Investigation method and equipment thereof

The exploration of ocean polymetallic nodule mineral resources requires the comprehensive application of various geophysical exploration methods and geological exploration methods. Geophysical exploration methods include: seabed topographic survey, gravity and magnetic survey and seismic survey; Advanced exploration systems such as multi-frequency detection and seabed photography, deep towing and multi-beam echo sounding. Various geological exploration methods include wired geological sampling, cable-free geological sampling, temperature-salinity-depth measurement and so on. The methods used in different exploration stages have different types and workload requirements. The following is a further description of various investigation equipment (sign II-2) and their methods.

3.2. 1 Geophysical exploration method and its investigation equipment

1. Submarine topographic survey and survey equipment

Submarine topographic survey is one of the essential survey items in ocean polymetallic nodule survey. Through bathymetry, we can understand the topographic characteristics and basic situation of the seabed, thus providing the necessary basic information for evaluating and mining the mining area.

In the stage of regional investigation, single-beam bathymeter is mainly used to reveal the seabed topography. The traditional method is to use echo sounder to measure the water depth in the investigation area in order to obtain the basic information of the terrain. In recent years, the application of some advanced testing instruments, such as SEABEAM and other multi-beam measuring equipment, makes the seabed topographic survey more accurate and reliable. The performance and related information of SEABEAM and other instruments and equipment will be described below. This paper will introduce the use of echo sounder to survey the seabed topography.

In the stage of regional survey, the commonly used instrument for water depth measurement is the 12.5kHz 10,000-meter bathymeter, and its measurement accuracy is determined by the positioning accuracy and sounding accuracy of the ship during navigation. The measured data can be corrected by water depth and sound velocity, and the corresponding water depth value can be obtained for drawing seabed topographic map. The disadvantages of this kind of bathymeter are that the sampling interval of water depth data is large (1km), so it is difficult to accurately reflect the topography, and the smaller topographic contour lines are often leveled, which makes the seabed smooth and simplifies the topography in complex areas.

2. Seismic exploration and its equipment

In order to understand the distribution characteristics, internal structure and basement fluctuation of seabed sediments, the acoustic exploration method of single-channel earthquake is often used in the exploration of ocean polymetallic nodules. The equipment configuration scheme is NEC-20C single channel profiler, digital seismograph, air gun, floating cable, etc. The data is recorded in analog or digital mode, and the gun number is recorded in digital mode on the magnetic tape of satellite navigation system. The working speed is usually 6kn. The starting and ending points of the survey line should be qualified navigation and positioning points, and the digital records of single-channel earthquakes are often combined with other acoustic wave detection results to explain the distribution of polymetallic nodules.

The combination of single-channel seismic data and multi-frequency detection data can often obtain better interpretation results, and this kind of investigation is often used in the initial stage of polymetallic nodules.

3. Multi-frequency detection and its equipment

Multi-frequency exploration data processing system is a computer data processing system that uses multi-frequency sound waves to detect the abundance and granularity of deep-sea polymetallic nodules. The system can work at the normal sailing speed (10 ~ 12kn), and can process the obtained data on the ship to quickly obtain the abundance and particle size of polymetallic nodules.

Multi-frequency exploration data processing system is mainly composed of three parts: acoustic wave transmission and reception, analog signal detection and data processing. The acoustic wave transmitting and receiving part is equipped with shallow profiler (SBP), depth sounder (PDR) and narrow beam depth sounder (NBS). The function of analog signal detection part is to amplify and filter the sound signal. The data processing part digitizes, stores and processes the sound signal. At present, three different frequencies are used: SBP-3.5 kHz, PDR- 12 kHz, NBS-30 kHz, and the corresponding receiving instruments.

