fiducial source model to be the mini-QSO. We first study in great detail the simplistic situation where there is a single isolated source in the FOV, and then consider a more realistic situation where there are multiple sources in the field.

Isolated source {#res_isolated}
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We assume that the isolated source is completely isolated and situated at the centre of the FOV. The fiducial parameters of the mini-QSO model, as mentioned earlier, are taken to be $M_\star = 10^7 ~ {{\rm M}_{\odot}}$, $f_{\rm esc}=0.1$, $f_X=0.05$, $\alpha=$1.5 and age $t_{\rm age}=20$ Myr. We assume the IGM density contrast $\delta=0$. We choose the fiducial angular resolution for imaging as 2. The spatial length scale corresponding to this resolution is $\sim 6$ cMpc, which is similar to the radial distance to the strongest absorption signal around the fiducial source.

### Signal and the system noise {#RES_SI_NS}

First, let us consider a scenario where we can ignore the complexities arising from the foregrounds. Even in this simple case where we deal only with the signal and the system noise, we find that the noise is much larger than the cosmological signal as shown earlier in Figure \[image\_p4tbsins\_nosmt\].

One method of increasing the SNR is 