1、Designation: D7145 05 (Reapproved 2010)1Standard Guide forMeasurement of Atmospheric Wind and Turbulence Profilesby Acoustic Means1This standard is issued under the fixed designation D7145; the number immediately following the designation indicates the year oforiginal adoption or, in the case of rev
2、ision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1NOTEEditorially corrected Equation 6 in April 2010.1. Scope1.1 This guide describes the application of acousti
3、c remotesensing for measuring atmospheric wind and turbulence pro-files. It includes a summary of the fundamentals of atmosphericsound detection and ranging (sodar), a description of themethodology and equipment used for sodar applications, fac-tors to consider during site selection and equipment in
4、stalla-tion, and recommended procedures for acquiring valid andrelevant data.1.2 This guide applies principally to pulsed monostaticsodar techniques as applied to wind and turbulence measure-ment in the open atmosphere, although many of the definitionsand principles are also applicable to bistatic c
5、onfigurations.This guide is not directly applicable to radio-acoustic soundingsystems (RASS), or tomographic methods.2. Referenced Documents2.1 ASTM Standards:2D1356 Terminology Relating to Sampling and Analysis ofAtmospheres3. Terminology3.1 DefinitionsRefer to Terminology D1356 for generalterms an
6、d their definitions.3.2 Definitions of Terms Specific to This Standard:Note: The definitions below are presented in simplified, com-mon, qualitative terms. Refer to noted references for moredetailed information.3.2.1 acoustic beam, nfocused or directed acoustic pulse(compression wave) propagating in
7、 a radial direction from itspoint of origin.3.2.2 acoustic power, nrelative amplitude or intensity(dB) of an atmospheric compression wave.3.2.3 acoustic refractive index, nratio of reference (at astandard temperature of 293.15 K and 1013.25 hPa pressure)speed of sound value to its actual value.3.2.4
8、 acoustic scatter, nthe dispersal by reflection, refrac-tion, or diffraction of acoustic energy in the atmosphere.3.2.5 acoustic scattering Cross-section Per Unit Volume (s,m1), nfraction of incident power at the transmit frequencythat is backscattered per unit distance into a unit solid angle.3.2.6
9、 acoustic attenuation (f, dB/100m ), nloss of acous-tic power (acoustic wave amplitude) by beam spreading,scattering, and absorption as the transmitted wavefront propa-gates through the atmosphere.3.2.7 backscatter, npower returned towards a receivingantenna.3.2.8 beamwidth (degrees), none way angul
10、ar width (halfangle at 3dB) of an acoustic beam from its centerlinemaximum to the point at the beam periphery where the powerlevel is half (3 decibels below) centerline beam power.3.2.9 bistatic, adjsodar configuration that uses spatiallyseparated antennas for signal transmission and reception.3.2.1
11、0 clutter, nundesirable returns, particularly fromsidelobes, that increase background noise and obscure desiredsignals.3.2.11 decibel (dB), nlogarithmic (base 10) ratio of powerto a reference power, usually one-tenth bell; for power P1 andreference power P2, the ratio is given by 10log10(P1/P2).3.2.
12、12 directivity, nconcentration of transmitted power(dB) within a narrow beam by an antenna, measured as a ratioof power in the main beam to power radiated in all directions.3.2.13 Doppler frequency (fD, Hz), nshifted frequencymeasured at the receiver from the scattered acoustic signal.3.2.14 effecti
13、ve antenna aperture (Ae,m2), nproduct ofantenna area with antenna efficiency.3.2.15 gain (G), nincrease in power (dB) per unit areaarising from the product of antenna directivity with efficiency.nnon-dimensional effective aperture amplification factorarising from an antennas directivity.3.2.16 inter
14、 pulse period (tmax, s), ntime between the startof successive transmitted pulses or pulse sequences.1This guide is under the jurisdiction of ASTM Committee D22 on Air Qualityand is the direct responsibility of Subcommittee D22.11 on Meteorology.Current edition approved April 1, 2010. Published July
15、2010. Originallyapproved in 2005. Last previous edition approved in 2005 as D7145 - 05. DOI:10.1520/D7145-05R10E01.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to t
16、he standards Document Summary page onthe ASTM website.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.3.2.16.1 DiscussionThe inter pulse period (IPP) is theinverse of the pulse repetition frequency (PRF) in Hertz (Hz).3.2.17 monostat
17、ic, adjsodar configuration that uses thesame antenna for transmission and reception.3.2.18 Neper, nnatural logarithm of the ratio of reflectedto incident sound energy flux density at a given range.3.2.19 pulse, nfinite burst of transmitted energy.3.2.20 pulse length (t,s), nduration of a single puls
