Embedded computing a crucial enabler of bistatic radar and sonar

Two surveillance technologies that have been in common use for more than half a century - radio detection and ranging (radar) and sound navigation and ranging (sonar) - may undergo substantial enhancements with the addition of remote transmitters.

John Keller

Two surveillance technologies that have been in common use for more than half a century - radio detection and ranging (radar) and sound navigation and ranging (sonar) - may undergo substantial enhancements with the addition of remote transmitters.

These offboard transmitters could create a new generation of bistatic radar and sonar that could not only enhance the performance of these systems, but also preserve the stealthiness of weapons platforms like jet fighter aircraft and fast attack submarines. Read J.R. Wilson's special report on the new frontiers in passive radar and sonar on page 6.

Radar and sonar, in essence, represent relatively simple concepts: They both transmit energy that bounces off objects nearby and detect targets by receiving energy from the return signals. Radar bounces radio waves off targets, while sonar does the same with sound waves. An added benefit of radar and sonar is the ability to estimate the target's distance from the transmitter, based on the time it takes for the signal to bounce back. They detect potential enemies and give reasonably accurate estimates of how far away the enemies might be.

The problem with conventional radar and sonar systems, however, is their lack of stealth; any adversary in the vicinity knows someone's looking for him when he detects the radio emissions of radar systems or the sound emissions of sonar. It's a lot like turning on a flashlight in a darkened room; you can see things easily, but the world knows you're there.

Now take a moment to consider radar and sonar transmitters that are in different locations from their receivers. A detected enemy aircraft would be certain of the presence of a radar-transmitting aircraft, but a receive-only aircraft nearby would remain concealed. A receiving aircraft, based on return signals, could calculate a firing solution and launch air-to-air missiles before the enemy aircraft even knew he was there.

It could be the same scenario for attack submarines. A submerged adversary would know of a sonar-transmitting submarine, while a receiving submarine would remain concealed and could ready a sudden torpedo attack from an unanticipated direction.

Now let's consider a different approach. What if an attack aircraft could launch an unmanned aerial vehicle (UAV) with a radar transmitter on board, while the host aircraft kept its radar and electronics quiet? It could add a new dimension to the fight and create a fast-moving triangulating game of cat-and-mouse that could put adversaries in a big disadvantage at a crucial moment.

Apply the same idea to an attack submarine. That vessel could launch a torpedo-shaped unmanned underwater vehicle (UUV) with a sonar transmitter, detect and range enemy submarines in the area, and enable the quiet attack submarine to calculate a firing solution. This submarine-and-UUV scenario is exactly what the U.S. Defense Advanced Research Projects Agency (DARPA) is working on with the new Mobile Offboard Command and Control and Approach (MOCCA) program.

There's a reason bistatic radar and sonar haven't caught on in a big way: signal processing. Conventional systems involve two points (transmitter/receiver and target); the bistatic approach adds a third point: transmitter, target, and receiver. This third point complicates the sonar signal processing challenge, and adds difficulties of time lag, potential uncertainty of the relative positions of transmitter and receiver, and a host of factors that would require systems with supercomputer-like power.

Such challenges may be getting a solution with high-performance embedded computing (HPEC) technology. Embedded versions of the Intel Xeon processor could provide supercomputer power to deployed aircraft and submarines, and even new generations of UAVs and UUVs.

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