The Manastash Ridge Radar
Status Update
Frank D. Lind
August 31, 1998
 
 

Introduction

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.

Current Status

The Manastash Ridge Radar Has Observed Its First Auroral Echoes!!!

The geomagnetic storm that occured between August 26-28 produced our first Auroral Echoes! The aurora was observed on the ground and via satellite during this time period, and was picked up quite clearly by the radar. Some of the data is shown below and more is yet to be processed.

We have been operating the current equipment for about 11 months 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, although we have made several modifications in order to fix some minor problems. The system design and theory has been described in Radio Sci. Bull. 284, 4-7, 1998.

Our current system consists of two 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 5 dB of directional gain, and we use a simple folded dipole for the UW receiver. The Manastash Ridge side receiver also has an additional baseband gain block. The system can be operated remotely using the internet with the software still in a somewhat primitive state.

Our current bottleneck is data processing and management. We are still limited by available computational power to small amounts of data. (It takes 30 minutes to process 10 seconds of data). Typically we will take and process between 100 and 500 seconds of data a week but we expect a significant improvement in this over the next few months (at least a factor of 4).

We are currently working with a group in UW CSE to produce a VLSI correlator chip that will be capable of real time data processing. Currently an FPGA prototype of this system has been funded and is under construction. For postprocessing of the data we intend to construct a small Beowulf class cluster computer sometime in the next year. We are presently converting to the use of NetCDF for data management and this process will be complete by the end of the summer. We also intend to upgrade the control software to be more capable and to extend our automated data  acquisition and processing capabilities. At the present a somewhat clumsy script interface is being used to provide system automation. Ultimately we intend to produce a graphical user interface for the system using the java programing language. Future versions of the radar will be made avaiable to the public and scientific community for use in research and education.

In the data that we have processed so far we have observed: E-Region Irregularities! from the geomagnetic storm of August 26-28, a weak signal getting over the Cascade mountains, a strong scattered signal that is definitely from Mt. Rainier (a large local mountain), and lots of aircraft (1-3 per night). We have also demonstrated ~1 km range resolution and ~1.5 m/s velocity resolution on real targets.  We are also planning an improved antenna system for the next generation of the receivers and this will be very important for improving the SNR of the auroral echoes.  We hope to have some output from the radar available on a daily basis by mid to late fall.




An RTI for a several hours at 5 seconds of data per minute, smoothed with a gaussian filter.
The signals closer than 200 km are due to scatter from Mt. Rainier and structure in the FM radio signal. 
The strong echoes beyond 200km are due to E-region irregularities. The normalization on this plot isn't quite right yet.


A velocity - range plot for a case when strong E-region irregularities are detected. This time corresponds
to the strong return in the RTI above.  Note the ability of the radar to unambiguiously determine range and
doppler information without aliasing.


Here is a close up of the E-region irregularities for the above time period.
Much of the structure is probably due to statistical variance.


Here is a frame from a Polar UVI image taken 8 seconds prior to the above radar data.
BIG Thanks to the UVI crew for pointing the imager right at the Manastash Ridge Radar!
 
 
 

This is an overview of the system.

The UW Receiver is 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.
 

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.

This is a cross ambiguity showing multiple aircraft as observed by the radar in 10 seconds of data. The processing was done for maximum doppler resolution and the aircraft is travelling at -21.5 +/- 1.5 m/s. The clutter at zero doppler is produced by signal propagating over the Cascade mountains and by scatter from Mt. Rainier. We have verified the scatter from Mt. Rainier by varying the antenna pointing.