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Ground Based Sensor for measurement of V and W band satellite link propagation channel


OBJECTIVE: Develop a ground based sensor to measure the propagation characteristics along the earth-space path for the V and W bands of 71-76 GHZ and 81-86 GHz. DESCRIPTION: Development of new satellite communications capabilities in the allocated V and W frequency bands of 71-76 GHz and 81-86 GHz require measurement of the atmospheric attenuation characteristics at these frequencies. This includes measurement of the fade dynamics as well as the long term attenuation statistics (exceedance probabilities). Since the key design parameter for satellite communication systems is link margin, measurements of multi-year attenuation statistics for a variety of global locations and climates are a necessity. Predictive attenuation models derived from beacon measurements have been developed for frequencies at Ka-band and below, however none exist for the V and W bands. Extrapolation of these Ka-band models to the V and W band frequencies is uncertain. There is a dearth of relevant data at millimeter wave frequencies available to test or develop predictive models. The usual approach to collecting attenuation statistics utilizes geo-stationary beacon(s) and multiple receiver locations. Alternately, a stand-alone ground based sensor that is capable of determining the attenuation characteristics without the need for a beacon is attractive. Such a ground based sensor capability can provide the much needed data at a much lower cost and greater flexibility in site location than approaches requiring a geo-stationary beacon. Performance goals call for a capability to determine the attenuation over a dynamic range greater than 20 dB with an uncertainty of less than 10%. The sensor should be able to determine attenuation under most atmospheric and weather conditions including light and moderate rainfall. It should be designed to operate over a broad range of elevation angles; from 20 degrees to 90 degrees . The sensor should be designed as a capable of operating continuously with minimal direct operator control. The proposed effort will develop an architecture and a sensing strategy, including the desired measurement suite and retrieval algorithm(s). It is expected that the sensing strategy will require integration of multiple measurement capabilities including meteorological data. Passive radiometry offers one possibility to collect the needed attenuation statistics. Radiometers have been widely used for passive (remote) sensing and retrieval of various atmospheric properties. Radiometers have been used for accurate attenuation measurements in an absorptive atmosphere, but with limited dynamic range. The brightness temperature measured by a radiometer is related to the absorption and scattering of the atmosphere. Calculating attenuation from brightness temperature measurements (retrieval) is the central issue for such an approach to ground based sensing. These sensors will provide key data needed to define satellite communication system architectures. Multiple sensors will be required to collect the attenuation characteristics at a variety of geographic locations. Additionally, this type of sensor may be used in an operational capacity for short term predictive forecasting and dynamic adaptive fade mitigation, and may be generalized for use with other frequency bands. PHASE I: Conduct analysis to determine the sensing strategy and expected performance of a ground based system to measure atmospheric attenuation for a satellite communication system in the V and W bands. Specify the hardware to provide measured input data for the attenuation retrieval algorithms. Indentify critical engineering challenges to building the ground based sensor. PHASE II: Build a prototype ground station that includes the necessary suite of atmospheric measurement capabilities. The effort should demonstrate the expected system performance through analysis and simulation. PHASE III: Produce a multitude of ground stations based on the phase II prototype in order to perform multi-year attenuation measurements at a variety of global locations. The commercial satellite industry can use these technologies. REFERENCES: 1. G. Brussaard and P.A. Watson,"Atmospheric modeling and millimeter wave propagation,"Chapman & Hall, 1995. 2. E. Westwater, S. Crewell, C. Matzler,"Surface-based microwave and millimeter wave radiometric remote sensing of the troposphere: a tutorial", IEEE Geoscience and Remote Sensing Society Newsletter, March 2005. 3. F. Ulaby, R. Moore, and A. Fung,"Microwave Remote Sensing", Addison-Wesley, 1981.
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