The two agencies were exploring these ideas in an effort to create an ocean-focused surveillance and early warning system.
The workshop focus was on the feasibility of using a bistatic radar system to create the surveillance and early warning system and to determine if a bistatic system would be more successful than a monostatic system.
Just to give a brief overview of the two systems being discussed by DARPA and the Navy, the monostatic system is the radar system that most of us think of when we hear the term radar. In a monostatic system, the transmitter and the receiver are at the same location. They even share the same antenna.
In contrast, a bistatic system has its transmitter and receiver separated by a specific distance. This distance, obviously, keeps the transmitter and the receiver from sharing the same antenna.
The benefits of using a bistatic system, especially in terms of surveillance, are the ability to operate it in secret, to move the receiver covertly and quickly, and an enhanced radar cross section.
Unfortunately, the bistatic system does have its drawbacks, such as a complex initial setup, increased communication costs, and an overall reduction in coverage. However, the five-day workshop was designed to provide information on whether the advantages outweighed the disadvantages.
The workshop researched five different methods, or modes: two monostatic and three bistatic. The two monostatic systems were the Sky Wave-Sky Wave and the Surface Wave-Surface Wave.
In the monostatic sky wave method, the transmitter and the receiver are housed together. The transmitter bounces radio waves off of the ionosphere. Those waves reach the target and are bounced back up to the ionosphere, which reflects back to the receiver.
This was a promising method because by using the ionosphere, detecting beyond the horizon was easily feasible. The monostatic surface wave method bounces radio waves directly off of the targets. A similar example would be how bats hunt; emit a signal. The signal hits the target and bounces back. Though effective, this method is not conducive to over-the-horizon monitoring.
The other three methods were bistatic techniques which included: Sky Wave-Surface Wave, Direct Wave-Surface Wave via buoy and Direct Wave-Sky Wave via a buoy.
Sky Wave-Surface works similar to its monostatic counterpart, with the exception that the receiver is not housed with the transmitter. The idea was that the receiver would be placed on a ship out in the ocean. Direct Wave-Surface Wave via buoy would transmit a signal from a buoy out in the ocean. That signal would detect the target and reach the receiver, which would be placed onshore.
Direct Wave-Sky Wave via a buoy would transmit a signal from a buoy located in the ocean that would detect the target. The signal would then bounce off of the ionosphere and reach the onshore receiver.
What Was Learned?
What did DARPA and the Navy conclude? Initially, they stated more information and data would have to be gathered before either agency would settle on a technique.
However, initial findings lead the workshop participants to lean towards Sky Wave – Surface Wave method. According to a declassified report outlining Project May Bell:
“It is concluded that the hybrid skywave/surface-wave system suggested above and summarized in Figure 11 offers a practical solution to the Navy’s problem of OTH surveillance, and it is recommended that steps be taken toward implementation of such a system.” (1)
It seemed that Project May Bell solved one of the most difficult problems in a long-range ocean-targeted surveillance and early warning system, that of over-the-horizon monitoring.