Accession Number : AD0766241

Title :   Geomagnetic Field Models for Ray Tracing.

Descriptive Note : Environmental research papers,

Corporate Author : AIR FORCE CAMBRIDGE RESEARCH LABS L G HANSCOM FIELD MASS

Personal Author(s) : Wong,Ming S. ; Vanguri,Krishna-Sastry ; Friedman,Manfred P.

Report Date : 08 MAY 1973

Pagination or Media Count : 49

Abstract : An accurate geomagnetic-field model, consisting of the dipole plus seven higher-order harmonics in dipolar coordinates, is incorporated into a computer program for three-dimensional ray tracing. Three options of using magnetic-field models are provided: (1) using accurate field in computing both the ray trajectory and the propagation-aspect angle between the geomagnetic-field vector and the wave-normal vector associated with each point along the ray; (2) using the dipole field for computing rays but using the accurate field for computing aspect angles; (3) using the dipole field for both the rays and aspect angles. Comparisons are made among the results computed, using the three options, in the HF band for a nighttime polar ionosphere and for a noontime equatorial ionosphere. Typical differences of few to ten degrees occur in the aspect angle, for aspect angles near 90 degrees -- the value under which geomagnetic-field-aligned ionization, if present, would give rise to maximum backscatter of HF waves and thus cause clutter in Over-the-Horizon radars. (Author)

Descriptors :   (*IONOSPHERIC PROPAGATION, GEOMAGNETISM), MAGNETIC FIELDS, MATHEMATICAL MODELS, ELECTRON DENSITY, HIGH FREQUENCY, COMPUTER PROGRAMS

Subject Categories : Atmospheric Physics
      Radiofrequency Wave Propagation

Distribution Statement : APPROVED FOR PUBLIC RELEASE