ABSTRACT
The first section of this chapter describes the advantages of using the Global Navigation Satellite System (GNSS) to obtain zenith tropospheric delay (ZTD) and the research background of using GNSS ZTD with El Niño-Southern Oscillation (ENSO) to indicate climate change. The second section describes the basic measurement principles and solution models of ZTD using GNSS technology. The third section analyzes the spatial and temporal variation characteristics of GNSS ZTD in mainland China. Spatially, the GNSS ZTD shows an increasing trend from northwest to southeast, and the regional pattern is consistent with the five major climate-type divisions in mainland China; temporally, there are significant annual periods, 9-month periods, semi-annual periods, seasonal periods, diurnal and semi-diurnal waves, and other significant variation periods in the GNSS ZTD. The fourth and fifth sections quantitatively analyze the response patterns of GNSS ZTD time-frequency variations to ENSO events in mainland China. The multivariate ENSO index (MEI) thresholds for GNSS ZTD anomaly in different regions response to ENSO events and the significant periodic amplitude variation characteristics of GNSS ZTD under the influence of ENSO events are obtained. The final section summarizes the chapter.
