ADA is an instrument the principle of which is based on empirical relations among rainfall rate, reflectivity, and attenuation. It is used in connection with a weather radar which provides a display of the attenuation due to rain at 10 GHz over the radar line of sight. With ADA a large amount of data applicable to the assessment and design of satellite communication systems can be accumulated in a relatively short period of time. It is estimated that the ADA-measured attenuations, expressed in decibels, are accurate to within a factor of two.