scholarly journals Study of MPLNET-Derived Aerosol Climatology over Kanpur, India, and Validation of CALIPSO Level 2 Version 3 Backscatter and Extinction Products

2012 ◽  
Vol 29 (9) ◽  
pp. 1285-1294 ◽  
Author(s):  
Amit Misra ◽  
S. N. Tripathi ◽  
D. S. Kaul ◽  
Ellsworth J. Welton
Keyword(s):  
Extinction Coefficient ◽  
Extinction Ratio ◽  
Orthogonal Polarization ◽  
Good Comparison ◽  
Aerosol Backscatter ◽  
Source Of Error ◽  
Level 2 ◽  
Aerosol Type

Abstract The level 2 aerosol backscatter and extinction profiles from the NASA Micropulse Lidar Network (MPLNET) at Kanpur, India, have been studied from May 2009 to September 2010. Monthly averaged extinction profiles from MPLNET shows high extinction values near the surface during October–March. Higher extinction values at altitudes of 2–4 km are observed from April to June, a period marked by frequent dust episodes. Version 3 level 2 Cloud–Aerosol Lidar with Orthogonal Polarization (CALIOP) aerosol profile products have been compared with corresponding data from MPLNET over Kanpur for the above-mentioned period. Out of the available backscatter profiles, the16 profiles used in this study have time differences less than 3 h and distances less than 130 km. Among these profiles, four cases show good comparison above 400 m with R2 greater than 0.7. Comparison with AERONET data shows that the aerosol type is properly identified by the CALIOP algorithm. Cloud contamination is a possible source of error in the remaining cases of poor comparison. Another source of error is the improper backscatter-to-extinction ratio, which further affects the accuracy of extinction coefficient retrieval.

scholarly journals Synergy between CALIOP and MODIS instruments for aerosol monitoring: application to the Po Valley

2010 ◽  
Vol 3 (2) ◽  
pp. 1323-1359 ◽  
Author(s):  
P. Royer ◽  
J.-C. Raut ◽  
G. Ajello ◽  
S. Berthier ◽  
P. Chazette
Keyword(s):  
Signal To Noise Ratio ◽  
Extinction Ratio ◽  
Orthogonal Polarization ◽  
Aerosol Extinction ◽  
Large Area ◽  
Total Uncertainty ◽  
Aerosol Model ◽  
Po Valley ◽  
The Mean ◽  
Level 2

Abstract. We propose here a synergy between Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations/Cloud-Aerosol LIdar with Orthogonal Polarization (CALIPSO/CALIOP) and Moderate Resolution Imaging Spectroradiometer (MODIS) onboard Aqua and Terra in order to retrieve aerosol optical properties over the Po Valley from June 2006 to February 2009. Such an approach gives simultaneously access to the aerosol extinction vertical profile and to the equivalent backscatter-to-extinction ratio at 532 nm (BER, inverse of the lidar ratio). The choice of the Po valley has been driven by the great occurrences of pollutant events leading to a mean MODIS-derived aerosol optical thickness of 0.27(±0.17) at 550 nm over a large area of ~120 000 km2. In such area, a significant number of CALIOP level-1 vertical profiles can be averaged (~200 individual laser shots) leading to a signal-to-noise ratio greater than 10 in the planetary boundary layer (PBL) sufficient to perform a homemade inversion of the mean lidar profiles. The mean BER (together with the associated variabilities) over the Po Valley retrieved from the coupling between CALIOP/MODIS-Aqua and CALIOP/MODIS-Terra are ~0.014(±0.003) sr−1 and ~0.013(±0.004) sr−1, respectively. The total uncertainty on BER retrieval has been assessed to be ~0.003 sr−1 using a Monte Carlo approach. These mean BER values retrieved have been compared with those given by the level-2 operational products of CALIOP ~0.016(±0.003) sr−1. The values we assessed appear close to what is expected above urban area. A seasonal cycle has been observed with higher BER values in spring, summer and fall, which can be associated to dust event occurring during this period. In most of cases, the mean aerosol extinction coefficient in the PBL diverges significantly between the level-2 operational products and the result of our own inversion procedure. Indeed, mean differences of 0.10 km−1 (~50%) and 0.13 km−1 (~60%) have been calculated using MODIS-Aqua/CALIOP and MODIS-Terra/CALIOP synergies, respectively. Such differences may be due to the identification of the aerosol model by the operational algorithm and thus to the choice of the BER.

