Shipborne polarimetric weather radar: Impact of ship movement on polarimetric variables

Ground based polarimetric radars are providing important new information on cloud microphysics and quantitative precipitation measurement for both research and operational applications. Recent plans now include the operation of polarimetric radar from ships such as the new Australian research vessel, the RV Investigator, that is currently under construction, to allow cloud studies around the globe in key climate regimes ranging from the tropics to the deep Southern Ocean. While Doppler radar usage on ships is well established, the impact of ship motion on polarimetric radar is less well explored. This paper investigates the effect of the ship motion on polarimetric radar variables using scattering simulations. One-minute drop size distribution data from a 2D video disdrometer in SE Queensland are used as input to the scattering calculations. Several hundreds of minutes of data, with the median volume diameter ranging from 0.5 mm to 3 mm, were used. To assess the impacts of ship motion, the mean canting angles were varied, and a narrow, Gaussian, canting angle distribution is also assumed with a standard deviation of 5 deg. Clearly at a tilt of 45 deg, all polarimetric information is lost. For other angles, the simulations show that for expected ship motion of ~ +/- 15 degrees, the effects are tolerable. Furthermore, the results from the scattering simulations can be used to determine correction factors to be applied to compensate for the ‘apparent' non-zero canting angles. Results will be presented for Zh, Zdr, Kdp, rho_hv and LDR at C-band.