The reduction of the laser hazard distance range using atmospheric attenuation has been tested with series of lidar
measurements accomplished at the Vidsel Test Range, Vidsel, Sweden. The objective was to find situations with low
level of aerosol backscatter during this campaign, with the implications of low extinction coefficient, since the lowest
atmospheric attenuation gives the highest ocular hazards.
The work included building a ground based backscatter lidar, performing a series of measurements and analyzing the
results. The measurements were performed during the period June to November, 2014.
The results of lidar measurements showed at several occasions’ very low atmospheric attenuation as a function of height
to an altitude of at least 10 km. The lowest limit of aerosol backscatter coefficient possible to measure with this
instrument is less than 0.3•10-7 m-1 sr-1. Assuming an aerosol lidar ratio between 30 – 100 sr this leads to an aerosol
extinction coefficient of about 0.9 - 3•10-6 m-1.
Using a designator laser as an example with wavelength 1064 nm, power 0.180 W, pulse length 15 ns, PRF 11.5 Hz,
exposure time of 10 sec and beam divergence of 0.08 mrad, it will have a NOHD of 48 km. With the measured aerosol
attenuation and by assuming a molecule extinction coefficient to be 5•10-6 m-1 (calculated using MODTRAN (Ontar
Corp.) assuming no aerosol) the laser hazard distance will be reduced with 51 - 58 %, depending on the lidar ratio
The conclusion from the work is; reducing of the laser hazard distance using atmospheric attenuation within the NOHD
calculations is possible but should be combined with measurements of the attenuation.