Mapping function induced bias in tropospheric delay estimation using GPS

To estimate total absolute tropospheric zenith delays in a global network of GPS stations, residual delays are estimated as corrections to an a priori delay model using a zenith angle dependent mapping function. Because the a priori model relies on a standard atmosphere and the wet and hydrostatic delays have different zenith angle dependence, the total zenith delay estimates are biased. A simulation has shown that biases of several mm are possible, especially when a crude mapping function, large zenith cut-off angles and no zenith angle dependent weighting is used.