Atmospheric Refraction Predictions Based on Actual Atmospheric Pressure and Temperature Data

Abstract

Calculations of atmospheric refraction are generally based on a simplified model of atmospheric density in the troposphere that assumes the temperature decreases at a constant lapse rate L from sea level up to a height , and that afterward it remains constant. In this model, the ratio To/L, where To is the temperature at the observer’s location, determines the length scale in the calculations for altitudes . But daily balloon measurements across the USA show that in some cases there is an inversion so that the air temperature actually increases from sea level up to a height , and only after reaching a plateau with temperature at this height, it decreases at an approximately constant lapse rate. Hence, in such cases the relevant length scale for atmospheric refraction calculations in the range is , and the contribution for has to be calculated from actual measurements of air density in this range. Moreover, in three examples considered here, the temperature does not remain constant for , but continues to decreases to a minimum at , and then increases at higher altitudes at a lower rate. Calculations of atmospheric refraction based on this actual atmospheric data are compared with the results of current simplified models.