The invention relates to generating regional tropospheric correction information for correcting observations useful for estimating phase ambiguities and/or a position of global or regional navigation satellite systems (NSS) receiver(s). For each of a plurality of reference stations, at least one troposphere correction parameter is estimated by evaluating NSS observation equations using i) precise satellite information or the information derived from the precise satellite information, and ii) received multiple-frequency-signals-based raw observations or a linear combination thereof. The regional tropospheric correction information is then generated based on the estimated troposphere correction parameter(s) per reference station, the tropospheric correction information comprising a regional tropospheric delay function(s) and coefficients representing a tropospheric delay affecting a NSS signal passing through the troposphere in a region of interest. The generated tropospheric correction information may then be sent to NSS receiver(s) and used by the receiver(s) for example to facilitate position determination.