Apr 27, 2000 - Syed Ismail, Edward V. Browell, and Richard A. Ferrare. NASA Langley ... the radiative fields associated with these aerosols [Russell et al.,. 1999a]. ..... where dr is the incremental range interval (data element) along the lidar ...
JOURNAL OF GEOPHYSICAL RESEARCH,VOL. 105,NO. D8, PAGES9903-9916,APRIL 27, 2000
LASE measurementsof aerosoland water vapor profiles during TARFOX SyedIsmail, Edward V. Browell, and Richard A. Ferrare NASA LangleyResearchCenter,Hampton,Virginia
SusanA. Kooi, Marian B. Clayton,and Vincent G. Brackett SAIC/NASA LangleyResearchCenter,Hampton,Virginia
Philip B. Russell NASA Ames Research Center, Moffett Field, California
Abstract. The Lidar AtmosphericSensingExperiment(LASE) was operatedautonomouslyfrom the NASA high-altitudeER-2 aircrafton nineflightsduringJuly 10-26, 1996, aspart of the Tropospheric AerosolRadiativeForcingObservational Experiment(TARFOX). LASE measured high-resolution profilesof watervaporandaerosolsin regionsof urbanhazeplumesover the U.S. easternseaboard.Real-timeLASE aerosolmeasurements were usedto guidethe in situ aircraftto samplehazelayers. In thispaperthe verticalandhorizontaldistributionsof aerosolbackscatter measuredby LASE are presentedalongwith the temporalevolutionof the haze layers. The aerosolbackscatter dataalsoidentifythe presenceof gradientsin the aerosolplumes,the presence of low-altitudeclouds,andopticallythin cirrus. This informationis usefulfor manyof the radiometericobservations madeduringTARFOX andcan help explainobservationaldifferences amongground,airborne,and satelliteobservations.An iterativeprocedureis discussedwhich was usedto invertlidar datato retrieveaerosolscatteringratios,extinction,andtotal opticaldepths from the LASE measurements.The sensitivityof theseretrievalsto assumedparametersis discussed andthe resultsof retrievalsare alsocomparedto the well-knownBernoulli method. LASE watervapormeasurements were madeacrossthe entiretroposphereusinga three"line pair" methodto coverthe rangeof water vapor mixing ratio from 1000 km) from aircraft, (3) profiles of haze layers from
be readily obtained from either visual observationsor from
real-timedatathatwereprovidedto in situsamplingaircraft,(4)
satellite
examples of observations of visibleandsubvisible cirrus,and(5) examplesof haze layer characteristics derivedfrom LASE measurements. In thispapera simpleprocedure for theretrieval of aerosolscattering ratioprofiles,extinction profiles,andaerosol opticaldepthsfromLASE datais presented.Theresultsof the retrievalare comparedwith the resultsfrom the well-known
measurements.
LASE
real-time
data were received
on
the groundthrough a telemetry link to the ER-2 and analyzedto obtain aerosol and water vapor profiles. The LASE data were analyzed and information concerning the aerosol backscatter distributionassociatedwith the haze layers was communicatedto in situ sampling aircraft which were airborne at that time. The LASE
measurements
also included
aerosol and visible/subvisible
cloud information at altitudes above the haze layers which was providedto the TARFOX experimentteam. The LASE airborne lidar systemprovided high-resolutionprofiles to determinethe vertical structureof aerosollayers and their horizontalgradients. Repetitive flights over the same region could then provide information on the evolution of the haze layer characteristics. During the postmission analysis the aerosol scattering ratio, extinction profiles, and aerosoloptical depthswere derived by taking advantage of aerosol extinction-to-backscatter ratio measurementsobtainedby the ground-basedRamanlidar at WFF [Ferrare et al., this issue(a)]. LASE also measuredwater vapor profilesover the entire troposphereduringTARFOX. Thesedata are useful for any radiative field calculations that take into accountthe influenceof water vapor absorptionin the IR (both shortwave and longwave). In situ measurementsof aerosol
II 90%i
II
Bernoulli method, and the sensitivityof the retrievedaerosol
properties to inputparameters is discussed. The TARFOXfield experiment providedan opportunity for LASE dataproducts to be compared with otherremoteandin situmeasurements, and thesearepresented in thecompanion papers[Ferrareet al., this issue(a, b)].
2. LASE Instrument and OperationsDuring TARFOX
The LASE instrumentis a compactand highly engineered DIAL system that has progressed through systematic development,testing [Moore et al., 1997], and validation [Browellet al., 1997] processes.LASE operatedautonomously from the ER-2 duringTARFOX. A schematic blockdiagramof theLASE systemis givenin Figure1, andthelidarparameters of
ilO%
I
II
I I
I CH B
,ON t ', OFF
HIGH GAIN CH A
', I I
PCM DOWN LINK
t LASER OUTPUT COMMANDS
FIBEROPTIC(to) TRANSMIl'FER
& DATA
• ON • OFF • RECEIVER
CONTROL & DATA (CDS)
Figure 1. Block diagram of the lidar atmosphericsensingexperiment(LASE) system. G1, G2, and G3 are the amplifiersthat control the gain of the three signal channelsCH A, CH B, and CH C/D to cover the full signal dynamic range. LASE data are transmittedto the ground station for real-time processingvia the pulse code modulation (PCM) downlink.
ISMAlL ET AL.: LASE MEASUREMENTS OF AEROSOLS AND WATER VAPOR
Standard Temperature and Pressure (STP).
Table 1. LASE Parameters Value
Parameter
Transmitter
Energy
100mJ(on-lineandoff-
Line width
0.25 pm
Repetition rate Wavelength Beamdivergence
5 Hz 813-818nm 0.6 mrad
line)
Pulse width
50 ns
Aircraft altitude
7-11 km
Aircraftvelocity
230 m/s Receiver
Area(effective) Field of view
1.1 mrad
Filter bandwidth
0.4 nm (day), 1.0 nm (night)
Opticaltransmittance
29%(day),49% (night)
Detectorefficiency
80% (APD)
Noiseequivalent power(NEP)a
2.5x 10-14W/Hz1/2(at 1.6 MHz)
ExcessNoiseFactor(XNF)a
2.5
This line has a
groundstate energy level of 224.8 cm-1 and it is relatively temperatureinsensitive[Browell et al., 1991] for water vapor mixing ratio and number density measurements. During this mission, a three line-pair combination was implemented. A schematicdiagram of the position of "on-line" and "off-line" positionswith respectto the water vapor absorptionprofile for the three line-pair combination is given in Figure 2. The three-line pairs were transmittedin the "center-line off-line," "side-line 1 off-line," and "side-line 2 off-line" pair sequencesat a time separationof 0.2 s. This procedureprovided uniform sensitivityand near-simultaneousmeasurementsof water vapor in the low-, middle-, and upper tropospheric regions. The center-line
0.11 m2
9905
off-line,
side-line
1 off-line,
and side-line
2
off-line combinations were optimum for mixing ratio measurementsin the range
