Objectives The fusion of spaceborne light detection and ranging (LiDAR) and interferometric synthetic aperture radar (InSAR) is widely used in understory terrain estimation, tree height inversion, digital elevation model (DEM) accuracy evaluation and correction, etc. However, due to limitations in onboard platforms, imaging technology and data processing, the deviations still exist in plane position and height measurement of InSAR DEM. Therefore, the effective registration of spaceborne LiDAR and InSAR DEM is the key premise of the fusion application.

Methods We propose an improved registration model which fully considers the changes in plane offset and elevation variation under different topographic factors. The proposed model includes a stochastic model and a functional model. The stochastic model is proposed based on the relationship between changes in terrain slope and plane offset, while the functional model linearizes the original registration model. Finally, the plane offset can be solved by the registration model with the least squares adjustment method. In order to verify the validity of the registration method, four test areas with different terrain conditions and land cover types in Spain are selected for testing.

Results The experimental results show that root mean square error (RMSE) of height difference after registration in these four test areas reach 0.931 m, 1.381 m, 1.034 m and 4.526 m, respectively. Compared with the accuracy before registration, the accuracy after registration is improved by 33.02%, 8.78%, 37.67% and 10.00%, respectively. For a canopy height of 15 m compared to 5 m, the contribution of slope greater than 45° to the overall registration of elevation changes in these four test areas reach 72%⁃99%, while the registration accuracy decreases from 33.02%, 8.78%, 37.67%, 10.00% to 20.60%, -0.27%, 35.89%, 4.62%, respectively.

Conclusions The proposed method weakens the systematic error variation of height deviation caused by plane offset under the influence of terrain slope and aspect. The experimental results verify the effectiveness of the proposed model for the registration of spaceborne LiDAR and InSAR DEM in complex terrains.