SODAR

1
SODAR

• SEDA SAHIN
• 110020230

2
BRIEFLY

• 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.  Other names used for sodar systems
  include sounder, echosounder and acoustic radar. 
  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 (e.g., submarines) by
  means of sonic waves reflected back to the
  source.  Sodar systems are similar except the
  medium is air instead of water and reflection is
  due to the scattering of sound by atmospheric
  turbulence.

3
BRIEFLY

• Most sodar systems operate by issuing an acoustic
  pulse and then listen for the return signal for a
  short period of time.  Generally, both the
  intensity  and the Doppler (frequency) shift of
  the return signal are analyzed to determine the
  wind speed, wind direction and turbulent
  character of the atmosphere.  A profile of the
  atmosphere as a function of height can be
  obtained by analyzing the return signal at a
  series of times following the transmission of
  each pulse.  The return signal recorded at any
  particular delay time provides atmospheric data
  for a height that can be calculated based on the
  speed of sound.  Sodar systems typically have
  maximum ranges varying from a few hundred meters
  up to several hundred meters or higher.  Maximum
  range is typically achieved at locations that
  have low ambient noise and moderate to high
  relative humidity.  At desert locations, sodar
  systems tend to have reduced altitude performance
  because sound attenuates more rapidly in dry air.

4
BRIEFLY

• Sodar systems can be used in any application
  where the winds aloft or the atmospheric
  stability must be determined, particularly in
  cases where time and cost are of the essence. 
  Some typical applications include atmospheric
  dispersion studies, wind energy siting, wind
  shear warning, emergency response wind
  monitoring, sound transmission analyses,
  microwave communications assessments and aircraft
  vortex monitoring.

5
BRIEFLY

• Some of the advantages of sodar systems are
  obvious compared to erecting tall towers with
  in-situ wind and temperature sensors.  First, a
  sodar system can generally be installed in a
  small fraction of the time it takes to erect a
  tall tower.  And when all of the costs are
  considered, a sodar system will generally offer a
  very attractive alternative.  Also, the practical
  height limit for meteorological towers is about
  150 m (500 ft).  Most sodar systems will obtain
  reliable data well beyond this altitude.  Using a
  sodar system instead of a tall tower will also
  avoid many liability issues.  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.  Another consideration is
  that 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.  This is
  because to obtain a wind measurement sodar
  systems sample over a volume and at multiple
  points in space and time, whereas an in-situ wind
  sensor on a tall tower samples instantaneously at
  a point in space and time.

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SOME SODAR HISTORY

• Sound propagation in the atmosphere has been
  studied for at least 200 years, but it has only
  been in the last 50 years that acoustic
  scattering has been used as a means to study the
  structure of the lower atmosphere. 
• 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 and to monitor the
  structure of temperature inversions.
• During the 1970's, the engineering design of
  acoustic sounders was seriously pursued by
  several groups of researchers in the United
  States.  One of the earliest commercial systems
  was the Model 300 developed by AeroVironment,
  Inc. in California.
• In 1974, NOAA developed the Mark VII which was a
  portable system that was called an acoustic
  echosounder.  Both the Model 300 and the Mark VII
  were designed around a single 1.2-meter (4-foot)
  diameter parabolic dish, and a facsimile recorder
  was used to provide an analog record of
  backscatter data.
• During the early 1980's, Radian Corporation used
  the SES Echosonde as the basis for developing a
  microcomputer-based three-axis Doppler sodar
  system.
• Phased-array sodar systems were developed in the
  United States during the late 1980's and early
  1990's by Xonics, Radian Corporation and
  AeroVironment, among others. 

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SODAR THEORY OF OPERATION
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SODAR THEORY OF OPERATION

• 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.
• 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.

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SODAR THEORY OF OPERATION

• In a bistatic sodar system, the transmitting and
  receiving antennas are at different locations,
  and hence scattering angles other than 180
  degrees are relevant.  At a scattering angle
  other than 180 degrees, both thermal and
  mechanical turbulence come into play.  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, 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.

