A team ofscientists has detected the lowest frequency radar echo off the moon everpicked up by Earth-based receivers, it was announced today.
In thelunar echo experiment, high-power radio waves were sent toward the moon with atransmitter in Alaska. The reflected signals, weakened by the long journey tothe moonand back, were detected 2.4 seconds later by receiving antennas in New Mexico.
Thetransmitter sent out two-second pulses every five seconds over a period of twohours each day of the two-day study period (Oct. 28 to 29, 2007), one hour foreach frequency at which it operated.
The echo signalsat 7.4075 megahertz, made by the pulse bouncing off the moon, are believed tobe the lowest frequency (or longest wavelength) at which these radarmeasurements have been conducted.
This radarexperiment, and others such as NASA's Clementinemission that looked for ice at the lunar poles, work similarly to sonarexperiments over the ocean, telling scientists more about the moon's structure.
"Analysisof the echo gives information on the properties of the sub-surfacetopography, because the low-frequency radar waves propagate to varyingdepths below the visible surface of the moon," said Naval Research Laboratoryconsultant scientist Paul Rodriguez.
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