LINET

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LINET

Lightning Detection Network

 

Design Overview

 

a VLF/LF network for lightning detection

 

 

LINET (Lightning Detection Network) is a particularly sensitive network working at VLF/LF range with 3D capability.

 

The efficiency of the system allows for unprecedented low-amplitude detection power. Below ~10 kA an order of magnitude more signals are identified compared to conventional networks, even for equal baseline. Since abundant IC (intra-cloud) events are located an effective discrimination against CG (cloud to ground) is required. The chosen solution consists in the employment of a new 3D-technique (Betz et al., 2004) which is independent of any adjustable parameters. Preferentially, the TOA (time of arrival) method is used for locating the horizontal and vertical position of lightning strikes. The system can measure the time, the horizontal and vertical location of VLF-sources as well as the amplitude and the polarity of these events.

 

System Components 

LINET station installation at Araraquara (Brazil) during TROCCINOX-2 in Feb-Mar 2005

Each station of the LINET (6 station DLR network, >15 stations LMU network) consists of:

 

  • a crossed loop antenna for measuring the magnetic field,
  • a GPS antenna for measuring the precise time reference and
  • a PC for data aquisition.

 

Lightning location analysis can be done once the data of at least 4 stations are available for TOA (Time of Arrival) analysis. Typically, a special analysis PC is used for that purpose.

 

DLR operates a 6-station network which is deployed during field measuring campaigns and special observational applications. LMU and NowCast Mobile GmbH run an operational network of >15 stations in Southern Germany. Both networks have been combined during the 2005 summer convective season with an enhanced number of stations around the POLDIRAD radar site of DLR.

 

The system was designed and build by the Sferics research group of LMU (Betz et al.)

 

Measuring and Analysis Technique 

    Electromagnetic emissions of lightning can be measured in a broad frequency spectrum. In the VHF range lightning channels can be observed in great structural detail. Especially the formation of the leader can be followed whereas other phases of a flash, like the return stroke or other continuous processes, are emitting more pronounced in VLF/LF range. While VHF detection is confined to relatively short distances from the sources (line of sight), the longer wavelengths at VLF/LF can be observed at much larger distances.

     

    The LINET antennas measure the magnetic field emitted by a flash, either CG or IC. LINET is a particularly sensitive network working at VLF/LF range with 3D capability. The efficiency of the system allows for unprecedented low-amplitude detection power. Below ~10 kA an order of magnitude more signals are identified compared to conventional networks, even for equal baseline. All signals are processed and no rejections due to waveform criteria are applied. Preferentially, the TOA (time of arrival) method is used for locating the horizontal and vertical position of lightning strikes.

     

    Since abundant IC (intra-cloud) events are located an effective discrimination against CG (cloud to ground) is required. The chosen solution consists in the employment of a new 3D-technique (Betz et al., 2004) which is independent of any adjustable parameters.

     

     

    The analysis delivers the time, the horizontal and vertical location of VLF/LF-sources as well as the amplitude and the polarity of these events.

     

    Illustrations 

       

      Supercells on 8 July 2004 close to the POLDIRAD site at DLR-Oberpfaffenhofen. Upper panel shows PPI of radar reflectivity at 2 degree elevation and lower panel shows the corresponding vertical structure about 10 min earlier. The strokes are colourized according to IC (red dots) and CG (green dots) and have been measured during a 4 min time period centered around the radar scan time. In the PPI overlay all strokes have been projected to the plotting plane, the stroke locations shown in the RHI were located within a 10 km thick layer.  For plotting reasons the height of the CGs is set to 1.5 km. Both cells have predominantly IC strokes at that time of development mostly located at heights above 8 km within the large overhanging echo region.

       

       

      References 

       

      Schmidt, K., H.-D. Betz, W. P. Oettinger, M. Wirz, O. Pinto Jr., K.P. Naccarato, H. Hoeller, Th. Fehr, G. Held, 2005:

        A comparative analysis of lightning data during the EU-Brazil TROCCINOX/TroCCiBras campaign. VIII International Symposium on Lightning Protection (SIPDA), São Paulo/ Brazil, November 2005, submitted.

       

      Betz, H.-D., K. Schmidt, W. P. Oettinger, and M. Wirz, 2004:

        Lightning Detection with 3D-Discrimination of Intracloud and Cloud-to-Ground Discharges. J. Geophys. Res. Lett., Vol. 31, L11108, doi:10.1029/2004GL019821, 2004.

       

       

      For further information contact 

       

      Dr. Hartmut Höller,  DLR, Institute of Atmospheric Physics, 82230 Oberpfaffenhofen, Germany

      Hartmut.Hoeller@dlr.de

       

      Prof. Dr. H.-D. Betz, Physics Department LMU München, Sferics Research, Am Coulombwall 1, 85748 Garching
      Germany

      Hans-Dieter.Betz@physik.uni-muenchen.de

       

       

       

      (Oberpfaffenhofen, August 2005)

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