The Manastash Ridge Radar
Frank D. Lind
November 3, 1997
The Manastash Ridge Radar system is a passive radar system that utilizes common FM radio broadcasts as its signal source. The system is designed to observe ionospheric turbulence that occurs in the same region as the aurora, or northern lights. This is a short status report to indicate our current state of progress for those people who have indicated an interest.
The Manastash Ridge Radar is currently online and operational! We have been operating the current equipment for approximately two weeks now. One receiver is deployed at the University of Washington while the other is deployed at Manastash Ridge Observatory. The system is stable, both mechanically and electronically, and we expect to successfully operate it without modification at least until summer. The system design and theory will be described in a forthcoming issue of Radio Science.
Our current system consists of two identical direct conversion receivers, matched PC based streaming digitizers, and two GPS clocks for time synchronization. The Manastash Ridge receiver has a log periodic antenna with about 6 dB of directional gain, and we use a simple folded dipole for the UW receiver. The system can be operated remotely using the internet with the software still in a somewhat primitive state.
Our current bottleneck is our data processing software which can take several hours to process 10 seconds of data (over a reasonable set of ranges). We are currently obtaining faster computers and rewriting the software to improve this situation. We also intend to upgrade the control software to be more robust and to provide automated data transport and processing. Currently only data aquisition is properly automated. Ultimately we intend to provide a graphical user interface for the system (at least for internal use), using the java programing language.
In the small quantitiy of data that we have processed so far we have observed: a weak scattered signal getting over the mountains, a strong scattered signal which is probably a reflection off Mt. Rainier, and other stuff we don't understand yet. We expect to see high altitude aircraft and auroral echoes soon but this depends largely on looking at enough data. To do this we will have to get our signal processing faster by at least a factor of 100. We expect this will happen in the next couple of weeks. Hopefully we will begin continious, automated observations by January 1, 1998.
This is an overview of the system.
The UW Receiver will be located here in the new Electrical Engineering building.
The Manastash Ridge Observatory, where the remote receiver is located.
Looking approximately NE from MRO is Eastern Washington and its farming communities.
Here is a block diagram of the direct conversion receiver.
This is the UW receiver itself and the GPS unit. The computer is to the right.
Here is the IQ signal from the UW receiver taken with 12 bit data. Note an FM signal is constant modulus and should be a circle. The width of the circle is caused largely by ground clutter.
Here is a spectral plot of the same 12 bit data for 1 complete second. You can see the FM signal quite clearly.
This is a spectral plot from MRO of data taken using only the sign bit of the digitizers. Notice the signals from adjacent stations leaking into the band that contains a station on the UW side. This data is simultaneous with the figure below.
Here is the FM signal that was broadcast from the UW side of the mountains. Again we use only the sign bit.
The log plot of the cross ambiguity for the previous two signals shows what we believe to be a signal scattered by Mt. Rainier. We have seen the signature in most the data we have processed.
The zero doppler shift cut from the cross ambiguity of the two received signals. The precursor peak may be the direct signal leaking over the mountains, or perhaps a different scatterer.
This is the log plot of the self ambiguity of the signal that was transmitted. Note the sidelobes that show up here also show up in the cross ambiguity. The central peak is missing here due to a plotting problem.
This is the same self ambiguity but on a linear scale. Note the wonderful sharpness of the FM self ambiguity.