Over the past 24 years, the AErosol RObotic NETwork (AERONET) program has provided highly accurate remote-sensing characterization of aerosol optical and physical properties for an increasingly extensive geographic distribution including all continents and many oceanic island and coastal sites. The measurements and retrievals from the AERONET global network have addressed satellite and model validation needs very well, but there have been challenges in making comparisons to similar parameters from in situ surface and airborne measurements. Additionally, with improved spatial and temporal satellite remote sensing of aerosols, there is a need for higher spatial-resolution ground-based remote-sensing networks. An effort to address these needs resulted in a number of field campaign networks called Distributed Regional Aerosol Gridded Observation Networks (DRAGONs) that were designed to provide a database for in situ and remote-sensing comparison and analysis of local to mesoscale variability in aerosol properties. This paper describes the DRAGON deployments that will continue to contribute to the growing body of research related to meso- and microscale aerosol features and processes. The research presented in this special issue illustrates the diversity of topics that has resulted from the application of data from these networks.
The AErosol RObotic NETwork project (AERONET; Holben et al., 1998) has
provided significant contributions to remote sensing of aerosols during the
course its 24-year history. Observations have largely been utilized to
validate satellite retrievals of aerosol optical depth (AOD) (e.g., Ichoku et
al., 2002; Kahn et al., 2005; Remer et al., 2002; Sayer et al., 2012),
characterize aerosol absorption and size distributions (e.g., Dubovik et al.,
2002), and evaluate model products (e.g., Kinne et al., 2003; Sessions et
al., 2015) and more recently forecasts through assimilation (e.g., Randles et
al., 2017; Rubin et al., 2017) of aerosol properties. These investigations
have largely been dominated by the highly accurate observations of extensive
properties such as spectral AOD, and as more data became available, the
intensive products retrieved from inversions of the radiative transfer
equation such as a complex index of refraction and particle size distribution
have come to the fore. The accuracy of the ground-based AERONET
quality-assured (Level 2) point observations of aerosol optical depth is very
high and therefore is considered a “ground truth” for most satellite and
model comparison purposes. AOD is a direct measure of a column-integrated
spectral property and can be derived from essentially an instantaneous
measurement. Thus, the only uncertainty arises from calibration and
contamination from outside influences such as optical and digital
contamination in the instrument in some rare cases and cirrus clouds (e.g.,
Chew et al., 2011). Given the accuracy of the calibration (Eck et al., 1999)
and processing algorithms (Smirnov et al., 2000, and manual quality assurance
assessment), the accuracy of Level 2 AOD is estimated to be
The accuracy of the intensive AERONET aerosol properties (single scattering
albedo, particle size distribution, and complex index of refraction) is less
clear due to larger uncertainties in the inversion retrievals and difficulty
in obtaining adequate verification data from other methodologies. These
properties are extinction-weighted atmospheric-column integrated properties
that exhibit different uncertainties than the wide variety of techniques
associated with in situ measurements and estimates. The retrieval
uncertainties of the column-integrated aerosol properties inverted by the
Dubovik and King (2000) algorithm are well discussed in Dubovik et
al. (2000); however, the additional uncertainty ins the measurement techniques
is very difficult to assess due to atmospheric variability during the time
of observations. The uncertainties associated with in situ techniques are
well discussed by Reid et al. (2003, 2008b, 2005, 2006) for the size
distributions of dust, smoke, and sea salt aerosols. Andrews et
al. (2017) found that, provided the AERONET guidelines of only using
absorption or an index of refraction data when 440 nm AOD
AERONET and other ground-based remote-sensing systems have the distinct
advantage of the time domain with direct sun measurement frequencies of
seconds to minutes throughout the day and in some instances at night.
Nominally, the AOD sampling frequency for AERONET network measurements is
15 min, and more recently 3 min, intervals for sites with sufficient
communication infrastructure. The measurements of sky radiance used to
retrieve the inversion products are nominally taken hourly for AERONET but in
some instances are taken more frequently such as early in the morning and
late in the afternoon when optical air mass changes rapidly. Other networks
such as the SKYNET network
(
Individual ground-based systems inherently do not represent the spatial variation in aerosol properties. Thus, they complement the satellite retrievals and regional and global model predictions. Typically, a spatial-scale bridge to the ground-based measurements (including in situ) to satellite and model assessments has been through aircraft observations. Aircraft flights occur over ground-based point observations from profiles and various altitude transects extending tens, hundreds and thousands of kilometers and can provide spatial continuity during intensive field operations that enables scaling point location observations to the satellite observations and regional model simulations.
