What is a crucial feature of mobile surveillance?

Mobile surveillance is characterized by its flexibility and ability to adapt to various environments and situations. One of the crucial features that distinguishes mobile surveillance is its potential to utilize vehicles. This capability allows operatives to cover greater distances, track subjects efficiently, and respond quickly to changes in the subject's movements or location. The use of vehicles enhances the operatives' ability to remain inconspicuous while maintaining a safe distance from the subject being monitored.

In contrast, the other options present limitations or misconceptions that do not align with the nature of mobile surveillance. While surveillance can occur on foot, restricting it solely to foot-based operations would significantly limit its effectiveness and reach. Legal requirements, such as the necessity of a warrant, might be applicable in certain circumstances or jurisdictions, but they do not define the essential nature of mobile surveillance itself. Lastly, mobile surveillance can effectively involve multiple operatives to help ensure thorough monitoring, especially in complex environments, rather than being constrained to a single operative.