The conventional pulse radar echo signal may occur range migration because of various reasons.In order to solve this problem
analyze the theoretical knowledge of the echo signal coherent integration and introduce three ways to realize Keystone transform which includes DFT-IFFT
Sin interpolation and Chirp Z-transform(CZT)
and then put forward a coherent integration method which based on Keystone transform.It is proved by Matlab that this method can correct range migration effectively
and make detection of radar altimeter more precise
and the feasibility and accuracy of this method are verified by experiment.