Solar Radio Astronomy at Metsähovi
The Metsähovi Radio Observatory, a separate research institute of the Helsinki University of Technology since May 1988, operates a 14 m diameter radio telescope at Metsähovi, Kylmälä, 24o 23' 38''E, 60o 13' 05''N elevation 60 m. The Cassegrain telescope system can be used at frequencies 10-100 GHz (wavelengths 3 cm - 3 mm). Part of the telescope observing time has been used for solar research since 1976. Solar mapping with mini-computer based recordings started in 1978.
Annually the telescope has been reserved for solar measurements for 4-10 weeks, typically during summer months. Measurements include maps of the whole or part of the Sun, tracking of active regions and solar oscillation monitoring. Most of the solar observations have been done using receiver operating at 36.8 GHz. The sensitivity of the receivers is good enough for 0.1 sfu resolution. In the temperature scale the resolution is better than 100 K and it is limited by short term changes in the atmospheric attenuation.
Solar maps are measured by scanning the solar disk in right ascension and by changing the declination in small steps between the subsequent scans (an example of a map here). Tracking of an active region is done by pointing the beam of the telescope to the area in question and then by taking samples at a selected rate, usually 10-20 samples per second (an example of a track plot here). The output of the receiver is connected to an A/D-converter. The digitalized data is stored on a MicroVAX II computer and is later processed and calibrated for graphic presentation.
| Frequency (center) [GHz] |
Wavelength [mm] |
Telescope Beam size [arc min] |
Estimated quiet sun level [K] |
s.f.u. |
|---|---|---|---|---|
| 22.2 36.8 86 |
13.5 8.2 3.3 |
4.0 2.4 1.0 |
9000 7800 7200 |
24.3 21.1 19.4 |
A list of solar reports is also available.
In the year 2001 the Metsähovi Radio Observatory started to do continuous Sun measurements. For that purpose was built measurement system (control system, antenna (diameter 1,8 m), data collection system) which measures total intensity level of the Sun at frequency range 10,7 - 11,7 GHz (wavelength 2,7 cm). Data will be collected both linear and logarithm scale by taking 50 samples per second. Data will be also collected by taking samples every 12 seconds.