Field campaigns are of limited duration and aircraft flights are often discontinuous during the measurement campaign. The following question arises: is there a need for continuous high spatial- and temporal-resolution aerosol data that neither a single point nor airborne, satellite, or model results address? Furthermore, is there an approach that will clarify the uncertainty in comparisons of in situ and remote-sensing aerosol properties? In hindsight and with some foresight, the answers have proven to be yes and yes.
The series of Distributed Regional Aerosol Gridded Observation Network
(DRAGON) campaigns began in 2011 primarily as a means to encourage
collaboration between remote-sensing and in situ communities to compare
measurements and retrievals of the intensive properties of aerosol particles,
such as single scattering albedo (SSA), particle size distribution, and
complex index of refraction. Note that earlier DRAGON-like campaigns (e.g.,
UAE Unified Aerosol Experiment, UAE
Principle intensive parameters retrieved by sun and sky scanning spectral radiometers for five aerosol types. Sixteen published validations/comparisons of these retrievals against in situ measurements were made during field campaigns prior to 2010. Ra: Ramanathan et al. (2001); Re: Remer et al. (1997); H: Haywood et al. (2003); L: Leahy et al. (2007); B: Bergstrom et al. (2003); Chand et al. (2006); E: Eck et al. (2010); M: Müller et al. (2010); Mü: Müller et al. (2012); Rp: Reid et al. (2003); Ru: Reid et al. (2008b); S: Smirnov et al. (2003); Sc: Schafer et al. (2008); T: Toledano et al. (2011); O: Osborne et al. (2008); and J: Johnson et al. (2009). Note that most categories are incomplete (–), are not updated for the current inversion algorithm, and/or not relevant to total-column ambient retrievals.
The aerosol types detectable from remote-sensing (RS) techniques and compared with in situ field measurements. We show only those direct RS–in-situ comparisons. Unlike Table 1, here the aerosol type describes the properties of the aerosols rather than sources. We acknowledge that aerosol typing is difficult and still subjective and incomplete. (C: Corrigan et al., 2008; E: Esteve et al., 2012; Sc: Schafer et al., 2014, 2017). Some studies appearing below are given in the caption of Table 1.
The description of the aerosol size distribution is of primary importance as
a first-order physical and optical parameter corresponding to particle size
and the associated concentration of variously sized particles. Coarse-mode
aerosol is sometimes considered to have a particle radius of greater than
1 micron (
Generally, natural sources for coarse-mode hygroscopic sea salt aerosol are
breaking waves and associated bursting water bubbles. These particles are
nominally spherical at most ambient relative humidity over the ocean, with
AOD typically dominated by particles larger than 0.5
The fine-mode (or accumulation-mode) aerosols are sometimes loosely referred
to in the literature as either urban/industrial or biomass burning. These
terms were convenient in the early days of remote sensing but are only a
rough guide to our greater understanding of their diversity and properties.
The range of fine-mode aerosol types that contribute to remote sensing can be
rather daunting and often does not exist in a single type distribution in the
atmosphere. Artaxo et al. (1994) in early work and continuing with Fuzzi et
al. (2007), among many others, have made extensive
investigations of the smoke aerosol generated during the burning season in
the Amazon basin that includes both black carbon particles from flaming-phase
burning and primarily brown carbon particles that are organic and from both
flaming and smoldering combustion (Falkovich et al., 2005). Particle sizes
are generally less than 1
Table 2 shows those studies that have objectively assessed all of the known direct comparisons of aerosol properties of AERONET to in situ measurements.
The DRAGON field campaigns were developed in consideration of the spatial and temporal advantages and disadvantages of remote-sensing systems and in situ systems for ground-based, aircraft-based, and remote-sensing systems. In the previous section we described generally the assets available for a typical AERONET deployment. Table 3 presents an overview of the DRAGON campaigns, including the dominate aerosol type, the time frame, the approximate range of aerosol characteristics from a remote-sensing perspective, and the principle contact for each campaign. We have attempted to provide an exhaustive list up to the time of this writing, and this table will be maintained and updated on the AERONET website as new information is received.
