1、Designation: D7145 05 (Reapproved 2015)Standard 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 revi
2、sion, 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.1. Scope1.1 This guide describes the application of acoustic remotesensing for measuring atmospheric wind and tu
3、rbulence 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 equipmentinstallation, and recommended procedures for acquiring v
4、alidand relevant 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
5、radio-acoustic soundingsystems (RASS), or tomographic methods.1.3 The values stated in SI units are to be regarded asstandard. No other units of measurement are included in thisguide.2. Referenced Documents2.1 ASTM Standards:2D1356 Terminology Relating to Sampling and Analysis ofAtmospheres3. Termin
6、ology3.1 DefinitionsRefer to Terminology D1356 for generalterms and their definitions.3.2 Definitions of Terms Specific to This Standard:Note: The definitions below are presented in simplified,common, qualitative terms. Refer to noted references for moredetailed information.3.2.1 acoustic beam, nfoc
7、used or directed acoustic pulse(compression wave) propagating in 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 101
8、3.25 hPa pressure)speed of sound value to its actual value.3.2.4 acoustic scatter, nthe dispersal by reflection,refraction, or diffraction of acoustic energy in the atmosphere.3.2.5 acoustic scattering Cross-section Per Unit Volume (,m1), nfraction of incident power at the transmit frequencythat is
9、backscattered per unit distance into a unit solid angle.3.2.6 acoustic attenuation (, 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
10、a receivingantenna.3.2.8 beamwidth (degrees), none way angular 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 spatiallyse
11、parated antennas for signal transmission and reception.3.2.10 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 andr
12、eference power P2, the ratio is given by 10log10(P1/P2).3.2.12 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 th
13、e receiver from the scattered acoustic signal.3.2.14 effective antenna aperture (Ae,m2), nproduct ofantenna area with antenna efficiency.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 ap
14、proved April 1, 2015. Published April 2015. Originallyapproved in 2005. Last previous edition approved in 2010 as D7145 05 (2010)1.DOI: 10.1520/D7145-05R15.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of AST
15、MStandards volume information, refer to the standards Document Summary page onthe ASTM website.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States13.2.15 gain (G), nincrease in power (dB) per unit areaarising from the product of antenna d
16、irectivity 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 transmitted pulses or pulse sequences.3.2.16.1 DiscussionThe inter pulse period (IPP) is theinverse of the
17、 pulse repetition frequency (PRF) in Hertz (Hz).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 density at a given range.3.2.19 pulse, nfinite burst of transmitt
18、ed energy.3.2.20 pulse length (, 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, nsampling ambiguity that ariseswhen returns are received fro
19、m 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 from which acoustic returnscan be resolved.3.2.25 range res
20、olution (Dr, m), nlength of a segment ofthe scattering volume along the axis of beam propagation.3.2.25.1 DiscussionRange resolution equals half the prod-uct of speed of sound and pulse length (r=c2).3.2.26 received power (Pr, W), nelectrical power receivedat an antenna during listening mode; the pr
21、oduct 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 propagates.3.2.27.1 DiscussionThis is commonly calculated from the3
22、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 the calculated re-ceived signal power to the calculated noise
23、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.ninstrument that performs these functions.3.2.31 temperature str
24、ucture 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 transmit frequency (f, Hz), nselected frequency orfrequencies
25、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 conversion efficiency from electrical to acousticpower.3.3 Symbol
26、s: = 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,R= receiver electromechanical efficiency,T= transmitter electromechanical efficiency,f = central acoustic frequenc
27、y 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 between transmission of an acoustic pulse andreception of returning
28、echoes, s,TK= temperature in Kelvins, K,tmax= IPP, the maximum listening time between transmittedpulses or pulse sequences, s,Vt= target velocity, ms1,r = range resolution, m,m= combined viscous and molecular attenuation factor,x= excess attenuation factor, = acoustic wavelength, m, = acoustic scatt
29、ering crossection per unit volume, m1,and = 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 sodar equipment, site selection, andequipment installation procedures are
30、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 theatmosphere, particularly in the gap between meteorologicaltowers and the lower range gates of wi
31、nd profiling radars. Thesodars far field acoustic power is also used for refractive indexcalculations and to estimate atmospheric stability, heat flux,D7145 05 (2015)2and mixed layer depth (1-5).3Sodars are useful for thesepurposes because of strong interaction between sound wavesand the atmospheres
32、 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 surface, provides the basis for wind measurement.Advantages
33、 offered by sodar wind sounding technology in-clude reasonably low procurement, operating, and maintenancecosts, no emissions of eye-damaging light beams or electro-magnetic radiation requiring frequency clearances, and adjust-able frequencies and pulse lengths that can be used to optimizedata quali
34、ty 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 averaging periods of 1 to 60 minutes.6. Monostatic Sou
35、nd 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 direction.Other designs, to include non-phased ante
36、nnas 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 beamforming, steering, and the simplified monos
37、tatic sodarequation, the information provided below is generally appli-cable to those designs as well.6.2 Description of Operation. A phased array monostaticsodar emits acoustic pulses (adiabatic compression waves) at atransmit frequency or frequencies. Pulses from each antennaare formed into a coni
38、cal beam or wavefront with its vertex atthe antenna. Individual transducer pulse timing or phaseshifting methods, indicated by in Fig. 1, are used to shape thebeam and steer it in the desired direction. As it travels along aradial direction through the atmosphere at speed of sound (c),this acoustic
39、wave experiences attenuation by spreading,absorption, and scattering as described below. Temperatureinhomogeneities and sharp gradients encountered by the propa-gating beam deform and scatter the beam. Wind velocitycomponents along the axis of propagation also Doppler- shiftthe acoustic frequency of
40、 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 acoustic signals. Returning signals are char-acterized b
41、y 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), speed of sound (c), and radial range (r)to the scatte
42、ring 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 homogeneity in thewind field above the sodar, trigonom
43、etry 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, and signal quality arefunctions of sodar performance
44、 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 transmitted power (Pt) at its transmittedfrequency(ies), effect
45、ive antenna aperture (Ae), transmitter andreceiver efficiency factors (Tand R), and pulse length ().Atmospheric scattering factors include the acoustic scatteringcrossection () and attenuation factors mand x. Attenuationfactor mrepresents “classical” viscous losses plus the com-bination of molecular
46、 rotational and vibrational absorption.The second factor (x) represents excess attenuation due tocomplex interactions of the acoustic beam with larger scaleatmospheric features. The sodar performance and atmosphericfactors are combined in a simplified monostatic sodar equationfor received power:Pr5
47、$sodar performance% $atmospheric factors%5 $PtAe!TR!c/2!% $mx% (2)6.4 Sodar Performance. Sodar performance characteristicsinclude the sodar transmitted acoustic power, and the efficiencywith which power is transmitted and received. PtAeis thepower-aperture product. Ae=AGr2is the solid angle sub-tend
48、ed 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 (r=c/2) is the length (m), along the radial axis of signalpropagation, of the instantaneous scattering volume and de-fines the vo
49、lume 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 return.6.5 Pulse Length and Inter Pulse P
