docs: def storage_type(self):
          """Depending on input data type, the storage type is either
          "field" (complex) or "phase" (real)."""
          nf = np.load(str(self.path), mmap_mode="c", allow_pickle=False)
          if np.iscomplexobj(nf):
              st = "field"
          else:
              st = "phase"
          return st