There are advantages to non-radar sensors as well and these sensors can augment radar to aid in target recognition in a System of Systems (SoS) construct. However, any robust solution is likely to require a radar system for primary detection. Table 1 shows the trade space of radar-only options that include Ground Based Radar, Airborne Radar, and Transponder solutions.
C. Ground Based Radar Details The largest benefits of Ground Based Radars include:
• Large Size, Weight, and Power (SWaP) availability to survey a large volume • Single sensor can cover multiple UAS, which saves cost and reduces RF spectrum usage in dense target environments • No need for extra equipment on the craft, saving payload for the primary mission • Emplacement (and freqeuncy) can be optimized ahead of time, including coordination with the FCC • Redundant source of position/velocity of craft if communications are lost • Ability to detect non-cooperative targets
The largest drawbacks of Ground Based Radars include:
• Line of Sight (LOS) limitations for low flying targets • Required infrastructure for long range or remote operations • General radar/transponder inability to detect stationary targets such as water towers or telephone poles for collision avoidance
The pros and cons make the optimal sensor mission dependent. For example, if instrumenting a city or large area for UAS usage, a ground based sensor can be sited to avoid LOS limitations, operate at a single frequency carefully coordinated with the FCC, and cover many UAS with a single sensor to provide a robust and cost effective solution. Multiple airborne radars requiring mobile coordination of spectrum would be very problematic in this case.
However, a mission that included a Long Endurance (LE) UAS traveling hundreds of kilometers in remote locations (say for wildlife monitoring) would be better suited for an airborne sensor. LOS limitations and the large area requiring instrumentation would make ground based technology prohibitive; not counting localized operations that could use aground mobile solution.
As previously discussed, transponders are very useful but are not sufficient for all situations due to non-cooperative targets.
II. DEVELOPMENT
A. Research Tasks The following tasks are proposed as steps to determining the requirements for BVLOS operations. These are research oriented and are meant to be completed through analysis and simulation.
1) Targets of interest a) Survey of present sUAS characteristics: altitude of operation, ground speeds, ascent/descent rates, turn rates, physical and RF size, mission specific behaviors, failure modes, etc. These should be extrapolated based on design trends.
b) Survey of manned aircraft expected to occupy the same airspace as the sUAS. Use similar characteristics list as above.
c) Analysis of other non-cooperatives expected, for example looking at bird density fluctuations over time for different regions.
2) Concept of operation a) Select a few representative, varied missions requiring BVLOS operation of sUAS : Precision Agriculture, Emergency Responders, Power Line inspection, and Commercial Deliveries.
b) Specify hypothetical System of Systems (SoS) to enable each one of the missions for BVLOS oepration. This includes the full sensor suite required both on the ground and on the vehicles.
c) Define an error budget for the System of Systems including the craft characteristics, mission specifics, and residual needed by ground and air sensors for DAA along with tracking and fusion algorithms needed to make real-time decisions. This task includes basic simulation to test the bounds of the problem space.