Performance of Single-Epoch EWL/WL/NL Ambiguity-Fixed Precise Point Positioning with Regional Atmosphere Modelling

Precise point positioning (PPP) with ambiguity resolution (AR) can improve positioning accuracy and reliability. The narrow-lane (NL) AR solution can reach centimeter-level accuracy but there is a certain initialization time. In contrast, extra-wide-lane (EWL) or wide-lane (WL) ambiguity can be fixed instantaneously. However, due to the limited correction accuracy of the empirical atmospheric model, the positioning accuracy is only a few decimeters. In order to further improve the real-time performance of PPP while ensuring accuracy, we developed a multi-system multi-frequency uncombined PPP single-epoch EWL/WL/NL AR method with regional atmosphere modelling. In the proposed method, the precise atmosphere, including zenith wet-troposphere delay (ZWD) and the slant ionosphere, is extracted through multi-frequency stepwise AR, which then is both interpolated and broadcast to users. By adding regional atmosphere constraints, users can achieve single-epoch PPP AR with centimeter-level accuracy. To verify the algorithm, four sets of reference networks with different inter-station distances are used for experiments. With atmosphere constraints, the accuracy of the single-epoch WL solution can be improved from the decimeter level to a few centimeters, with an improvement of more than 90%, and the epoch fix rate can also be improved to varying degrees, especially for the dual-frequency case. Due to the enlarged noise of the EWL combination, its accuracy is at the decimeter level, while the accuracy of the WL/NL solution can reach several centimeters. However, reliable NL ambiguity-fixing tightly relies on atmosphere constraints with sufficiently high accuracy. When the modelling of the atmosphere correction is not accurate enough, the NL AR performance is degraded, although this situation can be improved to a certain extent through the multi-GNSS combination. In contrast, in this case, the WL ambiguity can be successfully fixed and can support the precise positioning with an accuracy of several centimeters.

TWO VIEWING THEORY ON ATMOSPHERE CORRECTION IN OCEAN COLOR ALGORITHM

A new algorithm for retrieving optical thickness and surface reflectance, data in the visible bands from satellites is developed. The proposed algorithm is to solve the simultaneous equation of two unknown variables, i.e. aerosol optical thickness and surface reflectance (r). In term of difference from the conventional and, one directional retrieval algorithm, we do not need the spectral characteristics of aerosol. We solve the equation by forward calculation using the 6S transfer code. The two observational equations change linearly within the domain where we solve the solution. We estimate the chlorophyll-a concentration from the evaluated r. This method is validated against Global Imager (GLI) data, which has two independent data for one pixel in both tilting and nadir viewing. Keywords, GLI, 6S, Radiative Transfer, Reflectance, Rayleigh, Mie.