No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
Advanced Airborne UV DIAL System for Stratospheric and Tropospheric Ozone and Aerosol Measurements
Abstract
An advanced UV DIAL system for airborne measurements of ozone and aerosol distributions across the troposphere and lower stratosphere was developed at the NASA Langley Research Center during 1995. This paper describes the system and its improved performance including examples from the recent TOTE/VOTE field campaign.
... 355 nm is usually chosen as the operating wavelength for laser wind measurement radars due to the low absorption and high scattering of ultraviolet light in atmospheric molecules, a typical example being the ALADIN developed by European Space Agency (ESA) [24,25]. In addition, 355 nm UV lasers are used in space debris removal [26], the Aerosol/Cloud/Ecosystems (ACE) to be developed by National Aeronautics and Space Administration (NASA) [27,28], the 3-D Winds for space-based measurement of tropospheric winds with global coverage [29] and the Global Atmospheric Composition Mission (GACM) for the Ozone DIAL system [30,31]. In addition, laser-induced damage in the UV band is more susceptible to the effects of space radiation than in other bands, as space radiation damage causes mainly degradation of optical properties in the UV band. ...
... 355 nm is usually chosen as the operating wavelength for laser wind measurement radars due to the low absorption and high scattering of ultraviolet light in atmospheric molecules, a typical example being the ALADIN developed by European Space Agency (ESA) [24,25]. In addition, 355 nm UV lasers are used in space debris removal [26], the Aerosol/Cloud/Ecosystems (ACE) to be developed by National Aeronautics and Space Administration (NASA) [27,28], the 3-D Winds for space-based measurement of tropospheric winds with global coverage [29] and the Global Atmospheric Composition Mission (GACM) for the Ozone DIAL system [30,31]. In addition, laser-induced damage in the UV band is more susceptible to the effects of space radiation than in other bands, as space radiation damage causes mainly degradation of optical properties in the UV band. ...
... Data were collected for 14 flights (including two pre-mission test flights before the deployment to Kiruna). Details of this instrument may be found in Browell et al. (2003), Browell et al. (1998), andRichter et al. (1997). ...
Ozone measurements from ozonesondes, ARO- TAL, DIAL, and POAM III instruments during the SOLVE- 2/VINTERSOL period are composited in a time-varying, flow-following quasi-conservative (PV- ) coordinate space; the resulting composites from each instrument are mapped onto the other instruments' locations and times. The mapped data are then used to intercompare data from the different in- struments. Overall, the four ozone data sets are found to be in good agreement. AROTAL shows somewhat lower values below 16 km, and DIAL has a positive bias at the upper limits of its altitude range. These intercomparisons are consistent with those obtained from more conventional near-coincident profiles, where available. Although the PV- mapping tech- nique entails larger uncertainties of individual profile differ- ences compared to direct near-coincident comparisons, the ability to include much larger numbers of comparisons can make this technique advantageous.
... The NASA-DC-8 Ozone DIAL system and configuration implemented during the campaign is described by Richter et al. (1997). The instrument provides simultaneous zenith and nadir profiles to cover the troposphere and lower stratosphere. ...
During the 2008 International Polar Year, the POLARCAT (Polar Study using
Aircraft, Remote Sensing, Surface Measurements, and Models of Climate
Chemistry, Aerosols, and Transport) campaign, conducted in summer
over Greenland and Canada, produced a large number of measurements from three
aircraft and seven ozonesonde stations. Here we present an observation-integrated analysis based on three different types of O3
measurements: airborne lidar, airborne UV absorption or chemiluminescence
measurement, and intensified electrochemical concentration cell (ECC)
ozonesonde profiles. Discussion of the latitudinal and vertical variability
of tropospheric ozone north of 55° N during this period is performed
with the aid of a regional model (WFR-Chem). The model is able to reproduce
the O3 latitudinal and vertical variability but with a negative
O3 bias of 6–15 ppbv in the free troposphere above 4 km,
especially over Canada.
For Canada, large average CO concentrations in the free troposphere above
4 km ( > 130 ppbv) and the weak correlation (< 30 %) of O3
and PV suggest that stratosphere–troposphere exchange (STE) is not the major
contributor to average tropospheric ozone at latitudes less than
70° N, due to the fact that local biomass burning (BB) emissions
were significant during the 2008 summer period. Conversely, significant STE
is found over Greenland according to the better O3 vs. PV
correlation ( > 40 %) and the higher values of the 75th PV percentile.
