We propose observation system of crustal movement at the area of earth stations using two quasizenith satellites which have retro-directive antenna on board. Inthis sysyem, the crustal movement is obtained by interfering with two singnals from retro-directive antennas which transmit the receiving waves from the earth station antenna towarad the direction of the earth station antenna.
From the link budget of this system, for the earth station anntenna we select the spherical reflector anntenna having two anntena beams.