Meteorologists, atmospheric physicists, civil and military airport directors, communication engineers, and safety teams at sites subject to major technological risks (nuclear power plants, highly polluting chemical complexes, ...) may now breathe easier. Thanks to the REMTECH DOPPLER SODAR, these groups already have accurate measurements of horizontal wind speed and direction as well as vertical wind speed and turbulence in the lower layers of the atmosphere.

But, in order to forecast the complex behaviour of air masses, essential data such as the temperature of the different layers of air was missing. Alternatives such as radio sondes or tethered balloons, being costly in time and material, could surely not fulfill the needs for real-time continuous vertical temperature profiles.

REMTECH now fills in this gap with the development of the RASS, or Radio Acoustic Sounding System, for accurate measurements of remote temperature.

An important complement to the SODAR, the RASS radar takes advantage of the combination of two technologies, acoustic and electromagnetic, to provide a real time temperature profile and deduce from it, with good temporal resolution, the "strength" of the temperature gradient. For risk assessment applications, a RASS together with a SODAR makes it easy to measure inversion phenomena responsible for trapping pollutants and storing them in the elevated layers of the first two thousand meters of the atmosphere.

The RASS also provides essential data for the improvement in models for real time fog forecasting at airports.

The RASS is a unique tool for civil and military telecommunications. It can detect if an inversion is present, how "strong" this inversion is, and therefore, better understand, and then control, the aberrations related to the propagation of radio waves. With RASS data, the real time optimization of transmitting frequency and antenna orientation is possible.

As for future developments, one can easily imagine the amount of information a RASS could provide to the operation of high power lasers.

Yes, with the RASS, the atmosphere will look more and more familiar.

 

The RASS applies a simple principle of physics: the relationship of the speed of sound and air temperature. A RASS processes a small part of the energy from a continuous radio wave backscattered by the inhomogeneities in the atmosphere caused by an acoustic pulse transmitted from the vertical antenna of the SODAR. Doppler processing of the signal received by a second radar antenna makes it possible to measure the speed of the vertically moving "target", here the acoustic wave train, and extract from it the air temperature. However it required the expertise of REMTECH engineers in the field of micrometeorology to transform this simple principle of physics into an accurate and reliable system such as the RASS. The system can operate even with high horizontal winds where the acoustic waves have drifted away from the antennas.

The numerical models and manufacturing techniques, which were successfully developed over many years for the SODAR, have been applied to the RASS antennas. Secondary lobes are considerably reduced, resulting in small scale antennas. These can be easily transported from one site to another on a trailer.

From its inception, the SODAR electronic case was designed to accept the input of an extra signal. Thanks to this design, every REMTECH SODAR ,manufactured to date can accept a RASS radar; antennas, amplifiers, filters and mixer. A new RASS software takes care of extracting the necessary information to provide profiles both of wind and temperature.

The above block diagram illustrates the RASS signal processing: after mixing the received radio frequency and the transmitted frequency, the frequency of the signal is of the same order of magnitude as the acoustic frequency transmitted by the SODAR antenna. This "audio" signal can therefore be processed (filtering, amplification, Fast Fourier Transform, "doppler" software) in the identifical manner utilizing the standard SODAR computer.

The RASS thus takes advantage of the expertise gained over the years by REMTECH with software processing of noisy and very low amplitude signals. It also profits from the accuracy of the three-dimensional SODAR taking into account the influence of horizontal and vertical wind speeds on the received radar frequency.

Don't stay in the fog any more! The RASS brings useful answers to problems previously without solutions, such as:
- the forecast, in real time and with a good accuracy, of the onset of fog at airports, thanks   to continuous temperature profiles,
- the control of aberrations in radio wave propagation due to temperature inversions which   disturb radio links and radar
   coverage,
- the optimal use of high power lasers.

The RASS also complements the SODAR in its classical applications:
- the improvement of risk assessment models at sites which involve major technological risks   (nuclear power plants, chemical
   industries, urban pollution alert networks, ...),
- the development of complex terrain models for which continuous temperature profiles are   necessary,
- the better understanding of noise propagation (aircraft noise certification, ...).