Global navigation satellite systems (GNSSs) have become an important tool for remotely
sensing water vapor in the atmosphere. In GNSS data processing, mapping functions and
gradient models are needed to map the zenith tropospheric delay (ZTD) to the slant total
tropospheric delay (STD) along a signal path. Therefore, it is essential to investigate the
spatial–temporal performance of various mapping functions and gradient models in the
determination of STD. In this study, the STDs at nine elevations were first calculated by …