Airborne and satellite observations have successfully extracted a wealth of information about clouds, aerosols, and the Earth’s surface. These observations can be significantly complemented by the long-term ground-based radiation data provided by the Multi-Filter Rotating Shadowband Radiometers (MFRSRs) supported by the U.S. Department of Energy’s (DOE) Atmospheric Radiation Measurement (ARM) Program. Until recently, ARM-supported MFRSRs measured total irradiance and its direct and diffuse components at six wavelengths (415, 500, 615, 675, 870, and 940 nm). The limited number of wavelengths and the narrow spectral range of these MFRSRs prevent improved retrievals of aerosol, cloud, and surface characteristics. For example, spectrally resolved aerosol optical depth derived from the direct irradiance measured across a wide spectral range offer a valuable avenue for improved estimations of aerosol size distributions, especially for large particles. To address these limitations, ARM has supported the development of two successors to the MFRSR. The first, the MFRSR-7nch, includes a seventh narrowband channel at a 1625 nm wavelength, while the second, the Shortwave Array Spectroradiometer-Hemispheric (SAS-He), features increased spectral coverage (350-1700 nm) and hyperspectral capabilities. The performance of these successors is thoroughly evaluated under a wide range of atmospheric conditions, including different aerosol and cloud types and significant variability in aerosol loading. Our presentation will highlight the design, evaluation, and anticipated applications of these advanced radiometers.
Knowledge of the spectral behavior of aerosol optical depth (AOD) over the solar spectrum is required for realistic estimates of aerosol radiative forcing. To describe this behavior over an extended period, individual AOD records provided by several co-located ground-based instruments with different design and operation characteristics need to be combined. There are three main challenges associated with such combining; these stem from differences between the instruments in terms of: (1) data quality, (2) continuity, and (3) the measurement wavelengths of each instrument . The first two challenges have been addressed successfully using our approach (Kassianov et al., 2021). Here we demonstrate how the third challenge can be addressed to generate combined AODs at different wavelengths. In particular, we consider generation of the combined AODs at five wavelengths (415, 500, 615, 673, 870 nm) for a 21-year period (1997-2018) using individual AOD records obtained from four instruments deployed at a US continental site. We also discuss wavelength-dependent uncertainties of the generated AODs and future applications of this extended approach for different sets of wavelengths and locations.
Kassianov, E., Cromwell, E., Monroe, J. et al. Harmonized and high-quality datasets of aerosol optical depth at a US continental site, 1997–2018. Sci Data 8, 82 (2021). https://doi.org/10.1038/s41597-021-00866-2
For many years, in-person SPIE Conferences stimulated active and fruitful discussions regarding the remote sensing, its impressive applications and future directions. This year, digital Conference takes place. Conference Chairs and SPIE Organizing Committee welcome all participates and their valuable contributions. These contributions will be highlighted by invited and contributed presentations during two live-stream sessions arranged on Monday and Tuesday. We encourage all speakers to give condensed talks and reserve time for short discussions. It is expected that total duration of talks and subsequent discussions will not exceed 15 minutes for invited presentations and 10 minutes for contributed presentations. Participants can virtually raise their hands to ask questions or submit them in Q and A box. Several factors, such as different time zones and technical issues associated with unacceptable connections, can represent challenges for the arranged live-stream sessions. Well, let us do our best to manage these sessions smoothly and include networking and live elements to our online meeting.
Long-term records of aerosol optical depth (AOD) with high quality, suitable temporal continuity and spatial coverage are of immense interest to climate-related research activities. Both satellite- and ground-based measurements of AOD are typically provided by instruments with different designs, and distinct data acquisition and processing schemes. Thus, the corresponding AOD records likely have different accuracy, spatial coverage, and temporal resolution. Several studies have been focused on the synergy of multi-sensor satellite AOD products. Here we combine multi-year (1997-2018) AOD records available from four collocated ground-based instruments deployed at the mid-continental Southern Great Plains (SGP) Central Facility supported by the U.S. Department of Energy Atmospheric Radiation Measurement (ARM) Program. We demonstrate how to minimize drawbacks (patchy spots) and to maintain benefits (high quality) of these records. Our demonstration finds a combined AOD obtained at two wavelengths (500 and 870 nm), with high temporal resolution (1-min), and provides the user with an estimate of the AOD uncertainty. Finally, we highlight expected applications of the merged dataset and its future extensions.
