Systemdesign und Fehlerabschätzung der radio–akustischen Temperaturmessung

Contactless temperature and flow velocity measurement is of enormous importance, both in climate research and in industrial applications. It is crucial for the optimization of the systems to be able to estimate the expected measurement errors. In this article, one of the methods the radio-acoustic sounding system (RASS) is extensively investigated. Measurement systems operating on this method use the acoustic-electromagnetic interaction to infer the prevailing gas temperature from the spatially resolved speed of sound, but also, if necessary, to infer the spatially acting component of the flow velocity in the measurement direction. In order to achieve the goal of analyzing the measurement system in its entirety, the so-called RASS equation and the necessary collocation condition of the sources are discussed first. The expression of the backscattered power indicates which factors have a decisive influence on the system behavior. Appropriate matching of the sound and Radar wavelengths and perfect collocation of their sources are essential for a sufficiently accurate estimate of the temperature-dependent Doppler frequency. Afterwards, to the best knowledge of the authors, an optimal system design is derived for the first time based on the Cramér-Rao lower bound. It can be seen that the variance of the temperature estimate is inversely proportional to the 4th power of the number of interacting sound cycles. It is also demonstrated that the temperature and the flow velocity cannot be estimated independently of one another. In this article a setup is presented that allows the temperatures to be measured with a standard deviation of about ±0,2 °C. A temperature profile measurement is presented as a demonstration.