The technique of remote measurement was developed of some parameters of optical instability and atmospheric turbulence at daytime based on the use of a coherence interferometer with a small angular aperture. Measurements of the degree of spatial coherence were carried out during observations of direct sunlight and solar aureole with the following interpretation of interferograms. It was shown experimentally that the light scattered by solar aureole possessed partial spatial coherence. Measurements of the atmospheric coherence diameter by Fried method were conducted. A criterion of optical instability was proposed based on the measurement of the light coherence scattered by solar aureole. The interferometer can be applied to investigation of light scattering in the turbulent atmosphere.