Re: Can you detect stealth aircraft with filtration?

Greetings:

Your point is correct, birds and aircraft can be filtered. Frequency filtering has been used in radar signal processing since it’s beginnings. Moving targets reflect energy to ground based radars that are Doppler shifted in frequency. The amount of Doppler shift is determined by the speed of the target and the direction of the target relative to the radar set. Targets moving directly toward or directly away from a radar have the maximum Doppler frequency shift. Targets moving at right angles to a radar beam have zero Doppler shift. By directing the received radar energy through banks of Doppler filters, moving targets are sorted by velocity from fixed or slow targets such as insects or birds. In radar terms this is often called a Moving Target Indicator (MTI). The National Weather Service now uses Doppler radars to detect severe storms and winds by the Doppler shift. This radar and it’s display can be seen at the following web site under NEXTRAD (WSR-88D radar): http://www.nws.noaa.gov/modernize/. I've read that scientists are studing bird and butterfly migrations using the NEXTRAD data!

Airborne pulse Doppler radars have a more difficult processing job because reflections from the ground are Doppler shifted by the moving radar in the aircraft. However, the aircraft knows what it’s velocity is and a notch filter can be used to reject the ground reflections. In recent times digital computers have been used to do doppler filtering, greatly improving airborne systems such as AWACS and JSTARS now being used in the mid east.

The F-117 stealth aircraft might have the radar reflection of a golf ball; however, the golf ball is moving hundreds of miles per hour and if the radar is sensitive enough to detect it, then the Doppler shift filters will remove other slower targets. The hard part is detecting the golf ball sized target at distances more than a few miles away.

Best regards, Your Mad Scientist
Adrian Popa