It is related to the persistence of cyclonic activity during the summer over
Baffin Bay.
Using differences between average concentration above Northern and Southern
Canada, a weak negative latitudinal summer ozone gradient of −6 to
−8 ppbv is found in the mid-troposphere between 4 and 8 km. This is
attributed to an efficient O3 photochemical production from BB
emissions at latitudes less than 65° N, while the STE contribution
is more homogeneous in the latitude range 55–70° N. A positive
ozone latitudinal gradient of 12 ppbv is observed in the same altitude range
over Greenland not because of an increasing latitudinal influence of STE, but
because of different long-range transport from multiple mid-latitude sources
(North America, Europe, and even Asia for latitudes higher than
77° N).
For the Arctic latitudes (> 80° N), free tropospheric O3
concentrations during summer 2008 are related to a mixture of Asian pollution and stratospheric
O3 transport across the tropopause.
... High power laser light sources operating in the ultraviolet (UV) spectral region have received a great deal of interest for numerous applications in science and technology such as semiconductor processing, micromachining, remote sensing with Lidar, engine combustion diagnostics, spectroscopy, medicinal and biological applications. . . [1][2][3][4][5][6]. Hence, there is a great deal of interest for the development of high-power, all-solid-state UV lasers of convenient operating procedures. ...
We review the recent progresses in generation and amplification of ultraviolet laser emissions using Ce$^{3 + }$:LiCaAlF$_{6}$ (Ce:LiCAF) material as a gain medium. Basing on comparative studies, we have investigated improvements and proposed possibilities to generate and amplify ultraviolet short-pulse Ce:LiCAF laser emission to high peak power of terawatt.
... The current version of NASA Langley's airborne UV DIAL system has been described in detail in two recent publications (Richter et al., 1997;Browell et al., 1998a). This system uses two 30-Hz, frequency-doubled Nd:YAG lasers to sequentially pump two dye lasers that are frequency-doubled into the UV to produce the on-line (288.2 nm/301 nm) and offline (299.6 nm/310 nm) wavelengths for DIAL O 3 measurements during tropospheric and stratospheric missions, respectively. ...
Airborne lidar systems have proven very useful for atmospheric and oceanic studies during the past three decades and more recently for surface and vegetation canopy studies. Typical applications of airborne lidar for atmospheric studies include studying the long-range transport of pollutants, taking large-scale surveys of tropospheric aerosols and ozone (O3) over remote regions of the Earth, studying water vapor (H2O) and the hydrologic cycle, and investigating various processes associated with biomass burning emissions, desert dust transport, stratospheric aerosol transport following volcanic eruptions, polar O3 changes and polar stratospheric clouds (PSCs), and metal ion concentrations in the ionosphere. Airborne lidar systems that are participating in studies of aerosols, O3, and H2O can also be used to make correlative measurements of space-based remote-sensing instruments and serve as test beds on the way to space-based lidar systems. In addition to atmospheric studies, airborne lidar systems have been used for diverse hydrospheric studies, including measurements of chlorophyll, phytoplankton, dissolved organic matter, inorganic suspended material, water depth, and even fish school detection. Airborne lidar systems have been used to study surface properties such as the infrared (IR) reflectivity of desert geological features. Airborne lidar systems have also recently been applied to study the density and structure of the vegetation canopy in forests. The main advantages of airborne lidar systems are that they expand the geographical range of studies beyond those possible by surface-based fixed or mobile lidar systems by virtue of being able to fly to high altitudes and to remote locations. Thus, they permit measurements at locations inaccessible to surface-based lidar systems. For atmospheric studies, they permit measurements over large regions in times that are short, compared with atmospheric motion, so that large-scale patterns are discernable. Another advantage of an airborne lidar is that the normal lidar technique, which uses aerosols and molecules as distributed reflectors, performs better in the nadir direction than in the zenith direction since the atmospheric density increases with range r (decreasing altitude), compensating somewhat for the 1/r2 falloff in lidar signal with range. For the zenith direction, the advantage is that the airborne lidar system is higher and thus closer to the atmosphere being measured. The main disadvantage of using an airborne lidar is the complexity and cost of conducting aircraft operations, a fact that limits the number of airborne missions. This chapter will examine the specific requirements for airborne lidar, review the important application areas of airborne lidar, and then indicate the direction of future airborne lidar applications.
