-LIDAR Light Detection And Ranging -RADAR Radio Detection .
Active methods with focus on time information-LIDARLight detection and ranging-RADARRadio detection and ranging-SODARSound detection and ranging
Basic componentsEmitted signal (pulsed)Radio waves, light, soundReflection (scattering) at different distancesScattering, FluorescenceDetection of signal strength as function of time
Scattering processes:Rayleigh-scattering (r λ)Raman-scattering (r λ, inelastic)Particle-scattering (e.g. Mie-scattering)Bragg-scattering (turbulence elements)
Rayleigh-scattering (r λ)The incident light induces a periodically varying dipoleat the place of the scattering particle.This dipole then itself becomes an emitter of radiation.The angular dependence of the scatteringprobability is referred to as ‚phase 9Reihe15330210824063007270red: p-polarisation, blue: s-polarisation
Influence of inelastic scatteringReflectivity‚Filling-in‘ ofspectral structures:Ring effect320340360380400Wavelength [nm]Reflectivity0.60.40.20.0300400500600Wavelength [nm]700800
If the extension of a particle is larger than the wavelength,interference effects become importantThe scattering particle can be thought of as build up of manyindividual emitting dipoles
Wavelength dependence of scattering processesMie extinction cross section (r: 500 nm, refractive index: 1.5)5Sigma(relative to geometric cross section)4.543.532.521.51Particle radius:500 nm0.500500100015002000Wavelength [nm]λ r σ λ-4(Rayleigh scattering)λ r σ λ-0(Clouds)for typical aerosol size distributions:σ λ-1 to λ-1.52500
Angular and polarisation dependence of scattering processesλ rλ : s-polarisation, blue: p-polarisationλ r
Comprehensive theory for spherical particles: Mie scatteringI 0λ (i1 i2 )I (Θ, R ) 2 28π R2Mie intensity parameters i1 and i2 (for perpendicular polarisedlight) are complex functions of the refractive index of thescatterer, the size parameter and scattering angleSize parameter:α 2πrλ
The (complex) refractive index describes the scattering andabsorption properties:n nr (1 – ai)Withnr : real refractive indexa: constant proportional to the absorption coefficient
In reality atmospheric aerosols contain a mixture of different radii.Thus the interference patterns smear-out due to the overlap of thescattering dependencies of many particles
Information on distance from time delay: t (2*d)/ccEM 3*108m/scsound 3*102m/s
Dependence of the speed of sound on temperature
Active methods with focus on time information-LIDARLight detection and ranging-RADARRadio detection and ranging-SODARSound detection and ranging
LIght Detection And Ranging: LIDARLASERSpurenstoff- oderAerosol- WolkeDetektorRPrinzip:Kurze Strahlungsimpulse einer starken, gebündelten Lichtquelle (üblicherweiseeines LASERs) werden in die Atmosphäre ausgestrahlt.Laufzeit ergibt Höhe (Echo), Intensität ergibt Streustärke (Konzentration) räumliche Verteilung von Aerosol bzw. Spurengasenin der Richtung des ausgesandten Strahles
Laufzeit der Signalet 2R/cR Abstand aus der die (betrachtete)Strahlungsintensität zurückgestreut wird.c Lichtgeschwindigkeitt Zeit (nach Aussenden des Laserpulses) zu der das Signal denDetektor erreichtFür Pulslänge dt ergibt sich die AuflösungdR dt c/2(1 µs Laserpuls gibt Höhenauflösung von150 m)Frequenz 10-100 Hzhttp://www.aad.gov.au/asset/information/photos 2/lidar.jpg
kleines Sendeteleskop,großes (0.3-1.5 m)Empfängerteleskophttp://aposf02.cityu.edu.hk/ mcg/remote sensing/Lidar/images/Lidar profiling.gif
Aerosolmessungen mit Mie-LIDAR
PSCs over Kiruna C.-F. Enell
DifferentLIDARsignalsof PSCsAmplitude Particle amountRatio of intensity atdiferent wavelengths Particle sizeRatio of intensity atdiferent polarisation Thermodynamicalstate
Aerosolschicht nach Ausbruch des Pinatubo 1991Scattering ratio Mie-scattering / Rayleigh scattering3. August 1991 – 28. Feb.1992The eruption of Pinatubo in thePhilippines, 12 June 1991, the largestvolcanic eruption since 1912.
