prop-618/data/P839

The files h0.txt is from ITU-R P.839-4 (https://www.itu.int/dms_pubrec/itu-r/rec/p/R-REC-P.839-4-201309-I!!ZIP-E.zip).

This file contains h₀ = ‘0 degree isotherm height (in km and above mean sea level)’, as required by ITU-R P.839, on a regular 2d grid of latitude: +90:-1.5:-90 and longitude: 0:1.5:360, with Lon changing fastest.