Research And Development Of Distributed Underwater Magnetic Anomaly Data Acquisition System

The ocean is an important subject of economic development and scientific research,and the development of underwater moving target detection systems is of great significance.Underwater target detection is mainly based on acoustics detection.The active sonar working in the offshore is affected by environmental factors such as sea water and seabed terrain.The channel transmission interference and the background noise are very serious.Passive sonar detection has strong concealment,however,with the development of degaussing technology for underwater targets,the detection range is subject to certain restrictions.Underwater magnetic anomaly detection takes magnetic anomalies on the surface(ships),underwater(submarines)or below the seabed(submarine optical cables,geological anomalies,sunken ships,etc.)as the physical premise,and uses magnetic sensors to perform vector,total field or gradient measurement,which is widely used in military,national defense,structural geology,geophysical prospecting and other fields.Target detection based on magnetic anomaly has the advantages of strong recognition ability,good positioning accuracy and low cost.Underwater magnetic anomaly detection usually relies on ship,unmanned aerial vehicle,autonomous underwater vehicle,etc.,it measures the target area according to the established route,which is flexible and efficient,but there are disadvantages such as low signal-to-noise ratio and short endurance time;the seabed fixed observation method can be used for long-term hidden observation,which has practical needs.This design is based on the principle of magnetic anomaly detection,and has carried out hardware development and software development according to the seabed fixed observation method.The system is characterized by multi-node synchronous measurement,and the collected data is transmitted to the user terminal through the data transmission bus,and can be distributed under water for long-term magnetic anomaly signal observation.The node circuit of distributed underwater magnetic anomaly data acquisition system is composed of communication board and acquisition board,the communication board includes power isolation,signal isolation,M-LVDS drive circuit and RS422 drive circuit;the acquisition board includes three channels of magnetic anomaly signal acquisition circuit,main control circuit and data storage circuit.The system uses the RS422 bus to connect multiple nodes with a bus architecture.The master node collects node data through multiple-address polling,and then sends the data to the host computer;meanwhile,it outputs the sampling clock of the system and sends it to each node through the M-LVDS bus to realize acquisition synchronization.This design also writes a master control program based on STM32 to complete the functions of multi-node master-slave communication logic,ADC data storage,etc.,and developed a host computer program based on C#language to realize the functions of system state control,node data storage and display.The indoor test results show that the distributed underwater magnetic anomaly data acquisition system has realized 20 nodes of long-distance(about 1km)power supply,acquisition and data transmission,the range of node circuit reaches 20V_pp,and the equivalent noise is 12pT/rt(Hz)@1Hz,the dynamic range is 121.6dB,and the synchronization accuracy is within 2?s@10 hours.The distributed underwater magnetic anomaly data acquisition system can realize all-weather covert detection of magnetic anomaly signals without relying on the detection platform,which is of great significance for underwater target detection in coastal areas such as ports and waterways.