Research About The Effects Of Stability Of Observation Marks And Electromagnetic Environment Of The High Voltage Transmission Lines To The Observation Of Crustal Movement

The high-precision observation of crustal movement might be affected by factorssuch as error of the observation technology, performance of the devices, stability ofthe observation marks, and different kinds of external observation environment. Inthis paper, research about the effects of stability of observation marks andelectromagnetic environment of the high voltage transmission lines to thehigh-precision observation of crustal movement was taken out.In the Crustal Movement Observation Network Of China, forced centering marksare adopted on the GNSS observation pillars, the influence of stability of theobservation marks cannot be ignored on the identification of the crustal movementinformation. The stability of the observation marks can be affected by many aspects,such as the foundation, meteorological conditions, locations, seasonal and annualchanges and the like. The tests were taken on the GNSS observation pillars inHuangmei and Jingmen to research the influence of meteorological factors to thestability of the bedrock observation marks by using vertical pendulum tiltmeter, alsoto judge the feasibility of the use of vertical pendulum tiltmeter in this experiment.The experiment indicated a regression daily offset movement of the pillars both in theS-N direction and E-W direction, and a bigger offset in S-N over E-W direction. Theresults showed that most of the amplitude of the daily offsets and the daily averageoffsets of the pillars in S-N direction is within3mm and1mm, while the maximum is3.5mm and1.3mm, respectively, while within2mm and0.2mm in E-W direction,and the maximum2.9mm and0.25mm, which keep stable with the change ofseasons. The main reason why the offset movements of the pillars occurred is becauseof the changes of the temperature differences of the piers caused by the sunshine,which has a high correlation with changes of the offset movement. Also, the stabilityof the observation marks has no significant relationship with the rainfall, the changesof the air pressure and the solid tide of the earth. From the experimental data, the dailyoffset movement of the bedrock pillars is considered to have an effect on thehigh-precision observation of crustal movement, especially as much as1~2mm in the S-N direction, which reminds us to take temperature protection against the pillars, oruse special design of the pillar with a lower thermal expansion rate. By analyzing theexperimental data, we found that the range, accuracy, stability and reliability of thevertical pendulum tiltmeter have reached the requirement of experiment and theobservation results authentically reflect the tilt of the pier, so that the tiltmeter canabsolutely be applied to the experiment.The performance of the GNSS receiver, quality of the received data and accuracyof calculation might be affected by the electromagnetic environment, including thepower frequency electrical field, power frequency magnetic field and radio inferencecaused by the high voltage transmission lines and the shielding, reflection andscattering of the signal caused by the high-voltage towers and lines as a large metalconductor. In this paper, experiments were taken in the area of500kv and220kvhigh voltage transmission lines to research the effect of high voltage transmissionlines to GNSS observations. The results showed that the electromagnetic interferenceand radio interference caused by the high voltage transmission lines have nosignificant effect on the internal noise of the GNSS receiver. The multipath effects aresignificantly impacted by the high voltage transmission lines. The closer from thelines and the higher the voltage is, the multipath effects are more serious. The highvoltage transmission lines have no significant effect on the ability of the GNSSreceiver to capture the data, the stability of the receiver clock, signal-to-noise ratio ofthe L1and L2carrier, cycle slip of the observation data, and the accuracy ofcalculation of the baselines and coordinates.It has some margin of the50metersdistance from the high voltage transmission lines to the observation instrumentsstipulated by 《The global positioning system (GNSS) measurement specifications》,so in the activities of GNSS sites building or field observations, we can grasp thedistance between the instruments and high voltage lines according to the actualsituations.