def crosscorr_time(u, v, model, **kwargs):
    """
    Cross correlation of forward and adjoint wavefield

    Parameters
    ----------
    u: TimeFunction or Tuple
        Forward wavefield (tuple of fields for TTI or dft)
    v: TimeFunction or Tuple
        Adjoint wavefield (tuple of fields for TTI)
    model: Model
        Model structure
    """
    w = kwargs.get('w') or u[0].indices[0].spacing * model.irho
    return w * sum(vv.dt2 * uu for uu, vv in zip(u, v))