Polymetallic nodules are distributed in sheets on the surface of the seabed, and the surface sediments are generally siliceous clay, deep-sea clay, siliceous ooze or calcareous ooze. This kind of sediment is rich in pore water, soft and uniform in texture, and its sound velocity is close to or slightly lower than that of water. The reflectivity of sound waves in this layer is very low, which can be approximately considered as an unimpeded penetration of this sedimentary layer (that is, the sound-permeable layer). Polymetallic nodules, together with the underlying sediments, appear as a non-reflective zone or a weak reflective zone (i.e., an acoustically transparent layer) on the shallow profile of 3.5kHz. The sea area with too high or too low deposition rate is not conducive to the growth of nodules, and only an acoustically transparent layer with a specific thickness is conducive to the production of polymetallic nodules. Multi-frequency detection system uses MFES- 100B multi-frequency detection data processing system, 3.5kHz shallow profiler and 12kHz echo sounder to measure nodule abundance, and 30kHz narrow beam profiler is needed to measure nodule granularity. The combination of multi-frequency detection and single-channel seismic detection data can often get better interpretation effect.

Multi-frequency detection combined with other methods can get satisfactory results, including geological sampling and other means. Some countries use multi-frequency detection system to investigate polymetallic nodules. Compared with the actual grab sampling results, the correlation coefficient is 0.7.

When the multi-frequency exploration data processing system is used with other acoustic detectors of the survey ship (such as echo detector and deep-sea shallow profiler), the distribution density and size of polymetallic nodules on the seabed can be continuously measured. In this case, theoretically, the frequencies of echo sounder and deep-sea profiler should be in the following ranges: 3 ~ 5 kHz, 8 ~ 15 kHz, 25 ~ 3~5kHz. Because the diameter of the nodule to be detected ranges from several centimeters to +00 centimeters, the multi-frequency detection data processing system can be used in combination with any common acoustic detection instrument as long as the acoustic output signals measured from these instruments are linearly amplified and controlled to avoid saturation.

The specific working method of multi-frequency survey is similar to other geophysical methods, and the layout of survey network depends on different survey stages. According to different precision requirements and scales, the appropriate data acquisition time interval is selected, usually 3 ~ 4 points are collected every kilometer, so different acquisition time intervals are needed for different speeds to ensure the exploration precision requirements.

Compared with cableless grab or cabled grab, multi-frequency detection system has the following advantages:

(1) fast;

(2) continuous data of the whole survey line can be obtained;

(3) The correlation coefficient is 0.7 ~ 0.9;

(4) The work is convenient, safe and reliable.

Compared with underwater photography and underwater television, the multi-frequency detection system is low in cost, fast, safe and reliable, and is not affected by obstacles such as seabed topography and seamounts. It is suitable for large-scale continuous marine survey.

4. Gravity and magnetic measurement and its instruments and equipment

Gravity and magnetic surveys are often carried out in the early stage of marine polymetallic nodules survey, with the aim of understanding the structural characteristics, magmatic activities and the controlling factors of submarine topography changes in the survey area. The existing survey ships in China are often equipped with this kind of equipment, such as KSS-5 marine gravimeter and G82 1G nuclear magnetic gradient instrument used by Ocean 4. Xiang Yanghong 16 is equipped with KSS-5 marine gravimeter and CHHK-2 marine nuclear magnetometer.

5. Underwater photography and its equipment

Through seabed photography, we can directly observe the occurrence state of polymetallic nodules on the ocean surface, obtain their coverage, particle size and abundance, and understand the characteristics of seabed surface sediments and the activities of benthos. Underwater photography usually adopts two methods and equipment:

(1) Self-returning seabed photography system This equipment can cooperate with the self-returning sampling device to photograph the distribution characteristics of seabed sediments and polymetallic nodules at the sampling point. The improved 420 1 self-return grab produced by Boathos Company of the United States is equipped with an underwater camera system. In this system, a pocket-sized 135 camera is installed in a high-pressure sealed box. The camera is equipped with a 2.0kg weight, and the electromagnetic shutter is activated when it touches the seabed. Before sampling, photos are triggered, and the maximum photographed seabed area is 2.1m×1.4m. ..

