摘要 : In 1972 and again in 1989-1990 measurements of the incidental radio noise from two cities in central Illinois were made in the range 144-412 MHz by flying over in a light airplane equipped with downward looking antennas. The citie... 展开 In 1972 and again in 1989-1990 measurements of the incidental radio noise from two cities in central Illinois were made in the range 144-412 MHz by flying over in a light airplane equipped with downward looking antennas. The cities were well resolved by the antennas, so the data could be expressed as brightness temperatures. Care was taken to avoid contamination of the data by radiation from transmitters and the airplane's systems. Variation of brightness with frequency, time of day, and season of the year was determined. Comparison of the 1972 and 1989-1990 data shows no significant changes between epochs. 收起