The simulated methane concentrations described in the following section do not include background concentrations that are present in the atmosphere. Therefore, we must first remove background concentrations from the CMS observations before comparing them to simulation predictions. We do so for each sensor separately by using the spike detection algorithm proposed in Section 2.1. Summarizing this procedure at a high level, we group identified spikes that are close together in time, background correct each group using the concentration observations immediately preceding and following the group, and then set all observations that are not in a group to zero.