Unlike conventional SSL methods which generally ray-trace backwards using a single angle of incidence and azimuth, TASSEL uses the incident angles on a receiving array of two or more simultaneous paths (e.g. 1 and 2 hop F2) to determine both an updated ionosphere model (corresponding to the prevailing conditions) and the location of the target transmitter. Use is made of analytic models for the ionosphere and analytical formulae for the propagation paths and a Nelder Mead (1965) simplex function minimisation algorithm for the optimisation. A menu driven graphical interface is used for input/output and also permits a choice of different analytical models for the calculation of the propagation path. Measured angles of elevation to known transmitters and measured time differences of propagation between different modes can also be employed to improve the optimisation. Initial and final (optimised) ionospheric profiles are plotted.
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