Characteristics Analysis of BeiDou Melbourne-Wübbena Combination

Abstract

Melbourne-Wübbena (MW) combination, which has characteristics of geometry-free and ionosphere-free (first-order), has been often used for cycle slip detection and facilitating ambiguity resolution in GNSS dual-frequency data processing. The constellation of BeiDou Navigation Satellite System (BDS) is different from that of GPS. GPS constellation includes only Medium Earth Orbit (MEO) satellites, while BDS constellation is composed of three types of satellites: Geostationary Orbit (GEO), Inclined Geosynchronous Orbit (IGSO) and MEO satellites. We studied the characteristics of BDS MW combinations of different types of satellites with static observations. The results indicated that: all un-differenced MW combinations of BDS observations show obvious systematic biases. These biases cannot be cancelled out by single-differencing between satellites. On the contrary, they are amplified due to the superposition of the systematic biases of two satellites observations. By single-differencing between receivers, different characteristics are shown for different types of satellites and different baseline distances. The systematic biases of IGSO and MEO MW combination series can be cancelled out by single-differencing between receivers over short and medium baselines, however, they cannot be cancelled out over long baselines. For GEO MW combinations series, their systematic biases cannot be cancelled out over both short and long baselines. The further analysis of the DD (Double-differenced) MW combinations indicated that the systematic biases which cannot be cancelled out by single-differencing between receivers also cannot be cancelled out by double-differencing between both receivers and satellites. By summing up these results, we analyzed the sources of the systematic biases of BDS MW combination: the systematic biases of IGSO and MEO MW combination series mainly originate from multipath errors of satellite; the systematic biases of GEO MW combination series also originate from multipath errors, however, it is not sure that they originate from satellite multipath, receiver multipath, or the combined influence of both satellite and receiver multipath.