pysteps.cascade.decomposition.decomposition_fft(field, bp_filter, **kwargs)#

Decompose a two-dimensional input field into multiple spatial scales by using the Fast Fourier Transform (FFT) and a set of bandpass filters.

  • field (array_like) – Two-dimensional array containing the input field. All values are required to be finite.

  • bp_filter (dict) – A filter returned by a method implemented in pysteps.cascade.bandpass_filters.

  • fft_method (str or tuple) – A string or a (function,kwargs) tuple defining the FFT method to use (see pysteps.utils.interface.get_method()). Defaults to “numpy”. This option is not used if input_domain and output_domain are both set to “spectral”.

  • normalize (bool) – If True, normalize the cascade levels to zero mean and unit variance. Requires that compute_stats is True. Implies that compute_stats is True. Defaults to False.

  • mask (array_like) – Optional mask to use for computing the statistics for the cascade levels. Pixels with mask==False are excluded from the computations. This option is not used if output domain is “spectral”.

  • input_domain ({"spatial", "spectral"}) – The domain of the input field. If “spectral”, the input is assumed to be in the spectral domain. Defaults to “spatial”.

  • output_domain ({"spatial", "spectral"}) – If “spatial”, the output cascade levels are transformed back to the spatial domain by using the inverse FFT. If “spectral”, the cascade is kept in the spectral domain. Defaults to “spatial”.

  • compute_stats (bool) – If True, the output dictionary contains the keys “means” and “stds” for the mean and standard deviation of each output cascade level. Defaults to False.

  • compact_output (bool) – Applicable if output_domain is “spectral”. If set to True, only the parts of the Fourier spectrum with non-negligible filter weights are stored. Defaults to False.

  • subtract_mean (bool) – If set to True, subtract the mean value before the decomposition and store it to the output dictionary. Applicable if input_domain is “spatial”. Defaults to False.


out – A dictionary described in the module documentation. The number of cascade levels is determined from the filter (see pysteps.cascade.bandpass_filters).

Return type