| As a high-tech method in the 21st century,GNSS has deeply applicated in many fields such as modern surveying and mapping,military,transportation,public security,as well as modern agriculture.GNSS direct signal has been widely used in atmospheric temperature and humidity,weather forecasting,meteorology,ionospheric monitoring and other fields.At present,it is a hot research topic using reflection of GNSS signal for feature extraction on the target surface(water level,sea surface height,soil moisture,vegetation water content,snow water equivalent,snow depth,etc.)and it has potential applications in the earth’s environment fields.In this paper,GNSS technology is applied to water level retrieval.We introduce a method and experiment of using GNSS technology to retrieve water level,and achieve the method of retrieving dam water level by single GPS antenna.Then we analyze dam deformation using the retrieved water level and temperature as factors.Multiple linear regression and principal component analysis are used to analyze the influence of water level and temperature on the deformation of dam in time domain.In frequency domain,frequency spectrum characteristics of the dam deformation,water level and temperature are analyzed.The research contents and achievements are presented as follows:(1)we studied GNSS reflected signal theory and SNR signal characteristics,analyze the effective satellites of stations.Besides,we summarized the signal characteristics of the effective reflection area.SNR signal changes periodically with the satellite altitude angle,the lower the satellite altitude angle,the lower the intensity of the signal.Signal intensity has obvious difference in Ll carrier and L2 carrier,L1 SNR signal power is 20 dB-Hz higher than that of L2,SNR signal power of the new L2C code is higher than L1 code,so as the precision.When water level changes,the frequency and phase of SNR sequence change too.(2)We developed water level retrieval method based on signal to noise ratio spectrum method and retrieved water level of Xilongchi reservoir with the precision better than 0.2m.We compared retrieved water level with measured water level for the first six months of 2013 to validate correctness of the retrieved results.Retrieved results of the same station different satellite are agreed,with the RMS error better than 0.05m;differiences between retrived and measured results are better than 0.4m;results between different stations are approximately equal.The retrieved and measured water level prove to be agreed with correlation better than 90%after analyzing 6 months of data,which indicates that retrieved and measured water level have strong correlation.In the case of no gross error,the precision of the method is better than 0.2m.(3)In time domain,we used multiple linear regression analysis and principal component analysis to find out the relationship between dam deformation and environment such as water level and temperature.Two methods have the approximate result,fitting values of the east direction for S071 station match well with the original displacement,in which seasonal change(temperature)plays an important role.But the fitting value can not explain the jump in every summer.Residual error of the fitting values from other stations improved a little,which means the impact of temperature and water level for deformation is small,the impact is easily covered by other deformation factors.(4)In frequency domain,we analyzed spectrum of deformation,temperature and water level using Lomb-Scargle method.Water level and temperature both have a one-year periodicity as well as specific frequency.The main frequencies of water level are 0.98 yr-1,0.62 yr-1,1.50yr-1 and 0.31 yr-1.The main frequencies of temperature are 1.5 yr-1,1 Yr-1,0.70 yr-1 and 0.50 yr-1.All the four stations have the same one-year periodicity as well as the similar specific frequency.So we think water level and temperature have influence on the deformation of dam.(5)We analyzed the dynamic deformation data of dam for 7 days to study the influence of water level for dam deformation in a short time.Spectrum analysis is implement for four stations in hydraulic direction and we found that there are consistent frequencies,which means there are same regularity for the four stations in the hydraulic direction,and it can be considered to be caused by the change of water level. |
