This is not measured data but expected total antineutrino emissions according to the model that they created ((anti)neutrinos come in three different flavors an

This is not measured data but expected total antineutrino emissions according to the model that they created ((anti)neutrinos come in three different flavors and can oscillate between them). It looks like they modeled different sources like Earth's crust, mantle and artificial sources (nuclear reactors) separately, e.g. by using known distributions and ratios of radioactive elements or locations and power of nuclear reactors and in one case actual measurements by detectors in Italy and Japan. They then ran simulations on this and summed up the total flux in different energy ranges ("bins"). https://www.nature.com/articles/srep13945#Sec7 https://www.nature.com/articles/srep13945#Sec7