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Dr. Steven Bienvenu captured these echoes of transmissions from US Navy's Space Surveillance Radar (NAVSPASUR) from both passing satellites and Leonid meteor ion trails in the atmosphere. Dr. Bienvenu used a simple observing setup consisting of an ICOM R7000 radio receiver in USB mode tuned to 216.980 mHz, with a slight frequency offset to center the NAVSPASUR signal in the receiver band pass. An ordinary TV/FM antenna mounted on a camera tripod was used. During the Leonid meteor shower of November 17, 1998, he pointed the antenna toward the direction of the NAVSPASUR transmitter in Kickapoo, Texas as seen from his location in Louisiana. Meteor trails are formed just 80 km above the atmosphere, so the antenna was pointed just 8 degrees above the horizon. The audio output of his receiver was recorded at a sampling rate of 11 kHz using the sound card in a Windows 120 MHz Pentium computer. Because satellites move through the NAVSPASUR beam very quickly, their echoes appear as very short, Doppler shifted returns. Although the meteors are also moving very fast, the ion trails that they leave behind in the atmosphere are relatively slow moving and persist for several seconds. As a result, the radar echoes from the meteor trails appear as extended warbling whistles. For more detailed information, see the excellent article in the December 1998 NASA Space Science News. |