Aerosolschicht nach Ausbruch des Pinatubo 1991
Lidar-Messung der Signal-Stärke entlang des Flugweges der Falcon am 19. April 2010; dieschwarze Linie zeigt den Flugweg und die Flughöhe an; rote-schwarze Farben zeigen hoheSignale von Wolken (niedrige Wolken in 2-3 km und hohe Cirrus-Wolken) und Aerosol in derbodennahen atmosphärischen Grenzschicht; Vulkan-Aerosolschichten sind im südlichenBereich von München bis Leipzig zu erkennen, wohingegen zwischen Leipzig und Hamburgkeine Schichten oberhalb von 3 km zu erkennen d-2342/6725 read-23886/
Lidar-Messung der Signal-Stärke entlang des Flugweges der Falcon am 19. April 2010; dieschwarze Linie zeigt den Flugweg und die Flughöhe an; rote-schwarze Farben zeigen hoheSignale von Wolken (niedrige Wolken in 2-3 km und hohe Cirrus-Wolken) und Aerosol in derbodennahen atmosphärischen Grenzschicht; Vulkan-Aerosolschichten sind im südlichenBereich von München bis Leipzig zu erkennen, wohingegen zwischen Leipzig und Hamburgkeine Schichten oberhalb von 3 km zu erkennen d-2342/6725 read-23886/
http://polly.tropos.de/martha/
LIDAR equation for β and αGeneral problem:-Two unknown quantities (β and α) should be determined from one observation-in particular, no absolute value of aerosol extinction can be derivedSimple solution: assume (constant) extinction-to-backscatter ratio(lidar ratio)-high values indicate low probability for back-scattering-8.4 sr for Rayleigh-scattering-30 sr is a common value for submicron aerosols
Extinction-to-backscatter ratio (lidar ratio) depends ona) Single scattering albedo (1- ratio of absorption and extinction)Single scattering albedo 0 only absorptionSingle scattering albedo 1 only scatteringSingle scattering albedofor different aerosol types(Takemura et al., J. of Climate, 2002)
Extinction-to-backscatter ratio (lidar ratio) depends ona) Single scattering albedo (1- ratio of absorption and extinction)Single scattering albedo 0 only absorptionSingle scattering albedo 0 only scatteringb) Phase functionExtinction-to-backscatter ratio-8.4 sr for Rayleigh-scattering-30 sr is a common value for submicron aerosols
Sofisticated (instrumental) solutionsa)Combined LIDAR and sun photometer observations:-From the LIDAR, the high-resolved (relative) extinction profile isderived-from the sun-photometer, the total optical depth of aerosol extinctionis determined From combination the high-resolved absolute extinction profile
Sofisticated (instrumental) solutionsb)RAMAN-LIDAR:-Observe light at wavelength slightly shifted to emitted wavelength the received light is RAMAN-scattered only by air molecules forwhich the total cross section and the LIDAR-ratio is known-the attenuation term contains both the extinction due to molecules(known) and aerosols From RAMAN-LIDAR the absolute optical depth of aerosol extinctioncan be determinedProblem: low signal to noise, operation often only during night
Sofisticated (instrumental) solutionsb)RAMAN-LIDAR:Wavelength at whichthe light is emitted inthe atmosphereLight observed at a‚Raman wavelength‘is only scattered frommolecules The effects ofscattering andabsorption areseparated
Raman-LIDAR für N2SpektralaufgelöstMauerThe reflectionpeak from thewall is missingin the Ramansignal
UV Raman Lidar System DetailsParameters of the LIDARsystem:Transmitter:Receiver:Wavelength 354.7 nmWavelengths 353.0 nmMax. power 0.35 J per pulse353.9 nmAverage Power 17.5W354.7 nmPulse width 7 ns386.7nmRepetition rate 50 Hz407.8 nmBeam diameter 0.1 mRange resolution 6 mBeam divergence 0.1 mrField-of-view 0.3 mrMirror diameter 0.45 mhttp://www.chilbolton.rl.ac.uk/lidarsystem.htm
Analysis of theRaman signalMessung von Temperaturprofilen:-Extrem kleine Wellenlängenänderungen durch Rotationsübergänge-Besetzungswahrscheinlichkeit der Rotationszustände ist temperaturabhängig:-Messung an N2, O2Bis htm
Raman-LIDAR for H2OIn contrast to N2 or O2, the H2O concentration is highly variable
