A front extraction method for a raster image of sea surface temperature (SST)is presented. Considering that the front was distributed unevenly

a low-pass filter is used to smooth the SST gradient image. The gradient image is then divided into target and background parts by a split threshold calculated from the iteration algorithm. By mathematical morphology image thinning

a SST front skeleton is extracted from the target one

and the tiny branches are trimmed. After the vectorization of the SST front skeleton

the vectorized SST front lines are smoothed using the erasing angle method. An example of SST front extracting process in the west Pacific is presented at last. The results show that the method is feasible and effective.