We develop a new climatology of the macrophysical properties of single-layer shallow cumuli (ShCu), such as cloud amount and cloud base/top heights, observed during 19 summers (2000-2018) at the Atmospheric Radiation Measurement (ARM) Program’s Southern Great Plains (SGP) Central Facility in northern Oklahoma, USA. Similar to the established datasets, the climatology incorporates the well-known advantages of the narrow field-of-view (FOV) lidar-radar measurements to resolve the vertical structure of clouds along the wind direction. In contrast to these datasets, the climatology combines the well-known advantages of the wide-FOV sky images to describe the horizontal changes of cloud amount across the wind direction. The recent update includes (1) a new tool for visualization of these across-wind changes with user-selected spatial and temporal resolutions, (2) an additional macrophysical property, the so-called cloud equivalent diameter (CED), estimated over a wide range of cloud sizes (about 0.01–3.5 km) with high temporal resolution (30s) and (3) environmental parameters. Our development of the extended climatology is aimed to enhance understanding of the environmental impact on the diurnal evolution of the cloud macrophysical properties and thus to improve performance of ShCu parameterizations.
Substantial difference between cloud amounts obtained from active and passive remote sensing has been documented by previous studies. The difference is typically attributed to two main factors: the different field-of-view (FOV) (first factor) and different sensitivity to cloud properties (second factor) of the active and passive ground-based instruments. The relative impact of these two main factors on shallow cumuli cloud amount is demonstrated in this study. The demonstration involves a new multi-year (2000-2017) product, which integrates both the active and passive remote sensing data collected at the mid-continental Atmospheric Radiation Measurement (ARM) Southern Great Plains (SGP) Central Facility. Cloud fraction (CF) obtained from the narrow-FOV lidar-radar observations and wide-FOV fractional sky cover (FSC) acquired from sky images are key components of the integrated product. Results of this study indicate that (1) CF tends to overestimate FSC and this overestimation can be large (~40% on average) even at extended temporal scales (several years) and (2) the observed overestimate is primarily due to different sensitivity of the active and passive remote sensing instruments to shallow cumuli, while the limited FOV of active remote sensing instruments plays a minor role in such overestimation.
The total aerosol burden in the atmosphere is typically represented by aerosol optical depth (AOD). To capture important and climate-relevant signatures of the aerosol burden, such as year-to-year and seasonal variability, continuous multi-year AOD observations are required. For more than two decades, these observations have been performed at the mid-continental Atmospheric Radiation Measurement (ARM) Southern Great Plains (SGP) Central Facility (CF) using ground-based passive remote sensing. The partially overlapping and fragmentary AOD records at the ARM SGP CF have been provided by four individual instruments, namely two co-located (C1 and E13) Multifilter Rotating Shadowband Radiometers (MFRSRs), a Normal Incidence Multifilter Radiometer (NIMFR), and a Cimel Sunphotometer (CSPHOT). Since these individual records are sporadic with instrument- and time-dependent data quality, development of a continuous multi-year high-quality AOD dataset is a challenging task. In this work, an initial development of a continuous 20-year (1997-2017) high-quality AOD product is introduced. The development involves (1) incorporation of the available data quality information and delivery of the historical time series of AOD with high quality from four individual instruments, (2) comparison of multiple AOD retrievals to identify potential instrument-related issues and/or retrieval problems, and (3) merging these individual time series, generation of a two-decade continuous climatology of high-quality AOD and reporting of the uncertainty estimations of the merged product.
Cloud amount is an essential and extensively used macrophysical parameter of cumulus clouds. It is commonly defined as a cloud fraction (CF) from zenith-pointing ground-based active and passive remote sensing. However, conventional retrievals of CF from the remote sensing data with very narrow field-of-view (FOV) may not be representative of the surrounding area. Here we assess its representativeness using an integrated dataset collected at the U.S. Department of Energy (DOE) Atmospheric Radiation Measurement (ARM) program's Southern Great Plains (SGP) site in Oklahoma, USA. For our assessment with focus on selected days with single-layer cumulus clouds (2005-2016), we include the narrow-FOV ARM Active Remotely Sensed Clouds Locations (ARSCL) and large-FOV Total Sky Imager (TSI) cloud products, the 915-MHz Radar Wind Profiler (RWP) measurements of wind speed and direction, and also high-resolution satellite images from Landsat and the Moderate Resolution Imaging Spectroradiometer (MODIS). We demonstrate that the root-mean-square difference (RMSD) between the 15-min averaged ARSCL cloud fraction (CF) and the 15-min averaged TSI fractional sky cover (FSC) is large (up to 0.3). We also discuss how the horizontal distribution of clouds can modify the obtained large RMSD using a new uniformity metric. The latter utilizes the spatial distribution of the FSC over the 100° FOV TSI images obtained with high temporal resolution (30 sec sampling). We demonstrate that cases with more uniform spatial distribution of FSC show better agreement between the narrow-FOV CF and large-FOV FSC, reducing the RMSD by up to a factor of 2.
