We recently developed a method1 to measure the gradient of the refractive index of the atmosphere, by using the lateral fluctuations of thin laser beams along a given path. We showed that the horizontal and vertical instantaneous fluctuations of a ray on a screen, at the end of a path of length L, are related to the horizontal and vertical components, averaged along the path, of the refractive index gradient, respectively.
Our method, which is based on the geometrical optics approximation, requires that the beams are "thin", that is that their transverse dimension be not larger than the dimensions of the smallest inhomogeneities of the atmosphere (inner scale of turbulence). In practice, it allows "local" measurements, that is measurements over short horizontal paths, even few meters' paths. Experiments were made in the open air.
Here we describe the method and present results of measurements made in different locations and conditions, at near ground levels. Temperature and transverse wind velocity were also measured and some correlation of these quantities to the refractive index gradient will be presented. Some cases of strong vertical anisotropy are also shown, which can be related to the local air convective movements from the ground.