scholarly journals An accuracy assessment of the CALIOP/CALIPSO version 2/version 3 daytime aerosol extinction product based on a detailed multi-sensor, multi-platform case study

2011 ◽  
Vol 11 (8) ◽  
pp. 3981-4000 ◽  
Author(s):  
M. Kacenelenbogen ◽  
M. A. Vaughan ◽  
J. Redemann ◽  
R. M. Hoff ◽  
R. R. Rogers ◽  
...  
Keyword(s):  
Accuracy Assessment ◽  
High Spectral Resolution ◽  
Calibration Coefficient ◽  
Orthogonal Polarization ◽  
Aerosol Layer ◽  
Aerosol Extinction ◽  
Backscatter Coefficient ◽  
Aerosol Backscatter ◽  
Level 2

Abstract. The Cloud Aerosol LIdar with Orthogonal Polarization (CALIOP), on board the CALIPSO platform, has measured profiles of total attenuated backscatter coefficient (level 1 products) since June 2006. CALIOP's level 2 products, such as the aerosol backscatter and extinction coefficient profiles, are retrieved using a complex succession of automated algorithms. The goal of this study is to help identify potential shortcomings in the CALIOP version 2 level 2 aerosol extinction product and to illustrate some of the motivation for the changes that have been introduced in the next version of CALIOP data (version 3, released in June 2010). To help illustrate the potential factors contributing to the uncertainty of the CALIOP aerosol extinction retrieval, we focus on a one-day, multi-instrument, multiplatform comparison study during the CALIPSO and Twilight Zone (CATZ) validation campaign on 4 August 2007. On that day, we observe a consistency in the Aerosol Optical Depth (AOD) values recorded by four different instruments (i.e. space-borne MODerate Imaging Spectroradiometer, MODIS: 0.67 and POLarization and Directionality of Earth's Reflectances, POLDER: 0.58, airborne High Spectral Resolution Lidar, HSRL: 0.52 and ground-based AErosol RObotic NETwork, AERONET: 0.48 to 0.73) while CALIOP AOD is a factor of two lower (0.32 at 532 nm). This case study illustrates the following potential sources of uncertainty in the CALIOP AOD: (i) CALIOP's low signal-to-noise ratio (SNR) leading to the misclassification and/or lack of aerosol layer identification, especially close to the Earth's surface; (ii) the cloud contamination of CALIOP version 2 aerosol backscatter and extinction profiles; (iii) potentially erroneous assumptions of the aerosol extinction-to-backscatter ratio (Sa) used in CALIOP's extinction retrievals; and (iv) calibration coefficient biases in the CALIOP daytime attenuated backscatter coefficient profiles. The use of version 3 CALIOP extinction retrieval for our case study seems to partially fix factor (i) although the aerosol retrieved by CALIOP is still somewhat lower than the profile measured by HSRL; the cloud contamination (ii) appears to be corrected; no particular change is apparent in the observation-based CALIOP Sa value (iii). Our case study also showed very little difference in version 2 and version 3 CALIOP attenuated backscatter coefficient profiles, illustrating a minor change in the calibration scheme (iv).

scholarly journals Minimum aerosol layer detection sensitivities and their subsequent impacts on aerosol optical thickness retrievals in CALIPSO level 2 data products

