Laser radar in adverse weather

Abstract

Laser radar images of an outdoor target scene were collected in adverse weather such as rain and fog during the course of one year. Included in this collection is imagery in fogs with visibilities less than 2 km and rains with rain rates of up to 60 mm/hr. The targets were calibrated panels at 510 m and 1 km. The laser radar system used was a direct- detection 1.06 micrometers system designed to operate at 2 km in clear weather. For the purposes described here, though, the maximum range gate was set to 1.5 km. The system used a correlation technique for detection and discrimination, which significantly reduced the number of false returns in fog. Using these collected images, dropout pixels and false returns were correlated with rain rate and visibility. Extinction coefficients for 1.064 micrometers laser light were also calculated as a function of rain rate and visibility in fog and rain conditions. These coefficients were found to be consistent with those measured previously at 0.55 micrometers , 0.63 micrometers and 10.6 micrometers . These coefficients can be used to predict the performance of any circular polarized 1.064 micrometers LADAR system in rain and fog conditions.