Abstract
Recently, the network of MF marine radio beacon stations covering the whole coast of Japanese Archipelago has been completed for DGPS positioning. The DGPS receiver is widely used on the ocean, by navigators, ship handling examiners and so on. The DGPS positioning needs the correction data continuously. However the reception condition on the ocean hitherto has been rarely reported. This paper describes the result of observing the reception rate of DGPS data onboard. GPS receivers were used that received the beacon signal for DGPS positioning. The receivers indicate the data reception rate and electric field reception level averaged for five seconds besides indicating the position. The data were acquired on the voyage of a training ship Hokuto-Maru (Length 125m, 5877 gross tonnage) from Tokyo to Mikawa-wan (middle part of Japan) for 18hours. The received electric field level depend on the distance from station and the data reception rate decreased clearly when the distance exceeds 200km that is the nominal service area of MF beacon stations. The data reception rate was high when the received electric field level was more than 30dBμV. The DGPS data receivers select the station only by field strength, even though the station is getting farther and the other station closer. They begin to search the other station when the field strength of the station under reception become below the threshold. So the authors proposed a method to select the station according to data reception rate and the distance from the station besides the field strength and proved that the method improve the data reception rate by the offline simulation using the data acquired onboard. The method is also effective to obtain the information of oceanic conditions on Type 16 format disseminated by MF radio beacon.
