Atmospheric Research RASS Page

The ARPL RASS

The Atmospheric Research Radio-Acoustic Sensor System (RASS) is a state-of-the-art design which operates on the principle of finding the acoustic frequency at which the Bragg reinforcement occurs at each height, as opposed to the cw RF, Doppler method, (which compromises temperature resolution), and the pulsed RF Doppler method, (which incurs higher costs and compromises height resolution).

The Bragg-Reinforcement-Search technique (BRS) offers good height resolution with superb virtual temperature accuracy. The temporal resolution of 10-15 minutes is more than sufficient for short term stable atmospheric work.

The AR RASS is a compact unit, decreasing the low temperature bias at low heights that can occur with other RASS systems. The AR RASS experiences a bias to low temperatures of not more than 0.2 degrees at 50m, and nill at 100m. The RF operating frequency of 1270 MHz has been chosen to be the most suitable for operation and licencing in compliance with WRC requirements.

The Atmospheric Research RASS uses active nulling of coupling between the transmit and receive antennae, to minimise coupling and maximising the signal to noise performance of the instrument.

Why Use an Atmospheric Research RASS?

Options for the RASS

1. A ground sensor suite (temperature, relative humidity, atmospheric pressure) to provide the virtual temperature at the ground.
2. A complete ground-level meteorological sensor suite (temperature, relative humidity, atmospheric pressure, wind velocity and direction), with data logging by the RASS computer.
3. Integration of the RASS and a SODAR. The baseline RASS is not supplied as an add-on to a SODAR. This is not recommended and gives a performance compromise. If the customer needs a combined RASS/SODAR, however, a combined unit can be delivered.
4. ARPL can provide tailoring of software to user requirements. Such software modifications are undertaken on a firm fixed price basis, to an agreed specification, unless otherwise agreed.
5. ARPL can design and install client-specific communications interfaces from the RASS control computer output port.

Overhead Presentation

Background to RASS Theory and Applications

Technical Specifications for the RASS

Performances of the ARPL SODAR

Parameter	Performance
Temperature Accuracy	0 =/- 0.5 Degrees Celcius (virtual temperature*
Height Resolution	35m
Height Coverage	Greater than 700m above ground level **
RF Frequency	1270 MHz (nominal, 900 MHz ISM Band also available
RF Power	15W

*Virtual temperature is the temperature that a parcel of dry air must have to equal the density of moist air of the same pressure.
** The performances are quoted under good atmospheric conditions, ie low wind and turbulence. These are, of course, the particular conditions under which an inversion may form.

Physical and Environmental Specifications

Property	Range
Power Supply	240V, 50Hz via 10amp GPO
Operating Temperature	Field Unit: -10C to +45C
Operating Temperature	Computer: +5C to +30C (domestic airconditoned environment);
Relative Humidity	0 - 90% Non-condensing
Data Interface	Serial Interface, RS232, at computer. Other interface and transmission options can be supported, please request options and prices.
Data Format	Virtual* temperature versus height, with Data Quality parameter. Potential virtual temperature versus height available as an option. Sample files can be supplied on request.
Data Frequency	Samples on approximately 2 minute basis, with running average on 10-15 minutes. Timing varies with temperature variation with height of the atmosphere at the time.

cwRASS under test at ARPL Fieldsite prior to export. The Tx and Rx antennae are shown, with a shielding fence between them, and an external fence which provides additional shielding, and prevents access to the instrument during operation. The sound source, based on that for the medium frequency SODAR, is behind the RF shield in this picture.

RASS, with SODAR behind. Our instruments, (and our staff!) work in any weather.

[ TOP ]

This page maintained by Elissa Milford, © Atmospheric Research Pty Ltd 2001. eroberts@a-research.com.au
Last updated on December 29, 2001.