LDP Verification of atmospheric attenuation
Publish date: 2015-03-20
Report number: FOI-R--4049--SE
Pages: 69
Written in: Swedish
Keywords:
- LDP
- laser
- lidar
- designator
- atmospheric attenuation
- extinktion coefficient
- irradiance measurement
Abstract
This project "Verification of atmospheric attenuation" is funded by the Swedish Defence Materiel Administration, FMV. The aim of the project is to create a model of atmospheric attenuation as a function of altitude for the laser wavelength 1064 nm. The model for atmospheric attenuation was created to be used at calculation of the laser hazard distance, using an alternative method, applicable for the designator laser in the Laser Designator Pod (LDP) used by the JAS Gripen aircraft. The work included analyzing collected data from lidar systems in Sweden, or from lidar measurements made by satellites over Sweden. A model of the atmospheric attenuation as function of height was created based on the initial analysis. Furthermore, the work also included to build a ground based lidar in the Vidsel area, perform measurements and analyze the results. In addition, measurement and logging of the laser intensity at flight tests with designator laser in the LDP was implemented. The original model must be verified alternatively be adjusted based on the results of the measurements carried out. The report describes the development of the necessary equipment and implementation of both lidar and irradiance measurements. The report also describes the model of atmospheric attenuation developed based on the lidar measurement of backscatter from aerosols and calculated atmospheric gas attenuation. The atmospheric model should in some sense describe the smallest and yet realistic attenuation that occurs in the neighborhood of RFN's test field in Vidsel. The results of lidar measurements showed that the atmospheric attenuation as a function of height might be very low up to high altitudes using this wavelength. The low atmospheric attenuation has the consequence that the reduction of the laser hazard distance becomes very small. The method to calculate the reduced laser hazard distance using the developed atmospheric model does not produce the desired reduction. Flight tests with the LDP showed that turbulence breakup of the laser beam and laser spot walk on laser target gave rise to the variation of irradiance, which could not be clearly linked to the distance between the target and the LDP. The highest measured irradiance was about 0.5-0.8 J/m2.