DIfferential Absorption LidarDIALZur Bestimmung von Spurenstoffkonzentrationen werden im Gegensatz zum “gewöhnlichen”( Aerosol-) LIDAR wenigstens zwei verschiedene Wellenlängen verwandt:σ(λ)Ähnliche Streuquerschnitte (Mie, Rayleigh)aber unterschiedliche Absorptionλλ1λ2 (λon)Die DIAL – Gleichung erhält man durch Division zweier LIDAR – Gl.für λ1 bzw. λ2: E (λ2 , R ) exp 2(σ 2 σ 1 ) n A (r ) drE (λ1 , R )0 R Annahme:σSR und σS fürλ1 bzw. λ2 gleich sind.Gerechtfertigt solange λ λ2 - λ1hinreichend klein ist (wenige nm)
DIAL NO2 on-off resonanceon resonanceratioAerosol peaksNO2-Absorptionoff resonancemixing ratio
Launch: April 28, 2006CALIPSO: Cloud LIDARCloudSat: Cloud Profiling Radar (CPR)CALIPSO and CloudSat fly in formation with threeother satellites in the ‘A-train constellation’CloudSat and CALIPSO were launched togetherfrom Space Launch Complex 2W at VandenbergAir Force Base, California, on a two-stage Delta7420-10C launch vehiclehttp://cloudsat.atmos.colostate.edu/mission
A-TRAIN CONSTELLATIONThe Afternoon or "A-Train" satellite constellation presently consists of three satellites flying in formationaround the globe (NASA's Aqua and Aura satellites and CNES' PARASOL satellite). The CALIPSO andCloudSat satellite missions were inserted in orbit behind Aqua in April 2006. A sixth spacecraft, OCO, isplanned for launch in 2008 and will be placed ahead of Aqua.
CALIPSO PAYLOADCharacteristics CALIOPlaser: Nd: YAG, diodepumped, Q-switched,frequency doubledwavelengths: 532 nm,1064 nm pulse energy:110 mJoule/channelrepetition rate: 20.25 Hzreceiver telescope: 1.0 mdiameter polarization: 532nm footprint/FOV: 100 m/130 µrad verticalresolution: 30-60 mhorizontal resolution: 333m linear dynamic range:22 bits data rate: 316 kbpsThe CALIPSO payload consists of three co-aligned nadir-viewing instruments: the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) the Imaging Infrared Radiometer (IIR) the Wide Field Camera (WFC)
nasa.gov/products/lidar/
ww-calipso.larc.nasa.gov/products/lidar/
CALIPSO, s/iceland-volcano-plume-archive1.html
Active methods with focus on time information-LIDARLight detection and ranging-RADARRadio detection and ranging-SODARSound detection and ranging
RADARScattering of electromagnetic radiation is caused by different‘objects’:-aerosols-cloud drops-raindrops-snow flakes, hail-insects, birds, airplanes -turbulence elements
Remote sensing in different parts of the EM spectrumCloud dropletsrain droplets100GHzmmRadarCloudsataerosolsmolecules
RADARScattering of electromagnetic radiation is caused by different‘objects’:-aerosols-cloud drops-raindrops-snow flakes, hail-turbulence elementsirregularities in the radio refractive index ofthe atmosphere; most sensitive toscattering by turbulent eddies whose spatialscale is ½ the wavelength of the radar Braggscattering-insects, birds, airplanes 100 GHz ( 2mm) 1 GHz ( 20cm)to50 MHz ( 5m)
95 GHz Doppler Polarimetric Cloud com/radar36.com/radar36.html
VHF-Radar: Emitter und Empfänger (Kühlungsborn )Technische ParameterFrequenz 53,5 MHzSpitzenleistung 90 kWMittlere Leistung 4,5 kW (bei 5%Duty Cycle)3dB-Öffnungswinkel 6 Impulslänge 1 . 32 µsPulswiederholfrequenz 50 kHzHöhenbereiche (0,4) 1 . 18 km(65.95 km)Höhenauflösung 150 m, 300 m,600 m, 1000 mZeitauflösung 1 minSendesignal Einzelimpuls,KomplementärkodesImpulsformen Rechteck,modifizierter Gauß (für max.Leistung)
RADARBasic RADAR equation (for single scattering points)Modified RADAR equation (for volume scatterers)Beam path and scanned volume
0.5 bis 16 km Troposphärenwindprofiler
0.2 bis 3 km Grenzschichtwindprofiler
Meteorologisches Observatorium Lindenberg
Meteorologisches Observatorium Lindenberg
Meteorologisches Observatorium Lindenberg
The CWKR Environment Canada Weather Radar Station located in King City, Ontario.Elevation: 341 meters ASL.Latitude: 43 58' 0" N (deg min sec), 43.9667 (decimal), 4358.00N (LORAN)Longitude: 79 34' 0" W (deg min sec), -79.5667 (decimal), 07934.00W (LORAN)
ReflectivityReturn echoes from targets are analyzed for their intensities in order toestablish the precipitations rate in the scanned volume. The wavelengthused (1 to 10 cm) ensure that this return is proportional to theprecipitations rate because they are within the validity of Rayleighscattering which states that the targets must be much smaller than thewavelength of the scanning wave (by a factor of 10).
