Quantification of St. Marys River LORAN-C Time Difference Grid Instability. Volume I. Temporal Instability

摘要

Time Difference (TD) data collected in the St. marys River Loran-C chain coverage area between May 1979 and May 1980 are analyzed to quantify previously-reported temporal TD grid instability. The data included TD samples, nominally recorded every 15 min. at three fixed site monitors and the System Area Monitor (SAM), Local Phase Adjustment (LPA) data, and meteorological data from the National Weather Service Station at Sault Sainte Marie, Michigan. Assorted non-parametric data analyses, including spectral and correlation analyses, are conducted to separate diurnal and seasonal components of grid instability and identify relationships among the various TDs. The relative magnitude of the seasonal TD variations and the correlation of pairs of TDs are not consistent with expected weather-related variations in signal propagation time, thereby suggesting that the grid instability may be partially transmitter and/or receiver-related. The Loran-C data are also employed to evaluate the U.S. Coast Guard low-density (five 15-min. samples, twice daily) data analysis approach. The low-density approach is found to be adequate for monitoring seasonal TD variations, but inadequate for monitoring diurnal variations. An increase in the sampling rate is recommended for low-density Loran-C data collection in harbors. (Author)