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SODAR THEORY OF OPERATION

• 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
  radial velocity of the atmosphere at varying
  distances from the transmission antenna can be
  determined. Additional information can be
  obtained by transmitting consecutive pulses in
  the vertical direction and in two or more
  orthogonal directions tilted slightly from the
  vertical. Geometric calculations can then be
  used to obtain vertical profiles of the
  horizontal wind direction and both horizontal and
  vertical wind speeds.

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SODAR THEORY OF OPERATION

• 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 with sodar
  systems is ground clutter.  Interference from
  ground clutter 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.

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SOME APPLICATIONS

• Example of SODAR wind profile

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SOME APPLICATIONS

• Example of SODAR derived vertical velocities

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BACKSCATTER SIGNAL

• The sharp increase of the detected signal at 1954
  UTC is caused by strong acoustical noise
  generated by the gust front arriving at the SODAR
  site. Between 2010 UTC and 2240 UTC noise was
  added from the precipitation. Acoustical sounding
  is strongly disturbed by this noise. Therefor,
  also wind detection is unpossible. If the noise
  is removed from the data, the remaining signal
  actually contains no useful backscatter
  information.

15
INVERSION STUDIES

• Because routine measurement of the structure and
  the dynamics of temperature inversions are not
  available, SODAR (SOnic Detection And Ranging) 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). Procedures
  have been developed to determine inversion
  structure from acoustic sounding in combination
  with vertical profiles of automatic
  meteorological observations.

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AIR POLLUTION

• The health and environmental administration in
  the community of Stockholm has been using SODAR
  for more than 20 years as a tool for giving
  warnings to the public.
• The pictures show a typical situation with an
  increased air pollution concentration and causing
  a warning to the public. The SODAR is a key
  verification tool for the warning system. The
  SODAR data is obtained from a system running in
  the center of Stockholm City.
• The SODAR diagram is showing an increased
  stability (red color) in connection with a ground
  based temperature inversion lifting and
  disappearing during the day. We can also see a
  very good aggrement with the prediction of the
  expected air pollution concentration (red color,
  increased concentrations) made by the health
  administration.

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SODAR IN ANTARCTICA

• it's a multimode Sodar made of 3 antennas in
  different directions allowing for the computation
  of the 3-dimensional wind vector at various
  heights.
• Left The 3 Sodar antennas, next to each other,
  with Concordia in the background.
• Right The Sodar acquisition system inside the
  container the electronics and amplifier (blue
  and black boxes), the PC (on the ground) and the
  monitor. On the floor the blue boxes are the
  preamplifiers connected directly to the antennas.

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SODAR IN ANTARCTICA
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SODAR WIND ENERGY

• Knowledge of the boundary layer at the heights of
  todays large wind turbines can significantly
  impact turbine selection, predictions of energy
  production, wind plant maintenance, and proper
  site selection. In addition to providing
  high-resolution wind speed and direction data to
  significant heights, SODAR can also
• Quantify the individual horizontal and vertical
  wind flow components
• Measure turbulence levels
• Identify flow discontinuities that fixed towers
  miss
• Measure wind speed in a volume of air, not just
  at one point
• Confirm or revise the wind shear aloft defined by
  on-site fixed towers
• Reduce the number of conventional met towers
  needed to qualify a site.

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AVIATION APPLICATIONS

• 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.

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SODAR POWER PLANTS

• 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.

