We present a numerical method for calculating vertically averaged velocityfields using a mass conservation approach, commonly known as balancevelocities. This allows for an unstructured grid, is not dependent ona heuristic flow routing algorithm, and is both parallelizable and efficient.We apply the method to calculate depth-averaged velocities of the GreenlandIce Sheet, and find that the method produces grid-independent velocity fieldsfor a sufficient parameterization of horizontal plane stresses on flowdirections. We show that balance velocity can be used as the forward modelfor a constrained optimization problem that can be used to fill gaps andsmooth strong gradients in InSAR velocity fields.
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