A long-lived UV laser is an enabling technology for a number of high-priority, space-based lidar instruments. These include a next generation cloud and aerosol lidar that incorporates a UV channel, a direct detection 3-D wind lidar, and an ozone DIAL system. We have designed and built a TRL 6 demonstrator that has increased output power and space-qualifiable packaging that is mechanically robust, thermally-stable, and fully conductively cooled. Contamination control processes and optical coatings have been chosen that are compatible with multi-billion shot lifetimes. The diode pumped laser contains an essentially polymer free internal module that houses the third harmonic generator and expansion optics. When operated at 150 Hz the laser has demonstrated 275 mJ per pulse at 1064 nm, second harmonic conversion efficiencies of 70%, and third harmonic conversion efficiencies of 45%, thus meeting the 355 nm 100 mJ/pulse goal with margin.
At this time we have successfully completed a full power 532 nm life test, a half power (50 mJ/pulse) UV lifetest, and a full power (100 mJ/pulse @ 150 Hz) lifetest. These tests have validated the importance and success to our approach to contamination control for achieving a long lived UV laser as well as resurfacing the need for attention to the qualification of the pump laser diodes and attention to the external optical in a UV lidar system.
Eighteen long-range flights over the Pacific Ocean between 38°S to
20°N and 166°E to 90°W were made by the NASA DC-8 aircraft
during the NASA Pacific Exploratory Mission (PEM) Tropics B conducted
from March 6 to April 18, 1999. Two lidar systems were flown on the DC-8
to remotely measure vertical profiles of ozone (O3), water
vapor (H2O), aerosols, and clouds from near the surface to
the upper troposphere along their flight track. In situ measurements of
a wide range of gases and aerosols were made on the DC-8 for
comprehensive characterization of the air and for correlation with the
lidar remote measurements. The transition from northeasterly flow of
Northern Hemispheric (NH) air on the northern side of the Intertropical
Convergence Zone (ITCZ) to generally easterly flow of Southern
Hemispheric (SH) air south of the ITCZ was accompanied by a significant
decrease in O3, carbon monoxide, hydrocarbons, and aerosols
and an increase in H2O. Trajectory analyses indicate that air
north of the ITCZ came from Asia and/or the United States, while the air
south of the ITCZ had a long residence time over the Pacific, perhaps
originating over South America several weeks earlier. Air south of the
South Pacific Convergence Zone (SPCZ) came rapidly from the west
originating over Australia or Africa. This air had enhanced
O3 and aerosols and an associated decrease in H2O.
Average latitudinal and longitudinal distributions of O3 and
H2O were constructed from the remote and in situ
O3 and H2O data, and these distributions are
compared with results from PEM-Tropics A conducted in August-October
1996. During PEM-Tropics B, low O3 air was found in the SH
across the entire Pacific Basin at low latitudes. This was in strong
contrast to the photochemically enhanced O3 levels found
across the central and eastern Pacific low latitudes during PEM-Tropics
A. Nine air mass types were identified for PEM-Tropics B based on their
O3, aerosols, clouds, and potential vorticity
characteristics. The data from each flight were binned by altitude
according to air mass type, and these results showed the relative
observational frequency of the different air masses as a function of
altitude in seven regions over the Pacific. The average chemical
composition of the major air mass types was determined from in situ
measurements in the NH and SH, and these results provided insight into
the origin, lifetime, and chemistry of the air in these regions.
The National Oceanic and Atmospheric Administration/Earth System Research Laboratory/Chemical Sciences Division (NOAA/ESRL/CSD) has developed a versatile, airborne lidar system for measuring ozone and aerosols in the boundary layer and lower free troposphere. The Tunable Optical Profiler for Aerosol and Ozone (TOPAZ) lidar was deployed aboard a NOAA Twin Otter aircraft during the Texas Air Quality Study (TexAQS 2006) and the California Research at the Nexus of Air Quality and Climate Change (CalNex 2010) field campaigns. TOPAZ is capable of measuring ozone concentrations in the lower troposphere with uncertainties of several parts per billion by volume at 90-m vertical and 600-m horizontal resolution from an aircraft flying at 60 m s(-1). The system also provides uncalibrated aerosol backscatter profiles at 18-m vertical and 600-m horizontal resolution. TOPAZ incorporates state-of-the-art technologies, including a cerium-doped lithium calcium aluminum fluoride (Ce:LiCAF) laser, to make it compact and lightweight with low power consumption. The tunable, three-wavelength UV laser source makes it possible to optimize the wavelengths for differing atmospheric conditions, reduce the interference from other atmospheric constituents, and implement advanced analysis techniques. This paper describes the TOPAZ lidar, its components and performance during testing and field operation, and the data analysis procedure, including a discussion of error sources. The performance characteristics are illustrated through a comparison between TOPAZ and an ozonesonde launched during the TexAQS 2006 field campaign. A more comprehensive set of comparisons with in situ measurements during TexAQS 2006 and an assessment of the TOPAZ accuracy and precision are presented in a companion paper.
