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Seasonal Variations in GPS Station Positions? Temperature Variations Can’t Be Ignored
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Update time: 2017-03-16
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Expanding with heat and contracting with cold is a natural phenomenon. Surface of our Earth is no exception. In fact, variations of surface temperature is an important contributor of surface deformation. To provide various verified GPS observation parameters to users accurately, it’s key to assure the precise positions of GPS stations.  

In recent years, more attention has been paid to the contributions of surface temperature variations to seasonal displacements of GPS stations, mainly on seasonal height (radial) changes. Recently, Dr. XU Xueqing et al. from Shanghai Astronomical Observatory calculated the displacements due to surface temperature variations based on a global thermoelastic model. Compared with the observed annual deformations in GPS stations, they found that the seasonal GPS observations, the transverse displacements in particular, are better explained after considering the thermoelastic effects due to temperature variations. This work has been accepted for publication by GPS Solution. 

XU said, earlier studies often simply assume that despite of surface temperature variations, the transverse displacements is always zero. However, it’s not true in reality. To obtain more accurate results, it’s necessary to consider the transverse displacement due to surface temperature variations.  

“Utilizing a global thermoelastic model, based on the surface temperature observed by National Oceanic and Atmospheric Administration, we calculated the displacements due to surface temperature variations.” Dr. XU said, “We found that the largest annual radial deformation is found to be about 3 mm, while the transverse displacements are generally smaller than those of the radial component, with the largest amplitude being about 1.5 mm.” 

Moreover, they further calculated the annual thermoelastic surface deformation at the 234 global GPS sites, which were then compared with GPS observations. XU said, “our work indicates that with the annual thermoelastic effects included, it would improve about 7–9% in the reduction ratio for vertical and transverse components, respectively. Our results reveal that the deformation induced by land surface temperature variations is large enough to affect the stability of the terrestrial reference frame, which is also an important source for the remaining seasonal variations in GPS position, especially for the horizontal components.”  

XU states that, “in the future, we will focus on finding other subtler factors, such as poroelastic deformation.” 

Fig 1. N-S annual amplitude of GPS position on the transverse direction (red line and arrow), annual contribution of the mass-loading (blue line and arrow) and deformation summation of the annual mass term and thermoelastic term (black line and arrow) at 234 GP stations with known coordinates. (Image by XU et al.)

Link to the research paper:

http://link.springer.com/article/10.1007/s10291-017-0609-6

Science Contact:

XU Xueqing, Shanghai Astronomical Observatory (www.shao.ac.cn), xqxu@shao.ac.cn

News Contact:

ZUO Wenwen, Shanghai Astronomical Observatory (www.shao.ac.cn), wenwenzuo@shao.ac.cn

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