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The Acoustic Radars Working Group members are currently carrying out research on the developmentof a Switched Beam Digital Acoustic Radar System, titled SBEDAR.

In this page you may find useful information about Acoustic Radars in general and the SBEDAR system in detail. You may also find Examples of the Special Operating software, developed to control the system's setup and operation in a Menu driven-User Friendly mode and Pictures of the SBEDAR system!

What is an Acoustic Radar?

Figure 1 An acoustic radar is a device acting as the well known radars, with the difference that the transmitted and the received signals have frequencies in the acoustic region. An alternate name for this class of instruments is 'Sodar', due to the SOund Detection And Ranging'. A short acoustic pulse is transmitted in the atmosphere. While it is travelling in there, it is scattered from the atmospheric irregularities. Here, the irregularities don't mean a 'target' object, as in the usual electromagnetic or microwave radars. A change in the wind velocity, a turbulent layer, a temperature inversion e.t.c. cause scattering of the acoustic waves. A part of the scattered signal returns to the receiver, where it is collected and processed.
There are various configurations for a sodar device.
Figure 3
  • A monostatic system

  • These systems use the same antenna for transmitting the acoustic pulse and receiving the backscattered acoustic waves.
  • A bistatic system

  • These systems use two antennas, one for trasmission of the acoustic pulses and one for the reception of the signals scattered to the direction the receiving antenna points to.
  • A tristatic system
  • Here we have three monostatic antennas pointing to three no coplanar directions. These systems permit the measurement of atmospheric parameters having a 'vector' nature (i.e. winds' velocity).
An example of an old monostatic system is presented in Figure 3. The antenna is constructed from an electrodynamic transducer in the focal point of a parabolic dish reflector. It is clear that the system is heavy and it is difficult to move it in hard to reach places.
Figure 5 An important point in the evolution of the sodars was the usage of array antennas. An antenna constructed from Celestions acoustic transducers, in a square planar topology, is presented in the figure left. You can also see in this figure the screening of the antenna using sound absorbing material. The screening is used to supress the sidelobes of the antenna (i.e. to reduce the undesired signal received from the sidelobes).
Figure 4 Example of the antenna of a modern tristatic sodar (METEK's MODOS Model).
Figure 2 Example of a modern antenna of a phased array sodar (REMTECH's PA2 Model). Due to the number of elements used and electronic 'apodization' (sidelobe suppression through the usage of different amplitudes for the signals feeding the elements) of the beam, the resulting main lobe's directivity and sidelobe levels are excellent and there is no need for shielding the antenna.
Figure 6 Figure 7

Examples of facsimile recordings of the signal received from a sodar system (in Black&White or Color Mode). The intensity of the received signal is used to show the existense of layers in the atmospheric boundary layer and their evolution with time.

What is a Switched Beam Radar?

A switched beam radar is a system that switches its' beam in different directions throughout space, by electronic means, i.e. by changing the phase differences of the signals used to feed the antenna elements, or received from them.
Note that there is no mechanical system to 'rotate' the antenna in the desired direction. The antenna is steady, but it's sensitivity and directivity are changed, by electronically controlling the radiating and receiving elements.

What is a digital Radar?

A digital radar is a device where the most of the electronic components used to construct it are 'Digital'. Some of the units of such a system (as an example we use the preamplifiers) are 'analog' from their nature. A digital system is a system that may include 'analog' modules, but the most of it has to be 'digitally constructed'. Compare this philosophy with that of your 'CD Player'. It is a 'digital' device, BUT the sound it reproduces from the 'CD' record, and drives to the loudspeakers, has an analog nature!

What is our Scope?

The Acoustic Radars Working Group members are currently carrying out research on the development of a Switched Beam Digital Acoustic Radar System, titled SBEDAR. This system is an acoustic radar, having capability to electronically switch its' beam in the desired direction(s) and being digitally constructed.
This project is the 'target' of the PhD course taken from Mr. Taxiarhis Liaskas.

Some examples of the Operating software, developed to control the system's setup and operation, in a Menu Driven - User friendly mode, may be found here.
Some photos of the SBEDAR System, may be found Here!!