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SOME MODELS
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SOME SYSTEMS

• Phased Array SODAR DSDPA.90-xx
• Accidental release of pollutant
• Air pollution studies and forecasting
• Routine operation in monitoring networks
• Observation of inversion layers
• Airport shear wind warning
• Observation of frontal passages
• Atmospheric research

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Phased Array SODAR DSDPA.90-xx

• Technical Specifications of DSDPA.90-24
• Frequency1000 ... 3000 Hz, 2200 ... 2500 Hz
  recommended Wind speed 0 - 50 m/sWind direction
  0 - 360 degree Vertical wind speed gt - 10 m/s
  Operating temperature - 30 C to 55 C (all
  without pos. 3) 5 C to 45 C (indoor
  components, pos. 3) Operating humidity 10 - 100
  (outdoor), 20 80 (indoor) Integration time
  10 seconds or more or instantaneous according to
  the signal repetition, increment 1 sec for wind
  speed and wind direction, standard deviations of
  u-, v-, w-component 10 minutes or more are
  recommended Number of gates adjustable, 1- 50
  Minimum measuring height adjustable, 15 m,
  increment 1mHeight resolution gt 5 m, lt 500 m,
  adjustable in 1 m increments values of more
  than 100 m are not very informative, typical
  values are 10 - 30 m Typical measuring height
  depends on atmospheric and site conditions, we
  define 70 availability (for wind speed and
  direction,30 m, 900 s, 50 dB stationary noise
  level, cluster algorithm for data evaluation)
  350 m Maximum measuring height gt 1000 m
  Transmission frequency adjustable within 1700 -
  3000 Hz(2200 2500 Hz recommended) Signal
  power max. 800 W (elect.), automatically
  adjusted Antenna gain typ. 20 dB, dependant on
  frequencySensitivity of receiver 10-6 N/m2,
  dependant on frequency Beam width typ. 7 -12 ,
  dependant on frequency Qualifying according to
  german DIN 3786 (11), KTA1508 (nuclear power
  regularity) Power consumption depends on pulse
  repitition rate 250 W
• Complete sets of operation parameter can be
  stored under up to 40 different user generated
  parameter set name. A complete parameter set is
  activated by entering such parameter set name.
  Various parameter set names can be entered also
  into a parameter name list of max. 40 names which
  will sequently activate the corresponding
  parameters sets. This list will be repeated after
  the last entry has been processed.

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Phased Array SODAR DSDPA.90-xx

• SODAR PC (Midi tower type), Indoor
• Minimum configuration
• 600 MHz Celeron
• 10 GB hard disc, 64 MB RAM,
• 1.44 MB floppy disc drive, CD-ROM 24 x, zip-drive
  100 MB
• 17-colour screen (1280 x 1024)
• keyboard, compatible type WINDOWS 98, 104 keys,
  mouse and mousepad
• ink jet colour printer, 600 x 600 dpi, A4, 6
  pages/minute (b/w mode)
• Ethernet port
• MODEM unit for remote system access, Hayes AT
  compatible, supports V.90
• WINDOWS 2000/NT english installed
• Y2K compliance for hard and software
• implementation of cluster algorithms for
  derivation of wind speed and direction

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Phased Array SODAR DSDPA.90-xx

• SODAR PC Control and Data Visualization Software
• Operating system WINDOWS 2000
• Control subsystem "sodar control" run time
  license (3 x)
• offers access to and control of all system
  parameters, measuring variables, port selections
  
• offers remote system access for system control
  and system testing (e.g. via cellular Modem)
• stores data and handles data files automatically
  in a tree structured file system
• data sets are ASCII coded files, optional the
  structures can be defined according to the needs
  of the customer
• To set up a remote control with a modem the
  customer needs a second pc-station where the
  WINDOWS NT software "sodar control" is installed.
  If enabled you will connect via modem to the
  SODAR pc, independent of the type of the MODEM
  (line or GSM).
• Graphic subsystem METEK grafik run time license
  (3 x)
• offers a variety of powerful data presentation
  tools
• profiles, time series, vector plot, contour plot
  (smooth or raw)
• time intervals (day, week, month, special) and
  height ranges selectable or automatically
  scaled)
• time increments selectable
• off-line presentation (also batch mode for long
  term data evaluation) or on-line display function
  with automatic real time refresh
• 1 or 4 or 9 plots in one frame
• presentation of all measuring variables as time
  series, profiles, vector plots
• selectable plausibility check validity/data
  acceptance
• selectable smoothing weighting function for all
  data with export feature
• SODARgramm display with selectable resolution

