In the southern South America, various types of aerosols have been observed including biomass burning aerosols from the Amazon region, flying ashes from the volcanic eruptions coming from the Andean Volcanic Belt, mineral dust from the Patagonian Desert, and air pollution aerosols from urban areas. To monitor such aerosols continuously, we developed a lidar observation network in Argentina and Chile. Eight lidars were installed in Argentina and one in Punta Arenas, Chile. Backscattering signals are measured at three wavelengths: 355, 532, and 1064 nm. Eight of those instruments are measuring depolarization ratio at 355 and 532 nm to detect non-spherical aerosols. In addition, four lidars are equipped Ramans channels and two high-spectral-resolution channels to measure backscattering and extinction coefficients quantitatively. Lidar operation, data analysis, and products release are implemented within the South American Environmental Risk Management Network (SAVER-Net) system, which was developed by a trinational project among Japan, Argentina, and Chile. Using lidar data, hazard information on the aerosol type and extinction coefficient at low altitude is provided for public in a near real time. In addition, plume height and qualitatively concentration for volcanic ashes are estimated. The information on volcanic ashes may be effectively used for advising aircraft landing and departing when volcanic eruptions occurs.
Aerosol observations with ceilometers have been made worldwide recently. To use ceilometer data to retrieve aerosol profiles, raw signals should be accurately converted to the attenuated backscattering coefficient. Hence, the calibration coefficient for the system constant has to be determined correctly. We conducted a ceilometer–lidar comparative experiment to evaluate the Lufft CHM15k Nimbus product. The attenuated backscattering coefficient using CHM15k was smaller by a factor of 1.48 compared to that of lidar. The calibration coefficient should be periodically corrected using the ceilometer signal itself since lidar data are generally unavailable in the field observations. We recalibrated the product using both Rayleigh fitting and cloud attenuation methods. The correction factor, determined from the recalibration, was 15% (9%) smaller when using the Rayleigh fitting (cloud attenuation) method than the factor determined from lidar. Uncertainties from backscattering ratios at the reference height and the lidar ratio can cause systematic errors in the correction factor determined from the Rayleigh fitting method. Uncertainties due to the multiple scattering factor contribute to systematic errors for the cloud attenuation method. We propose a calibration method using depolarization ratios for future polarization-sensitive ceilometers, which can estimate the calibration coefficient without multiple scattering factors.
A regional elastic-scattering lidar network called Asian dust and aerosol lidar observation network (AD-Net) has operated for 15 years (since 2001) in East Asia. In this network, the extinction coefficient of aerosols below an altitude of 9 km is continuously obtained when conditions are clear; the coefficient is divided into two parts: dust extinction and spherical extinction coefficients. The dust extinction coefficient has been compared with several parameters measured by other instruments and utilized by various studies, including studies on the epidemiology of Asian dust. Recent expansion of the lidar system at some observatories allows more optical parameters to be retrieved at those observatories. All AD-Net products are used for monitoring global environmental change as an activity of global atmospheric watch lidar observation network.
Continuous observations of aerosols are being conducted with the Asian Dust and aerosol lidar observation Network
(AD-Net). Currently, two-wavelength (1064 nm and 532 nm) polarization-sensitive (532 nm) lidars are operated at 20
stations in East Asia. At the primary stations (6 stations), nitrogen vibrational Raman scattering is also measured to
obtain the extinction coefficient at 532 nm. Recently, continuous observations with a three-wavelength (1064 nm, 532
nm and 355 nm) lidar having a high-spectral-resolution receiver at 532 nm and a Raman receiver at 355 nm and
polarization-sensitive receivers at 532 nm and 355 nm) was started in Tsukuba. Also, continuous observations with
multi-wavelength Raman lidars are being prepared in Fukuoka, Okinawa Hedo, and Toyama. A data analysis method for
deriving distributions of aerosol components (weak absorption fine (such as sulfate), weak absorption coarse (sea salt),
strong absorption fine (black carbon), non-spherical (dust)) has been developed for these multi-parameter lidars. Major
subjects of the current studies with AD-Net include data assimilation of multi-parameter lidars, mixing states of Asian
dust with air pollution particulate matter, and validation of EarthCARE ATLID based on the aerosol component analysis
method.
