Estimate the rainfall rate with the signal received from a television dish

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    This time I present to you a study done some time ago.

    The satellite television or satellite television , is television that reaches users in broadcast or multicast by means of radio waves emitted by transmitters placed on satellites to geostationary telecommunications .

    The transmitted signals are modulated on a carrier to and from the satellite. In general, the types of telecommunications satellite systems differ from each other in their technical characteristics based on the application or intended use (eg broadcasting, satellite telephony, satellite internet, radio localization and radio navigation systems).

    The frequencies used for television setellite , in general, are those of the Ku band (12–18 GHz) , while those for satellite internet are usually on the Ka band (26.5–40 GHz) .

    Rainfade

    While watching a TV show, almost everyone has encountered a loss of signal during a thunderstorm. Contrary to what many believe, it is not the thickness of the cloud cover that attenuates the satellite signals but the concentration of water droplets in the atmosphere and in the clouds themselves . In practice it is the same phenomenon that manifests itself in the operation of a microwave oven. A high- frequency electromagnetic radiation (such as that generated by satellite transmissions and by the Magnetron present in the oven) produces oscillations in molecules that have polarization such as water: by increasing the motion, the energy is converted into heat and the signal becomes weaker.

    The signal received from a radio source can be measured in various ways but in particular, in the world of digital radio communications, a parameter is used that takes into account the number of bits that can be transferred with that particular signal. The value of this parameter called E b / W or e for a television dish is almost always the same during the beautiful days and is dependent on the diameter, the aiming and other small factors that make it slightly oscillate around a base value.

    On such high frequencies the Rain fade is very evident and there are even mathematical methods to calculate it based on the power of the emitted signal, the angle of reception of the dish and other factors. Here is a sample article on how it can affect .

    The KWOS has an image receiving station of the Meteosat Second Generation using a geostationary satellite called EUTELSAT 10th to send them to the ground in broadcast. One of the software used by the system is BDADataEx which allows interfacing the tuner with the PC. This software has the logging function in which it writes the value of E b / W o many times per minute .

    By monitoring this value and with subsequent processing based on checking the daily deviation of the signal or signal drops caused by the passage of the Sun, it is possible to estimate the rain rate.

    BDADataEx

    Here is an example of how it compares to other rain monitoring systems .

    alt text

    On the same image there is also the result of another project based on the same phenomenon: Nefocast

    In addition to the two Rain rates calculated from the signal of the two parabolas, as a comparison, two types of rain gauges have been chosen: double layer tilting rain gauge and a 26GHz mini radar that uses the doppler effect. In addition, the electric field is represented, which is dependent on the electric charge contained within the clouds : the greater the Kvolts / meter recorded, the greater the cumulonenbo that will pass through the survey station.

    Two articles explain how to obtain the Rain Rate from the received signal attenuation:
    Rainfall Detection and Rainfall Rate Estimation Using Microwave Attenuation
    Rainfall measurement from the opportunistic use of an Earth – space link in the Ku band

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