SODAR

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Nov 14, 2013 (3 years and 8 months ago)

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SODAR

SEDA ŞAHİN

110020230

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.


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.

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.


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.

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.



SODAR THEORY OF
OPERATION



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.

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
C
T
2

function
,
which, in turn, is related to the thermal structure and stability
of the atmosphere. C
T
2

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.

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.

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.

SOME APPLICATIONS…


Example of SODAR wind profile…

SOME APPLICATIONS…


Example of SODAR derived vertical
velocities…

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.

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.

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.

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.

SODAR IN ANTARCTICA


SODAR & WIND
ENERGY


Knowledge of the boundary layer
at the heights of today’s 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.



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.


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.


SOME MODELS…

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






Technical Specifications of DSDPA.90
-
24


Frequency:1000 ... 3000 Hz,

2200 ... 2500 Hz recommended Wind speed: 0
-

50 m/sWind direction: 0
-

360
degree Vertical wind speed: > +
-

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: > 5 m, <
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 > 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.


Phased Array SODAR DSDPA.90
-
xx

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

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;


statistics (relative and absolute histogramms and wind roses in adjustable classes);


automatic or user selectable ordinate and abscissa scaling;


indication of numerical values depending on the pointer position;


zoom
-
function and smooth function for all data;


manual invalidation procedure;


WINDOWS supported global print routine;


various export formats fpr plots(Windows bitmap, Windows metafile, agfa SCODL, HPGL, LOTUS 1
-
2
-
3, PIC, GIF,
TIFF, GEM, Encapsulated Postscript, CGM)


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


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

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 >=10m/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

MODOS

Mobile Doppler SODAR


System Specifications


Antenna 3x7 exponential horns Aperture

1 m
2



Transmit Power

1 kW (electric)


Wind velocity


Vertical


North/South, typical 20
°

tilt West/East, typical 20
°

tilt


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.


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


SOURCES…


http://www.awstruewind.com/inner/services/meteorology/sodar.ht
m



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?id=32



http://
apollo.lsc.vsc.edu/.../ remote/image_gallery.html