Airborne East Coast/Midwest Urban Survey at 121.5/243 MHz

This paper describes final results of a National Aeronautics and Space Administration (NASA) airborne measurement survey of environmental, radio-frequency (RF) interference over East Coast and Midwest urban centers. The measurements were made in the emergencydistress, Search and Rescue (S&R) frequency bands at 121.5 MHz ± 25 kHz and 243 MHz ± 25 kHz, applicable to a Search and Rescue Satellite. Observations were made at an altitude of 25 000 ft. The purpose of the airborne survey was to collect RF interference data to verify noise-temperature maps used for computing the RF link power budget from the earth to a Search and Rescue Satellite in low-earth orbit. Initial findings were reported both at Montreux, Switzerland (2nd Symposium and Technical Exhibition on Electromagnetic Compatibility June 1977) and Seattle, WA (1977 IEEE International Symposium on Electromagnetic Compatibility, August 1977). Presented are 121.5-and 243-MHz antenna-noise temperature profiles, measured over urban/ suburban areas extending several hundred miles, not previously published. Included are a series of minutelymedian, profile plots of antenna-noise temperature, computed from RF interference power measurements at the output terminal of a quarter-quatrerwavelength, monopole antenna, for both daytime and nighttime observations over urban centers. A steady maximum value of noise temperature was observed approximately over the geographical center of a given urban area. Typical data indicates daytime maximum values of 280 000-450 000 K, at 121.5 MHz over New York City, which are 3-to 5-dB above steady maximum values for Philadelphia, PA.