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Sensing and Monitoring Volcanic Ash for Air Travel Safety PXI

lscea.jpg"The seamless integration between LabVIEW and PXI made customizations  easy and gave us the ability to react quickly in the event of an  environmental disaster. In addition, the solution is available for  immediate use if a new volcanic eruption occurs."

The eruption of the Icelandic volcano Eyjafjallajökull disrupted air travel  across western and northern Europe in April and May 2010. At the request  of the French government, various agencies set out to detect and  characterize the volcanic ash over French airspace. The National Center  for Research (CNRS), French Meteorological Service (Météo France),  National Center for Space Studies (CNES), and French Aircraft and  Environmental Research (Safire) used a Falcon 20 aircraft to conduct  scientific flights for the mission.

The team based the airborne monitoring system on a light detection  and ranging (LIDAR) system from Leosphere’s optical head. The Atomic  Energy Commission and Alternative Energies (CEA) and CNRS developed the  LIDAR system in 2004 to control atmospheric particle pollution. The CEA  evolved the instruments to be used for mobile applications such as cars,  weather balloons, ultra light aircrafts, and oceanographic vessels for  environmental and climate studies.

Controlled with LabVIEW graphical system design software, the LIDAR system includes  three subassemblies for active remote sensing, which consist of a  transmitter (laser), receiver (telescope or refracting telescope), and  signal acquisition hardware.

The laser pulses at a broad frequency ranging from several to  thousands of Hertz. We required a frequency of 20 Hz for the volcanic  ash monitoring application. The laser transmission is synchronized with  the time base of a digitizer, and the beam is transmitted to the  atmosphere where it interacts with the air molecules, aerosols which  volcanic ash are part of, and clouds. From this interaction, a small  portion of the incident photons is backscattered to the receiver and  converted into voltage by the chain of acquisition via the  photomultiplier and digitizer. The user-defined width of the laser ray  and sampling frequency determine the vertical resolution.

The original LIDAR, manufactured by Losphere, included an NI PCI-5122 14-bit digitizer integrated into a PC. However, to develop a system  best suited for an airborne mission, the research team customized the  LIDAR by choosing NI PXI instrumentation for better resistance to  vibrations and shocks in the rugged airborne environment. The team used  an NI PXI-1000B chassis capable of housing eight PXI modules. We implemented an NI PXI-5124 12-bit digitizer module to take measurements with a vertical resolution  of the 0.75 m LIDAR with 200 MHz sampling, which gave us the ability to  detect surface structures.

The digitizer acquires LIDAR signals simultaneously with GPS  coordinates and flight parameters such as pitching, rolling, and  heading. Data are transferred between the instruments and the PXI module  through an NI  PXI-8430/4 RS232 interface data acquisition (DAQ) module. We also  selected an NI PXI-6221 DAQ module to control voltage on the photomultipliers of the LIDAR  chain of detection and generate a TTL signal to synchronize the laser  transmission and the digitization.

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