Aerosol optical depth (AOD) derived from hyperspectral measurements can serve as an invaluable input for simultaneous retrievals of particle size distributions and major trace gases. The required hyperspectral measurements are provided by a new ground-based radiometer, the so-called Shortwave Array Spectroradiometer-Hemispheric (SAS-He), recently developed with support from the Department of Energy (DOE) Office Atmospheric Radiation Measurement (ARM) Program. The SAS-He has wide spectral coverage (350-1700nm) and high spectral resolution: about 2.4 nm and 6 nm within 350-1000 nm and 970-1700 nm spectral ranges, respectively. To illustrate an initial performance of the SAS-He, we take advantage of integrated dataset collected during the ARM-supported Two-Column Aerosol Project (TCAP) over the US coastal region (Cape Cod, Massachusetts). This dataset includes AODs derived using data from Aerosol Robotic Network (AERONET) sunphotometer and Multi-Filter Rotating Shadowband Radiometer (MFRSR). We demonstrate that, on average, the SAS-He AODs closely match the MFRSR and AERONET AODs in the ultraviolet and visible spectral ranges for this area with highly variable AOD. Also, we discuss corrections of SAS-He total optical depth for gas absorption in the near-infrared spectral range and their operational implementation
Areal-averaged albedos are particularly difficult to measure in coastal regions, because the surface is not homogenous, consisting of a sharp demarcation between land and water. With this difficulty in mind, we evaluate a simple retrieval of areal-averaged surface albedo using ground-based measurements of atmospheric transmission alone under fully overcast conditions. To illustrate the performance of our retrieval, we find the areal-averaged albedo using measurements from the Multi-Filter Rotating Shadowband Radiometer (MFRSR) at five wavelengths (415, 500, 615, 673, and 870 nm). These MFRSR data are collected at a coastal site in Graciosa Island, Azores supported by the U.S. Department of Energy’s (DOE’s) Atmospheric Radiation Measurement (ARM) Program. The areal-averaged albedos obtained from the MFRSR are compared with collocated and coincident Moderate Resolution Imaging Spectroradiometer (MODIS) whitesky albedo at four nominal wavelengths (470, 560, 670 and 860 nm). These comparisons are made during a 19-month period (June 2009 - December 2010). We also calculate composite-based spectral values of surface albedo by a weighted-average approach using estimated fractions of major surface types observed in an area surrounding this coastal site. Taken as a whole, these three methods of finding albedo show spectral and temporal similarities, and suggest that our simple, transmission-based technique holds promise, but with estimated errors of about ±0.03. Additional work is needed to reduce this uncertainty in areas with inhomogeneous surfaces.
We introduce and evaluate a simple retrieval of areal-averaged surface albedo using ground-based measurements of atmospheric transmission alone at five wavelengths (415, 500, 615, 673 and 870nm), under fully overcast conditions. Our retrieval is based on a one-line semi-analytical equation and widely accepted assumptions regarding the weak spectral dependence of cloud optical properties, such as cloud optical depth and asymmetry parameter, in the visible and near-infrared spectral range. To illustrate the performance of our retrieval, we use as input measurements of spectral atmospheric transmission from the Multi-Filter Rotating Shadowband Radiometer (MFRSR). These MFRSR data are collected at two well-established continental sites in the United States supported by the U.S. Department of Energy’s (DOE’s) Atmospheric Radiation Measurement (ARM) Program and National Oceanic and Atmospheric Administration (NOAA). The areal-averaged albedos obtained from the MFRSR are compared with collocated and coincident Moderate Resolution Imaging Spectroradiometer (MODIS) white-sky albedo. In particular, these comparisons are made at four MFRSR wavelengths (500, 615, 673 and 870nm) and for four seasons (winter, spring, summer and fall) at the ARM site using multi-year (2008-2013) MFRSR and MODIS data. Good agreement, on average, for these wavelengths results in small values (≤0.015) of the corresponding root mean square errors (RMSEs) for these two sites. The obtained RMSEs are comparable with those obtained previously for the shortwave albedos (MODIS-derived versus tower-measured) for these sites during growing seasons. We also demonstrate good agreement between tower-based daily-averaged surface albedos measured for “nearby” overcast and non-overcast days. Thus, our retrieval originally developed for overcast conditions likely can be extended for non-overcast days by interpolating between overcast retrievals.
