berdasarkan Kombinasi Data Pengukuran Sub-Bottom Profiler Dan Single Beam Echosounder (Studi Kasus: Alur Akses Timur Surabaya)

Pelabuhan merupakan salah satu fasilitas umum yang memiliki peran penting dalam keselamatan navigasi pelayaran. Shipping yang aman harus didukung dengan pemantauan dan pemeliharaan secara berkala untuk mendapatkan informasi terkini tentang kedalaman, dasar laut, dan sedimentasi. Jika sedimentasi terakumulasi secara terus menerus dalam waktu singkat di alur akses (jalur pelayaran), maka dapat meningkatkan kemungkinan terjadinya kecelakaan kapal. Kajian ini mencoba memetakan dan menganalisis kondisi batimetri dan sedimentasi untuk mendukung pemantauan dan pemeliharaan rutin alur akses Timur Pelabuhan Tanjung Perak Surabaya. Metode yang digunakan dalam penelitian ini adalah survei akustik berdasarkan data pengukuran Sub-Bottom Profiler (SBP) dan Single Beam Echosounder (SBES). Data yang diperoleh kemudian dikoreksi oleh Sound Velocity Profiler (SVP), data pasang surut, dan draft transduser. Kualitas data kemudian diuji berdasarkan IHO SP-44 2008 dan uji t-studentized dengan tingkat kepercayaan 95%. Hasil dari penelitian ini adalah model 3 dimensi, profil kedalaman, ketebalan, dan volume lapisan sedimen dasar laut. Hasil penelitian menunjukkan bahwa alur akses Timur Surabaya memiliki empat lapisan dasar laut yaitu permukaan dan tiga lapisan sedimen di bawahnya. Kedalaman lapisan bervariasi antara 3 m sampai 16,8 m. Kualitas data kedalaman lapisan atas dikontrol oleh IHO S-44 2008 dengan nilai uji hitung 0,509 (nilai toleransi ± 0,509), sedangkan kualitas data SBP (diukur menggunakan t-studentized uji) mendapatkan nilai hitung sebesar -1,287 dengan toleransi ± 1,96. Artinya kualitas datanya bagus. Berdasarkan model 3d, rata-rata ketebalan lapisan secara berurutan adalah 5,84 m, 1,072 m, 0,758 m, dan 6.355 m, sedangkan total volume sedimen adalah 24.894.422,949 m3.

Sound Velocity Measurement of Shock-Compressed Quartz at Extreme Conditions

The physical properties of basic minerals such as magnesium silicates, oxides, and silica at extreme conditions, up to 1000 s of GPa, are crucial to understand the behaviors of magma oceans and melting in Super-Earths discovered to data. Their sound velocity at the conditions relevant to the Super-Earth’s mantle is a key parameter for melting process in determining the physical and chemical evolution of planetary interiors. In this article, we used laser indirectly driven shock compression for quartz to document the sound velocity of quartz at pressures of 270 GPa to 870 GPa during lateral unloadings in a high-power laser facility in China. These measurements demonstrate and improve the technique proposed by Li et al. [PRL 120, 215703 (2018)] to determine the sound velocity. The results compare favorably to the SESAME EoS table and previous data. The Grüneisen parameter at extreme conditions was also calculated from sound velocity data. The data presented in our experiment also provide new information on sound velocity to support the dissociation and metallization for liquid quartz at extreme conditions.

Self-diffusion coefficient and sound velocity of Fe-Ni-O fluid: implications for the stratification of Earth’s outer core

It is experimentally reported that the stratified layer atop Earth’s outer core is hundreds of kilometers thick with a maximum sound velocity reduction of 0.3% relative to the preliminary reference Earth model. However, why the sound velocity atop the outer core is reduced remains theoretically unclear. In this paper, the Ni and vital light O in the outer core were both considered to have implications for the stratification of Earth’s core, including the stratification thickness and the sound velocity profile. Ab initio molecular dynamics simulations were performed on the Fe-Ni-O fluid under the conditions of Earth’s outer core, and the self-diffusion coefficients and ion-ion dynamic structure factors were calculated. The self-diffusion coefficient of O is (19.56±0.83)×10-9 m2s-1 at the core-mantle boundary. Combining the diffusion equation with the time evolution of the O self-diffusion coefficient, the calculated stratification thickness at present is 194.7 km. The calculated ion-ion dynamic structural factors indicate that the sound velocity in the outmost outer core near the stratified layer is 7.86 km/s. These results show that Fe-Ni-O is a possible composition of the stratified layer atop the outer core featuring an appropriate thickness and a reduced sound velocity, thereby shedding light on the dynamic behavior of Earth’s core.

A Novel Factor Graph and Cubature Kalman Filter Integrated Algorithm for Single-Transponder-Aided Cooperative Localization

Cooperative localization (CL) of underwater multi-AUVs is vital for numerous underwater operations. Single-transponder-aided cooperative localization (STCL) is regarded as a promising scheme for multi-AUVs CL, benefiting from the fact that an accurate reference is adopted. To improve the positioning accuracy and robustness of STCL, a novel Factor Graph and Cubature Kalman Filter (FGCKF)-integrated algorithm is proposed in this paper. In the proposed FGCKF, historical information can be efficiently used in measurement updating to overcome uncertain observation environments, which greatly helps to improve the performance of filtering progress. Furthermore, Adaptive CKF, sum product, and Maximum Correntropy Criterion (MCC) methods are designed to deal with outliers of acoustic transmission delay, sound velocity, and motion velocity, respectively. Simulations and experiments are conducted, and it is verified that the proposed FGCKF algorithm can improve positioning accuracy and robustness greatly than traditional filtering methods.