1、Designation: D 7145 05Standard Guide forMeasurement of Atmospheric Wind and Turbulence Profilesby Acoustic Means1This standard is issued under the fixed designation D 7145; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year o
2、f last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 This guide describes the application of acoustic remotesensing for measuring atmospheric wind and turbulence pro-fi
3、les. 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 installa-tion, and recommended procedures for acquiring valid andrelev
4、ant 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 configurations.This guide is not directly applicable to radio-acousti
5、c soundingsystems (RASS), or tomographic methods.2. Referenced Documents2.1 ASTM Standards:2D 1356 Terminology Relating to Sampling and Analysis ofAtmospheres3. Terminology3.1 DefinitionsRefer to Terminology D 1356 for generalterms and their definitions.3.2 Definitions of Terms Specific to This Stan
6、dard: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 a radial direction from itspoint of origin.3.2.2 acoustic power,
7、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 acoustic scatter, nthe dispersal by reflection, refrac-tion, or d
8、iffraction 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 acoustic attenuation (f, dB/100m ), nloss of acous-tic power (aco
9、ustic 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 angular width (halfangle at 3dB) of an acoustic beam from its centerlin
10、emaximum 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.3.2.10 clutter, nundesirable returns, particularly fromsidelobes, that
11、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 directivity, nconcentration of transmitted power(dB) within a n
12、arrow 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 effective antenna aperture (Ae,m2), nproduct ofantenna area with antenna
13、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 pulse period (tmax, s), ntime between the startof successive tran
14、smitted pulses or pulse sequences.3.2.16.1 DiscussionThe inter pulse period (IPP) is theinverse of the pulse repetition frequency (PRF) in Hertz (Hz).1This guide is under the jurisdiction of ASTM Committee D22 on Air Qualityand is the direct responsibility of Subcommittee D22.11 on Meteorology.Curre
15、nt edition approved March 1, 2005. Published May 2005.2For 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 the standards Document Summary page onthe ASTM website.1Copyri
16、ght ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.3.2.17 monostatic, 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 densi
17、ty at a given range.3.2.19 pulse, nfinite burst of transmitted energy.3.2.20 pulse length (t,s), nduration of a single pulse.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,
18、nsampling ambiguity that ariseswhen returns are received from a transmission that was madeprior to the latest transmitted pulse sequence, usually from ascattering surface located beyond the maximum unambiguousrange.3.2.24 range gate, nconical section of the atmospherecontaining the scattering volume
19、 from which acoustic returnscan be resolved.3.2.25 range resolution (Dr, m), nlength of a segment ofthe scattering volume along 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), nelectri
20、cal power receivedat an antenna during listening mode; the product of receivedacoustic power with receiver conversion efficiency 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 propaga
21、tes.3.2.27.1 DiscussionThis is commonly calculated from the3 dB beamwidth.3.2.28 sidelobes, nacoustic energy transmitted in 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 t
22、he calculated re-ceived signal power to the calculated noise power, frequentlyabbreviated as SNR.3.2.30 sound detection and ranging (sodar), adjremotesensing technique that generates acoustic pulses that propagatethrough the atmosphere, and subsequently samples the scat-tered atmospheric returns.nin
23、strument that performs these functions.3.2.31 temperature structure parameter (CT2, K),nstructure constant for measurement 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 t
24、ransmit frequency (f, Hz), nselected frequency orfrequencies at which an acoustic transmitters output isachieved.3.2.33 transmitted power (Pt, W), nelectrical power inwatts measured at the antenna input; acoustic power radiatedby an antenna is the product of transmitted electrical powerwith the conv
25、ersion efficiency from electrical to acousticpower.3.3 Symbols: = viscous and molecular sound absorption coefficient,Nepers 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= transmi
26、tter electromechanical efficiency,f = central acoustic frequency transmitted by the sodar,Hz,fD= Doppler frequency, Hz,G = 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 betwe
27、en transmission of an acoustic pulse andreception of returning echoes, s,TK= temperature in Kelvins, K,tmax= IPP, the maximum 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= e
28、xcess attenuation factor,l = acoustic wavelength, m,s = acoustic scattering crossection per unit volume,m1, andt = pulse length, 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 sod
29、ar equipment, site selection, andequipment installation procedures are presented.4.3 Data acquisition and quality assurance procedures aredescribed.5. Significance and Use5.1 Sodars have found wide applications for the remotemeasurement of wind and turbulence profiles in the atmo-sphere, particularl
30、y in the gap between meteorological towersand the lower range gates of wind profiling radars. The sodarsfar field acoustic 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
31、 strong interaction between sound wavesand the atmospheres thermal and velocity micro-structure thatproduce acoustic returns 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 s
32、urface, provides the basis for wind measurement.Advantages offered by sodar wind sounding technology in-clude reasonably low procurement, operating, and maintenance3The boldface numbers in parentheses refer to the list of references at the end ofthis standard.D7145052costs, no emissions of eye-damag
33、ing light beams or electro-magnetic radiation requiring frequency clearances, and adjust-able frequencies and pulse 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
34、and turbulence profileinformation at height ranges from a few tens of meters to overa kilometre for typical averaging 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 design
35、composed of a planar array of acoustic transmitters that formthe emitted beam and steer it towards the desired direction.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 sign
36、alsscattered from small scale velocity fluctuations that are notavailable in monostatic configurations. Except for 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 phas
37、ed array monostaticsodar emits acoustic pulses (adiabatic compression waves) at atransmit frequency or frequencies. 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
38、, are used to shapethe beam and steer it in the desired direction.As it travels alonga radial direction through the 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 gradien
39、ts encountered by the propagat-ing beam deform and scatter the beam. Wind velocitycomponents along the axis of propagation also Doppler- shiftthe acoustic frequency of backscattered signals. A schematicdrawing of acoustic wavefront generation and backscatter froma reflecting surface is presented in
40、Fig. 1.After its transmissionof an acoustic pulse train, the sodar switches to listening modefor backscattered acoustic signals. Returning signals are char-acterized by their intensity (amplitude), spectral width,Doppler-shifted frequency, and lapsed time (t) from initialpulse transmission. Returns
41、from lower heights are receivedsooner than returns from greater heights. The relationshipbetween lapsed time (t), 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 profil
42、ing sodars thattransmit a minimum of three radial beams resolve horizontaland vertical wind components. Assuming homogeneity 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 present
43、ed with avertical profile of wind, turbulence, and signal strength infor-mation. Height ranging, range resolution, 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 prod
44、uct of sodar performance andatmospheric attenuation factors. Sodar performance factorsinclude effective transmitted power (Pt) at its transmittedfrequency(ies), effective antenna aperture (Ae), transmitter andreceiver efficiency factors (eTand eR), and pulse length (t).Atmospheric scattering factors
45、 include the acoustic scatteringcrossection (s) and attenuation factors fmand fx. Attenuationfactor fmrepresents “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
46、acoustic beam with larger scaleatmospheric features. The sodar performance and atmosphericfactors are combined in 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 characteris
47、ticsinclude the sodar transmitted acoustic power, and the efficiencywith which power is transmitted and received. 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 at
48、range (r) from the scattering volume. Range resolution (Dr=ct/2) is the length (m), along the radial axis of signalpropagation, 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.Scat
49、tering 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 return.6.5 Pulse Length and Inter Pulse Period (IPP). Pulse lengthand IPP (tmax) define height and velocity limits for valid sodarsignals. Pulse length and system settling time (time of recover
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