Water vapour profiling of surface layer, which constitutes the lowest hundred meters from earth’s surface, can aid in
the understanding of spatial variability of atmospheric turbulence and the dynamics of boundary layer. In lidars, the
effective area of an optical fiber-based receiver, also called the aperture stop diameter, controls the field of view of
the telescope which in turn governs the overlap function. We determined overlap function vs altitude for different
aperture stop diameters which showed that lower altitude profiling requires fibre receivers of larger effective area
positioned at the location of blur disk or the position of maximum capture of back scattered light. We report on the
design of a receiver which comprises of a converging lens system in conjunction with a commercially available fibre
bundle of fused hexagonal shaped fibres of adequate numerical aperture and enhanced effective light capturing area.
For a specified biaxial Raman lidar system with an excitation laser emitting at 532 nm, placing a one inch diameter
lens at the plane of blur disk of diameter ~21 mm and the aforesaid fibre bundle of diameter 7.3 mm at the image
plane of the blur disk was found to be suitable for relatively efficient light capture to enable profiling from an
altitude of ~8m and above. The light capturing efficiency of the system was determined and compared with that of a
conventional circular fibre-based bundle of same diameter. The proposed receiver design offers potential solution
for low altitude profiling with reduced central obscuration.
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