The distribution of DRAGON campaigns conducted from 2004 to 2016 are framed in yellow with red labels. Yellow labels indicate larger campaigns with dashed frames that include DRAGON networks.
The method of the DRAGON campaigns was to establish a high density of ground-based sun and sky scanning spectral radiometers within a local or mesoscale region to capture small-scale aerosol variations. For this discussion we present those distributions over tens to hundreds of kilometers and a time period of weeks to months. Very early studies dating back to the 1950s by Flowers et al. (1969) showed regional to continental-scale variations across the US, and in the 1980s sun photometry documented regional Sahelian aerosol loading during the drought (d'Almeida, 1986; Holben et al., 1991). The 1990s brought AERONET regional measurements to the Amazon Basin (Holben et al., 1996), the boreal forests in Canada called BOREAS (Markham et al., 1997), and southern Africa, with two campaigns called ZIBBIE (Eck et al., 2001) and SAFARI2000 (Swap et al., 2003; Eck et al., 2003). These and other regional investigations brought tremendous knowledge of aerosol properties over regions dominated by a single aerosol type; however, they could not address the variability in small-scale regional aerosol processes. They also came largely before the massive data collection ushered in by the EOS satellite era that began with Terra in 2000 and continues today from an expanding series of spaceborne quantitative Earth monitoring platforms. Figure 1 shows the location of DRAGON field experiments relevant to this paper.
The UAE
The CATZ campaign was the first AERONET Intensive Operation Period (IOP) to support CALIPSO aerosol retrievals. This was temporally synchronized with CALIPSO over-flights to assess the aerosol variability within the along-track averaged CALIPSO retrieval. Up to 12 AERONET sites were placed along 230 km of the daytime Aqua track within the CALIPSO footprint on the Delmarva Peninsula on seven different dates from late June to mid-August 2007. Very low to high aerosol loadings occurred, which were all fine mode dominated.
The TIGERZ campaign was an effort during the pre-monsoon of May 2008 to characterize the complex and high loading aerosol environment in the Indo-Gangetic Plain (IGP) of northern India in support of CALIPSO satellite-borne lidar validation. The deployment of additional instruments was centered around the long-term monitoring site on the IIT campus in the industrial city of Kanpur. The pre-monsoon aerosol environment is characterized by regional fine-mode haze from fossil fuel emissions, mostly from coal with episodic dust events both locally generated and regionally transported from the northwest. The local Kanpur City aerosol plume was enhanced by a megawatt power plant plume and numerous coal-fired brick kilns dotting the region. Despite local strong sources, the Kanpur aerosol properties were similar to a village site 400 km downwind (Giles et al., 2011). Sites were established specifically to be in and very near the CALIPSO footprint, and during May, captured the spatial variability and provided validation of CALIPSO retrievals. Sites were local to the descending CALIPSO track but had a radius of up to a 300 km around Kanpur.
The 7-SEAS interdisciplinary research program has a rich history of ground-based measurements in Southeast Asia beginning in 2007, including region-wide deployments of AERONET sites throughout the Maritime Continent (Indonesia, Malaysia, Philippines, Singapore) and peninsular Southeast Asia (Laos, Thailand, and Vietnam). Overall AERONET properties can be found in Reid et al. (2013). Specific to the DRAGON concept, the AERONET program collaborated with local scientists to develop two DRAGON programs during the August–September 2012 burning season. These programs were based at the National University Singapore (NUS) for Singapore and Universiti Sains Malaysia for Penang, Malaysia.
Penang Island is mountainous with an eastern coastal plain and lies 2 to 15 km offshore of mainland peninsular NW Malaysia, within the Strait of Malacca. Its densely populated capital of Georgetown (2 million) is across the Penang Strait from industrial Butterworth, while the Malacca Strait side of the island is rural. Anchored ships, industry, and automobile traffic contribute to fossil fuel emissions, while episodic pulses of biomass burning aerosols from Riau, Sumatra, Indonesia, added to a background of sea salt aerosol within the sampled 30 km transect. During September 2012, Universiti Sains Malaysia staff maintained eight AERONET stations. In addition to satellite and model validation, research was conducted specific to coastal areas with these data sets utilized for air quality investigations (see Tan et al., 2015a).
