where Ps and P0 are the atmospheric surface pressures (in hPa) at heights hs and h0 (in m), respectively. In Eq. (7) hs and h0 can either be ellipsoidal or orthometric heights, provided they are both in the same height system.
Eq. (7) is a simplified expression for the height dependence of atmospheric pressure in which any dependence on the temperature is neglected. More precise expressions can be found in the literature, most of them equivalent to the formula by Hopfield (1969), adopted by authors such as Boehm et al. (2007) and Salstein et al. (2008):