| dc.description.abstract | Global positioning system (GPS) is usually used for researches of plate tectonics and crustal deformation. In most studies, GPS time series considered only time-independent noises (white noise), but time-dependent noises (color noise: flicker noise, random walk noise) which were found by nearly twenty years are also important to the precision of data. The rate uncertainties of stations will be underestimated if the GPS time series are assumed only time-independent noise. Therefore, studying the noise properties of GPS time series is necessary in order to realize the precision and reliability of velocity estimates. The lengths of GPS time series are from 541 stations around Taiwan with time spans longer than 2.5 years up to 22 years. The GPS stations include different monument types such as deep drilled braced, roof, metal tripod, concrete pier etc., and the most common type in Taiwan are the metal tripod and roof. I investigated the noise properties of continuous GPS time series by using the spectral index and amplitude of the power law noise. During the process I first remove the data outliers, and then estimate linear trend, size of offsets, and seasonal signals, and finally the amplitudes of the power-law and white noise are estimated simultaneously. The results show that the noise amplitudes of the north component are smaller than that of the other two components, and the largest amplitudes are in the vertical. I also find that the amplitudes of white noise and power-law noises are positively correlated in three components. Amplitude of white noise do not change with time, called time-independent noise. Amplitude of flicker noise and random walk noise change with time, considered be time-dependent noise, called color noise. Comparisons of noise amplitudes of different monument types in Taiwan reveal that the deep drilled braced monuments have smaller velocity uncertainties and amplitudes, are more stable than other monuments. | en_US |