2018 ◽  
Vol 11 (1) ◽  
pp. 499-514 ◽  
Author(s):  
Travis D. Toth ◽  
James R. Campbell ◽  
Jeffrey S. Reid ◽  
Jason L. Tackett ◽  
Mark A. Vaughan ◽  
...  
Keyword(s):  
Optical Thickness ◽  
Aerosol Optical Thickness ◽  
Orthogonal Polarization ◽  
Aerosol Layer ◽  
Aerosol Extinction ◽  
Noise Floor ◽  
Data Products ◽  
Moderate Resolution Imaging Spectroradiometer ◽  
Level 2 ◽  
Global Mean

Abstract. Due to instrument sensitivities and algorithm detection limits, level 2 (L2) Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) 532 nm aerosol extinction profile retrievals are often populated with retrieval fill values (RFVs), which indicate the absence of detectable levels of aerosol within the profile. In this study, using 4 years (2007–2008 and 2010–2011) of CALIOP version 3 L2 aerosol data, the occurrence frequency of daytime CALIOP profiles containing all RFVs (all-RFV profiles) is studied. In the CALIOP data products, the aerosol optical thickness (AOT) of any all-RFV profile is reported as being zero, which may introduce a bias in CALIOP-based AOT climatologies. For this study, we derive revised estimates of AOT for all-RFV profiles using collocated Moderate Resolution Imaging Spectroradiometer (MODIS) Dark Target (DT) and, where available, AErosol RObotic NEtwork (AERONET) data. Globally, all-RFV profiles comprise roughly 71 % of all daytime CALIOP L2 aerosol profiles (i.e., including completely attenuated profiles), accounting for nearly half (45 %) of all daytime cloud-free L2 aerosol profiles. The mean collocated MODIS DT (AERONET) 550 nm AOT is found to be near 0.06 (0.08) for CALIOP all-RFV profiles. We further estimate a global mean aerosol extinction profile, a so-called “noise floor”, for CALIOP all-RFV profiles. The global mean CALIOP AOT is then recomputed by replacing RFV values with the derived noise-floor values for both all-RFV and non-all-RFV profiles. This process yields an improvement in the agreement of CALIOP and MODIS over-ocean AOT.

scholarly journals Synergistic Use of Hyperspectral UV-Visible OMI and Broadband Meteorological Imager MODIS Data for a Merged Aerosol Product

2020 ◽  
Vol 12 (23) ◽  
pp. 3987
Author(s):  
Sujung Go ◽  
Jhoon Kim ◽  
Sang Seo Park ◽  
Mijin Kim ◽  
Hyunkwang Lim ◽  
...  
Keyword(s):  
Spatial Data ◽  
Estimation Method ◽  
Weighting Factor ◽  
Data Availability ◽  
Orthogonal Polarization ◽  
Aerosol Layer ◽  
Ozone Monitoring Instrument ◽  
Uv Visible ◽  
Type Classification ◽  
Aerosol Type

