code: def asd(self, fftlength=None, overlap=None, window='hann',
              method=DEFAULT_FFT_METHOD, **kwargs):
          
          return self.psd(method=method, fftlength=fftlength, overlap=overlap,
                          window=window, **kwargs) ** (1/2.)
docs: Calculate the ASD `FrequencySeries` of this `TimeSeries`
  
          Parameters
          ----------
          fftlength : `float`
              number of seconds in single FFT, defaults to a single FFT
              covering the full duration
  
          overlap : `float`, optional
              number of seconds of overlap between FFTs, defaults to the
              recommended overlap for the given window (if given), or 0
  
          window : `str`, `numpy.ndarray`, optional
              window function to apply to timeseries prior to FFT,
              see :func:`scipy.signal.get_window` for details on acceptable
              formats
  
          method : `str`, optional
              FFT-averaging method, see *Notes* for more details
  
          Returns
          -------
          psd :  `~gwpy.frequencyseries.FrequencySeries`
              a data series containing the PSD.
  
          See also
          --------
          TimeSeries.psd
  
          Notes
          -----
          The accepted ``method`` arguments are:
  
          - ``'bartlett'`` : a mean average of non-overlapping periodograms
          - ``'median'`` : a median average of overlapping periodograms
          - ``'welch'`` : a mean average of overlapping periodograms