Computations of nighttime field intensity versus distance are made for a 23.4‐kHz signal radiated from Hawaii and for propagation paths to Seattle, Ontario (California), Samoa, and Wake Island. The computations were made by using the waveguide computer program developed at the Naval Electronics Laboratory Center to obtain waveguide mode constants, each 2° of arc or 222 km along each path. An exponential electron‐density profile defined by β = 0.5 km−1 and h′ = 85.5 was assumed, where β and h′ are defined by Wait [1964]. The resultant field was computed by using a WKB approximation to allow for the variation of mode constants along the paths. Experimental measurements of 23.4‐kHz signals from NPM were made aboard an airplane as it flew along these propagation paths. (NPM are the call letters for the Lualualei Navy Radio Station in Hawaii.) Good agreement was obtained, between the theoretical calculations and experimental measurements, strongly supporting the validity of the theoretical approach used (the β = 0.5, h′ = 85.5 km profile assumed) and the conclusion that the increased attenuation observed for propagation to the south is an effect of the geomagnetic field.

In previous works, two mode conversion models, based upon slab approximations, were presented for treating lateral inhomogeneity along the path of propagation in the earth‐ionosphere waveguide. One model (termed Full MC in this paper) requires full‐wave determination of a biorthogonal set of height gains as well as numerical evaluation of their associated integrals. In the other model (termed Fast MC in this paper) height gain functions are discarded above some height h in the guide and are approximated below height h by Airy functions. No adjoint waveguide is introduced, and the associated integrals are performed analytically. Results of the two models are compared in this paper for air to air transmissions in laterally inhomogeneous environments. Results for both the vertical and transverse electric field are given for source electric dipoles of arbitrary orientation. It is found that the Fast MC model gives excellent agreement with the Full MC results.

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A solution of the single-scattering lidar equation requires a relationship between the coefficients of backscatter beta(r) and extinction sigma(r) to be of the form beta(r) = C2sigma(r)k, where C2 and k are parameters independent of range r. The sensitivity of a particular lidar inversion algorithm to uncertainties in C2 and k is investigated using a measured lidar return which indicated the atmosphere to be essentially horizontally homogeneous during a reduced visibility condition. Starting with the measured power returned as a function of range, extinction coefficients and average visibilities are calculated using the inversion algorithm for different values of C2 and k and compared with those inferred from the lidar return using the slope method. The calculated extinction coefficients (and visibilities) were found to be extremely sensitive to uncertainties in C2. This questions the usefulness of the lidar inversion algorithm for aerosol extinction applications when the air mass characteristics change along the measurement path.