Abstract
Strong attenuation of millimeter wave due to precipitation particles is the most serious problem when we use K-band (0.86cm wavelength) radar for the observation of the precipitation. In this paper, we calculated the attenuation of K-, X- (3.2cm) and C-band (5.6cm) waves based on a model of precipitation, for three precipitation intensities, i, e., heavy (32mm/hr), ordinate (4mm/hr) and weak (0.5mm/hr) precipitations. And, we surveyed any possibility of the observation with weak affection of the attenuation using the bands. The observation of the precipitation was executed in Part II.
The results show that the attenuation coefficient is larger in the melting layer by one order or two orders than in the lower raindrop region. The results also indicate that the affection of the size distribution to the attenuation abruptly increases as the attenuation is enhanced. The attenuations of X- and C-band waves are small enough to be neglected except for the heavy precipitation. In the case of heavy precipitation, K-band wave is severely attenuated, especially in the melting layer, so that the signals cannot be detected by the radar receiver. In the cases of ordinary and weak precipitations, however, we can obtain true radar reflectivity factor of K-band wave by corrections of the attenuation. In addition, the correction method using the radar reflectivity factor of the X-band radar was investigated. We can mention conclusively that after the correction the precipitations weaker than about 4-7mm/hr can be safely observed within an error of 2dB by the twowavelength radar technique using K- and X-band radars in the raindrop region. In the melting layer, the correction method can be utilized without large error when the precipitation is weaker than about 2-4mm/hr.
