One of my idle pastimes this week is trying to persuade the world about the following idea. Tell me: would it work?

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Passive Radar Detection At Home

The objective of “Passive Radar Detection At Home” is to make archives of radar data available on the web. Web pages would display the current data in some graphic formats. These maps would not be a “real time” maps. They would have a time lag similar to the lag in weather radar maps on the web.

This project is unrelated to the maps of airline traffic that are currently available on the web. Those maps are based on the FAA's "Aircraft Situation Display To Industry" (ASDI) data. As I understand that data, it is not based on radar detection, but rather on the transponders carried by the aircraft.

The maps of "Passive Radar Detction At Home" would not neccesarily identify airline flights by their number. They might not even be able to identify individual targets by a symbol. They might look like weather radar maps. The numerical data underlying the maps would be available to the public for further processing. People might figure out various ways to recognize targets in the data or coordinate the data with ASDI data.

What is the use of doing this? I just think it would be a neat thing to have. Perhaps archives of the map could be used to investigate aircraft disappearances or accidents. On the other hand, I suppose some government agencies would argue that public access to such data would be a bad thing and try to censor it.

The method for getting the data is suggested by the “SETI At Home” project and also by a paper on “Passive Radar Detection” on the website of the National UFO Reporting Center. People that believe we are visited by extraterrestrials would probably be interested in using the data to investigate UFO incidents. I would welcome their participation, but investigating UFOs is not the exclusive goal of the project.

“Passive Radar Detection” is a well known idea. In such a system, you don’t build any equipment to emit radar signals. Instead you use “public” sources of signals like commercial radio stations or radar transmitters belonging to other people. You put some antennas near the sources to get a reference signals. Ideally, you put other antennas in places where they only get theses signals if they are reflected from aircraft. Or you may have receivers that filter out the direct signals. By doing computations that compare the reference and reflected signals, you can find aircraft locations.

“SETI At Home” is socio-technical project. Signal data (received from space) is collected at a central location. The data is sent out over the web to people who volunteer the use of their computers. It is processed and the results are sent back to a centralized location.

The idea that I call “Passive Radar Detection At Home” is a reverse-analogy to “SETI At Home”. Recruit volunteers all over the world to attach radar receivers to their PCs. They will collect the signal data and send it back to a central location. At the central location, the data is organized and stored. Some processing of the data is done to produce the current radar maps.

Hopefully, a volunteer's radar receiver could be a simple device, not a big scanning dish. The PC would run software to transmit data about received signals over the web to the central location. It might also do other simple functions. For example, if the job of the volunteer site is to receive reflected signals, the software could decided when it was worthwhile to send information over the web vs when the site is only seeing empty sky.

Data would include a time stamp since the central site can’t rely on getting the information instantaneously. This means that each volunteer site would need to have an accurate clock. Let me emphasize that the central site is not trying to analyze the data within milliseconds of receiving it. Nor does data about a received signal have to be processed within milliseconds of the time the signal is emitted from a radar. A computer analyzing the data can look at the time stamps and see that a signal was emitted at a certain time and that another signal was received milliseconds afterward. The computer might be analyzing the data minutes or hours after the data was recorded. Furthermore the data doesn't have to collected every second of the day. It would be enough to take "snapshots" of the sky. Perhaps a second or two of data could be recorded every few minutes.

Since this is a socio-technological idea, some the “socio” aspects are interesting to discuss. However, at the moment, I’m mainly interested in whether the “techno” side is feasible.

I suspect that radar specialists will take a dim view of it. The business of having dispersed recievers that may turn off or on, each one possibly having different specs - it just sounds like bad design. However it might interest mathematicians and computer scientists who like the challenges of noisy data.