Reply [to "comment on 'The feasibility of radio sounding of the magnetosphere' by W. Calvert et al."]

W. Calvert and colleagues reply to the comment on their paper titled, 'The feasibility of radio sounding of the magnetosphere'. Greenwald h as asserted that the loss of 21 dB of coherent integration gain as a result of the Doppler shifts which are caused by target velocity, target rotation, target structure and spacecraft motion will remove any possibility of imaging the magnetopause with a radio sounder. As pointed out by Greenwald, pulse compression requires a Doppler shift which causes no more than about one quarter of a wavelength phase shift during an echo pulse. At 30 kHz, for the sounding parameters which were specified in the paper, this corresponds to a velocity of about 25 km/s, and according to the ISEE 1 and ISEE 2 observations of Berchem and Russell. The magnetopause velocity exceeds this value about three quarters of the time. The relevant point raised by Greenwald is that coherent integration may not work for the highest velocities which have been detected at the magnetopause. This, however, is not expected to compromise the usefulness of radio sounding for magnetospheric search since useful mages of the magnetopause with roughly angular resolution would still be possible virtually all of the time without having to rely upon coherent integration. Greenwald then asserts that the coherent integration gain for spectral integration cannot be realized as a result of unknown and unmeasured accelerations at the magnetopause. Although such accelerations cannot be ruled out, this would require a change in velocity of approximately 10 km/s in less than a minute, and it is simply unknown whether such accelerations are typical of the magnetopause.