Concept Development for a Ground Radio Array for Space Weather Monitoring and Forecasting, 15-R8092

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Principal Investigators
Timothy A. Howard
Kerry L. Neal
Craig D. DeForest
Joe Peterson

Inclusive Dates:  08/10/09 – 10/02/09

Background - Space weather is an important phenomenon in technology development, as it can be responsible for damaging systems such as spacecraft, communications and power stations, and increase radiation dosage to aircraft passengers and astronauts. The most serious space weather is caused by coronal mass ejections (CMEs), which are eruptions of solar plasma and magnetic field. While there are a large number of scientific instruments available to scientifically investigate CMEs, no operational (weather-service class) instrument has been constructed to monitor them. A major limiting factor is the high cost of spacecraft.

This project investigated the concept of deploying a ground-based radiotelescope for operational CME monitoring and for developing space-weather forecasts from CME observations. The instrument can be built at a small fraction of the cost of a spacecraft and can be just as effective if designed carefully, with the added possibility of new magnetic field measurements that are important for space-weather prediction, but impossible by other means. The planned ground telescope will monitor interplanetary scintillation, which is the fluctuation of distant radio signals as a result of the passage of a mass ejection passing between the source and observer. Interplanetary scintillation has been known to detect coronal mass ejections to large distances from the Sun for 40 years, and modern techniques in computer hardware and software can improve the technique significantly to where it can yield even better results than wide-field visible light imaging. A new experimental option for CME detection using radio was also investigated. This is the potential of remotely measuring the internal magnetic field of the CME by monitoring changes to the Faraday rotation of polarized radio sources. As severe space weather effects are mostly caused by the orientation of the magnetic field of the ejection and the density and speed, being able to remotely measure all of these from a low-cost ground instrument would be ideal for space weather monitoring.

Approach - The objective of this project was to investigate the concept of deploying a radio array for coronal mass ejection monitoring. This involved investigating both interplanetary scintillation and Faraday rotation. Previous work using interplanetary scintillation and modern developments in radio astronomy were researched, and leading workers in the field were interviewed. Software was acquired for beam construction, and a preliminary design based on the beam requirements was developed. Frequency requirements, possible sites and the integration of scintillation and Faraday rotation to a single array were also investigated. Finally, the space weather forecast tool was constructed based on the modification of an existing model of ejection reconstruction.

Accomplishments - An array can be constructed to provide at least three simultaneous beams, separated by 30° right ascension (two hours) with the capability of producing three daily full-sky maps of scintillation in the radio sky. Observing at two frequencies (74 MHz and around 200 MHz) provides observations close to and far from the Sun, and allows for monitoring the passage of the CME through the sky further and longer than existing spacecraft instruments. A number of possible deployment sites were found, but further negotiation is required before a decision can be made. Importantly, it was found that the entire processing can be done at the software level, removing the need for large hardware structures and improving SwRI's maneuverability in beam design. One technique that can be employed with this is digital adaptive beam construction. A space weather forecast can be produced using the ejection reconstruction method called the TH Model, adapted for radio observations. Finally, although sufficiently sensitive polarization measurements may be possible, basic radioastronomy work is needed to determine whether there are sufficient polarized radio sources at the low frequencies contemplated. Results from this study show that the construction of an array for interplanetary scintillation is feasible and desirable. The array can be modernized with great advantages and can be operated and pipelined rapidly enough to allow near-real-time forecasting. Further demonstration is needed for hardware and software requirements, particularly constructing a small prototype and benchmarking commercially available processors, before the concept is sufficiently low risk for NASA or NOAA funding.

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