generated per pulse, it is clear that the correlation enhancement of the intensity correlation protocol is limited to the low mean probe photon number per pulse regime. This is in agreement with the previous analysis with the mutual information criterion.\

The Transmission Estimation (Fisher Information) Figure Of Merit
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Although the previously mentioned definitions of target detection signal and figure of merit demonstrate the quantum enhancement of intensity correlation protocols compared to their classical counterparts, they are implementation-dependent and artificial to some extent. For example, the definition of SNR cannot be easily generalized for the QTC protocol. Therefore, to quantify and compare the performances of different correlation enhanced target detection protocols, a more general definition of target detection signal and figure of merit is needed. The solution to this problem to formulate target detection as a transmission estimation problem: from the experimentally measured photo-detection statistics, it is possible to obtain an estimation $\hat{\eta}_p$ of the total transmission $\eta_p$ of the probe light [^3]. The estimated transmission $\hat{\eta}_p$ is a natural choice of the ‘target detection signal’ since its average value is positive if and only if the target object is present. The variance of transmission estimation, on the other hand, 