Ceilometer instruments are simple backscatter lidar systems and are usually set in airports for detecting the
base of clouds. The instrument can also measure aerosol vertical distribution. Since ceilometers barely detect
the molecular backscatter signals, retrieval of aerosol optical properties is an issue. This study investigates
applicability of ceilometers to retrieval of optical properties. We make an idealized signal profile with the lidar
ratio of 50 sr and calculate the retrieval errors caused by 30% errors of lidar ratio. In the forward inversion,
useable (small error) optical properties are backscattering coefficients and the retrieval errors are less than 15% if
the aerosol optical depth (AOD) is less than 0.2. The initial backscattering coefficients must be determined from
other instruments (e.g., multi-wavelength lidar). Whereas in the backward inversion, if the AOD of idealized
signals is larger than 1.5, extinction coefficients converge to the true value (within 5% errors), regardless of lidar
ratios and initial conditions. Since there is no need for the system constant or molecular backscatter in this
method, ceilometers can be an effective tool for retrieving extinction coefficients of dense aerosols in East Asia.
Aerosol component analysis methods for characterizing aerosols were developed for various types of lidars including polarization-sensitive Mie scattering lidars, multi-wavelength Raman scattering lidars, and multi-wavelength highspectral- resolution lidars. From the multi-parameter lidar data, the extinction coefficients for four aerosol components can be derived. The microphysical parameters such as single scattering albedo and effective radius can be also estimated from the derived aerosol component distributions.
We have conducted ground-based lidar network observations in wide areas of East Asia using two-wavelength (532 and
1064nm) backscatter and one-wavelength (532nm) depolarization Mie-scatter lidars for more than ten years. To realize
more advanced aerosol classification and retrieval, we improved the Mie-scatter lidars at several main sites by adding a
N2 Raman scatter measurement channel (607nm). This Mie-Raman lidar system provides 1α+2β+1δ data at nighttime: extinction coefficient (α) at 532nm, backscatter coefficients (β) at 532 and 1064nm, and depolarization ratio (δ) at 532nm. We also developed an algorithm to estimate vertical profiles of 532nm extinction coefficients of black carbon,
dust, sea-salt, and air-pollution aerosols consisting of a mixture of sulfate, nitrate, and organic carbon substances
(SF-NT-OC) using the 1α+2β+1δ data. With this method, we assume an external mixture of aerosol components and prescribe their size distributions, refractive indexes, and particle shapes. The measured lidar data are automatically
transferred to the NIES data server. We developed an algorithm to estimate particle optical properties (1α+2β+1δ data),
planetary boundary layer (PBL) height, and scene classification identifiers representing molecule-rich, aerosol-rich, or
cloud-rich layer automatically and provide their quick-looks in semi-realtime on the website
(http://www-lidar.nies.go.jp/shingakujutsu/Raman/).
A yellow dust event with moderate strength was observed on 9 April 2012 at Sendai in North part of Japan. Backward
trajectory calculations with NOAA HYSPLIT showed the complex flow of aerosols into the North Japan. The sharp edge
of this dust cloud was recognized by the data taken at several observatories, and the dust cloud conducted by low
pressure system had heterogeneous structure, therefore very complicated interaction among aerosols may occur. Mie
scattering lidar data was used to reproduce the radiative effect caused by this yellow dust event at Sendai with radiative
transfer model. The results estimated every 15 minutes of radiative forcing at the top of the atmosphere and at the bottom
of the atmosphere. The results show the slight warming effects < 6.5 W/m2 during night time both at the top and the
bottom of the atmosphere, and during day time the large cooling effects < 150 W/m2 at the bottom and < 60W/m2 at the top of the atmosphere.
This paper presents the results of recent studies on tropospheric aerosols, including Asian dust and forest fire smoke
using the NIES Lidar Network, CALIPSO/CALIOP and chemical transport models. The NIES Lidar Network is a
network of two-wavelength (532nm, 1064nm) polarization (532nm) lidars in East Asia. Currently the lidars are
continuously operated at about 20 locations in Japan, Korea, China, Mongolia, and Thailand, in cooperation with various
research institutes and universities. The network is a part of the Asian Dust Network (ADNet), SKYNET, and the GAW
Aerosol Lidar Observation Network (GALION). The data from most of the lidar stations are transferred to NIES in
realtime and automatically processed to derive the attenuated backscattering coefficients at 532nm and 1064nm, the
volume depolarization ratio at 532nm, and the estimated dust and spherical aerosol extinction coefficients at 532nm. The
data from the network are used in various research activities on Asian dust, regional air pollution, and the effects of
aerosols on climate and the environment. The data are also used for real-time monitoring (for early warning assessment)
of Asian dust. The results of recent studies on long-range transport of Asian dust, optical characteristics of forest fire
plumes, aerosol climatology, etc. will be described.
