this paper studies interferometric capabilities of TanDEM-X mission during an orbit period and tries to get the change of relative height error in a global scope.Firstly
based on HILL-equation of the helix formation
effective baseline
including the range and azimuth effective baseline
which has a great impact on interferometry is analyzed in detail during an orbit period.Then the influence of baseline decorrelation imposing on interferometric phase error is discussed detailedly
which is the most important influence on relative height error.At last relative height model is established and relative height error or TanDEM-X system is presented further.The computer simulating result shows the validity of analysis.