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Scientists detect lowest ever frequency radar echo from the moon

Scientists have detected the lowest ever frequency radar echo from the moon ever seen with earth-based receivers.

Washington, Jan 9 : Scientists have detected the lowest ever frequency radar echo from the moon ever seen with earth-based receivers.

The detection was made by the lunar echo experiment, carried out by a team of scientists from the Naval Research Laboratory, the Air Force Research Laboratory's (AFRL's) Research Vehicles Directorate, Kirtland Air Force Base, N.M., and the University of New Mexico (UNM).

As part of the experiment, the team launched high power radio waves toward the moon. The reflected signal, weakened because of the long distance to the moon and back, was detected by receiving antennas in New Mexico.

The lunar echo measurements at 7.4075 MHZ are believed to be the lowest frequency (longest wavelength) at which bistatic radar measurements have been conducted.

"Even though lunar echoes have been detected before at higher frequencies, it was really exciting to see them arrive in real time out under the full moon in the New Mexico desert," said NRL's Brian Hicks.

According to NRL consultant scientist Dr. Paul Rodriguez, who conceived and proposed the experiment, analysis of the echo gives information on the properties of the lunar sub-surface topography, because the low frequency radar waves propagate to varying depths below the visible surface of the moon.

"It is somewhat like sonar, except that we are using electromagnetic waves rather than sound waves, said Rodriguez. "The experiment also allows us to study the interaction of the echo signal with the earth's ionosphere along its return path, because the ionosphere is only partially transparent at low frequencies," he added.

Both the transmitted signal and the echo from the moon were detected by NRL Remote Sensing Division scientist, Dr. Kenneth Stewart, and NRL engineer Brian Hicks with antennas built for the Long Wavelength Array (LWA).

"Detecting the very weak radio signals after their round trip to the moon and back was challenging and required careful modification of the LWA antennas to improve their performance at these frequencies," said Stewart.

ANI