Singapore is a highly industrialized urbanized center on an island at the southern tip of the Malay Peninsula, with dimensions of approximately 30 km east–west by 20 km north–south . The regional population including Johor Bahru is well over 5 million. Thus, fossil fuel emissions from cars, petrochemical industries, and ships constitute a major portion of the aerosol sources; however, maritime aerosol from the South China Sea and the Straits of Malacca provide a rather constant but weak background regime. Biomass burning primarily from Sumatra and Kalimantan imposes an episodic and at times massive aerosol burden on the region. The September 2012 DRAGON campaign, in collaboration with NUS' Centre for Remote Imaging, Sensing and Processing (CRISP), afforded the opportunity to assess the variability in the aerosol loading in response to local and regional sources from six well-distributed AERONET sites and a suite of detailed ground-based measurements across the region.
DISCOVER-AQ was a NASA-sponsored Earth Venture Suborbital 4-year campaign
(2011 to 2014) to relate remote-sensing measurements to air quality
assessments at four selected sites across the United States (central
Maryland; Houston, TX; San Joaquin Valley, CA; Denver Front Range Region,
Colorado;
This campaign selected a highly urbanized and industrial region of the
mid-Atlantic that is subjected to high summertime humidity and periodic
pollution buildup. The studied region was approximately 125 km long,
following the I-95 corridor from the Washington Beltway north to the
Maryland–Delaware state line, and about 40 km wide, encompassing Baltimore,
agricultural fields, suburbs, and the Chesapeake Bay. Forty-three AERONET
sites were established 1 month prior to the campaign and continued
monitoring for approximately 1 month after. The meteorology was classic
mid-Atlantic for July, with daytime temperatures approaching 39
The San Joaquin Valley occupies the southern half of California's Central
Valley which is bounded by the convergence of the high Sierra Nevada range to
the east and a series of coastal mountain chains to the west. The valley is
flat, with intensive irrigated agriculture. The region is notable for the air
quality challenges to its 3 million inhabitants: freeway corridors and
intensive agriculture, including ammonia emissions and fugitive dust that
contributes to particularly strong air pollution in January and February. The
planetary boundary layer (PBL) is typically shallow at
Houston is a massively sprawling city with a downtown center approximately
30 km north of Galveston and the Gulf of Mexico. A dense petrochemical
industry borders the ship channel that bisects southern Houston, with
numerous sources of gases and aerosols complemented by automobile emissions
and other industry. Climatology showed that air quality is poorest during
August; thus, like the Maryland campaign, it afforded the best opportunity to
understand the processes relating emissions and air quality issues to remote
sensing. The aircraft tracks were largely square racetrack circuits with six
intensive vertical profiles over ground-based supersites. Seventeen DRAGON
AERONET sites were used to characterize the column aerosol properties for
3 months (July–September). A wide range of aerosol
conditions of mostly fine-mode aerosols with AOD ranging from
The northeastern plains of the front range of the Rockies formed the backdrop
for the last DISCOVER-AQ campaign conducted in July 2014. The airborne and
ground-based measurement campaign track included diverse landscapes and aerosol sources from central Denver
to suburban Fort Collins 130 km N and continued 50 km east to rural Greeley feedlots. The track turns south 30 km to Platteville, which is dominated by irrigated crops and intense fossil fuel exploration
and extraction. The track is closed by returning to Denver 40 km to the southeast. High temperatures and intense solar radiation characterized
July 2014. Aerosol optical depths averaged 0.2 at 500 nm and day-to-day
variations were typically small; however, several days of fine-mode aerosol
events elevated the AOD to
Northeast Asia faces arguably the most severe air quality issues on the
planet owing to the very high population density coupled with high levels of
industrialization and, additionally, its position downwind of major dust
source regions. These contribute to significant trans-boundary aerosol
transport compounded by emissions from several megacities in the region.
Given the AERONET limitations for retrievals with low uncertainty
(AOD
Seoul was the focus for half of the 22 AERONET surface stations deployed from
March to June 2012, including five permanent sites in South Korea with
long-term records. Seoul is a megacity of 25 million (metropolitan region)
spread across a landscape of the Han River plains, hills, and low-elevation
forested mountains. Industry and fossil fuel power generation contribute
emissions to a significant pollution aerosol loading in addition to aerosol
advected from China. South Korea in general is a landscape that is
challenging for satellite retrievals of AOD due to significant variation in
background surface reflectance and a varied topography (
Osaka, Japan, was the focus of a DRAGON campaign with eight AERONET sites; this was coincident in time with the DRAGON-KOREA campaign from March through June 2012. Osaka is a megacity of very dense urban development that is bounded by low mountains on three sides and Osaka Bay to the south (see Sano et al., 2016). Industry and transportation emissions are sources of the dominant background aerosol loading, and, as in Seoul, episodic coarse-mode dust and transported fine-mode industrial aerosols were observed during the 4-month intensive measurement period. Owing to two nearby mountain sites, boundary layer assessments were possible and were also facilitated by a mobile handheld sun photometer.
