EM Sounder with RASS option


 The ARPL l-band Wind Profiler


Atmospheric Research offer an L-band electromagnetic wind profiling radar to compliment their SODAR and RASS range. Wind profilers provide higher altitude coverage than SODARs (up to several kilometres), and can operate in higher winds and higher ambient noise environments. The ARPL sounder can be run in RASS mode with the addition of sound source. Sounders have coarser vertical resolution than SODARs.


What is an EM Sounder (Wind Profiler)?


An electromagnetic (EM) sounder system is a RADAR for the measurement of wind velocity, remotely, from the ground. It operates by transmiting a short pulse of electromagnetic energy which is refracted by the small scale turbulence in the atmosphere. This turbulence is transported by the wind, and the radial velocity of the air can be determined by measuring the Doppler shift of the electromagnetic pulse being refracted from the turbulence. The range of the turbulence is determined from the delay between the transmission of the EM pulse, and the reception of the refracted signal. By repeating this process in three different directions, each direction having a large component being orthogonal to the other two directions, the three dimensional wind field can be calculated. It is the electromagnetic equivalent of the Dopper Acoustic RADAR, or SODAR.

The EM Sounder sends out an electromagnetic pulse every 40 milliseconds in one of the three directions, switching sequentially between these directions. The signal processing algorithm includes extensive filtering and averaging, to ensure a good signal to noise measurement. By varying the pulse duration and bandwidth, high or low vertical resolution operation can be obtained. The instrument may take successive measurements in both modes, if required.

The return signal (in X, Y, Z) versus altitude, is displayed on the instrument control computer for each pulse. The trend wind field is shown on the display computer, and is written to file for long term data logging.

The EM SOUNDER consists of three main subsystems;

  • Antenna Subsystem;
  • RF Electronics Subsystem;
  • Processing and Display Computer Subsystem.

The EM Sounder antenna subsystem consists of three parabolic dishes (typically about 2 metre diameter), and associated preamplifiers and RF processing electronics.

Modifications to the configuration of the hardware (eg larger diameter dishes, single dish with multiple feeds etc), or to the software (eg to the user display), may be undertaken by ARPL, as options within a contract, or as subsequent upgrade contracts.


EM Sounder Software (Windows) in RASS mode showing temperature profile.

EM Sounder Software (Windows) in RASS mode showing temperature profile.

Advantages of Wind Profiler (Sounder) Operation

EM SOUNDERs provide;

  • Continuous operation and measurement;
  • No intrusion into the space being sampled;
  • Low labour costs for measurements;
  • High altitude coverage;
  • Operation in high wind;
  • Operation in high acoustic noise environments;

The performances of the ARPL EM SOUNDER are summarised in the table below.


EM SOUNDERS can be used for;

  • Industrial process and thereby pollution control by real-time monitoring of the local atmospheric environment;
  • Meteorological research;
  • Characterisation of the local micro-climate;
  • Wind monitoring at airports, balloon launch sites and parachute drop zones;

Limitations of Sounder Operation

 The EM SOUNDER has very few limitations to its operation;

  • Operating Frequency about 1270 MHz. The exact frequency is set by Australian Communication Authority spectrum allocation requirements, in compliance with WARC agreements, or equivalent in other countries. A license is required to operate the EM Sounder;
  • Vertical Resolution. The EM SOUNDER has a coarser (larger) vertical resolution than a SODAR or mini-SODAR; typically 150m versus 10 – 30m for a mini-SODAR or SODAR. The EM Sounder can be run in a higher vertical resolution mode (75m) with a trade in vertical resolution (1500m versus 3500m). Both modes can be run by the same instrument.

 Specifications for the sounders are shown. Contact us with your custom hardware or interface requirements.


Sounder Specifications

Horizontal wind speed componentsRange 0-50 m/s, accuracy 0.5 m/s
Horizontal wind speed vectorsRange 0 - 50 m/s
Vertical wind speed componentsRange 0 - 50 m/sec, accuracy 0.5 m/s
Horizontal wind Direction0 - 359 degrees
Resolution of reading0.1 m/s
Sampling Height (normal mode)150 m - 3000 m AGL
Sampling Height (high resolution mode)75 m - 1500 m AGL
Sample Interval (normal mode)150m
Sample Interval (high resolution mode)75m
Data IntervalApproximately 10 minutes
Operating systemWindows
Display LatencyReal Time
Environmental Conditions-10C to + 50C, 0 - 100% humidity
Power Supply240V (others available)
Dimensions [mm] (antenna pad, 2.2m antennae)4500 x 2500
Specifications of ARPL l-band EM Sounder


Sounder Images



RF Electronics for l-band sounder. Modularity provides for ease of service and repair.

RF Electronics for l-band sounder. Modularity provides for ease of service and repair.

RF Front End Module, showing power amplifier, oscillator, upconversion and downconversion chain