Figure 3- 1 Underwater Photography System

(2) The towed submarine photography system is used to find out the occurrence of polymetallic nodules on the seabed, and the photos are used by researchers to calculate nodule coverage, calculate abundance and other explanations. Ocean 4 adopts CI800 and CI256 underwater photography systems produced by British Camera Alive company (Figure 3- 1). These two systems have the same structure and principle, and are composed of camera, flash lamp, sound pulse generator, trigger, DC power supply and synchronous controller. The former can shoot 800 135 color films continuously, while the latter can shoot 256 135 color films continuously (the camera lens is 3m away from the seabed, and the maximum picture coverage area of each film is 3.9rn×2.6m). When the camera system works, the steel cable is connected, and the 10,000-meter winch is retracted. The acoustic pulse generator and echo sounder transponder determine and control the submarine camera to reach the predetermined depth of the seabed, and trigger to take a photo at a time. The system has reasonable structure and good performance, and the success rate reaches about 80%.

There are also some countries that use submarine TV exploration system for seabed exploration in ocean polymetallic nodule areas. Of course, the technical performance of these equipment should also meet the following requirements: ① working depth-6000 m; (2) drag speed-2.5 kn; ③ The distance between the TV and the seabed is-3 ~10m; ④ The number of image frames is-2× 3150; ⑤ Television system-slow scanning standard.

6. Advanced exploration system and its equipment.

Advanced exploration systems, such as deep towing system and multi-beam echo sounder, are adopted by western countries in the exploration stage of polymetallic nodules, especially the deep towing system with TV/camera device, which can directly observe and evaluate polymetallic nodules on the seabed surface. Shallow profiler and side sonar equipped with deep towing device, as well as bathymeter, shallow profiler and side sonar equipped with multi-beam echo sounder, can provide information on seabed topography, composition [1], seabed structure and structure quickly and accurately. These devices are usually used in the later stages of exploration. This kind of equipment has been introduced in China, and these exploration systems can be used to obtain accurate and reliable data in the middle and late stage of nodule exploration in the pioneering area.

(1) Deep towing system Deep towing system is mainly composed of acoustic towing body and optical towing body. Take AMS-60SI deep drawing system manufactured by Simrad Company of the United States as an example. The acoustic trailer of the device is equipped with shallow profiler (4.5kHz), lateral sonar (56.7kHz) and other measurement systems, and has various acoustic measurement functions such as lateral sonar, strip water depth measurement and shallow stratum profile measurement. The optical trailer is equipped with a TV/camera system. The working water depth can reach 6000m. The equipment is also equipped with sensors for positioning correction of transverse sonar and shallow profile data. When the terrain distortion is caused by the change of towing depth during operation, it can be corrected by online automatic homing. The maximum towing speed of towing fish structure design is 8kn. However, when the system works with shallow profiler (4.5kHz), side sonar (56.7kHz) and other measuring systems, the deep towing device is placed 50m above the seabed, and the towing speed is1.5kn..

The deep towing equipment purchased in China includes an AMS-60SI standard acoustic towing cable car, a TV/photographic optical towing cable car, a deck control and data acquisition workstation, a post-processing workstation, a Dynacon diesel-hydraulic winch system and a 10,000-meter coaxial cable. In the acousto-optic trailer, the technical indicators of various equipment are as follows:

Side sonar

The emission frequency is 56.7kHz.

Transmit power 2000W (rms, high setting) 150W (rms, low setting)

Bandwidth level 1.5 0. 1 vertical 600

Minimum side discrimination compression of 20dB

Signal bandwidth. 8 khz

Fluxgate compass kvhc100,0 0. 10/0 resolution

The resolution of the rolling sensor is 0. 1

0.0 1m resolution of pressure/depth sensor

The strip sounding system is in-phase interferometry, and a group of transducers and related circuits are added, including the characteristic circuit of beam search and beam normalization.

Submarine profiler

The transmission frequency is 4.5kHz.

Transmit power 500W(RMS)

Bandwidth 25

Configuration of optical trailer

Colmek TVTM multiplex transmission system

Simrad photosea 5000D camera

The composition of SIMRAD photosea1500 SD flash ① refers to stratum stratification and layered structure.