The retrieval of optimal aerosol datasets by the synergistic use of hyperspectral ultraviolet (UV)–visible and broadband meteorological imager (MI) techniques was investigated. The Aura Ozone Monitoring Instrument (OMI) Level 1B (L1B) was used as a proxy for hyperspectral UV–visible instrument data to which the Geostationary Environment Monitoring Spectrometer (GEMS) aerosol algorithm was applied. Moderate-Resolution Imaging Spectroradiometer (MODIS) L1B and dark target aerosol Level 2 (L2) data were used with a broadband MI to take advantage of the consistent time gap between the MODIS and the OMI. First, the use of cloud mask information from the MI infrared (IR) channel was tested for synergy. High-spatial-resolution and IR channels of the MI helped mask cirrus and sub-pixel cloud contamination of GEMS aerosol, as clearly seen in aerosol optical depth (AOD) validation with Aerosol Robotic Network (AERONET) data. Second, dust aerosols were distinguished in the GEMS aerosol-type classification algorithm by calculating the total dust confidence index (TDCI) from MODIS L1B IR channels. Statistical analysis indicates that the Probability of Correct Detection (POCD) between the forward and inversion aerosol dust models (DS) was increased from 72% to 94% by use of the TDCI for GEMS aerosol-type classification, and updated aerosol types were then applied to the GEMS algorithm. Use of the TDCI for DS type classification in the GEMS retrieval procedure gave improved single-scattering albedo (SSA) values for absorbing fine pollution particles (BC) and DS aerosols. Aerosol layer height (ALH) retrieved from GEMS was compared with Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) data, which provides high-resolution vertical aerosol profile information. The CALIOP ALH was calculated from total attenuated backscatter data at 1064 nm, which is identical to the definition of GEMS ALH. Application of the TDCI value reduced the median bias of GEMS ALH data slightly. The GEMS ALH bias approximates zero, especially for GEMS AOD values of >~0.4 and GEMS SSA values of <~0.95. Finally, the AOD products from the GEMS algorithm and MI were used in aerosol merging with the maximum-likelihood estimation method, based on a weighting factor derived from the standard deviation of the original AOD products. With the advantage of the UV–visible channel in retrieving aerosol properties over bright surfaces, the combined AOD products demonstrated better spatial data availability than the original AOD products, with comparable accuracy. Furthermore, pixel-level error analysis of GEMS AOD data indicates improvement through MI synergy.

scholarly journals EARLINET evaluation of the CATS L2 aerosol backscatter coefficient product

2019 ◽  
Author(s):  
Emmanouil Proestakis ◽  
Vassilis Amiridis ◽  
Eleni Marinou ◽  
Ioannis Binietoglou ◽  
Albert Ansmann ◽  
...  
Keyword(s):  
Space Station ◽  
Backscatter Coefficient ◽  
Backscatter Signal ◽  
Evaluation Activity ◽  
Ground Station ◽  
Free Relative ◽  
Climate Studies ◽  
Aerosol Backscatter ◽  
Level 2 ◽  
Good Agreement

Abstract. We present the evaluation activity of the European Aerosol Research Lidar Network (EARLINET) for the quantitative assessment of the Level 2 aerosol backscatter coefficient product derived by the Cloud-Aerosol Transport System (CATS) onboard the International Space Station (ISS). The study employs correlative CATS and EARLINET backscatter measurements within 50 km distance between the ground station and the ISS overpass and as close in time as possible, typically within 90 min, from February 2015 to September 2016. The results demonstrate the good agreement of CATS Level 2 backscatter coefficient and EARLINET. Three ISS overpasses close to the EARLINET stations of Leipzig-Germany, Évora-Portugal and Dushanbe-Tajikistan are analysed here to demonstrate the performance of CATS lidar system under different conditions. The results show that under cloud-free, relative homogeneous aerosol conditions CATS is in good agreement with EARLINET, independently of daytime/nighttime conditions. CATS low negative biases, partially attributed to the deficiency of lidar systems to detect tenuous aerosol layers of backscatter signal below the minimum detection thresholds, may lead to systematic deviations and slight underestimations of the total Aerosol Optical Depth (AOD) in climate studies. In addition, CATS misclassification of aerosol layers as clouds, and vice versa, in cases of coexistent and/or adjacent aerosol and cloud features, may lead to non-representative, unrealistic and cloud contaminated aerosol profiles. The distributions of backscatter coefficient biases show the relatively good agreement between the CATS and EARLINET measurements, although on average underestimations are observed, 22.3 % during daytime and 6.1 % during nighttime.

scholarly journals Extinction and optical depth retrievals for CALIPSO's Version 4 data release

