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LIDAR is the method of remote atmospheric sensing based on the measuring the distance to the target by illuminating the target with the pulsing laser light and measuring the reflected light impulses. LIDAR does not require the establishment of line of sight or installation of retro- reflectors. DIAL is a special application of LIDAR, proposed to locate and measure the concentrations of pollutants in the atmosphere (Browell et al. 1998). The device sends the pulsing laser beam, alternating between two wavelengths, to the region of interest in the atmosphere. Upon reaching the region of measurements, the light of one wavelength is adsorbed by the compound of interest or scattered at reduced intensity, while the light of another wavelength is scattered elastically. This scattered light is collected by receiving optics, analysed and used to determine the concentration and location of the pollutant. The light of the wavelength, scattered at reduced intensity, is used to determine the concentration of substance of interest, while the light scattered elastically is used to measure background light scattering. Location of pollutant can be measured based on the delay of backscattered light to the detector. Raman LIDAR technique is seen as potentially interesting for CO2 measurements. A prototype has been developed in China and is capable to measure CO2 atmospheric concentrations, with night-time measurement limitations (Zhao et al. 2008).
 
LIDAR is the method of remote atmospheric sensing based on the measuring the distance to the target by illuminating the target with the pulsing laser light and measuring the reflected light impulses. LIDAR does not require the establishment of line of sight or installation of retro- reflectors. DIAL is a special application of LIDAR, proposed to locate and measure the concentrations of pollutants in the atmosphere (Browell et al. 1998). The device sends the pulsing laser beam, alternating between two wavelengths, to the region of interest in the atmosphere. Upon reaching the region of measurements, the light of one wavelength is adsorbed by the compound of interest or scattered at reduced intensity, while the light of another wavelength is scattered elastically. This scattered light is collected by receiving optics, analysed and used to determine the concentration and location of the pollutant. The light of the wavelength, scattered at reduced intensity, is used to determine the concentration of substance of interest, while the light scattered elastically is used to measure background light scattering. Location of pollutant can be measured based on the delay of backscattered light to the detector. Raman LIDAR technique is seen as potentially interesting for CO2 measurements. A prototype has been developed in China and is capable to measure CO2 atmospheric concentrations, with night-time measurement limitations (Zhao et al. 2008).
  
<div class="tablecaption" id="table12">TABLE 12 STRENGTHS AND LIMITATIONS OF LIDAR/DIAL</div>
+
TABLE 12 STRENGTHS AND LIMITATIONS OF LIDAR/DIAL  
{| class="wikitable"
 
|-
 
! scope="col" | Strengths
 
! scope="col" | Limitations
 
|-
 
! scope="row" | The concentration data is presented as a function of distance along the path of
 
laser beam
 
| Absorption characteristics of substances are dependent on ambient conditions, such as temperature and pressure, thus additional calibration according to the weather conditions might be needed
 
|-
 
! scope="row" | Easily portable, provides better overview of the atmospheric region when
 
measurements performed from several locations
 
| High cost of the system
 
|-
 
! scope="row" | Fast measurements (up to 15 minutes) over long distances (up to 3000 m)
 
| Beam path might be limited by the landscape
 
|-
 
! scope="row" | Can be mounted on the airborne platforms
 
| There must be sufficient backscattering in the atmosphere for the device to work correctly
 
|-
 
! scope="row" | Can measure the concentrations and state of multiple species
 
| Species with unique absorption bands are measurable. Species with the common absorption bands cannot be distinguished
 
|-
 
! scope="row" | Provides real time data
 
|}
 
Producers of LIDAR systems are listed in table 11
 
  
<div class="tablecaption" id="table13">TABLE 13 PRODUCERS OF DEVICES FOR LIDAR</div>
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TABLE13PRODUCERSOFDEVICESFORLIDAR
{| class="wikitable"
 
! scope="col" | Company
 
! scope="col" | website
 
|-
 
! scope="row" | National Physical Laboratory
 
| http://www.npl.co.uk/
 
|-
 
! scope="row" | Spectrasyne
 
| http://www.spectrasyne.ltd.uk/
 
|-
 
! scope="row" | ITT
 
| http://www.itt.com/
 
|-
 
! scope="row" | LASEN
 
| http://www.lasen.com/
 
|-
 
! scope="row" | GreenValley International
 
| http://greenvalleyintl.com/
 
|}
 
  
 
===2.1.3 Emerging techniques for GHG measurements===
 
===2.1.3 Emerging techniques for GHG measurements===

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