pysteps.extrapolation.semilagrangian.extrapolate

pysteps.extrapolation.semilagrangian.extrapolate(precip, velocity, num_timesteps, outval=nan, xy_coords=None, allow_nonfinite_values=False, **kwargs)

Apply semi-Lagrangian backward extrapolation to a two-dimensional precipitation field.

Parameters:

precip : array-like

Array of shape (m,n) containing the input precipitation field. All values are required to be finite by default.

velocity : array-like

Array of shape (2,m,n) containing the x- and y-components of the m*n advection field. All values are required to be finite by default.

num_timesteps : int

Number of time steps to extrapolate.

outval : float, optional

Optional argument for specifying the value for pixels advected from outside the domain. If outval is set to ‘min’, the value is taken as the minimum value of R. Default : np.nan

xy_coords : ndarray, optional

Array with the coordinates of the grid dimension (2, m, n ).

• xy_coords[0] : x coordinates
• xy_coords[1] : y coordinates

By default, the xy_coords are computed for each extrapolation.

allow_nonfinite_values : bool, optional

If True, allow non-finite values in the precipitation and advection fields. This option is useful if the input fields contain a radar mask (i.e. pixels with no observations are set to nan).

Returns:

out : array or tuple

If return_displacement=False, return a time series extrapolated fields of shape (num_timesteps,m,n). Otherwise, return a tuple containing the extrapolated fields and the total displacement along the advection trajectory.

Other Parameters:  

D_prev : array-like

Optional initial displacement vector field of shape (2,m,n) for the extrapolation. Default : None

n_iter : int

Number of inner iterations in the semi-Lagrangian scheme. If n_iter > 0, the integration is done using the midpoint rule. Otherwise, the advection vectors are taken from the starting point of each interval. Default : 1

return_displacement : bool

If True, return the total advection velocity (displacement) between the initial input field and the advected one integrated along the trajectory. Default : False

References

[GZ2002] Germann et al (2002)