| The demand for metal mineral increases dayly as human society leading ahead, however, the depletion of known shallow deposits and declining rates of discovery for new deposits cause the declines in base metal reserves. To meet the need of society, the exploring for deep metal mineral is underscored. Nonseismic methods—such as electromagnetic,induced-polarization, and potential-field surveying techniques—have been the geophysical backbone of mineral exploration for decades. However, the underlying physical principles of these methods impose inescapable limitations on their sensitivity and resolving power at depth. So these methods can't detect the metal minerals below 500 metres. The seismic method from oil industry that can explore objects in depth of several kilometres with high vertical resolution can detect the minerals under 500 metres. So the seismic method is the most promising one to persue for deep exploration.Metal mineral always forms in terrain of complex geological conditions in China. In such terrain, the surface conditions is poor, elevation varies dramatically, vegetation develops and trafficking condition is bad. As a reslut, seismic data acquisition in such areas meet much difficulty. The explaration for oil and gas meets the same problem, as the major oil fields of China change from large-scale exploration in early years to development and management, the areas of complex topography in west and south of China become the focus for future exploration. Therefore, to carry out the seismic exploration in areas with complex topography of mountain regions is the trend of oil and gas seismic exploration for future.Characteristics of mountain terrain is mainly reflected in two aspects:①the terrain is complex and vicious with high mountains and deep valley. surface elevation changes dramatically, the relative elevation varies from 200 meters to 1000 meters.②the surface structure of mountains is complex and ever-changing, surface conditions is poor, such as large area of the exposed surface of high-speed formation, cave, and fracture. Valley areas are filled with gravel and sand, sediments formed by the accumulation lay in dense forest areas of gentle slope. Situations like this evoke requirment on seismic exploration instrument as following:①As for metal mineral area, the geological structure is complicated and often after a strong tectonic and magmatic activity, the mineral ore body doesn't form into a layer as idealy, the methods and principles of seismic reflection based on the layered media can not apply to these area directly.②The terrain conditions is complex, metal ore is always formed in the output of the belt with complex terrain conditions where the field work for data acquisition is very difficult to carry out.③The targets of detection is small and the metal mineral ore is smaller than the oil deposit.④As the mine area is filled with all kinds of interferences, the ratio of signal to noise is poor and reflection recordes with good qulity can't be attained. In spite of these conditions, the study for metal mineral deposit with 2D, 3D, and vertical seismic profile methods is conducted by researchers all over the world and obvious progress has been made.As for the requirements on technology above, relying on the national high technology plan (863 plan) project "Key Technology and Equipment for Metal Mineral Exploration", this paper advances the design idea of non-cable telemetry seismic instrument for complex mountain region, research on key technologies for which are carried out as followings:(1). The construction of ARM-Linux platformBased on the processor of 32-bit RISC ARM9, the non-cable telemetry seismic data collecting station is designed combining the technologies of 24-bit A/D, DA, large scale field programmable gate array and embeded ethernet. The CPU board is designed based on AT91RM9200 and has a SDRAM of 64M bytes, a flash chip of 16M bytes and a 100Mbps ethernet interface. The Linux kernel of version 2.6.12 is transplanted to the CPU board, a ramdisk file system is constructed based on BusyBox, and the driver programm for CF card in IDE mode, ethernet interace and the logic circuits designed in FPGA is finished. In addition, U-Boot is transplanted to the CPU board to implement the self-loader. Data acquisiton board is designed with 24-bit A/D and DA, and the related interface circuits are implemented with FPGA which is programmed in VHDL language.(2). Low-noise seismic data acquisition technologyThe seismic wave information of metal ore is very complex, multi-wave field mixed together, and the useful signal is very weak, requiring that seismic instruments for metal mining exploration have the ability of anti-interference, high sensitivity, low noise and wide dynamic range. The low noise design, wide dynamic range and high sensitivity mean the same performance: the low noise design of the circuit system. The inherent noise of electronic system is caused by the irregular movement of charged particles in resistors and semiconductor devices(thermal noise). In addition, interferences from the space environment and power supply systems will also increase the noise of the measurement system. In this paper, the Noise Coefficient is taken as the criteria to evaluate noise performance of circuit based on the En-In model for equivalent input noise. According to the principle of best noise match, amplifier with low noise level in the bandwidth of signal should be selected and the DC working point is set in order to meet: snnRE= I( Rs is the source resistance, En and In are the equivalent voltage and current of the selected amplifier ). According to the convention of seimic instrument design, as the geophone's resistance is middle high and its output signal varies from V level toμV level, no special coupling strategy is required and the system employ the direct coupling mode.An analog circuit composed of a low-pass filter, programmed-gain amplifier and a differential signal conversion modules is designed based on the principle of best noise match, following which a 24-bit A/D converter is employed to constitutes a seismic data acquisition channel. According to the calculation theory of En-In noise model and the quantization noise of 24-bit A/D, the theoritical noise of data acquisition is obtained: 5.080×10 ?7V. In order to eliminate the electronic interference from space, on the one hand the long line which connect the geophone and analog circuit is shielded, and on the other hand, the analog circuit is shielded by metal shell. In addition, a two order low-pass filter is used to filter the system power ripple. At the same time, the grounding system is improved by the following methods: using the ground plane instead of grounding lines and employing multi-point grounding strategy for analog component, and as a result the interference between ground lines is brought down.