Evaluation of the Loran-A System―I On the Accuracy of Rate 2L1, 2L2 as compared with the Navy Navigation Satellite System

Heretofor the evaluation of the Loran-A system has been carried out generally based on the astronomically observed position. At present, navigational receivers for the Navy navigation satellite system (NNSS) are installed in many ships and serve to give hightly accurate ship positions. The authors evaluated the Loran-A system based on the measurments of relative positional error which is defined as the difference between the position fixed by the NNSS and the one by the Loran-A system (Rate 2L1, 2L2). The data were collected during the cruise of T.S. Kakuyo-Maru in the South Western Pacific Ocean in 1977. The accuracy of these rates is decided by the distance from Master station, and its mean displacement was less than 1.0 nautical mile and the route mean square was ±0.5～±1.8. In the night-time, the probability density within 450 nautical miles was slightly inferior to the other reports, but it was superior to the one by astronomically observed position.測定海域内における,NNSSの位置を基準としたロランA(レート2L1,2L2)の夜間の平均偏位量は1.0'以下であるが,主局からの距離によりRMSは±0.5'～±1.8'となる。また測定時間差の誤差はRMSで±2.5～5.0μsecであった。位置の精度は,一般に云われているものより低いが,主局より450浬以内(昼間では550浬以内)の海域では天測による位置の精度にまさる