Performance Analysis of Pseudolite Tropospheric Delay Models Using Meteorological Radiosonde with Flight Test Results

摘要

Pseudolite is a pseudo-GNSS satellite transmitting GNSSlikesignal for navigation. When the pseudolite is used inshort range, tropospheric delay could be negligible,because the lower troposphere causes signal delay about300～400 mm/km in general. However, as the coverage isbroadening, the tropospheric delay is becoming a majorerror source. As the pseudolite signal passes through thelower troposphere and experiences spatial atmosphericirregularities, the estimation of tropospheric delay is verydifficult. And the conventional tropospheric models usedfor GNSS couldn't be applicable.There have been several studies about developingtropospheric delay model for pseudolite applicaiton.However, most of them are about restricted use ofpseudolite such as aircraft landing, take-off and means ofassistance with GPS for limited navigation coverage. Onthe other hand, this study is about pseudolite-onlystandalone navigation system as an alternativeindependent navigation system with extended coverage.So, we performed the analysis of troposphere effect onpseudolite for a vast range use.We compared and analyzed existing tropospheric delaymodels for a large extent. As a reference model, raytracing method based on meteorological radiosondeobservation data has been used. From the comparisonresult, Hopfield model-based pseudolite troposphericdelay estimation method was chosen as a user model. Andthen, to reduce the residual model error, the error analysishas been done. For 110 days of 1 year, the observed datawere used to develop the error model. And it is used toreduce the residual error by enhancing the navigationfilter to estimate it.For the result, simulation and post-processing result offlight test data were addressed. We performed severalflight tests approaching to the area of ground pseudolitenetwork to see the performance of tropospheric delaymodels along the change of slant distance between userand pseudolite. For high altitude application, simulationhas been done. Simulation and the post-processing resultshowed that the estimation method of residual model errorcontributed to extending the coverage of pseudolitenavigation system.