What is an example of an indirect form of monitoring in CBRN operations?

Indirect forms of monitoring in CBRN operations involve methods that do not use real-time data collection or direct observation of current conditions. The choice of observation based on past data exemplifies this concept because it relies on historical records, trends, or previously gathered intelligence to assess the potential presence or effects of chemical, biological, radiological, or nuclear threats. This kind of monitoring does not involve active measurement or direct surveillance but rather analyzes previous information to draw inferences about current situations or potential risks.

In contrast, the other options represent more direct forms of monitoring. For example, surveillance using drones allows for real-time observation and data collection in the field. Monitoring through reconnaissance entails active exploration or surveying of the environment to gather current information. Reporting via radios suggests communication of real-time observations from operational units but does not rely on the analysis of historical data. Each of these forms is valuable in a CBRN context, but they do not align with the indirect monitoring category as effectively as utilizing past data does.