Estimation of radio refractivity structure using matched-field array processing

In coastal regions the presence of the marine boundary layer can significan tly affect RF propagation, The relatively high specific humidity of the und erlying "marine layer" creates elevated trapping layers in the radio refrac tivity structure. While direct sensing techniques provide good data, they a re limited in their temporal and spatial scope. There is a need for assessi ng the three-dimensional (3-D) time-varying refractivity structure. Recentl y published results (Gingras et al, [1]) indicate that matched-field proces sing methods hold promise for remotely sensing the refractive profile struc ture between an emitter and receive array, This paper is aimed at precisely quantifying the performance one can expect with matched-held processing me thods for remote sensing of the refractivity structure using signal strengt h measurements from a single emitter to an array of radio receivers. The pe rformance is determined,ia simulation and is evaluated as a function of: 1) the aperture of the receive array; 2) the refractivity profile model; and 3) the objective function used in the optimization. Refractivity profile es timation results are provided for a surface-based duct example, an elevated duct example, and a sequence of time-varying refractivity profiles. The re fractivity profiles used were based on radiosonde measurements collected of f the coast of southern California.