The Bottom Line Up Front
Infrared and visual video cameras aid in navigation of larger class UAVs and are helpful for safety but do not satisfy the legal requirements for unmanned aircraft to operate in US/international airspace. Instead, the use of onboard navigation systems like GPS, combined with air traffic control services and common flight safety rules allow safe navigation of high and medium altitude UAVs.
What UAVs Operate at High Altitude?
Northrop Grumman's "RQ-4" variants (e.g. USAF RQ-4B Global Hawk, US Navy MQ-4C Triton, NATO RQ-4D Phoenix) are the only widely recognized UAVs flown at high altitudes (FL500-600). The RQ-4 is also the largest UAV with a wingspan greater than a Boeing 757. All other UAVs, including the MQ-9 Reaper, operate at medium or low altitudes.
How Does the RQ-4 Navigate?
The RQ-4 has sophisticated, GPS & gyro-enabled navigation computers that ensure it always knows where it is and where it is going. To avoid airborne hazards like other aircraft or bad weather, it follows the same instrument flight 'rules of the road' that manned aircraft rely on when flying at night or in the clouds. Specifically, air traffic controllers use radar to track aircraft from the ground and alert the pilots if they see an unsafe situation on their radar screens. These instances are rare, however, because everyone follows their flight plan and obeys air traffic controllers' instructions in order to remain safely separated in the air--even remotely piloted aircraft.
Does the RQ-4 Have Any Cameras Used to Aid in its Control?
Yes. As a backup to air traffic control clearances to taxi, takeoff, and land, the RQ-4 has a forward-facing infrared video camera on the nose of the airplane. Although it is not legally required to have this camera, it is used only as a backup for the pilot to ensure the runway is clear of obstacles during taxi and prior to landing on the runway. Radio transmission of the video camera signal is via line-of-sight antennas only (not over satellites), so therefore it is limited only to the airfield/runway environment where the ground control station is located and is not used while away from the airfield during climb, cruise, or descent.
Note there are two small windows in the pressurized camera compartment: One upper window for the video camera lens and the lower window used to display the pressure dial for the camera compartment.
What About Medium/Low Altitude UAVs?
Medium altitude UAVs like the MQ-9 predator carry a variety of infrared (day/night) and electro-optical (day only) full motion video cameras used primarily for their mission rather than for navigation. Unlike the high-altitude RQ-4, they operate at the same altitude levels as commercial air traffic. They can follow the same instrument flight 'rules of the road' that manned aircraft do when flying at night or in the clouds. Often, their mission requires them to fly in areas where following these rules aren't required by all aircraft. In this type of airspace, pilots of smaller aircraft like gliders and crop-dusters don't have the radios to communicate to air traffic control and count on other aircraft to 'see-and-avoid' them instead. The MQ-9 does not have a pilot onboard to look out the window and avoid these 'visual flight only' aircraft, so it needs other solutions to ensure safe navigation.
The MQ-9 does have a powerful ball-mounted, full-motion video camera onboard. However, the USA's Federal Aviation Administration and the worldwide International Civil Aviation Organization has not deemed the use of this camera as a sufficient substitute for the see-and-avoid requirement. Therefore, despite the MQ-9's robust visual/infrared camera system, it must rely on other methods of deconfliction like temporary/military restricted airspace, special clearances, and even chase airplanes, in order to conduct its training in the US and its missions overseas. The same challenges exist with smaller, low-altitude military unmanned aerial systems and commercially operated drones.
Are Cameras Any Good For Long Range Navigation?
That depends on what you consider long range. Navigation using cameras, especially to avoid other aircraft, requires low-latency. It does little good to see a rogue aircraft filling your windscreen if, by the time you see it on the screen, the plane has already crashed into your UAV. This usually isn't a problem for FPV hobbyists because they have a line of sight video signal, directly from the RC aircraft, that feels instantaneous to the pilot wearing FPV goggles. On the other hand, truly long ranges require operation beyond line of sight, relying on satellites to pass information to/from the aircraft. This extra architecture causes video latency, sometimes up to multiple seconds, making it nearly impossible to visually react to a time-critical safety event.
A Better Alternative to Cameras
In addition to the video latency problem, video cameras on medium/high altitude UAVs are specialized to focus on small targets at long range--not scanning the skies for unidentified aircraft. Imagine trying to spot a fly buzzing around you while looking through a toilet paper tube. An additional, wide-angle navigation camera/lens could be carried on the aircraft but it would not be worth the additional cost, weight, space, and power consumption. Instead, long-range aircraft like the RQ-4 and MQ-9 rely on a framework of aircraft regulations, ground-based air traffic control, and segregated airspace to safely navigate.
Note: This response was drafted from scratch, solely to answer Rajath's question about cameras on high altitude UAVs. Thanks in advance for your feedback.