A New Multi-Resolution GNSS Tomography Method Based on Atmospheric Water Vapor Distributions

The global navigation satellite systems (GNSSs) water vapor tomography technique has been successfully used as a promising tool for sensing atmospheric water vapor and applied to weather forecasting in recent years. In most tomography models, the single grid resolution, i.e., the same horizontal resolution, is widely adopted to divide the 3-D tomographic domain into many small voxels. However, the single-resolution GNSS tomography (SRGT) method implements the grid-based parametrization of the physical domain and does not follow the vertical spatial heterogeneity of atmospheric water vapor. To this end, we develop a new multi-resolution GNSS tomography (MRGT) method that incorporates the vertical decline tendency of water vapor. The MRGT method generates different-resolution tomographic water vapor products in the lower, middle, and upper domains of the troposphere. Besides, a new indicator, known as the integrated water vapor (IWV) lapse rate, is introduced to determine the appropriate nonuniform stratification strategy. Eight tomography schemes were analyzed to compare the tomography results obtained from different tomography models based on the GNSS data in the Hong Kong region during June and July 2015. The results show that with respect to radiosonde data, the MGRT method reconstructs a more accurate water vapor distribution than the SRGT approach, with the average root mean square error of tomographic results reduced by 12%. Moreover, in rainfall conditions, the tomographic water vapor profiles from the MGRT model agree well with the radiosonde profiles, which highlights the potential of multi-resolution tomographic water vapor products for rainfall-related studies.