Aerial surveillance

A surveillance aircraft is an aircraft used for surveillance—collecting information over time. They are operated by military forces and other government agencies in roles such as intelligence gathering, battlefield surveillance, airspace surveillance, observation (e.g. artillery spotting), border patrol and fishery protection. This article concentrates on aircraft used in those roles, rather than for traffic monitoring, law enforcement and similar activities.

Surveillance aircraft usually carry no armament, or only limited defensive armament. A surveillance aircraft does not necessarily require high-performance capability or stealth characteristics. It may be a modified civilian aircraft. Surveillance aircraft have also included moored balloons (e.g. TARS) and unmanned aerial vehicles (UAVs).

The Global Hawk family's US DoD designation - RQ-4 - may belie the Block 40's true calling. "R" is the Pentagon's designator for reconnaissance, .... But the true calling ... is surveillance, not reconnaissance. … Reconnaissance missions are typically more oriented for long-term intelligence-gathering purposes. The surveillance mission is much more integral to the kill chain, with more tactically oriented operations servicing the short-term decision-making process.

In order to be surveillance, it is critical for the collection system, the target, and the decision maker to be in contact with each other in such a way that the actions of the enemy are relayed in real-time to those who can make decisions to counter the enemy actions.

The terms “surveillance” and “reconnaissance” have sometimes been used interchangeably, but, in the military context, a distinction can be drawn between surveillance, which monitors a changing situation in real time, and reconnaissance, which captures a static picture for analysis.

...
Wikipedia