Ground-based remote sensing and in situ observations of aerosol microphysical and optical properties have been
collected during summertime (June-August, 2012) as part of the Two-Column Aerosol Project (TCAP;
http://campaign.arm.gov/tcap/), which was supported by the U.S. Department of Energy’s (DOE’s) Atmospheric
Radiation Measurement (ARM) Program (http://www.arm.gov/). The overall goal of the TCAP field campaign is to
study the evolution of optical and microphysical properties of atmospheric aerosol transported from North America to
the Atlantic and their impact on the radiation energy budget. During TCAP, the ground-based ARM Mobile Facility
(AMF) was deployed on Cape Cod, an arm-shaped peninsula situated on the easternmost portion of Massachusetts
(along the east coast of the United States) and that is generally downwind of large metropolitan areas. The AMF site was
equipped with numerous instruments for sampling aerosol, cloud and radiative properties, including a Multi-Filter
Rotating Shadowband Radiometer (MFRSR), a Scanning Mobility Particle Sizer (SMPS), an Aerodynamic Particle Sizer
(APS), and a three-wavelength nephelometer. In this study we present an analysis of diurnal and day-to-day variability
of the column and near-surface aerosol properties obtained from remote sensing (MFRSR data) and ground-based in situ
measurements (SMPS, APS, and nephelometer data). In particular, we show that the observed diurnal variability of the
MFRSR aerosol optical depth is strong and comparable with that obtained previously from the AERONET climatology
in Mexico City, which has a larger aerosol loading. Moreover, we illustrate how the variability of aerosol properties
impacts the direct aerosol radiative forcing at different time scales.
The airborne Spectrometer for Sky-Scanning, Sun-Tracking Atmospheric Research (4STAR) is developed to retrieve aerosol microphysical and optical properties from multi-angular and multi-spectral measurements of sky radiance and direct-beam sun transmittance. The necessarily compact design of the 4STAR may cause noticeable apparent enhancement of sky radiance at small scattering angles. We assess the sensitivity of expected 4STAR-based aerosol retrieval to such enhancement by applying the operational AERONET retrieval code and synthetic 4STAR-like data. Also, we assess the sensitivity of the broadband radiative fluxes and the direct aerosol radiative forcing to uncertainties in aerosol retrievals associated with the sky radiance enhancement. Our sensitivity study results suggest that the 4STARbased aerosol retrieval has limitations in obtaining detailed information on particle size distribution and scattering phase function. However, these limitations have small impact on the retrieved bulk optical parameters, such as the asymmetry factor (up to 4%, or ±0.02) and single-scattering albedo (up to 2%, or ±0.02), and the calculated direct aerosol radiative forcing (up to 6%, or 2 Wm-2).
We use combined multi-year measurements from the surface and space for assessing the spatial and temporal distribution of aerosol properties within a large (~400x400 km) region centered on Cape Cod, Massachusetts, along the East Coast of the United States. The ground-based Aerosol Robotic Network (AERONET) measurements at Martha’s Vineyard Coastal Observatory (MVCO) site and Moderate Resolution Imaging Spectrometer (MODIS) sensors on board the Terra and Aqua satellites provide horizontal and temporal variations of aerosol optical depth, while the Cloud- Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) offers the altitudes of aerosol-layers. The combined ground-based and satellite measurements indicated several interesting features among which were the large differences in the aerosol properties observed in July and February. We applied the climatology of aerosol properties for designing the Two-Column Aerosol Project (TCAP), which is supported by the U.S. Department of Energy’s (DOE’s) Atmospheric Radiation Measurement (ARM) Program. The TCAP field campaign involves 12-month deployment (started July 1, 2012) of the ground-based ARM Mobile Facility (AMF) and Mobile Aerosol Observing System (MAOS) on Cape Cod and complimentary aerosol observations from two research aircraft: the DOE Gulfstream-1 (G-1) and the National Aeronautics and Space Administration (NASA) B200 King Air. Using results from the coordinated G-1 and B200 flights during the recent (July, 2012) Intensive Observation Period, we demonstrated that the G-1 in situ measurements and B200 active remote sensing can provide complementary information on the temporal and spatial changes of the aerosol properties off the coast of North America.
We apply recent (2009-2010) level 2.0 MAN-based AODs for assessing those from two MODIS sensors aboard Terra
and Aqua satellites with morning and afternoon equatorial crossing times, respectively. To compare correctly the
MAN- and MODIS-based AODs (550 nm), considerable attention is given to match ship tracks and satellite overpasses
both temporally (within ±1.5h) and spatially (within 10 km). Overall, analysis of collocated and coincident satellite and
shipboard data reveals capabilities of two MODIS sensors to capture the strong spatial and temporal variations of AOD
quite well, although a better agreement between the MAN- and MODIS-based AODs is observed for Aqua instrument.