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MODOS Mobile Doppler SODAR

• Preferred Applications
• Remote sensing of wind and turbulence in the
  atmospheric boundary layer
• Easy transportation, quick set up and prompt
  measurements
• Reliable unattended operation even under severe
  conditions
• Very low minimal measuring height, very fine
  height resolution
• Windows NT graphic package, LAN integration for
  raw spectra output
• Accidental release of pollutant
• Air pollution studies and forecasting
• Routine operation in monitoring networks
• Observation of inversion layers
• Airport shear wind warning
• Observation of frontal passages
• Atmospheric research

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MODOS Mobile Doppler SODAR

• Features
• Effective antenna shields allow measurements even
  under noisy conditions
• Individual alignment in zenith/azimuth for
  optimized system performance at difficult sites
• High system availability due to strict redudancy
  concept for critical components
• All operational parameters adjustable
• Very low minimal measuring height
• Very fine height resolution
• Effective antenna shielding
• Automatic system function monitoring
• Automatic restart after power failure
• Automatic antenna deicing (option)
• Automatic control of signal power
• Transmit frequency adjustable (1500 ... 3000 Hz)
• Reliable data validation algorithm

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MODOS Mobile Doppler SODAR

• Measuring Ranges
• Mobile Doppler SODAR MODOS
• Wind velocity 0 ... 35 m/s
• Direction 0 ... 360
• Standard deviation of radial wind components 0
  ... 3 m/s
• Finest height resolution gt10m/s
• Minimum measuring height Standard 30m Optionally
  10m Maximum measuring height (10 min averages)¹
  90 200m 80 300m 70 400m 60 500m
• Measuring Accuracy (10 min averages)
• Wind velocity for 0.0 ... 5.0 m/s 0.5 m/s for
  5.0 ... 35 m/s 10
• Wind direction for 0.8 ... 35 m/s 5
• Radial wind components 0.1 m/s
• Standard deviation of radial wind components
  0.15 m/s

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MODOS Mobile Doppler SODAR

• System Specifications
• Antenna 3x7 exponential horns Aperture 1 m2
• Transmit Power 1 kW (electric)
• Wind velocity
• Vertical
• North/South, typical 20 tilt West/East, typical
  20 tilt

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MODOS Mobile Doppler SODAR

• Available options include
• System operation with comfortable graphical user
  interface on a PC under Windows NT.
• Processing of quality flagged data on a PC under
  Windows NT for comfortable graphical
  presentation
• Statistics
• Time series
• Time height cross section using
• profile series,
• contours or
• vector plots
• Expansion with RASS for simultaneous temperature
  profiling.
• Ingestion and display of simultaneously measured
  data from USA-1 sonic anemometers and additional
  standard surface sensors.
• Integration to upper level networks and
  implementation of further features on request.

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CONCLUSION SODAR

• TOOL FOR
• Meteorologists
• Atmospheric physicist
• Health and environmental protection authorities
• Power plant industry

• APPLICATIONS
• 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

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SOURCES

• http//www.awstruewind.com/inner/services/meteorol
  ogy/sodar.htm
• http//www.sodar.com
• http//www.metek.de/
• http//www.slb.mf.stockholm.se/e/weather_now.htm
• http//www.gdargaud.net/Antarctica/WinterDC3.html
  
• http//www.pa.op.dlr.de/cleocd/sodar/q.htm
• eflum.epfl.ch/research/ sodar-rass.en.php
• http//www.aqs.se/Pages/airpollution.htm
• http//lcrs.geographie.uni-marburg.de/
  index.php?id32
• http//apollo.lsc.vsc.edu/.../ remote/image_galler
  y.html