5.4 Stochastic background
Stochastic background limits can be derived from the smoothed Doppler frequency power
spectrum [49
, 27]. If the background is assumed isotropic, spectra of two-way Doppler can be
converted to spectra of strain by dividing by the sky- and polarization-averaged GW response
function [49, 51, 19]. (If a background is not isotropic, then the spectral response function
is the square of the Fourier transform of the three-pulse response evaluated for the relevant
and averaged over polarization states.) From Sh the strength of the background can be
expressed relative to closure density or as a characteristic strain amplitude [102, 87, 66] (see
Section 6.4).