In situ and laser remote measurements of gases and aerosols were made
with airborne instrumentation to establish a baseline chemical signature
of the atmosphere above the South Pacific Ocean during the NASA Global
Tropospheric Experiment (GTE)/Pacific Exploratory Mission-Tropics A
(PEM-Tropics A) conducted in August-October 1996. This paper discusses
general characteristics of the air masses encountered during this
experiment using an airborne lidar system for measurements of the
large-scale variations in ozone (O3) and aerosol
distributions across the troposphere, calculated potential vorticity
(PV) from the European Centre for Medium-Range Weather Forecasting
(ECMWF), and in situ measurements for comprehensive air mass
composition. Between 8°S and 52°S, biomass burning plumes
containing elevated levels of O3, over 100 ppbv, were
frequently encountered by the aircraft at altitudes ranging from 2 to 9
km. Air with elevated O3 was also observed remotely up to the
tropopause, and these air masses were observed to have no enhanced
aerosol loading. Frequently, these air masses had some enhanced PV
associated with them, but not enough to explain the observed
O3 levels. A relationship between PV and O3 was
developed from cases of clearly defined O3 from stratospheric
origin, and this relationship was used to estimate the stratospheric
contribution to the air masses containing elevated O3 in the
troposphere. The frequency of observation of the different air mass
types and their average chemical composition is discussed in this paper.
Large-scale measurements of ozone (O3) and aerosol distributions were made from the NASA DC-8 aircraft during the Transport and Chemical Evolution over the Pacific (TRACE-P) field experiment conducted in February-April 2001. Remote measurements were made with an airborne lidar to provide O3 and multiple-wavelength aerosol backscatter profiles from near the surface to above the tropopause along the flight track. In situ measurements Of O3, aerosols, and a wide range of trace gases were made onboard the DC-8. Five-day backward trajectories were used in conjunction with the O3 and aerosol distributions on each flight to indicate the possible origin of observed air masses, such as from biomass burning regions, continental pollution, desert regions, and oceanic regions. Average latitudinal O3 and aerosol scattering ratio distributions were derived from all flights west of 150°E, and these distributions showed the average latitude and altitude dependence of different dynamical and chemical processes in determining the atmospheric composition over the western Pacific. TRACE-P (TP) showed an increase in the average latitudinal distributions of both O3 and aerosols compared to PEM-West B (PWB), which was conducted in February-March 1994. O3, aerosol, and potential vorticity levels were used to identify nine air mass types and quantify their frequency of occurrence as a function of altitude. This paper discusses the characteristics of the different air mass types encountered during TP and compares them to PWB. These results confirmed that most of the O3 increase in TP was due to photochemistry. The average latitudinal eastward O3 flux in the western Pacific during TP was found to peak near 32°N with a total average O3 flux between 14 and 46°N of 5.2 Tg/day. The eastward total CO flux was calculated to be 2.2 Tg-C/day with ∼6% estimated from Asia. The Asian flux of CO2 and CH4 was estimated at 4.9 and 0.06 Tg-C/day.
Low-ozone (< 20 ppbv) air masses were observed in the upper troposphere in northern midlatitudes over the eastern United States and the North Atlantic Ocean on several occasions in October 1997 during the NASA Subsonic Assessment, Ozone and Nitrogen Oxide Experiment (SONEX) mission. Three cases of low-ozone air masses were shown to have originated in the tropical Pacific marine boundary layer or lower troposphere and advected poleward along a warm conveyor belt during a synoptic-scale disturbance. The tropopause was elevated in the region with the low-ozone air mass. Stratospheric intrusions accompanied the disturbances. On the basis of storm track and stratospheric intrusion climatologies, such events appear to be more frequent from September through March than the rest of the year.