We present a systematic comparison of different analyses of
satellite-retrieved extinction profile based on the
satellite - measurements with those derived from ground based Lidar. Also compared is the Lidar-derived aerosol optical depth
(AOD) with passive sensor derived from the Moderate Resolution Imaging Spectroradiometer (MODIS). The
Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) satellite data are used as these comparisons and
that is a bit complex because spatial and temporal coincident data for clear sky conditions are needed for its comparisons
to other Lidar data. Although limitation of the number of coincident dataset and expected errors are unknown, the
satellite based aerosol extinction coefficients agree to those measured by ground-based Lidar within 0.02km-1. The two
different satellite-derived AODs differ by 30% in comparison to the average of the coincident.
Observations of tropospheric aerosols (mineral dust, air-pollution aerosols, etc.) and clouds are being conducted using a
network of two-wavelength (1064nm, 532nm) polarization (532nm) lidars in the East Asian region. Currently, the lidars
are operated continuously at 23 locations in Japan, Korea, China, Mongolia and Thailand. A real-time data processing
system was developed for the network, and the data products such as the attenuated backscatter coefficients and the
estimated extinction coefficients for non-spherical and spherical aerosols are generated automatically for online network
stations. The data are used in the real-time monitoring of Asian dust as well as in the studies of regional air pollution and
climate change.
Concentration of suspended particulate matter less than 2.5 μm (PM2.5) is a representative parameter of air quality.
Simultaneous measurements of PM2.5 and the column aerosol optical thickness (AOT) have been performed at a
NASA/AERONET station, Higashi-Osaka, Japan since March 2004. They successfully provide a linear correlation
between PM2.5 and AOT. A Mie scattering lidar instrument was deployed at the same observational site in April, 2008.
It provides us with the attenuated backscattering coefficients of aerosols at wavelengths of 0.532 and 1.064 μm, which
indicate the vertical distribution of aerosols. This work intends to improve the correlation between AOT and PM2.5 by
using the measurements of lidar.
We conduct network observations using ground-based Mie-scattering lidars in Asian region in cooperation with various research organizations and Universities. Primary purpose of the network is for studying generation and transport of Asian dust, observing air pollution and biomass burning aerosols for atmospheric environment studies, observing aerosol vertical distribution and temporal variation for atmospheric radiation studies and climatology, and for validation of chemical transport models and satellite remote sensors. At present, lidars are operated continuously at twelve locations in Japan, China, Korea, and Thailand. The lidars used in the network are two-wavelength (532 nm and 1064 nm) Mie-scattering lidars having depolarization measurement function at 532nm. Flashlamp-pumped compact Nd:YAG lasers are used as the light source. We developed a method for estimating the extinction coefficient of non-spherical air-pollution aerosols separately using the depolarization ratio. This method is based on a simple assumption that observed aerosols are external mixture of two types of aerosols, but it is practically very useful especially for inter-comparison with chemical transport models. We also studied a method for characterizing aerosols using the depolarization ratio and the wavelength dependence of the backscatter coefficient. Asian dust phenomena were observed with the network since spring of 2001. The frequency of the occurrence of dust events and the vertical distribution characteristics were analyzed. Also, seasonal and year-to-year variations were analyzed. At the same time, transport of dust and air-pollution aerosols were studied by comparing the temporal variation of lidar profiles with chemical transport model results.
This paper reports on the results of measurements of the aerosols and the clouds optical properties in the troposphere over Tsukuba, Japan (104.12°E, 36.05°N, 27 above sea level). We carried out the experiments using a high-spectral resolution lidar based on iodine absorption filter with a working wavelength 532 nm and have the opportunity of polarization characteristics of the lidar signal. The results from simultaneously observations of particle backscatter and extinction profiles, lidar ratio (extinction to backscatter ratio) and depolarization ratio during on the four annual seasons are presented. We analyzed the seasonal variations of the particle backscatter, extinction and lidar ratio to investigate climatology of aerosol optical properties, and especially lidar ratio, over this region. The experimental results are compared with results obtained over another places and techniques.