Our results further highlight the importance of unique MAN AODs for assessment of over-ocean satellite retrievals.
We perform a case study for estimating the impact of the vertical distribution of cloud fraction on the normalized cloud
radiative forcing (CRF) using a decade-long (2000-2009) high resolution dataset of cloud macrophysical and radiative
properties. This dataset is developed for fair-weather cumuli (FWC) observed at the U.S. Department of Energy's
Atmospheric Radiation Measurement (ARM) Southern Great Plains (SGP) site. The design of the case study reduces
effects associated with non-cloud factors, such as the diurnal changes of aerosol loading and solar zenith angle. The
results of the case study suggest that the impact of the vertical cloud structure can be substantial. Therefore, taking into
account the vertical distribution of clouds would be beneficial for more comprehensive parameterizations aimed to
portray the complex interactions between clouds and radiation more accurately.
One month of MFRSR data collected at two sites in the central California (USA) region during the CARES campaign
are processed and the MFRSR-derived AODs at 500 nm wavelength are compared with available AODs provided by
AERONET measurements. We find that the MFRSR and AERONET AODs are small (~0.05) and comparable. A
reasonable quantitative agreement between column aerosol size distributions (up to 2 μm) from the MFRSR and
AERONET retrievals is illustrated as well. Analysis of the retrieved (MFRSR and AERONET) and in situ measured
aerosol size distributions suggests that the contribution of the coarse mode to aerosol optical properties is substantial for
several days. The results of a radiative closure experiment performed for the two sites and one-month period show a
favorable agreement between the calculated and measured broadband downwelling irradiances (bias does not exceed
about 3 Wm-2), and thus imply that the MFRSR-derived aerosol optical properties are reasonable.
An approach for the obtaining column intensive aerosol properties, namely the single scattering albedo (SSA) and
asymmetry parameter (ASP), from the Multi-Filter Rotating Shadowband Radiometer (MFRSR) spectral observations
under partly cloudy conditions is described. The approach involves the MFRSR-based aerosol retrieval for clear-sky
periods and an interpolation of the retrieved column aerosol properties for cloudy periods. The observed weak diurnal
variability of SSA and ASP at the surface and the close association of the surface intensive aerosol properties with their
column counterparts form the basis of such interpolation. The approach is evaluated by calculating the corresponding
clear-sky total, direct and diffuse fluxes at five wavelengths (415, 500, 615, 673 and 870 nm) and compare them with the
observed fluxes. The aerosol properties provided by this approach are applied for (i) an examination of the statistical
relationship between spectral (visible range) and broadband values of the total normalized cloud radiative forcing and
(ii) an estimation of the fractional sky cover. Data collected during 13 days with single-layer cumulus clouds observed
at U.S. Department of Energy Atmospheric Radiation Measurement (ARM) Climate Research Facility (ACRF) Southern
Great Plains (SGP) site during summer 2007 are applied to illustrate the performance and application of this approach.
We outline a new method, called the ratio method, developed to retrieve aerosol optical depth (AOD) under broken
cloud conditions and present validation results from sensitivity and case studies. Results of the sensitivity study
demonstrate that the ratio method, which exploits ratios of reflectances in the visible spectral range, has the potential for
accurate AOD retrievals under different observational conditions and random errors in input data. Also, we examine the
performance of the ratio method using aircraft data collected during the Cloud and Land Surface Interaction Campaign
(CLASIC) and the Cumulus Humilis Aerosol Processing Study (CHAPS). Results of the case study suggest that the ratio
method has the ability to retrieve AOD from multi-spectral aircraft observations of the reflected solar radiation.
A novel method for the retrieval of aerosol optical depth (AOD) under partly cloudy conditions has been suggested. The
method exploits reflectance ratios, which are not sensitive to the three-dimensional (3D) effects of clouds. As a result,
the new method provides an effective way to avoid the 3D cloud effects, which otherwise would have a large (up to
140%) contaminating impact on the aerosol retrievals. The 1D version of the radiative transfer model has been used to
develop look-up tables (LUTs) of reflectance ratios as functions of two parameters describing the spectral dependence of
AOD (a power law). The new method implements an innovative 2D inversion for simultaneous retrieval of these two
parameters and, thus, the spectral behavior of AOD. The performance of the new method has been illustrated with a
model-output inverse problem. We demonstrated that the new retrieval has the potential for (i) detection of clear pixels
outside of cloud shadows, (ii) increased "harvest" of such pixels, and (iii) accurate (~15%) estimation of AOD for the
majority of them.
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