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Objectives
This activity developed the “Atmospheric Propagation and Profiling System” (ATPROP) advanced ground-based microwave radiometer, for radiowave propagation assessment at Ku, Ka, Q/V and W bands. The design of ATPROP is based on the requirements of SatCom, SatNav systems and Space Science Missions.
ATPROP consists of two independent subsystems, operating at Ka band, near the 60 GHz oxygen absorption band and at 15/90 GHz. ATPROP has a full non-GEO satellite tracking capability and uses switched Dicke reference to improve stability by. His performances allow to derive accurately atmospheric attenuation, sky noise, wet delay, and cloud, vapour and air temperature profiles.
Today satellite-based systems such as telecommunication, navigation and earth observation are fundamental to the course of modern life. In order to guarantee an unrestrained functionality of those systems, the assessment of atmospheric propagation effects and meteorological parameters is a key issue.
Radio propagation in the Earth’s atmosphere is affected by the atmospheric constituents, mainly gases and hydrometeors, which interact with electromagnetic radiation. The goal of this study is to assess radio propagation in the spectral range from 10 to 90 GHz, a spectral region which is becoming more and more important in the applications mentioned above.
For this purpose a highly stable microwave radiometer system (ATPROP) has been designed, constructed and tested which allows the investigation of
- Sky noise due to emission of atmospheric components such as gases and hydrometeors,
- Atmospheric attenuation due to gases and hydrometeors,
- Atmospheric excess path length mainly due to atmospheric gases.
For these purposes the system should allow observations with high spatial and temporal resolution and be capable of operating in a stable way for long periods, in remote locations, under severe environmental conditions and with no or sporadic manned instrument control.
Challenges
The project aims at the accurate assessment of propagation parameter by a ground-based system. The microwave radiometer system ATPROP was designed to achieve these requirements and to allow automatic stand-alone operation at arbitrary locations over long time periods. Therefore key issues of the study are the high precision and stability of the radiometer, accurate calibration procedures, flexible observation modes and suitable retrieval algorithms for propagation and meteorological parameters and a thorough assessment of the ATPROP specifications.
Plan
The project started with a critical review of atmospheric microwave radiometry for accurately deriving propagation parameters between 10 and 90 GHz. The baseline design of such a system including hardware and software components was reviewed.
In the second phase of the project the technical design was completed and an analysis of failure mode effects & criticality performed.
The third phase included the manufacturing of the ATPROP system and its operational tests. Retrieval algorithms for various propagation and meteorological parameters were developed.
The final fourth phase, concerning the field testing of ATPROP at the KNMI Remote Sensing Area in Cabauw, The Netherlands, in the framework of the Dutch CESAR project is still ongoing.
Current Status
A critical review of the system requirements has been performed including a frequency selection study. Based on the requirements the “Atmospheric Propagation and Profiling System” (ATPROP) has been designed and constructed. In order to achieve the longterm stable operation a new calibration approach including a Dicke switch has been designed. After laboratory checks the ATPROP system has been transported to the KNMI measurement site in Cabauw, The Netherlands.
Currently ATPROP is tested in various observation geometries at Cabauw. Retrieval algorithms for the various propagation and meteorological parameters have been developed and are applied to the data of the test campaign. ATPROP performance is currently specified by investigating radiometer stability during quiet atmospheric periods, simulated clear sky emissions calculated from radiosoundings at the close by De Bilt station, and intercomparison with further instrumentation available at Cabauw (rain gauge, cloud radar, rain radar, dual channel mw radiometer) provided by KNMI.