A second DRAGON network of six AERONET and one SKYNET sites on the small
(326 km
The SEAC
Additionally, another airborne and ground-based field campaign occurred during this time period called Southeast Nexus (SENEX; Warneke et al., 2016) that emphasized volatile organic compounds (VOCs) and aerosol precursors. This campaign was focused on Alabama, Georgia, and northern Florida. The regional network by its size captures the range of aerosol properties one would expect over the southeast US, including transported dust from west Africa, biogenic aerosols created from VOCs, fossil fuel emissions, coastal maritime aerosols, and biomass burning transported from fires in the western US.
Similarly to the DISCOVER-AQ campaigns, a focused airborne campaign called
KORUS-AQ was conducted across South Korea from 1 May to 12 June 2016 by the
National Institute of Environmental Research (NIER) and NASA. In situ and
remote-sensing resources were on board three aircraft flying from the near
surface to
In addition, a regional-scale campaign of ground-based remote-sensing and in situ measurements upwind and downwind of South Korea was conducted during this period. This included the Institute of Remote Sensing and Digital Earth SONET network, AERONET, and the China Aerosol Remote Sensing NETwork (CARSNET; Che et al., 2009, 2015) Cimel Sun–sky radiometer networks in NE China that contributed 20 stations focused eastward from Beijing and south to Shanghai. In collaboration with the Institute of Remote Sensing and Digital Earth of the Chinese Academy of Sciences and the University of Maryland, an airborne in situ aircraft-based study of the chemical composition of the atmosphere was also conducted during this period.
Coincidentally, an enhanced network of eight AERONET sites was distributed across Japan from Fukuoka in the south to Sapporo in the north. This network augments the extensive SKYNET network of sun–sky radiometers in Japan that provides similar aerosol observations to AERONET but also collocated lidar profiling and, in some supersite locations, in situ particle observations. Since there is overlap at some of the AERONET and SKYNET sites in South Korea and Japan, a unique and comprehensive comparison is planned between the networks.
The greater KORUS campaigns extensively sampled fine-mode aerosols from locally and regionally transported industrial and urban sources, biomass burning from Siberian fires, and regionally transported coarse-mode-dominated dust that strongly affected all countries on 5 May 2016 and to a lesser extent on several other days during the campaign. All aerosol types except for the Siberian biomass burning aerosols were also sampled during research aircraft flight days. The opportunity to assess accuracies and limitations of multiple satellite and AERONET retrievals and aerosol model forecasts for a variety of aerosol types and cloud and humidity conditions is expected to increase our understanding of the processes that govern air quality issues in NE Asia.
The NASA venture class suborbital program (ORACLES) is an ongoing airborne
campaign focused on biomass burning aerosol emissions from southern central
Africa transported over the South Atlantic to assess the aerosol–cloud
interaction over the persistent stratocumulus deck from August through
September 2016; it is planned for repeats in 2017 and 2018 (Zuidema et al.,
2016). Approximately 15 AERONET sites from Mozambique, Zambia, Angola,
Namibia, South Africa, St. Helena, and Ascension Island are providing regional context of aerosol
properties from source to receptor sites for the campaign. Additionally, a
tightly focused DRAGON network (seven sites in 20
DRAGON campaign summaries. D: dust; FF: fossil fuel;
B: biogenic; BB: biomass burning; M: maritime. Because of the time
period of measurement and the number and location of instruments and variable
aerosol types transported by synoptic-scale meteorology, AOD and particularly
SSA averages are approximate. Most campaigns are referenced at:
Three important research areas have emerged as a result of the DRAGON
campaigns: (1) in situ and remote-sensing aerosol properties comparisons;
(2) aerosol process studies; and (3) satellite and model validation studies.