1] The Tropospheric Emission Spectrometer (TES) is an infrared instrument that was launched on board NASA's Aura satellite in 2004. TES is the first instrument to provide vertical information on tropospheric ozone while simultaneously measuring CO on a global basis. Before they may be used for scientific study, TES profiles must first be validated to determine if there are any systematic biases present. In this study we present a validation of TES tropospheric ozone using airborne differential absorption lidar (DIAL) profiles obtained during the Intercontinental Chemical Transport Experiment–B (INTEX-B) campaign, which took place during March–May 2006. During INTEX-B the NASA DC-8 aircraft conducted several flights, which allowed the DIAL instrument to obtain ozone profile measurements that were spatially coincident with TES special observations in three different geographical regions. Here we present comparisons of TES and DIAL tropospheric ozone profiles that show that, on average, TES exhibits a small positive bias in the troposphere of 5–15%. We also examine the use of in situ profile observations for the validation of TES tropospheric ozone, and we find these to be of most use in clean regions where the background ozone field is homogeneous.
A highly efficient, compact and rugged 1 kHz tunable UV Ce:LiCAF laser pumped by the fourth harmonic of a diode–pumped commercial Nd:YLF laser for ozone DIAL measurements has been developed and the performance of this laser was investigated. The Ce:LiCAF laser delivered 1 mJ pulse energy at 290 nm wavelength and was able to be wavelength tuned from 281 to 316 nm that was achieved with a single fused silica dispersion prism in the laser cavity. Fast shot-to-shot wavelength switching was obtained by the harmonic motion of tuning mirror mounted on a servo-controlled high speed galvanometric deflector.
The airborne UV differential absorption lidar (DIAL) system participated in the Tropical Ozone Transport Experiment/Vortex Ozone Transport Experiment (TOTE/VOTE) in late 1995/early 1996. This mission afforded the opportunity to compare the DIAL system's stratospheric ozone measuring capability with other remote-sensing instruments through correlative measurements over a latitude range from the tropics to the Arctic. These instruments included ground-based DIAL and space-based stratospheric instruments: HALOE; MLS; and SAGE II. The ozone profiles generally agreed within random error estimates for the various instruments in the middle of the profiles in the tropics, but regions of significant systematic differences, especially near or below the tropopause or at the higher altitudes were also found. The comparisons strongly suggest that the airborne UV DIAL system can play a valuable role as a mobile lower-stratospheric ozone validation instrument.
In situ and laser remote measurements of gases and aerosols were made with airborne instrumentation to investigate the sources and sinks of tropospheric gases and aerosols over the tropical South Atlantic during the NASA Global Tropospheric Experiment (GTE)/Transport and Atmospheric Chemistry Near the Equator-Atlantic (TRACE A) field experiment conducted in September-October 1992. Gases from extensive fires in Brazil were transported by convective storms into the upper troposphere where tropospheric ozone (O3) was photochemically produced and advected eastward over the South Atlantic. In central Africa, the fires were widespread, and in the absence of deep convection, the fire plumes were advected at low altitudes (below ~6 km) over the Atlantic. There was a positive correlation between O3 and aerosols found in the plumes that were not involved in convection. High O3 [>75 parts per billion by volume (ppbv)] was observed in the low-altitude plumes, and also in the upper troposphere where O3 often exceeded 100 ppbv with low aerosol loading. The average tropospheric O3 distributions were determined for the following: Brazil and western South Atlantic, eastern and central South Atlantic, central and east coast of Africa, and the entire South Atlantic Basin. The tropopause heights and O3 columns across the troposphere were calculated for individual flights and for the average O3 distributions in the above regions. A maximum tropospheric O3 column of 56 Dobson units (DU) was found over the biomass burning region in Zambia and in the subsidence region over the central South Atlantic. The high O3 region over the South Atlantic from 4° to 18°S corresponded with the latitudinal extent of the fires in Africa. In situ and laser remote measurements were used to determine the frequency of observation and chemical composition of nine major air mass types. Biomass burning emissions contributed to most of the air masses observed over the South Atlantic Basin, and biomass burning was found to contribute up to half (28 DU) of the O3 column across this region.