The indirect effect of aerosols in the atmospheric radiation process, which is the effect of aerosols through the formation of clouds, is one of the most uncertain factors in the current climate models for predicting global warming. To study the effect of aerosols on cloud formation quantitatively, a method for measuring cloud particle size is indispensable. A bistatic lidar method was developed for measuring water cloud particle size at the cloud base. The method is based on single scattering Mie theory. A simple measurement system that consists of a single-wavelength laser and dual-polarization bistatic receivers was developed. Experiments were conducted using the 532 nm beam of the Mie scattering lidar on board the research vessel Mirai. An additional bistatic receiver having polarization analyzers was located at a suitable scattering angle. Cloud particle size (mode radius of the assumed size distribution) was derived from the ratio of the polarization components of the scattered light based on the single scattering Mie theory. Particle size of maritime cumulus and stratus near the cloud base was measured. The particle size profiles in the clouds up to a penetration depth of about 50 m were observed with the method. At a larger penetration depth, effect of multiple scattering dominated the return signals.
Automated Mie-scattering lidars
have been operated since March 2001 at Beijing,
Nagasaki and Tsukuba to reveal the time and height distribution
of Asian dust and its optical properties.
The lidars detect backscattering light from clouds and aerosols
at 532nm in both parallel and perpendicular polarization channels.
They continuously measure profiles every 15 minutes
regardless of weather conditions.
At first we eliminated clouds using vertical profiles of intensity,
then Asian dust was identified by the depolarization ratio.
In Beijing, close to the source region of the dust,
Asian dust events occurred 15 times in March April, and May 2001.
Each event continued for several days. The aerosol depolarization
ratio (ADR) frequently reached up to 40 %.
In Nagasaki, located western part of the Japan, Asian dust was
confirmed near the surface with a delay of a few days from
events in Beijing.
However, in Tsukuba, there were few surface dust events
and passing dust in the free troposphere was confirmed.
The ADR in Tsukuba were lower than those in other two observatories.
Internal mixing of mineral dust and anthropogenic aeorols,
and changing size distribution
may contribute the differences of ADR among observatories.
In Beijing, ground sampling of mineral dust was simultaneously
carried out.
Mass concentration by the sampler at the surface and
extinction coefficient near the surface derived from lidar observation
were compared to estimate the conversion factor from extinction
coefficient to mass concentration.
Utilizing this factor we estimated the vertical distribution of the mass
of Asian dust in Beijing.
The climatology of tropospheric clouds and aerosol layer are studied with the results of observation by Compact Mie- scattering Lidar (CML) located at Tsukuba, Japan. The operation of CML is fully automated and the data have been collected constantly every 15 minutes regardless of weather conditions. Therefore the results of the observation by CML are devoted to statistical analyses of characteristics of aerosols and clouds. Range-corrected signal intensity from the zenith during June 1996 and August 2000 was analyzed to detect the cloud base and the top of aerosol layer. Multi-modal distribution of clouds were detected and the annual and year-to-year variation of them were confirmed. Though the distribution of the top of aerosol layer also indicated temporal variations, the characteristics were little complicated and general tendency was obscure. Backscattering coefficients in the lower troposphere were also inferred using Fernald's method when there was no cloud in the lower layer. The annual and diurnal variations were examined and characteristics of profiles of backscattering coefficients were dependent on the seasons.
A new multi-FOV space-borne lidar named "A-lidar" is being studied by the National Space Development Agency of Japan (NASDA) for the earth radiation mission proposed as a joint program with the European Space Agency (ESA). The mission is named "EarthCARE". It was formerly called ATMOS-B1 or ERM. The lidar has a two-wavelength transmitter (1064 nm and 532 nm), a dual polarization receiver at 1064 nm, and a multi-field-of-view (multi-FOV) receiver at 532 nm. The multi- FOV feature of A-lidar will enable us to solve the multiple scattering problems with space lidar measurements of profiles of clouds and aerosols. The multi-FOV feature can also be used for characterization of aerosols.
Observations of aerosols and clouds have been conducted in the Pacific with a ship-board Mie scattering lidar using the research vessel Mirai. The purpose of the observations is to obtain global distribution of aerosols and clouds over the Pacific Ocean for climatology and studies of radiative processes and ocean-atmosphere interaction. The data are used also in the study of data reduction and utilization methods for the space-borne lidars. The lidar for R/V Mirai is a two-wavelength Miescattering lidar (532 nm and 1064 nm) using a flashlamp pumped Nd:YAG laser. It has a depolarization receiver at 532 nm. We have performed observations in six cruises of R/V Mirai since 1999. Cloud distribution, cloud phase, vertical distribution of aerosol, wavelength dependence of aerosol backscatter, etc. have been analyzed. The parameters measured with the lidar, i.e. backscatter at two wavelengths and depolarization, are similar to space-borne lidars such as PICASSO and the Japanese "A-lidar". The results of the observations demonstrate the usefulness of a two-wavelength polarization lidar.
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