The first DRAGON-like campaigns focused in part on in situ versus
remote-sensing comparisons of aerosol optical, radiative, and microphysical
properties. Although some of the associated publications both pre- and
postdate this issue, they do merit a brief discussion. Schafer et al. (2014)
showed an average difference of
Process studies have also broadened the research horizon possible from these data sets, some of which appear in this special issue. For example Eck et al. (2014) used the DISCOVER-AQ Maryland DRAGON network observations to study the effect of non-precipitating cumulus clouds on AOD in adjacent regions on a horizontal scale of a few kilometers. They found that on some days, the Ångström exponent and size distribution were relatively constant while AOD was significantly enhanced (sometimes doubling in less than 1 h) near moderately sized cumulus clouds. These results were corroborated by airborne lidar and airborne in situ measurements. This has potential implications for the need for a better understanding of small-scale high temporal variations in aerosol–cloud processes and potential particle formation in clouds.
Much of the research activity with the DRAGON campaigns focused on air
quality, relating remote-sensing parameters to surface PM
The DRAGON-Asia campaigns were used to broadly describe trans-boundary
advection of aerosols as a DRAGON-scale network in Osaka was imbedded in a
regional-scale network over southern Japan (Sano et al., 2016). This analysis
showed that, during episodic long-range trans-boundary transport, aerosol
loading was highest in the west of Japan but highly variable in space and
time both for fine- and coarse-mode aerosol events. The long-range
trans-boundary aerosols during this period were shown to follow the
NCEP-derived 700 to 850 mb wind vectors. Sano et al. (2016) investigated the
variability in AOD under clean and polluted days in Osaka using DRAGON
network measurements. They also detailed aerosol transportation over the city
using high spatial- and temporal-resolution measurements by DRAGON-Osaka.
Owing to two nearby mountain sites, boundary layer assessments were possible,
facilitated by nearby DRAGON-Osaka and AERONET stations. The DRAGON-Fukue
instruments did not capture the intense 10–11 March fine-mode event due to
cloud contamination. However, the authors successfully measured the event by
judiciously timed, handheld Microtops-II sun photometer observations (Nakata
et al., 2016). The value of AOD at 440 nm was over 2. Takami et al. (2013)
reported a particle composition of less than 1
Tan et al. (2015b) investigated the ability to use surface-based measurements
to predict AOD in the cloudy tropics of Penang, Malaysia, where data gaps can
be frequent and persistent. His predictive model had an
By far the largest application of the DRAGON data sets has been in the validation of satellite data. Most synoptic-scale validation teams assume a spatial uniformity about a ground-based control point, often citing the Anderson et al. (2003) nominal scale length of 100 km. Frequently, queries are made about the spatial representation of AERONET sites, for which there is no simple answer due to the proximity to aerosol sources and local and synoptic meteorology. The DRAGON campaigns have provided a better understanding for some specific circumstances that provide for a better assessment of the spatial resolution of various satellite products and also of high- and low-resolution model assessments. Prior to this issue, Munchak et al. (2013) noted the new Collection 6 MODIS 3 km AOD product could potentially assess local aerosol gradients missed by the standard 10 km resolution product. They used the MD DISCOVER-AQ airborne high spectral-resolution lidar and MD DRAGON data sets to assess the fidelity of the 3 km AOD product, finding improvement over the coarse-resolution product but some additional variability due to the complexity of urban cover types. Kim et al. (2016) used the DRAGON- NE Asia networks to refine the single scattering input to a single channel AOD retrieval model used with the GEO COMS Meteorological Imager (MI). They note that the surface-based inputs from DRAGON significantly improved the model to predict AOD, thereby reducing previous over-estimates.
The Ozone Monitoring Instrument (OMI) on board Aqua has been a pioneering instrument to retrieve SSA and AOD from space in the UV spectrum. Jeong et al. (2016) have used the DRAGON NE-Asia data set in an optimal-estimation procedure that provides error estimates while simultaneously retrieving inversion products. This method was shown to compare better to the ground-based measurements than the OMI operational retrieval. From this validation, the authors identified the parameters that most affected the AOD and SSA retrieval accuracy.
In a comprehensive comparison of the high temporal-resolution Geostationary Ocean Color Imager (GOCI) and polar orbiting VIIRS and MODIS instruments, Xiao et al. (2016) used DRAGON NE-Asia and additional AERONET observations in 2013, which encompassed a broad range of conditions from low to high aerosol loading. Their analysis suggests that the satellite products do a better job of tracking aerosol variability on a day-to-day basis than tracking the high-resolution spatial variability.