VelocityPetr Novák(petr novak@chmi.cz)Idialized example of Doppler output. Approachingvelocities are in blue and receeding one in red in the usualconvention. Notice the sinuosidal variation of speed whengoing around the display along a particular ring. (Source:Environment Canada).
PolarizationMost liquid hydrometeors have a largerhorizontal axis due to the drag coefficientof air while falling (water droplets). Thiscauses the water molecule dipole to beoriented in that direction so radar beams aregenerally polarized horizontally to receivethe maximal return.If we decide to send simultaneously twopulses with orthogonal polarization: verticaland horizontal, we receive two sets of dataproportional to the two axis of the dropletsthat are independentTargeting with dual-polarizationwill reveal the form of the droplet
Niederschlagsradar(gelb/blau), projiziert aufdas Satellitenbild derWolkenbedeckung. DasRegengebiet am Rheinentsprach der Realität, dasRadarecho im Nordenberuht auf einerTäuschung.es ist bekannt, dass die Briten und Deutschen im Zweiten Weltkrieg Stanniolfädenvom Himmel fallen ließen, um das gegnerische Radar zu stören. Heute werden dafürhauchdünne metallüberzogene Kunststofffäden genutzt, die Düppel. Sie sind wenigeZentimeter lang und werden in der Atmosphäre ausgestreut. So bildet sich eine Artunsichtbare Mauer, die Radarstrahlen DID 46421554 )
Niederschlagsbild: Baden-Württemberg So, 09.05. 00:00 - 09:00http://www.wetteronline.de
CloudSat's Cloud ProfilingRadar captured a profile acrossTropical Storm Andrea onWednesday, 9 May 2007 near theSC/GA/FL Atlantic coast. Theupper image shows an infraredview of TS Andrea from theMODIS instrument on the Aquasatellite, with CloudSat's groundtrack from 0718-0720 UTC (3:183:20 EDT) shown as a red line.The lower image is the verticalcross section of radar reflectivityalong this path, where the colorsindicate the intensity of thereflected radar energy. CloudSatorbits approximately one minutebehind Aqua in a satelliteformation known as the A-Train.[Images courtesy of the NavalResearch e.edu/
CloudSat
http://cloudsat.atmos.colostate.edu/
http://cloudsat.atmos.colostate.edu/
Synergy betweenCloudsat and CalipsoCloudSat 94 GHz reflectivityCALIPSO 532nm totalattenuated backscatterKahn, B. H., Chahine, M. T., Stephens, G. L., Mace, G. G., Marchand, R. T., Wang, Z., Barnet, C. D., Eldering, A.,Holz, R. E., Kuehn, R. E., and Vane, D. G.: Cloud type comparisons of AIRS, CloudSat, and CALIPSO cloud height andamount, Atmos. Chem. Phys. Discuss., 7, 13915-13958, doi:10.5194/acpd-7-13915-2007, 2007.
Active methods with focus on time information-LIDARLight detection and ranging-RADARRadio detection and ranging-SODARSound detection and ranging
SODAR Sound Detecting And RAngingSound (as acoustic pulses) is emitted into the atmosphere and the echos are recievedand analysed-the echo intensity varies according to thermal turbulence and structure-the frequency shift of the echo varies according to the wind speed (DOPPLER effect )
SODAR Sound Detecting And RAngingMono-static systems are usually operated in three directionsZenith anglestypically 15 to 30 two categories:a) individual antennas at multiple axissingle transducer focused into a parabolic dishb) single phased-array antennaarray of speaker drivers and horns (transducers), the beams areelectronically steered by phasing the transducers appropriately.
