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The slant wet delay of GPS signals is subjected to the non-uniform distribution of the water vapor in the atmosphere.The three dimensional field of water vapor can be recovered by the computerized tomography(CT) method through accurately determining the slant wet delays from satellites to antennas on the ground.Two sorts of methods for determining the slant wet delays,the point precise positioning(PPP) and the double-difference method,are introduced.Two CT approaches for obtaining the water vapor profiles((Gaussian) constraint and the Kalman filtering) are discussed.