Remote and in situ measurements of gases and aerosols were made with airborne instrumentation to investigate the sources and sinks of tropospheric gases and aerosols over the western Pacific during NASA Global Tropospheric Experiment (GTE)/Pacific Exploratory Mission-West A (PEM-West A) conducted in September-October 1991. This paper discusses the general characteristics of the air masses encountered during this experiment using an airborne lidar system for measurements of the large-scale variations in ozone (O3) and aerosol distributions across the troposphere and airborne in situ instrumentation for comprehensive measurements of air mass composition. In low latitudes of the western Pacific the airflow was generally from the east, and under these conditions the air was observed to have low aerosol loading and low ozone levels throughout the troposphere. Ozone was found to be below 10 parts per billion volume (ppbv) near the surface to 40-50 ppbv in the middle to upper troposphere. In the middle and high latitudes the airflow was mostly westerly, and the background O3 was generally less than 55 ppbv. On 60% of the PEM-West A flights, O3 was observed to exceed these levels in regions that were determined to be associated with stratospheric intrusions. In convective outflows from typhoons, near-surface air with low ozone (10 km). Several cases of continental plumes from Asia were observed over the Pacific during westerly flow conditions. These plumes were found in the lower troposphere with ozone levels in the 60-80 ppbv range and enhanced aerosol scattering. At low latitudes over the central Pacific the troposphere primarily contained air with background or low ozone levels; however, stratospherically influenced air with enhanced ozone (40-60 ppbv) was observed several times in the lower troposphere. The frequency of observation of the air masses and their average chemical composition are also discussed in this paper.
A number of commercial and custom-built laser mirror mounts were tested for angular alignment sensitivity during temperature cycling from room temperature (20 C) to 40 C. A Nd:YAG laser beam was reflected off a mirror that was held by the mount under test and was directed to a position-sensitive detector. Horizontal and vertical movement of the reflected beam was recorded, and the angular movement, as a function of temperature (coefficient of thermal tilt (CTT)) was calculated from these data. In addition, the amount of hysteresis in the movement after cycling from room temperature to 40 C and back was determined. All commercial mounts showed greater angular movement than the simpler National Aeronautics and Space Administration Lidar Atmospheric Sensing Experiment (NASA LASE) custom mirror mounts.
An airborne differential absorption lidar (DIAL) system has been developed for the remote measurement of gas and aerosol profiles in the troposphere and lower stratosphere. The multipurpose DIAL system can operate from 280 to 1064 nm for measurements of ozone, sulfur dioxide, nitrogen dioxide, water vapor, temperature,pressure, and aerosol backscattering. The laser transmitter consists of two narrow linewidth Nd: YAG pumped dye lasers with automatic wavelength control. The DIAL wavelengths are transmitted with a 00-,usec temporal separation to reduce receiver system complexity. A coaxial receiver system is used to collect and optically separate the DIAL and aerosol lidar returns. Photomultiplier tubes detect the backscattered laser returns after optical filtering, and the analog signals from three tubes are digitized and stored on high-speed magnetic tape. Real-time gas concentration profiles or aerosol backscatter distributions are calculated and displayed for experiment control. Operational parameters for the airborne DIAL system are presented for measurements of ozone, water vapor, and aerosols in the 290-, 720-, and 600-nm wavelength regions, respectively. The first ozone profile measurements from an aircraft using the DIAL technique are discussed in this paper. Comparisons between DIAL and in situ ozone measurements show agreement to within +/-5 ppbv in the lower troposphere. Lidar aerosol data obtained simultaneously with DIAL ozone measurements are presented for a flight over Virginia and the Chesapeake Bay. DIAL system performance for profiling ozone in a tropopause folding experiment is evaluated, and the applications of the DIAL system to regional and global-scale tropospheric investigations are discussed.
Airborne lidar measurements of aerosol and ozone distributions from the surface to above the tropopause over the Western Pacific Ocean are used to quantify the relative contributions of different ozone sources to the tropospheric ozone budget.
Differential absorption lidar (DIAL) is a powerful remote-sensing technique widely used to probe the spatial and temporal distribution of ozone and other gaseous atmospheric trace constituents. Although conceptually simple, the DIAL technique presents many challenging and often subtle technical difficulties that can limit its useful range and accuracy. One potentially serious source of error for many DIAL experiments is nonlinearity in the analog-to-digital converters used to capture lidar return signals. The impact of digitizer nonlinearity on DIAL measurements is examined, and a simple and inexpensive low-frequency dithering technique that significantly reduces the effects of ADC nonlinearity in DIAL and other applications in which the signal is repetitively averaged is described.
The differential absorption lidar (DIAL) technique for deriving O3 profiles from lidar measurements is discussed. The US National Aeronautics and Space Administration's airborne DIAL system is described, and examples of a broad range of O3 and aerosol measurements are presented from a number of field experiments. The airborne and ground-based DIAL measurements discussed demonstrate the outstanding capability of lidar for conducting O3 investigations throughout the troposphere and lower stratosphere under widely different atmospheric conditions.