Analysis of Reflected Signals During GPS Radio Occultation Observations of COSMIC Products in China

  Objectives  The global navigation satellite system (GNSS)radio occultation (RO) signals can be reflected on the earth surface during the propagation process. It is of great value to explore atmospheric information contained in the reflected occultation signal for improving the accuracy of weather forecast and climate monitoring.

  Methods  Using the constellation observing system for meteorology, ionosphere and climate (COSMIC) occultation data collected from January 2011 to December 2015 in China, this paper extracted the occultation profile containing the reflected signals, which were strong at oceans and weak at inland and also showed seasonal changes. It was found that the inland snowy areas and the ocean surface were easier to reflect the occultation signals. Further, the offshore areas of China were set into 5°×5° grids and the correlation between the percentage of occultation reflected signals and the reanalysis data from European Centre for Medium⁃Range Weather Forecasts in each grid was analyzed.

  Results  Around the offshore areas to the north of 10°N, the water vapor and temperature are negatively correlated with the percentage of occultation profile reflected signal, with a correlation coefficient from -0.28 to -0.58. However, around the offshore areas to the south of 10°N, affected by the monsoon at the South China Sea, the percentage of occultation profile reflection signal is positively correlated with the reanalyzed water vapor data, with a correlation coefficient from 0.32 to 0.34, but not significantly correlated with the reanalyzed temperature data.

  Conclusions  The RO reflected signals associate with atmospheric conditions, and it can be applied to the direct signals as supplementary data.