Osprey sitoe 1323 TV camera

600TV line 5× 10-4LUX

Television lighting lamp

Simrad Mesotech altimeter 1807

TV signal transmission rate Real-time black-and-white transmission 30 frames/second

This device should be able to meet the requirements of detailed investigation of polymetallic nodules in the later period.

(2) Multi-beam bathymeter seabed multi-beam measurement system can provide high-density and high-quality topographic survey data. At present, in some advanced countries, the use of this equipment has gradually replaced the single-beam bathymeter. Since 1980, France has used the sea-beam multi-beam echo sounder on the "Jean Charco", and has made great progress in understanding the landform of the seabed polymetallic nodule producing area. This system emits 16 narrow sound waves (each 2 40'), forming a complex series, which can automatically compensate the pitching and pitching of the ship. After inputting the navigation data of the ship itself, a long seabed topographic map equivalent to 2/3 of the seabed depth on both sides of the channel can be obtained. In the sea area with a water depth of 5000m, the measurement resolution shall not exceed 20 ~ 30m. The advantage of multi-beam bathymeter is that it can detect a large area in a short time. In the sea area with a water depth of 5000m m, it can complete the investigation area of 30,000 km2 in 25 days ... The multi-beam bathymeter can reveal some geomorphological and structural features that cannot be revealed by bathymeter. However, in the final stage of exploration, it still cannot replace the high-resolution deep-drawing system.

The sounding range of this measuring system is10 ~11000 m. The latest generation of submarine multi-beam measuring system includes: submarine sounding system, side sonar and shallow profiler. At present, ATLAS in Germany, SINRAD in Norway and SEABEAM Instruments in the United States have all produced this system.

Take SEABEAM 2100 produced by seabeam instruments company as an example. Its main equipment includes: transmitting transducer subsystem, hydrophone subsystem, transmitter subsystem, receiver and sonar processor subsystem, workstation, drawing processor and display storage subsystem.

The latest generation of multi-beam measurement system integrates the functions of sounding, lateral sonar and shallow stratum profiler, and can simultaneously measure and obtain seabed wide terrain data, lateral sonar image data and shallow stratum profile data, draw seabed isobath map, and reveal useful information such as topography fluctuation, composition, seabed structure and structure.

Main technical indexes of SEABEAM 2 100 multi-beam measurement system;

The depth range is10 ~11000m.

Frequency 2 ~ 7 kHz

The sound source level is 233 dB/(micro Pa m)

Transmit power 30kW (peak linear)

TX dynamic range is 70dB.

TX pulse window rectangle, cosine

3.2.2 Geological exploration method and its investigation equipment

In all stages of polymetallic nodule investigation, geological samples must be systematically collected by stations for direct observation, description and testing. Use different research purposes, different investigation requirements and different sampling equipment. Various sample collection devices and their uses will be listed below.

1. Cable geological sampler

Cable geological sampling projects include grab, box sampler, trawl, gravity sampler and gravity piston sampler.

Grab (1) Grab is the most commonly used equipment to collect samples of polymetallic nodules or surface sediments. The supporting device of the cable grab is a deep-sea winch, with a steel wire rope and an inverted L-shaped hanger or A-shaped frame, which is used for dropping and recovering the sampler. An acoustic pulse generator is installed on the steel cable 50 ~ 100 m away from the sampler, and the pulse signal and seabed reflection signal generated by the acoustic pulse generator are received by the bathymeter, so that the operator can grasp the situation that the grab bucket reaches the seabed and locate and recover it in time. The opening area of common grab bucket is 0.25m2(50cm×50cm). At present, the grab used in the survey of ocean polymetallic nodules in China is mostly Ocean 50 manufactured by Institute of Oceanography (Qingdao) of China Academy of Sciences.