18、e.3.2.21 pulse sequence, ntrain of pulses, often at differentfrequencies.3.2.22 range (r, m), ndistance from the antenna surface tothe scattering surface.3.2.23 range aliasing, nsampling ambiguity that ariseswhen returns are received from a transmission that was madeprior to the latest transmitted p
19、ulse sequence, usually from ascattering surface located beyond the maximum unambiguousrange.3.2.24 range gate, nconical section of the atmospherecontaining the scattering volume from which acoustic returnscan be resolved.3.2.25 range resolution (Dr, m), nlength of a segment ofthe scattering volume a
20、long the axis of beam propagation.3.2.25.1 DiscussionRange resolution equals half theproduct of speed of sound and pulse length (Dr=ct/2).3.2.26 received power (Pr, W), nelectrical power receivedat an antenna during listening mode; the product of receivedacoustic power with receiver conversion effic
21、iency from acous-tic to electrical power.3.2.27 scattering volume (m3), nvolume of a conicalsection in the atmosphere centered on the radial along whichthe acoustic beam propagates.3.2.27.1 DiscussionThis is commonly calculated from the3 dB beamwidth.3.2.28 sidelobes, nacoustic energy transmitted in
22、 a direc-tion other than the main beam (or lobe).3.2.28.1 DiscussionSidelobes vary inversely with antennasize and transmitted frequency.3.2.29 signal-to-noise-ratio, nratio of the calculated re-ceived signal power to the calculated noise power, frequentlyabbreviated as SNR.3.2.30 sound detection and
23、 ranging (sodar), adjremotesensing technique that generates acoustic pulses that propagatethrough the atmosphere, and subsequently samples the scat-tered atmospheric returns.ninstrument that performs these functions.3.2.31 temperature structure parameter (CT2, K),nstructure constant for measurement
24、of fast-response tem-perature differences over small spatial separations that ac-counts for the effects of molecular diffusion and turbulentenergy dissipation into heat.3.2.32 transmit frequency (f, Hz), nselected frequency orfrequencies at which an acoustic transmitters output isachieved.3.2.33 tra
25、nsmitted power (Pt, W), nelectrical power inwatts measured at the antenna input; acoustic power radiatedby an antenna is the product of transmitted electrical powerwith the conversion efficiency from electrical to acousticpower.3.3 Symbols: = viscous and molecular sound absorption coefficient,Nepers
26、 per wavelength, m1,Ae= effective antenna aperture, m2,c = speed of sound, ms1,CT2= temperature structure parameter, K m2/3,eR= receiver electromechanical efficiency,eT= transmitter electromechanical efficiency,f = central acoustic frequency transmitted by the sodar,Hz,fD= Doppler frequency, Hz,G =
27、antenna gain,Pr= received electrical power, W,Pt= transmitted electrical power, W,r = range from transmitter to a range gate, m,rmax= maximum unambiguous range, m,t = time between transmission of an acoustic pulse andreception of returning echoes, s,TK= temperature in Kelvins, K,tmax= IPP, the maxim
28、um listening time between transmit-ted pulses or pulse sequences, s,Vt= target velocity, ms1,Dr = range resolution, m,fm= combined viscous and molecular attenuation factor,fx= excess attenuation factor,l = acoustic wavelength, m,s = acoustic scattering crossection per unit volume,m1, andt = pulse le
29、ngth, s.4. Summary of Guide4.1 The principles of atmospheric wind and turbulenceprofiling using the sound direction and ranging technique aredescribed.4.2 Considerations for sodar equipment, site selection, andequipment installation procedures are presented.4.3 Data acquisition and quality assurance
30、 procedures aredescribed.5. Significance and Use5.1 Sodars have found wide applications for the remotemeasurement of wind and turbulence profiles in the atmo-sphere, particularly in the gap between meteorological towersand the lower range gates of wind profiling radars. The sodarsfar field acoustic
31、power is also used for refractive indexcalculations and to estimate atmospheric stability, heat flux,and mixed layer depth (1-5)3. Sodars are useful for thesepurposes because of strong interaction between sound wavesand the atmospheres thermal and velocity micro-structure thatproduce acoustic return
32、s with substantial signal-to-noise ratios(SNR). The returned echoes are Doppler-shifted in frequency.This frequency shift, proportional to the radial velocity of thescattering surface, provides the basis for wind measurement.Advantages offered by sodar wind sounding technology in-clude reasonably lo
33、w procurement, operating, and maintenance3The boldface numbers in parentheses refer to the list of references at the end ofthis standard.D7145 05 (2010)12costs, no emissions of eye-damaging light beams or electro-magnetic radiation requiring frequency clearances, and adjust-able frequencies and puls
34、e lengths that can be used to optimizedata quality at desired ranges and range resolutions. Whenproperly sited and used with adequate sampling methods,sodars can provide continuous wind and turbulence profileinformation at height ranges from a few tens of meters to overa kilometre for typical averag
