1. (sonic detection and ranging)
Sodar
(sonic detection and ranging) By
Dr. Ahmed Fattah

2. Sodar (sonic detection and ranging) systems are used to remotely measure the vertical turbulence structure and the wind profile of the lower layer of the atmosphere.  Sodar systems are like radar (radio detection and ranging) systems except that sound waves rather than radio waves are used for detection. 
A more familiar related term may be sonar, which stands for sound navigation ranging.  Sonar systems detect the presence and location of objects submerged in water by means of sonic waves reflected back to the source. 

3. SODAR HISTORY
In the United States during World War II, acoustic backscatter in the atmosphere was used to examine low-level temperature inversions as they affected propagation in microwave communication links. 
During the late 1950's, acoustic scattering from the atmosphere was investigated both experimentally and theoretically in the Soviet Union, and researchers in Australia showed that atmospheric echoes could reliably be obtained to heights of several hundred meters. 
Beginning in the late 1960's and early 1970's, scientists at the U.S. National Oceanic and Atmospheric Administration (NOAA) demonstrated the practical feasibility of using acoustic sounders to measure winds in the atmosphere by means of the Doppler shift to monitor the structure of temperature inversions.
In 1974, NOAA developed a portable system that called an acoustic echosounder.  designed from a single 1.2-meter diameter parabolic dish, and a facsimile recorder used to provide an analog record of backscatter data.
after that several develops in Sador devises continuous later.

4. SODAR antenna
The main component of SODAR is its antenna. SODAR antenna consists of dozens of sonic transducers. A transducer is an electronic device that converts one form of energy into another form. A sonic transducer is a transducer that converts sound waves into electric current or electric current into sound waves. In SODAR, a combination of speakers and microphones are used as sonic transducers. A microphone is an instrument that converts sound waves into electric current (electrical signals). A loudspeaker is a device that converts electric current (electrical signals) into sound waves.

5. How Sodar Operated ?
The motion of the atmosphere is the result of general wind flow and turbulence (the irregular fluctuations of small-scale horizontal and vertical wind currents). Atmospheric turbulence is generated by both thermal and mechanical forces. Thermal turbulence results from temperature differences, or gradients, in the atmosphere. Mechanical turbulence is caused by air movement over the natural or man-made obstacles that produce the “roughness” of the earth's surface. Turbulence from either source results in turbulent air parcels or eddies of varying sizes.
loudspeakers in SODAR convert the electric current into sound waves or sound pulses. The sound pulses or sound signals generated by the speakers of SODAR are then sent in three directions up through the atmosphere. One sound signal is in the vertical direction with respect to ground and the remaining two orthogonal signals are tilted approximately 17 degrees from the vertical sound signal. In order to measure the 3-dimensional wind velocity, at least three beams in different directions are needed.

6. When an acoustic (sound) pulse transmitted through the atmosphere meets an eddy, its energy is scattered in all directions. Although different scattering patterns result from thermal and mechanical turbulence, some of the acoustic energy is always reflected back towards the sound source. That backscattered energy (atmospheric echo) can be measured using a monostatic sodar system.  A monostatic sodar system is one in which the transmitting and receiving antennas are collocated, and thus the scattering angle between the target eddies and the sodar antenna is 180 degrees.  The backscattered energy is caused by thermally-induced turbulence only.

7. In a bistatic sodar system, the transmitting and receiving antennas are at different locations.  In principle, this provides for a stronger and more continuous signal, but nearly all commercial sodar systems are monostatic because their design is simpler and more practical.
Much information about the atmosphere can be derived from monostatic sodar systems. The intensity or amplitude of the returned energy is proportional to the CT2 function,( LOCAL TEMPERATURE STRUCTURE COEFFECIENT) which, in turn, is related to the thermal structure and stability of the atmosphere. CT2 has characteristic patterns during ground-based radiation inversions, within elevated inversion layers, at the periphery of convective columns or thermals, in sea breeze/land breeze frontal boundaries, and at any interface between air masses of different temperatures.

8. Due to the Doppler effect, measuring the shift in the frequency of the returned signal relative to the frequency of the transmitted signal provides a measure of air movement at the position of the scattering eddy. When the target (a reflecting turbulent eddy) is moving toward the sodar antenna, the frequency of the backscattered return signal will be higher than the frequency of the transmitted signal. Conversely, when the target is moving away from the antenna, the frequency of the returned signal will be lower. This is the physical characteristic that is used by Doppler sodar systems to measure atmospheric winds and turbulence.
By measuring the intensity and the frequency of the returned signal as a function of time after the transmitted pulse, the thermal structure and velocity of the atmosphere at varying distances from the transmission antenna can be determined Geometric calculations can then be used to obtain vertical profiles of the horizontal wind direction and both horizontal and vertical wind speeds.

10. ELEMENTS EFFECT ON RETERN SIGNAL
A sodar system transmits and receives acoustic signals within a specific frequency band. Any background noise within this frequency band can affect signal reception. Since the return signal strength usually varies inversely with target height, the weaker signals from greater heights are more readily lost in the background noise. Thus high levels of background noise may reduce the maximum reporting height to a level below that obtainable in the absence of noise.  Certain noise sources can also bias the sodar data. Thus, it is important to identify potential noise sources and estimate the background noise level when evaluating a candidate site for a sodar system.
One of the other principle problems is Interference from ground clutter, that occurs when side-lobe energy radiating from a sodar antenna on transmit is reflected back to the antenna by nearby objects such as buildings, trees, smokestacks or towers.  This reflected side-lobe energy can overwhelm the atmospheric return signal and cause the component wind speeds reported by a sodar system to be zero-biased.  Thus, sodar systems must either be located in areas with wide-open wind fetches (i.e., areas with no reflecting objects), or they must be designed to substantially eliminate side-lobe energy.

