FDOA post-Newtonian equations for the location of passive emitters placed in the vicinity of the Earth

The Frequency Difference of Arrival (FDOA) equations derived in this paper are intended to increase the standard accuracy of the Low Earth Orbit (LEO) satellites dedicated to locate non-cooperative emitters placed on the Earth surface or in orbit about the Earth. The equations contain terms that are of the order of the corrections already taken into account in Navigation by GPS. In particular, two of them should not be neglected to this end, since they can be of the order of 10−10.