1. A method for troposphere corrections in a positioning system with a ground based transmitter, the method comprising: estimating a range as a function of a signal from the ground based transmitter, the signal: (a) having an X-band or ISM-band carrier frequency; (b) having a modulation rate of code being at least about 30 MHz; or (c) having both the X-band or ISM-band carrier frequency and the modulation rate of the code being at least about 30 MHz; and applying a troposphere correction to the range.