35、ing periods of 1 to 60 minutes.6. Monostatic Sound Direction and Ranging6.1 Sodar Design Types. Most commercially available so-dars operate using a monostatic phased array antenna designcomposed of a planar array of acoustic transmitters that formthe emitted beam and steer it towards the desired dir
36、ection.Other designs, to include non-phased antennas for each beamand bi-static configurations, are also available. An advantageoffered by bi-static sodars is that they also utilize signalsscattered from small scale velocity fluctuations that are notavailable in monostatic configurations. Except for
37、 beam form-ing, steering, and the simplified monostatic sodar equation, theinformation provided below is generally applicable to thosedesigns as well.6.2 Description of Operation. A phased array monostaticsodar emits acoustic pulses (adiabatic compression waves) at atransmit frequency or frequencies
38、. Pulses from each antennaare formed into a conical beam or wavefront with its vertex atthe antenna. Individual transducer pulse timing or phaseshifting methods, indicated by F in Fig. 1, are used to shapethe beam and steer it in the desired direction.As it travels alonga radial direction through th
39、e atmosphere at speed of sound (c),this acoustic wave experiences attenuation by spreading, ab-sorption, and scattering as described below. Temperature inho-mogeneities and sharp gradients encountered by the propagat-ing beam deform and scatter the beam. Wind velocitycomponents along the axis of pro
40、pagation also Doppler- shiftthe acoustic frequency of backscattered signals. A schematicdrawing of acoustic wavefront generation and backscatter froma reflecting surface is presented in Fig. 1.After its transmissionof an acoustic pulse train, the sodar switches to listening modefor backscattered aco
41、ustic signals. Returning signals are char-acterized by their intensity (amplitude), spectral width,Doppler-shifted frequency, and lapsed time (t) from initialpulse transmission. Returns from lower heights are receivedsooner than returns from greater heights. The relationshipbetween lapsed time (t),
42、speed of sound (c), and radial range (r)to the scattering surface is given by:r 5 ct/2 (1)where the factor of 2 accounts for travel along outwardpropagating and return paths. Wind profiling sodars thattransmit a minimum of three radial beams resolve horizontaland vertical wind components. Assuming h
43、omogeneity in thewind field above the sodar, trigonometry is used to resolvedistance along each radial, which is then converted to heightabove the sodar antenna. The user is then presented with avertical profile of wind, turbulence, and signal strength infor-mation. Height ranging, range resolution,
44、 and signal quality arefunctions of sodar performance and its operating environment,as described below.6.3 The Sodar Equation. The power received (Pr)byasodars acoustic antenna is a product of sodar performance andatmospheric attenuation factors. Sodar performance factorsinclude effective transmitte
45、d power (Pt) at its transmittedfrequency(ies), effective antenna aperture (Ae), transmitter andreceiver efficiency factors (eTand eR), and pulse length (t).Atmospheric scattering factors include the acoustic scatteringcrossection (s) and attenuation factors fmand fx. Attenuationfactor fmrepresents “
46、classical” viscous losses plus the com-bination of molecular rotational and vibrational absorption.The second factor (fx) represents excess attenuation due tocomplex interactions of the acoustic beam with larger scaleatmospheric features. The sodar performance and atmosphericfactors are combined in
47、a simplified monostatic sodar equationfor received power:Pr5 $sodar performance%$atmospheric factors%5 $PtAe! eTeR! ct/2!%$sfmfx%. (2)6.4 Sodar Performance. Sodar performance characteristicsinclude the sodar transmitted acoustic power, and the efficiencywith which power is transmitted and received.
48、PtAeis thepower-aperture product. Ae= AG/r2is the solid angle sub-tended by an antenna of aperture (A, m2) multiplied by theeffective aperture factor (G, the antennas gain), as viewed atrange (r) from the scattering volume. Range resolution (Dr=ct/2) is the length (m), along the radial axis of signa
49、lpropagation, of the instantaneous scattering volume and de-fines the volume from which a backscattered signal is resolved.Note that range resolution determines range gate thickness.Scattering surfaces that produce useful acoustic returns oftenoccupy only a fraction of the scattering volume in the realatmosphere (see Fig. 1 and 6.6). The magnitude of the returnedsignals is directly proportional to the percentage of the scat-tering volume occupied by scattering surfaces and the intensityof the turbulence (CT2) producing the r
