Methods and systems for acquiring seismic data of four-component ocean bottom node (OBN)

A method for data acquisition of a system for acquiring seismic data of a four-component ocean bottom node (OBN), implemented by the system for acquiring the seismic data of the four-component ocean bottom node (OBN), the system comprising a plurality of ocean bottom submerged buoys, a plurality of ocean surface buoys, armored opto-electronic composite cables, a plurality of four-component OBN seismic data acquisition instruments, and an ocean surface seismic source vessel;

• wherein
• the plurality of four-component OBN seismic data acquisition instruments are deployed in an ocean bottom seismic data acquisition work area based on a pre-designed measurement grid;
• the plurality of ocean bottom submerged buoys are deployed around the ocean bottom seismic data acquisition work area, the plurality of ocean bottom submerged buoys being corresponding to the plurality of ocean surface buoys, respectively, and the plurality of ocean bottom submerged buoys being connected to the plurality of ocean surface buoys by the armored opto-electronic composite cables;
• the ocean surface seismic source vessel performs seismic source excitation below a water surface of the ocean bottom seismic data acquisition work area by an air gun seismic source towed at a stern of the vessel;
• each of the plurality of ocean bottom submerged buoys is provided with a hydroacoustic signal emission source with a built-in long baseline positioning system, a short baseline positioning system, or an ultra-short baseline positioning system, and a rechargeable battery;
• each of the plurality of ocean surface buoys is provided with a built-in GPS and a BeiDou satellite signal receiving antenna, a solar panel, a photoelectric conversion module, and a composite modulation and demodulation (modem) instrument;
• each of the armored opto-electronic composite cables is provided with a cable, and an outer layer of the each of the armored opto-electronic composite cables is encased with a high-strength sheath braided with Kevlar fibers or an armor twisted with one or more layers of stainless steel wires, and the cables include continuous grating optical fibers, single-mode and multi-mode optical fibers, coaxial cables, and twisted power supply cables;
• a top of each of the plurality of four-component OBN seismic data acquisition instruments is provided with a hydroacoustic transponder, the each of the plurality of four-component OBN seismic data acquisition instruments is a conventional four-component OBN seismic data acquisition instrument equipped with a built-in three-component conventional geophone and a piezoelectric hydrophone, or a fiber optic four-component OBN seismic data acquisition instrument;
• and
• the each of the plurality of four-component OBN seismic data acquisition instruments includes a pressurized chamber, the pressurized chamber is provided with a three-component fiber optic geophone, a fiber optic acoustic pressure hydrophone, a three-component attitude sensor, a semiconductor light source, an internal opto-electronic conversion module, a modem module, a pre-amplification and A/D conversion module, a data storage module, and a rechargeable battery module;
• wherein
• the method comprises:
• firstly, placing four ocean bottom submerged buoys around the ocean bottom seismic data acquisition work area, wherein tail ends of the armored opto-electronic composite cables are connected with the plurality of ocean bottom submerged buoys, and head ends of the armored opto-electronic composite cables are connected with the plurality of ocean surface buoys;
• laying the plurality of four-component OBN seismic data acquisition instruments to an ocean bottom of the ocean bottom seismic data acquisition work area by ropes, steel cables, or ROV based on coordinates of the pre-designed measurement grid;
• activating instruments in the plurality of ocean bottom submerged buoys and the plurality of ocean surface buoys, and sending positioning signals and timing signals received by the GPS and BeiDou satellite signal receiving antennas of the plurality of ocean surface buoys to the plurality of ocean bottom submerged buoys via the opto-electronic composite cables;
• transmitting, by the plurality of ocean bottom submerged buoys, the positioning signals and the timing signals to waters surrounding the plurality of four-component OBN seismic data acquisition instruments via the hydroacoustic signal emission sources;
• receiving, by the hydroacoustic transponders installed on the tops of the plurality of four-component OBN seismic data acquisition instruments, the positioning signals and the timing signals emitted from the plurality of ocean bottom submerged buoys, respectively, to perform accurate positioning and uninterrupted real-time timing;
• the optical fibers within the armored opto-electronic composite cables are connected with the composite modem instruments within the plurality of ocean surface buoys to obtain real-time and uninterrupted water temperature, pressure, density, and salt saturation of seawater along the armored opto-electronic composite cables from the ocean surface to locations of the plurality of ocean bottom submerged buoys;
• calculating real-time and three-dimensional water temperature, pressure, density, and salt saturation values of seawater within waters of a whole measurement work area through interpolation by using the water temperature data, the pressure data, the density data, and the salt saturation data measured by all the armored opto-electronic composite cables from the ocean surface to the locations of plurality of ocean bottom submerged buoys;
• performing real-time hydroacoustic velocity correction for each hydroacoustic propagation trajectory from the each of the plurality of ocean bottom submerged buoys to the each of the plurality of four-component OBN seismic data acquisition instruments based on a hydroacoustic propagation trajectory line between an accurate location of the each of the plurality of four-component OBN seismic data acquisition instruments and the each of the plurality of ocean bottom submerged buoys by using the calculated real-time and three-dimensional water temperature, pressure, density, and the salt saturation values of seawater within the waters of the ocean bottom seismic data acquisition work area;
• and
• performing real-time correction on the positioning data and the timing data of the each of the plurality of four-component OBN seismic data acquisition instruments by using an amount of real-time hydroacoustic velocity correction performed for the each hydroacoustic propagation trajectory from the each of the plurality of ocean bottom submerged buoys to the each of the plurality of four-component OBN seismic data acquisition instruments, to ensure that the positioning data and timing accuracy of the each of the plurality of four-component OBN seismic data acquisition instruments meets measurement error requirements of the measurement work area.