(2) box sampler box sampler (plate I-1) is used to collect undisturbed seabed sediment samples, with a sampling area of 0.25m2(50cm×50cm). The box sampler is connected by wire rope and released and recovered by the 10,000-meter winch. When dropping the samples collected on the seabed, confirm whether the sampler reaches the seabed according to the signal sent by the acoustic pulse generator.

(3) Trawl Trawl (Plate Ⅰ-2) is used to collect samples of polymetallic nodules and rocks by dragging on the seabed, and the mesh opening is 1.2m×0.6m, made of steel. The net is woven with nylon rope, the mesh is generally 1.5cm× 1.5cm, and the length is about 2m. A heavy hammer is fixed at the end of the net to maintain the stretched state of the net body. The retracting and towing operations are carried out with steel cables and 10,000-meter winches. If necessary, the ship will travel at a low speed.

(4) Gravity sampler The gravity sampler is used to collect columnar sediment samples, with a coring diameter of 7.3 cm and a length of 3.2 m. It is connected by steel cables and controlled by a 10,000-meter winch. Gravity samplers, like other wired samplers, need to install an acoustic pulse generator on the steel cable as a response means for the sampler to reach the seabed, which is convenient for the operator to control the release and recovery. At present, the 2 175 gravity sampler produced by Bentham Company in the United States is commonly used in the survey of ocean polymetallic nodule mineral resources in China.

(5) When collecting long columnar sediment cores, a large gravity piston sampler is often needed (Table I-3). The advantage of this sampler is that the collected sediment samples are undisturbed and the sediment cores with sufficient length can be obtained. The 2450 gravity piston corer produced by Benthos Company can obtain cores with the length of 15.2m, and even longer cores can be obtained after some modification. The length of the core depends on the need of research work and the size of the working face of the survey ship. When the gravity piston sampler with acoustic pulse generator reaches the seabed, the columnar sediment is pumped into the sample tube by the huge self-weight of the sampler and the pressure difference caused by the local vacuum at the bottom of the piston, and this long columnar sediment sample can be obtained. The response of acoustic pulse generator and echo sounder will ensure that the operator can correctly know the time when gravity piston coring pipe reaches the seabed, so as to control its retraction.

This coring device is only used systematically in detailed exploration in some locations. It can not only collect samples on the surface of sediments, but also collect deeper samples. These samples can not only be used to study soil characteristics, but also be used for scientific research on geological history of these nodule producing areas (such as sedimentology, geochemistry, biology, dating, etc.). ).

2. Geological sampling without cable

Cable-free geological sampling includes various sampling methods such as self-returning grab and self-returning gravity coring, as follows:

(1) Self-return grab Self-return grab is the most important means to take polymetallic nodules. China adopts American 420 1 self-return grab (plate Ⅰ-4) with a sampling area of 0.2m2 The working principle of self-return grab is that after the grab loaded with ballast (iron sand) sinks into the seabed, the automatic trigger device closes the grab sampling net with sediment samples and releases the ballast at the same time. Due to the existence of floating balls, the samples in the net are brought out of the water. Rely on navigation and positioning, signal flags, flashlights, wireless beacons and other devices to recover the self-returning grab. When the grab works in the sea with a water depth of about 5000m m, the working time of each station is about 3 ~ 4 hours. The biggest advantage of the self-returning grab operation is that the survey ship can collect samples during continuous navigation. Therefore, this is the main equipment for obtaining polymetallic nodules.

Install the camera on the sampler, and the seabed area involved in each photo is about 1m2, and the shooting direction slightly deviates from the vertical line. The sampling time is almost the same as the shooting time, and the theoretical sampling area is 0. 18m2.

The output of sampling system varies with nodule size, so the collected nodule weight cannot be directly converted into abundance (kg/m2). These necessary data are obtained through strict analysis and comparison of samples and seabed photos.

This sampling device is widely used in the early stage of deposit exploration. Practice has proved that its loss rate is about 1%, which is quite effective. Each sampling point is counted as a station. A group of stations (usually 5-7) constitute a station.

