Seismic images of subsurface structures are the most valuable outcome of seismic dataprocessing. The image quality is strongly affected by the accuracy of background velocity model.In this paper, we develop a gradient-descent velocity update algorithm based on our originalhigh-frequency asymptotics of the Double Square Root equation, i.e., a special one-wayapproximation of the wave equation describing single-scattered wave field only. We propose a lossfunction consistent with widely adopted imaging condition and derive equations for its gradientcomputation. We test our method on noise-free synthetic datasets in 2D settings.