5. Details of radioastronomy observatories Appendix 1A (Section F) of the Radio Regulations describes the information on observatories and on the observations in progress or planned, which Administrations should furnish to the IFRB for incorporation in the Master International Frequency Register. This information is published by the ITU from time to time, in the form outlined in the revision of Appendix 9 of the Radio Regulations (List VIIIA). Collected information and the activities of radioastronomy and radar observatories can be obtained upon application to the Secretary-General of 1UCAF, Appleton Laboratory, Slough, United Kingdom. B. PROTECTION CRITERIA FOR THE RADIOASTRONOMY SERVICE 6. Introduction The random radiation encountered in radioastronomy induces signals which have a Gaussian probability distribution in amplitude, and which qualitatively cannot be distinguished from the noise generated in the receivers or from thermal radiation from the Earth and its atmosphere. Furthermore, the intensity of cosmic radiation is usually much lower than that of noise, often by 30 dB or more. A full recognition of these facts is the key to understanding the interference problems encountered by the radioastronomy service. The radio astronomers’ signal-to-noise ratio is —30 dB or worse; in extreme cases a signal-to-noise ratio as low as —60 dB may yield useful data. In the following paragraphs the theoretical considerations leading to the sensitivity criteria in radioastronomy are described. 7. Sensitivity of radioastronomy systems 7.1 Theoretical considerations The output of the radiometer detector is a function of the total power at the input of the receiver. (It is assumed that the gain and other parameters of the receiving system remain constant during the observation.) The total input power consists of the wanted signal power Ps and the unwanted noise power P^ (e.g. thermal and receiver noise). Both Ps and PN are caused by random processes, and it is not possible to distinguish between them qualitatively. However, both have an average power level, and if these levels can be established with sufficient precision, the presence of the wanted signal can be detected. The statistical average of a stationary random variable such as noise power (P) can be found with a precision which is inversely proportional to the square root of the number of samples (/V), and the standard deviation of this average is: The standard deviation (AP) is often called root mean square or rms. By observing a sufficient number of samples (N), the measurement of the radio noise power can be made with any desired precision. By reducing the fluctuations ^P to a value less than the wanted signal power, Ps, detection of very weak signals is possible. N can be made very large by using wide bandwidths and long observing times. Within a band A4 approximately Af samples per second are measured by the radiometer, and by extending the observing time (t), (also called integration time), N can be made very large. which is the basic sensitivity relation in radioastronomy. The proportionality factor Ts which is needed to make (3) an equation, is dependent on details of the equipment and the observing technique. Conditions making this factor 1/^2 have been discussed by Kraus [1966], With this value adopted, the sensitivity equation becomes:
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