(2) automatic return gravity coring device

Self-returning gravity corer is used to collect seabed columnar sediment samples. Its coring diameter is 7.3cm, the maximum coring length is 1.22m, and its working principle is the same as that of the self-returning grab. The advantage of self-gravity coring is to obtain undisturbed columnar sediment samples, so as to study various geological information such as sedimentary characteristics of sediments at this depth. The recovery of collected sediment samples depends on navigation and positioning and the help of the flash lamp on the coring device, so it works well at night.

Although the self-returning coring device is simple to operate, the effect is unstable, and the reliability of operation (which can not be used to consolidate sediments) and the effectiveness of measurement are also unstable.

Figure 3-2 Temperature and Salt Depth (CTD) Measurement System

3. Temperature-salinity-depth measurement

At present, in the exploration of ocean polymetallic nodules, the comprehensive measurement of seawater temperature, salinity and water depth (hereinafter referred to as thermohaline depth) is often carried out by Mark-III thermohaline depth measurement system produced by American EG&G Company (Figure 3-2). Its main function not only meets the requirements of some geological survey projects, but also meets the needs of hydrological survey. The measurement items include the longitudinal distribution values of seawater temperature, salinity, depth, conductivity, pH value, dissolved oxygen, sound velocity and density, and water samples of 12 water layer with different depths can be collected. The volume of each water sample is 500ml, which is used for different research purposes.

Hydrometeorological observation

Although hydrometeorological investigation is an auxiliary work, its results are of great significance for discussing the geological causes and distribution of polymetallic nodules, and for formulating and implementing the investigation plan. The contents of hydrometeorological observation should include temperature and salt depth measurement, ocean current measurement and meteorological observation. At different stages, the contents and requirements of the survey are also different.

1. Hydrogeological survey

Hydrogeological investigation includes the investigation of temperature, salinity, water color transparency, ocean currents and waves. Hydrogeological survey generally adopts fixed-point survey, which is divided into cross-section observation, large-scale observation and continuous observation.

Hydrogeological survey is often fixed-point observation, and the temperature and salt sounding system (CTD) can meet the requirements of temperature and salt measurement while measuring the water depth of observation points. Therefore, the selected equipment must meet the applicable water depth range of the work area and the measurement requirements of the measured hydrological elements.

Ocean current observation mainly measures the speed and direction of ocean current, and assists in measuring wind speed and direction. In the process of measurement, the accuracy of current velocity is less than 3 cm/s; The flow direction accuracy is not greater than 10. The observation of ocean current mostly adopts acoustic Doppler profiler or self-contained ocean current meter, and is measured with the help of deep-sea ocean current measuring buoy system. In recent years, with the configuration of computer system, ocean current observation data can be processed in real time, and the processed data can be recorded on disk or tape.

Wave observation needs to measure wave height, period, direction, waveform and sea state. Ocean waves can be observed by visual observation and instrument measurement. Generally, buoy acceleration wave meter is used for instrument measurement. The wave meter equipped with data processing system can process the observed data in real time with the help of the microcomputer of the system, and get the wave height, effective wave period, maximum wave height and maximum wave period; The processed data can be displayed on the screen in real time, or recorded on disk and tape, and printed directly by the player and printer.

2. Meteorological survey

The marine survey of each voyage needs to carry out the meteorological survey of the sea surface, because it serves the purpose of weather forecast and hydrogeological survey. The meteorological survey data accumulated in marine exploration will also provide meteorological basis for the development and evaluation of polymetallic nodule mining areas in this sea area in the future.

The contents of marine meteorological investigation include sea ice, surface temperature, weather phenomena, visibility, clouds, wind, air temperature and humidity, air pressure and other meteorological elements. These projects are routine investigations and can be completed with conventional equipment. At present, in the exploration of marine polymetallic nodules, the data released by meteorological satellites can often be used to guide the implementation of marine surveys. However, adhering to this meteorological survey in the exploration of ocean polymetallic nodules is helpful to judge the correctness of the data released by meteorological satellites. The accumulated meteorological data will contribute to the correct meteorological assessment of the scheduled development zone.