Phase-diversity wavefront sensing has been implemented for the measurement of turbulence-distorted atmospheric wavefronts in applications of adaptive optics for essentially-horizontal propagation paths. The selected implementation of phase-diversity provides a wavefront sensor capable of estimating atmospheric distortions when observing extended scenes and provides a range-weighted sensing of the atmospheric distortions dependent on the angular region of the scene used for measurement. The data inversion, based on a Green's function analysis, is fast and robust enough for real-time implementation. For measurements of the atmospheric properties this wavefront sensor is being used with bright, compact sources to give high signal to noise measurements for integrated atmospheric effects along defined optical paths. The implementation used facilitates measurements of the atmospheric distortions along separate propagation paths. By simultaneous measurements along 3 separate paths a library of spatio-temporal atmospheric distortions and information about the isoplanicity of the distortions will be compiled for use in assessing applications of adaptive optics in horizontal propagation conditions. The principles of measurement, the details of implementation and some preliminary results will be described.