Scientists Detect Lowest Frequency Radar Echo from  the Moon

University Of New Mexico
A team of scientists from the Naval Research Laboratory  (NRL), the Air Force Research Laboratory's (AFRL's) Research Vehicles Directorate, Kirtland Air Force Base, N.M., and the University of New Mexico (UNM) has  detected the lowest frequency radar echo from the moon ever seen with earth-based  receivers.
In the lunar echo experiment (more properly called a  lunar bi-static radar experiment), the Air Force/Navy High Frequency Active  Auroral Research Program (HAARP) high power transmitter, located near Gakona,  Alaska, 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.
NRL consultant scientist Dr. Paul Rodriguez, of NRL's  Information Technology Division, who conceived and proposed the experiment explains, "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. 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."
During the experiment, which was carried out on Oct.  28 and 29, 2007, the radar signals from HAARP were at 7.4075 MHz and 9.4075  MHz. 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).
LWA is a radio interferometer being built in the desert  west of Socorro, N.M., by UNM, NRL, the Applied Research Laboratories at  the University of Texas at Austin, Virginia Tech, and Los Alamos National  Laboratory, for studies of space physics and astrophysics.
The LWA is intended to work below the 88 MHz edge of  the FM band, but to get down to the HAARP signal frequencies, the antennas  were equipped with digital receivers and specially designed matching networks  developed by Stewart, Hicks, and engineer Nagini Paravastu at NRL. "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," says Stewart.
NRL LWA Project Scientist Dr. Namir Kassim notes, "One  of the successful goals of this experiment was to demonstrate that the  LWA can work with instruments like HAARP at lower frequencies than its  nominal design."
The HAARP radar antenna array was "phased"  to point about 45 degrees away from the zenith, in order to track and directly  illuminate the moon. Its full total power capability, about 3.6 MW, was  used to transmit pulses two seconds in length every five seconds over a  period of two hours each day, one hour at each frequency. Using such a  pulse pattern makes the echo, which arrives back from the moon 2.4 seconds  later, immediately recognizable, allowing the scientists to distinguish  the moon's echo signal from the HAARP signal.
The HAARP signal reached the receiving antennas in New  Mexico by reflecting off the underside of the ionosphere, the region of  the Earth's atmosphere from 50 to 400 km in altitude that is partially  ionized by solar radiation. The lunar echo measurements at 7.4075 MHZ are  believed to be the lowest frequency (longest wavelength) at which bi-static  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," says NRL's  Hicks.
The team members involved in the HAARP-LWA lunar radar  experiment are: Dr. Paul Rodriguez, Dr. Kenneth Stewart, Brian Hicks, Dr.  Nagini Paravastu; and Edward Kennedy of NRL; Dr. Paul Kossey of AFRL's Research Vehicles Directorate; and Dr. Lee J Rickard of UNM.
Significant help in conducting the experiment was provided  by HAARP Program Managers Paul Kossey (Air Force) and Edward Kennedy (Navy); Mike McCarrick of BAE Systems-Advanced Technologies, which operates the  HAARP facility, and by Clinton Janes (UNM); Gerald O'Connell (National  Radio Astronomy Observatory); and Patrick Crane (NRL).
The Naval Research Laboratory is the Department of the  Navy's corporate laboratory. NRL conducts a broad program of scientific  research, technology, and advanced development. The Laboratory, with a  total complement of nearly 2,500 personnel, is located in southwest Washington, DC, with other major sites at the Stennis Space Center, MS; and Monterey, CA. The LWA Web site may be found at: <>Long Wavelength Array.
Media Contacts: NRL Public Affairs Office, (202)  767-2541; e-mail: <> or UNM, Steve Carr, (505) 277-1821; e-mail: <>