[hn9780470248775]

If you're talking about making a map of the astrophysical or cosmological backgrounds of gravitational waves -- you're right. As you integrate (i.e. capture more data), the noise will tend to cancel out while the signal will reinforce itself. But the problem is that the signal-to-noise-ratio is so small -- essentially zero -- that, with current detector sensitivity, it would take literally forever to get an image with any features at all.