11. advantage
determine wind speed, wind direction and turbulent character of the atmosphere depend on Doppler (frequency) shift.
provides atmospheric data with height based on speed of sound.
Low labour cost for measurements.
Continuous operation.
Continuous measurement.
Fast installation.
Easy to transport from one place to another place.
compared to erecting tall towers heights, carried wind and temperature sensors. Most Sodar systems obtained reliable data well beyond towers height.

12. DISADVANTGE
Sodar systems do have some drawbacks compared to tall towers fitted with in-situ wind sensors. Perhaps the most significant is the fact that sodar systems generally do not report valid data during periods of heavy precipitation.
sodar systems primarily provide measurements of mean wind.  Other wind parameters, such as wind speed standard deviation, wind direction standard deviation and wind gust, are usually either not available or not reliable.
Maximum range is typically achieved at locations that have low ambient noise and moderate relative humidity.  But at desert locations, Sodar systems tend to have reduced altitude performance because sound attenuates more rapidly in dry air.

13. Some aplications for SODOR
INVERSION STUDIES
SODAR is used for the monitoring of inversion dynamics. Time series of several years are examined in order to derive a climatology of inversion structure (thickness and stability).

14. 2- AIR POLLUTION

15. 3-WIND ENERGY Because SODAR can be used to:
Quantify the individual horizontal and vertical wind flow components.
providing high-resolution wind speed and direction data at significant heights,
Measure turbulence levels
Identify flow discontinuities that fixed towers miss
Measure wind speed in a volume of air, not just at one point
Confirm wind shear aloft that may be defined in fixed towers
Thus, large wind turbines installing selection site, predictions of energy production, wind plant maintenance, depend largely on Sodar system.

17. 4-AVIATION
The wind information given to the pilots, at take of and landing, normally include information of head and tail wind components together with the side wind component at the surface. A SODAR with a software package can calculate this information for all height intervals from ground .

18. 5-POWER STATIONS
SODARs with meteorological instruments nearby nuclear power stations ultimately provides emergency responders with a valuable picture of how and where accidental releases may be transported from the sites.

19. EXAMPLE ON SODAR DEVISES
VT-1 Sodar System Model
The Model VT-1 is a monostatic phased-array Doppler sonic detection and ranging (sodar) system. It provides a "virtual tower" for obtaining remote measurements of the wind profile up to a height of approximately 300 m (1000 ft). The system includes a 48-element acoustical array, supporting electronics and laptop computer. The Model VT-1 is entirely self-contained within a portable cabinet and is powered by a 12 VDC power supply or battery, thus making it suitable for use even at the most remote locations. All cabinet components are PVC plastic or stainless steel for durability. Due to its modular design, the entire system can be assembled without tools in a minutes.

20. Specifications Parameter Specification Maximum altitude
300 m (1000 ft)
Minimum altitude
15 m (50 ft)
Effective sampling depth
10 to 40 m (30 to 130 ft)
Transmit frequency
4600 Hz (adjustable)
Pulse duration
30 to 100 ms (adjustable)
Averaging interval
1 to 60 minutes (adjustable)
Wind speed range
0 to 25 m/s (0 to 55 mph)
Wind speed accuracy
+/-0.25 m/s (+/-0.55 mph)
Wind direction accuracy
+/-2 degrees
Power input (electrical)
40 watts (basic unit)
Voltage input (nominal)
12 VDC
Assembled system weight (w/o batteries)
135 kg (300 lbs)
Assembled system width
1.5 m (5 ft)
Assembled system length
1.8 m (6 ft)
Assembled system height

21. PCSodar Output Signal Display

22. PCSodar Input Signal Display
PCSodar's Input Signal display, which is optionally shown along the bottom of the Wind Summary Display, provides an oscilloscope-like representation of the strength of the signal returned for each transmit pulse from various heights. In this plot, height increases from left to right.

23. VT-1 PCSodar
Software
PC Sodar's Plotted Data screen is composed of three plotting areas, each one displaying data for one user-selected parameter. For each parameter, height is plotted on the vertical scale and the parameter value is plotted on the horizontal scale. The plots are updated at the end of each averaging period. An example of this display is shown below.

24. PCSodar Wind Component Display
At the end of each averaging period, data for the three wind components (W, V and U) is displayed on the Wind Component screen. The speed, reliability (R), number of valid samples (Num Val), signal-to-noise ratio (SNR), signal amplitude (Sig Amp), noise amplitude (Noi Amp) and standard deviation (Sdv) are shown for each range gate for each wind component. An example of this display is shown below.

25. CONCLUSION APPLICATIONS SODAR IS TOOL FOR Meteorologists
Predict dispersion of air pollution
Elevated temperature inversions
Atmospheric stability
Mountain/valley flow
Difuusion in complex terrain
Plume dispersion monitoring
Sea and land breeze
Weather forecasts
Climate research
SODAR IS TOOL FOR
Meteorologists
Atmospheric physicist
Health and environmental
protection
Power industry

26. REFERENCES http://lcrs.geographie.uni-marburg.de/ index.php?id=32
eflum.epfl.ch/research/ sodar-rass.en.php
index.php?id=32
remote/image_gallery.html

27. THANKS FOR ATTANTION
THANKS FOR ATTANTION