An Improved Spherical Earth Diffraction Algorithm for SEKE
Abstract
The spherical earth diffraction subroutine SPH35 in the radar propagation code SEKE has been known to cause errors in propagation loss computations for a range of combinations of antenna and target heights. In this report an efficient method to evaluate the Airy function in the complex plane is presented. This method uses the power series expansion near the origin and an integral representation elsewhere. It is more accurate and as fast as the method employed in the spherical earth diffraction subroutine SPH35 that evaluates every Airy function of Fock's series by a fourth-order polynomial fit to its logarithm. The algorithm presented was incorporated in a new spherical earth diffraction subroutine (SPH35N). It was found that, if SEKE uses this subroutine, no problems arise for normalized heights of up to 5000 (i.e. about 350 km at VHF or 17 km at Ku band). The subroutine SPH35N, described in this report, has been used in the versions of SEKE running at Lincoln Laboratory, and is in the version of SEKE currently being supplied to other users. Keywords: Spherical earth diffraction; Radar propagation; Airy function; Focks series; Polynomial fit.
Document Details
- Document Type
- Technical Report
- Publication Date
- Apr 15, 1988
- Accession Number
- ADA195847
Entities
People
- George H. Polychronopoulos
- Michael P. Shatz
Organizations
- Massachusetts Institute of Technology