(3). synchronous data acquisition technology among seismic acquisition stationsFor the non-cable telemetry seismograph system, the destination is to construct a 600 channels data acquisition system. Each seismic data collecting station is designed to recorde 4 channels analog signal and 150 data collecting stations in total are demanded to construct the whole system. The synchronization between these stations is a key problem. The seismic data collecting stations employ GPS receivers to achieve synchronization, when the GPS receiver captures 4 or above satellites, it uses the solution of GPS pseudo-range equations and the navigation messages to calculate the coordinated univeral time, and output a pulse per second with the precise of 50 ns. Each collecting station take this pulse as time referrence and trigger the data acquisition simultaneously at some full second to achieve the synchronization among all stations.However, metal mine is always formed in complex geological environment with undulating topography and much vegetation. As a result, the GPS signal is susceptible to be blocked losing the synchronous timing. So each seismic data collecting station employs a high precise RTC as the backup time base. Conventional RTC employs a low-frequency crystal oscillator to count, but because of the restriction of cutting technolgy, the quartz crystal has center frequency error and temperature drift which lead to a poor accuracy. While the counting clock of seismic data collecting station's RTC is derived from a oven-controlled crystal osillator with the precise of 0.1ppb in order to improve the counting accuracy. When the GPS receiver lost signals from satellites, the RTC replaces the GPS receiver and serves as the backup time base for collecting stations. The error analysis and calculation obtains that the precise of synchronization is±3.2μs. Test results show that the combination of GPS time and high-precision RTC can fully realize the synchronization among collecting stations.(4). high-precision GPS positioning technology for seismic data collecting stationsIn order to replace the conventional geological measurement task with GPS positioning technology, accurate position information is needed. Static absolute GPS positioning has less accuracy due to the satellite orbit error, GPS receiver clock error, signal propagation error and et al. 2 or 3 channels of C/A code pseudo-range absolute positioning can attain an accuracy of±20m, which can't meet geodesy requirement. While the technology of static relative positioning takes the carrier phase measurement as observation parameter and makes line combination of the carrier phase measurement, as a result, the errors mentioned above are significantly reduced and the static relative positioning technology is the most accurate method.System uses the GPS static relative positioning technology to replace conventional task of G,geological survey. GPS static relative positioning makes carrier phase measurement, the relative positions of the base line endpoints is determined through the adjacent receivers'synchronous observation of four or more same satellites, many receivers can constitute a baseline vector net. While many observation stations track the same satellites, the impact on relative observation value of satellite's clock, receiver clock's error and the refraction error of ionospheric and tropospheric is same or similar. Because of such relativity, making difference of carrier phase observation equations between observation stations, satellites or epoch can improve the mesurement precise of the base lines. There are three types of difference models: single difference, double difference and three difference. Finally, three-dimensional non-binding net adjustment is made to assess the measurement error and attain the three-dimensional rectangular coordinates under WGS-84 coordinate system providing precise position information for data processing. This article implement the GPS D-level network measurement based on the software of Caravel Net fulfilling the accuracy requirement of national GPS measurement norm for D-level net.(5). Instrument assembly and experiment.The prototype of non-cable telemetry seimograph with 24 channels is assembled, the system test in room and experiment combined with hammer seismic source are conducted. The result appers to be satisfactory.To sum up, this article advance the idea of metal mineral non-cable telemetry seismograph aiming at the metal mineral seismic exploration for the demand of metal ores of human society. The system controlling platform is constructed by employing 32-bit ARM processor combined with Linux operating system. And the 24-bit A/D combined with FPGA technology is used to design the digital interface and data acquisition system, based on which the technology of low noise analog data acquisition, the synchronization through the whole seismic data collecting stations and high precise static relative GPS positioning are studied significantly. At last, the prototype of non-cable telemetry seimograph with 24 channels is assembled and tested in room, and the experiment in field is also conducted. The promising performance parameters are fulfilled.
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