At Risø DTU’s test station for large wind turbines at Høvsøre in western Jutland, a so-called LIDAR follows the progress of the ash cloud from the Eyjafjallajökul volcano across Denmark. This has now been confirmed by comparing data from Risø with calculations made by the Danish Meteorological Institute (DMI) and the National Environmental Research Institute (NERI). LIDARs provide more details about the actual height and development of the ash cloud as well as qualitative measurements of the volcanic ash concentrations in the cloud.
What is a LIDAR?
Aerosol-LIDARs (LIght Detection And Ranging) are useful tools for measuring smoke plumes, cloud droplets and other particles in the atmosphere. The measurements can be conducted over time and across large areas.
The Aerosol-LIDAR shoots a laser beam up into the air where it hits particles and is reflected back to the LIDAR, providing information about particles in the atmosphere. LIDARs are, among other things, used to measure the height of the so-called boundary layer, i.e. to determine the altitude of any turbulence in the atmosphere, which has a considerable bearing on wind-turbine operations.
Moreover, Wind-LIDARs are used to calculate the instant speed and direction of the wind.
Professor Torben Mikkelsen, tel. +45 4677 5009, mobile +45 4131 5709 and DSc Sven-Erik Gryning, tel. +45 4677 5005, Wind Energy Division, Risø DTU
The good news comes after DMI has analysed LIDAR measurements from Risø. At DMI, Chief Consultant Jens Havskov Sørensen has exchanged data with Torben Mikkelsen from Risø DTU and compared the measurements from Risø’s LIDAR with DMI’s model cloud and cloud observations.
The conclusion is that DMI’s model calculations are well in line with Risø’s LIDAR observations.
Torben Mikkelsen and his colleague from Risø DTU, Sven-Erik Gryning, have now started collaborating with international colleagues and with DMI and NERI (National Environment Research Institute, Aarhus University) on using the LIDAR to map the ash cloud:
“We have already entered into international collaboration with Leosphere in France, a manufacturer of LIDARs, and via their LEONET of connected LIDARs they will submit online measurements of the ash cloud to the international meteorological organisations such as UKMO in the UK and WMO (under the UN),” says Torben Mikkelsen.
“Grounding aircraft solely on the basis of model calculations is problematic because we know that models do not always totally agree with reality. By means of LIDARs sited around Europe, we can now carry out measurements and collect real-time data of the cloud in the atmosphere. This means that assessments will be more accurate and help improve the calculation models used by the meteorologists,” says Torben Mikkelsen.
The figure shows Risø’s LIDAR measurements at Høvsøre from the ground and up to an altitude of approx. 10 km. The measurements were conducted from the early afternoon of Saturday 14 April until Monday 20 April. The bottom range (the first kilometre) shows the atmospheric boundary layer where there is always a lot of dust. The brown blobs are clouds which are sometimes so dense that they are impenetrable to the laser light (white background). The blue background stems from scattering from the atmospheric molecules. Especially the ‘sinking’ cloud which is evident from about the afternoon on 19 April until the following morning has been confirmed as being the ash cloud.