Low Elevation Angle Measurement Limitations Imposed by the Troposphere: An Analysis of Scintillation Observations Made at Haystack and Millstone
MASSACHUSETTS INST OF TECH LEXINGTON LINCOLN LAB
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Tropospheric angle-of-arrival and amplitude scintillation measurements were made at X-band 7.3 GHz and at UHF 0.4 GHz. The measurements were made using sources on satellites with 12-day orbits. The angle of arrival of the ray path to a satellite changed slowly allowing observations of fluctuations caused by atmospheric irregularities as they slowly drifted across the ray path. The fluctuations were characterized by the rms variations of elevation angle and the logarithm of received power log power. Over a one- year period, 458 hours of observation were amassed spanning every season, time of day, and weather conditions. The results show strong scintillation occurrences below 1 to 2 degree elevation angles characterized by a number of random occurrences of multipath events that produce deep fades, angle-of-arrival fluctuations, and depolarization of the received signal. The log power fluctuations ranged from 1 to 10 dB rms at elevation angles below 2 degrees to less than 0.1 dB at elevation angles above 10 degrees. The elevation angle fluctuations ranged from 1 to 100 mdeg at elevation angles below 2 degrees to less than 5 mdeg at a 10 degree elevation angle. Comparable fluctuations in elevation angle are expected for bias refraction correction models based upon the use of surface values of the refractive index.
- Active and Passive Radar Detection and Equipment
- Radiofrequency Wave Propagation