Large temporal variations have been observed in St. Marys River Loran-C time difference (TD) measurements. As a first step in determining the cause of this instability, the sensitivity of the TD grid to expected seasonal variations in Loran-C signal propagation conditions has been determined. The sensitivity analysis is based on theoretical propagation delay models and expected seasonal variations in the propagation parameters -- surface refractive index of air, the parameter associated with refractive index gradient, and ground conductivity. The analysis results show that conductivity, which is the parameter least amenable to measurement, is also the parameter which is most critical to grid stability. It is shown herein that the assumed variations in conductivity cannot explain observed variations in the TD data. Predicted TD variations due to seasonal grid instability are employed to predict the corresponding position errors at reiver waypoints. The resulting position errors are combined with those predicted for the case of no grid instability to provide predictions of total position error. (Author)

  • Corporate Authors:

    Analytic Sciences Corporation

    6 Jacob Way
    Reading, MA  United States  01867

    United States Coast Guard

    2100 Second Street, SW
    Washington, DC  United States  20593
  • Authors:
    • DePalma, L M
    • Gupta, R R
  • Publication Date: 1978-6

Media Info

  • Pagination: 61 p.

Subject/Index Terms

Filing Info

  • Accession Number: 00318391
  • Record Type: Publication
  • Source Agency: National Technical Information Service
  • Report/Paper Numbers: TASC-TIM-1119-3, USCG-D-33-80
  • Contract Numbers: DOT-CG-81-77-1785
  • Files: NTIS
  • Created Date: Oct 8 2002 12:00AM