Particle-size distribution of Iraqi sand and dust storms and theirinfluence on microwave communication systems

Several windblown and dustfall samples were collected in the spring, summer, and autumn of 1984 at 20 m above the ground surface during severe sand and dust storms in the city of Baghdad, Iraq. The particle-size distribution (PSD) of the samples was determined using five different measurement techniques (hydrometer, pipette, sedimentation balance, optical microscope, and Coulter counter). The results showed that the cumulative weight techniques yield almost identical results for all the samples tested. The mode of the number distribution was found to occur at around 2 and 3.5 μm for the blowing and falling dust samples, respectively. A computer program was developed to describe the measured distributions by some analytical functions. It was found that the cumulative distributions can be well described by a third-degree polynomial and log-normal functions for particle diameters ranging from 1 to 100 μm. The attenuation α and phase shift β for a microwave signal were estimated for up to 37 GHz utilizing the measured PSD and for different particle moisture contents. It was concluded that at 37 GHz and for 10 m visibility, the upper bound for α and β were 0.7 dB/km and 26.5 degree/km for 20% particle-moisture content