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The strength of backscattered signals for a Differential Absorption Lidar (DIAL) system operating in the mid infrared
band is estimated for the cases of (i) back scattering from topographic targets and (ii) Mie scattering from the aerosols.
The estimation is based on the following input parameters : (a) the energy of the lidar transmitted pulses is 20 mJ with
pulse duration of 10 nanoseconds and (b) the receiver system consists of a telescope with 500 mm aperture with a field
of view of 0.33 mrad.
The inherent noise of the detector, background noise due to solar radiation and the noise due to thermal radiation from
the objects within the field of view of the receiver, are separately estimated to obtain the total noise in the detection
setup.
For the case of topographic targets, the reflectivity is taken as 10%. It is shown that atmospheric trace gases like
methane with (path integrated) concentration upto 0.5 ppm-km, can be detected without difficulty upto ranges of 5 km.
For the Mie scattering from the aerosols, typical meteorological visibility of 10 km is assumed. The case for methane
detection is studied. It is shown that during day time, range resolved measurements of trace chemicals can made upto 3
km range, which can be extended to 5 km during night time.
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