Solar mapping and tracking in 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 Solar map can be seen in Picture 1.). 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 (see an example of a Solar track graph can be seen in Picture 2.). 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.
To view solar map images (including the latest ones) measured in Metsähovi Radio Observatory, please navigate to Metsähovi Solar observation gallery.
Picture 1. A Solar map measured in Metsähovi Radio Observatory. More solar maps can be found in Metsähovi Solar observation gallery
Picture 2. A graph of a Solar track measured in Metsähovi Radio Observatory
| 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 |
Table 1. Parameters of solar map measurements at Metsähovi Radio Observatory
A list of solar reports is also available.
In 2001 Metsähovi Radio Observatory started making continuous Solar observations. For that purpose a measurement system was built (control system, antenna (diameter 1,8 m), data collection system). The system measures the total intensity level of the Sun at a frequency range of 10,7 - 11,7 GHz (wavelength 2,7 cm). Data is collected on both linear and logarithmic scales by taking 50 samples per second and one sample every 12 seconds.
Picture 3. The Metsähovi Radio Observatory 1.8-meter 11 GHz Solar tracking antenna