DAS is comprised of six staring focal point arrays. These are infrared cameras flush-mounted on the skin of the airplane, which detect the entire sphere around the airplane. The entire sphere is about 41,000 square degrees whereas the radar sees about 10,000 square degrees. When there is an intersection of the two sensors i.e. when they’re both looking through the same angular volume of space, fusion will work them synergistically, and they can queue each other through the fusion engine. As soon as one sensor detects something, fusion then queues every other sensor to look along that line of sight and try to find information about the track.
The DAS performs a number of functions. It does short range situation awareness infrared search and track (IRST). For the pilot, the days of someone sneaking up on him are almost gone. In clear air, it can detect and track other airplanes by their thermal signature. It also does missile launch detection, which is its primary function. It’s tuned to a spectrum such that it can see rocket motors. When a threat is detected, fusion will place a symbol on the helmet visor around the missile and the launch point. The other function DAS performs is called GTL ground target launch. This is the ability of fusion to extrapolate the DAS missile track back to the ground. Fusion places a symbol on the head down display at the point of origin.
Likewise when fusion recognizes a DAS track is in the same angular space as the radar it will indicate to the APG-81 to go look along this line of sight and get range on the track that DAS found. Or if the radar has a track and it gimbals, or in other words, the track goes beyond the radar’s field of regard, fusion will tell DAS to keep updating this and hold onto the track for the pilot until it comes back into the field of regard of the radar or comes back into the field of regard of some other sensor on the airplane. These things are laborious for the pilot to control manually, but are easy for a computer to control algorithmically. There is a reason for the 8.5 million lines of code and why the F-35 program is taking so long.It is automating the Orient and Observe part of the OODA loop and compressing the pilot's decision cycle. This is besides the EOTS, and Barrcuda EW that get thrown into the pot. The plane's EW suite has multiple functions and performs in an integrated manner with fusion. Some of these functions include radar warning receiver (RWR), electronic support measures (ESM), and electronic countermeasure (ECM). In comparison, these functions are federated on most 4th generation fighters.
As the airplane flies through battlespace, the EWS is tasked by fusion to build a picture of the electronic order of battle. It identifies emitters, locates them, classifies them and then reports to the pilot what it detects in battlespace. The fused data are matched against the threat library to build a profile of the threats, priority of threats and navigation vector to optimally position the plane against these threats.
All these capabilities combined is defined as level 4 sensor fusion according to the JDL model. There are some 4+ gen platform that claims to have sensor fusion but is effectively a level 0 type sensor fusion.
In comparing 5th gen sensor fusion across platforms, there are several factors that come into the picture in determining sensor fusion capabilities besides the software and architectural design.
The F-35 sensor fusion architecture is that all the data from all the sensors are handled in one fusion engine whereas in 4th gen systems the individual sensor handle their own data and then transfer the data they consider important the sensor fusion engine. The sensor fusion in 4th gen systems is unaware how the sensors decide what signals are important. The sensor fusion engine by centralising data is able to build a more comprehensive composite picture but this requires a capable data bus. Modern AESA and optical staring arrays generate significant amount of data that needs to be moved. This means the databus architecture, bandwidth and latencies are important. Imagine trying to do video conferencing using dial up moderm. Rafael which claims to have sensor fusion have 20 Mbps max speed databuses (STANAG 3910 type). Most F-22 and F-35 have 20 times higher speed databuses (IEEE 1394b) with growth potential. Such data transfer rate is huge difference for sensor fusion and presenting information to a pilot.
To my knowledge, the Chinese are still using ARINC 429 databus architecture for the J10A/B and the Russians are using 1553B in the PAKFA. I don't know what the J-20 is using but that would be a key determinant on its sensor fusion capability if it does have one.
