Studies of the atmospheric correction for satellite laser ranging

A study is reported on the factors necessary to achieve further gains in accuracy in laser ranging. The present accuracy of laser ranging is approaching plus or minus 50 mm, which indicates a need to aim for a plus or minus 5 mm accuracy in the determination of the correction for atmospheric refraction. The Marini and Murray formulae are easily programmed and are widely used. They assume hydrostatic equilibrium and a constant vertical temperature gradient in the troposphere. It appears that some refinements are necessary to achieve the accuracy required. The atmospheric correction varies from 2.4 m at the zenith to 13 m at 10 degrees elevation. A number of small effects such as the geometric correction, the water vapor correction, and horizontal temperature gradients are all about plus or minus 30 mm in magnitude. In the study reported, the integral of refractivity is evaluated using numerical methods. The effects of the varying temperature gradients in the lowest kilometer, the boundary layer, have been investigated and a form of boundary layer correction, up to plus or minus 25 mm in magnitude, is suggested. Investigations are continuing, using a theoretical approach and sets of temperature observations on high towers.