An example of an old monostatic system is presented inFigure 3. The antenna is constructed from anelectrodynamic transducer in the focal point of a parabolicdish reflector. It is clear that the system is heavy and it isdifficult to move it in hard to reach places.phased-array antenna
SODAR Sound Detecting And RAnging-The horizontal components of the wind velocity are calculatedfrom the radially measured Doppler shifts and the specified tiltangle from the vertical.-A correction for the vertical velocity should be applied insystems with zenith angles less than 20 (or when the expectedvertical velocities are greater than about 0.2 ms –1)- The vertical range of sodars is approximately 0.2 to 2kilometers (km) depending on frequency, power output,atmospheric stability, turbulence, and, most importantly, thenoise environment in which a sodar is operated.-Operating frequencies range from less than 1000 Hz to over4000 Hz, with power levels up to several hundred watts.
SODAR Sound Detecting And RAngingMeteorologisches Observatorium Lindenberg
Radio Acoustic Sounding System (RASS)- Bragg scattering occurs when the wavelength of the acoustic signal matches the halfwavelength of the radar-As the frequency of the acoustic signal is varied, strongly enhanced scattering of the radarsignal occurs when the Bragg match takes place.-When this occurs, the Doppler shift of the radar signal produced by the Bragg scatteringcan be determined, vertical velocity.-the speed of sound as a function of altitude can be measured, from which virtualtemperature (Tv ) profiles can be calculated (The virtual temperature of an air parcel is thetemperature that dry air would have if its pressure and density were equal to those of asample of moist air)-three or four vertically pointing acoustic sources (equivalent to high quality stereo loudspeakers) are placed around the radar wind profiler's antenna,-The acoustic sources are used only to transmit sound into the vertical beam of the radar-The vertical resolution of RASS data is determined by the pulse length(s) used by theradar. RASS sampling is usually performed with a 60- to 100-m pulse length.-the altitude range is usually 0.1 to 1.5 km, depending on atmospheric conditions (e.g., highwind velocities tend to limit RASS altitude coverage to a few hundred meters because theacoustic signals are blown out of the radar beam).
Schematic ofsampling geometryfor a radar windprofiler with RASS
The 915 MHz Radar Wind Profiler (915RWP) and radio acoustic sounding system(RASS) at the North Slope of Alaska site in Barrow, Alaska.
Meteorologisches Observatorium Lindenberg
Summary active (time resolved) methods:-active methods:-mainly optical and microwave range-also sound is usedAdvantages:-highly resolved spatial information-measurement conditions can be freely chosenDisadvantages:-high instrumental effort-only small temporal and spatial coverage-often qualitative (not quantitative) information is retrieved
-LIDAR Light detection and ranging-RADAR Radio detection and ranging-SODAR Sound detection and ranging. Basic components Emitted signal (pulsed) Radio waves, light, sound Reflection (scattering) at different distances Scattering, Fluorescence Detection of signal strength as function of time.
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Illinois Airborne Light Detection and Ranging (LiDAR) Data Acquisition Plan September 2019 DRAFT PLAN Sheena K. Beaverson State Champion and Data Management Staff Sheena Beaverson serves as the state liaison for airborne Light Detection and Ranging (LiDAR) data projects within Illinois. Ms.
Light Detection and Ranging: Applications for transportation Light Detection and Ranging (LIDAR) is a surveying tool that utilizes an optical remote sensing technology to measure properties of scattered light to determine range and other information about a target. LIDAR allows highly accurate 3D (x, y and z) measurements to be taken.
Light Detection and Ranging LiDAR and the FAA FAA Review and Reclassification of LiDAR systems February 2014 . In an economy where you are counting every dollar, it is good to know you can count on MAPPS! What is MAPPS? The national professional association of private sector geospatial firms in the United States.
3.2 Laser imaging Detection and Ranging (LiDAR) Laser Imaging Detection and Ranging (LiDAR) is an optical remote sensing technology that can measure the distance to, or other properties of, targets by illuminating the target with laser light and analyzing the backscattered light (Figure 2). Lidar was used to provide contour
RRP 5-16 - Light Detection And Ranging (LiDAR) Asset Management PJ1400.docx Page 9 of 16 As already noted, the principal benefit of the LiDAR survey is to enhance UE's ability to improve its safety performance and reduce bushfire risks.
Lidar, which is commonly spelled LiDAR and also known as LADAR or laser altimetry, is an acronym for light detection and ranging. It refers to a remote sensing technology that emits intense, focused beams of . light . and measures the time it takes for the reflections to be . detected . by the sensor. This information is used to compute . ranges
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