Choi et al. (2016) used the DRAGON NE-Asia data sets to evaluate the GOCI AOD retrievals using the improvements to the GOCI Yonsei Aerosol Retrieval (YAER) algorithm. The algorithm makes retrievals over the Yellow Sea that often have Case II waters (highly turbid from sediment) as well as the highly variable South Korean landmass reflectances during periods with highly variable aerosol types and concentrations. GOCI YAER AOD correlated very well with AERONET but showed lower skill with the Ångström exponent, fine-mode fraction, and SSA.
Garay et al. (2017) have assessed the current 17.6 km resolution AOD products against multiple diverse DRAGON data sets collected around the world. They found that 75 % of the data fell within 0.05 of the AERONET surface-based measurements. They document the development and assessment of a prototype version of high-resolution (4.4 km) retrieval products compared to the same DRAGON data sets.
The DRAGON campaigns afford the opportunity to observe and assess aerosols
for a variety of aerosol types and meteorological conditions. Sixteen
multi-month mesoscale DRAGON campaigns were conducted and described that
measured and/or retrieved intensive and extensive aerosol properties at high
spatial and temporal resolution. The results shown in these studies challenge
the long-held assumptions of large-scale aerosol spatial uniformity as too
simplistic and provide data for the improvement of accuracies of higher-resolution satellite and model retrievals; they also afford a deeper
understanding of aerosol process studies. From the DRAGON campaigns, we now
know that (1) in situ and ground-based remote sensing of SSA has differences
averaging
The unique opportunities for the validation of high spatial-resolution satellite aerosol retrievals and the assessment of regional model estimates of aerosol optical, radiative, and microphysical properties are only beginning to be examined. The DISCOVER-AQ and KORUS-AQ campaigns in concert with in situ surface and airborne measurements provide for detailed comparison with and assessment against remotely sensed aerosol properties, and further results are expected. The papers presented in this issue demonstrate the variety of research opportunities and set the stage for new applications such as nighttime lunar mesoscale AOD assessments from the most recent KORUS-AQ and ORACLES campaigns, and also for future DRAGON networks.
The AERONET data described in this publication and the
DRAGON special issue represent Version 2 processing and are publicly
available from the AERONET website data tools:
The authors declare that they have no conflict of interest.
This article is part of the special issue “Meso-scale aerosol processes, comparison and validation studies from DRAGON networks”. It is not associated with a conference.
All of the AERONET scientists and technical staff have contributed to all
phases of the DRAGON-related campaigns since 2004. Their efforts have been
fundamental to the concept, data collection, and analysis of the DRAGON data.
Those not named as coauthors include Wayne Newcomb, Amy Scully, Oleg Dubovik,
Don Ho, Alex Tran, Jon Robriguez, and Jason Kraft. Each campaign had a
significant non-NASA team of which the PI lead is named in Table 3 and is a
co-author but was supported by their own team and institution. For AERONET
support, we wish to thank the EOS Project Science Office and the Radiation
Sciences Program at NASA HQ. We thank the Global Change Observation Mission – Climate project by JAXA (no.
JX-PSPC-434796) and JSPS KAKENHI Grant Number 15K00528 for their support in
Japan. The work in Korea was supported by the National Institute of
Environmental Research (NIER) of Korea, Ministry of Environment(MOE), as a
“Public Technology Program based on Environmental Policy (RE201702180)”.
The DRAGON network deployments for the four DISCOVER-AQ missions were
supported by the NASA Earth Venture – Suborbital program. We would like to
thank the flight crew from both NASA B200 and P-3B and the DISCOVER-AQ team
members for their support during these missions. The Naval Research
Laboratory staff participation was supported by the Office of Naval Research
Code 322 and the NASA Interdisciplinary Science program. ORACLES
contributions were funded under Earth Venture Suborbital-2 grant
13-EVS2-13-0028. The work of Qingyang Xiao and Yang Liu was partially
supported by the NASA Applied Sciences Program (grant nos. NNX16AQ28G,
NNX14AG01G, and NNX11AI53G). A special thank you goes to our in-country
partners Abdulla Al Mandoos and the National Centre for Metrology &
Seismology for the UAE