In the final step, we find the optimal sensor placement under a given sensor budget. Using the detection matrix D constructed in the previous step, we can model the optimization problem as a best subset selection problem. Recall that the rows of the detection matrix correspond to possible sensor locations and columns to emission scenarios. Given the sensor budget k, i.e, the number of sensors to install, selecting k sensors translates to selecting k rows from the detection matrix. In the resulting sub-matrix D (k) sub , we assess the column-wise sums which indicate the number of sensors that detect the corresponding emission scenario.