2018 ◽  
Vol 11 (10) ◽  
pp. 5701-5727 ◽  
Author(s):  
Stuart A. Young ◽  
Mark A. Vaughan ◽  
Anne Garnier ◽  
Jason L. Tackett ◽  
James D. Lambeth ◽  
...  
Keyword(s):  
Optical Depth ◽  
Satellite Observations ◽  
Orthogonal Polarization ◽  
Ice Clouds ◽  
Extinction Coefficients ◽  
Retrieval Algorithms ◽  
Data Release ◽  
Data Products ◽  
Lidar Ratio ◽  
Level 2

Abstract. The Cloud–Aerosol Lidar with Orthogonal Polarization (CALIOP) on board the Cloud–Aerosol Lidar Infrared Pathfinder Satellite Observations (CALIPSO) satellite has been making near-global height-resolved measurements of cloud and aerosol layers since mid-June 2006. Version 4.10 (V4) of the CALIOP data products, released in November 2016, introduces extensive upgrades to the algorithms used to retrieve the spatial and optical properties of these layers, and thus there are both obvious and subtle differences between V4 and previous data releases. This paper describes the improvements made to the extinction retrieval algorithms and illustrates the impacts of these changes on the extinction and optical depth estimates reported in the CALIPSO lidar level 2 data products. The lidar ratios for both aerosols and ice clouds are generally higher than in previous data releases, resulting in generally higher extinction coefficients and optical depths in V4. A newly implemented algorithm for retrieving extinction coefficients in opaque layers is described and its impact examined. Precise lidar ratio estimates are also retrieved in these opaque layers. For semi-transparent cirrus clouds, comparisons between CALIOP V4 optical depths and the optical depths reported by MODIS collection 6 show substantial improvements relative to earlier comparisons between CALIOP version 3 and MODIS collection 5.

scholarly journals Climatology of the aerosol optical depth by components from the Multiangle Imaging SpectroRadiometer (MISR) and a high-resolution chemistry transport model

2015 ◽  
Vol 15 (23) ◽  
pp. 33897-33929 ◽  
Author(s):  
H. Lee ◽  
O. V. Kalashnikova ◽  
K. Suzuki ◽  
A. Braverman ◽  
M. J. Garay ◽  
...  
Keyword(s):  
Aerosol Optical Depth ◽  
Optical Depth ◽  
Transport Model ◽  
Radiation Transport ◽  
Spectral Radiation ◽  
Chemistry Transport Model ◽  
Source Regions ◽  
Level 3 ◽  
Level 2 ◽  
Aerosol Type

Abstract. The Multi-angle Imaging SpectroRadiometer (MISR) Joint Aerosol (JOINT_AS) Level 3 product provides a global, descriptive summary of MISR Level 2 aerosol optical depth (AOD) and aerosol type information for each month between March 2000 and the present. Using Version 1 of JOINT_AS, which is based on the operational (Version 22) MISR Level 2 aerosol product, this study analyzes, for the first time, characteristics of observed and simulated distributions of AOD for three broad classes of aerosols: non-absorbing, absorbing, and non-spherical – near or downwind of their major source regions. The statistical moments (means, standard deviations, and skewnesses) and distributions of AOD by components derived from the JOINT_AS are compared with results from the SPectral RadIatioN-TrAnSport (SPRINTARS) model, a chemistry transport model (CTM) with very high spatial and temporal resolution. Overall, the AOD distributions of combined MISR aerosol types show good agreement with those from SPRINTARS. Marginal distributions of AOD for each aerosol type in both MISR and SPRINTARS show considerable high positive skewness, which indicates the importance of including extreme AOD events when comparing satellite retrievals with models. The MISR JOINT_AS product will greatly facilitate comparisons between satellite observations and model simulations of aerosols by type.

scholarly journals The CALIPSO version 4 automated aerosol classification and lidar ratio selection algorithm

2018 ◽  
Vol 11 (11) ◽  
pp. 6107-6135 ◽  
Author(s):  
Man-Hae Kim ◽  
Ali H. Omar ◽  
Jason L. Tackett ◽  
Mark A. Vaughan ◽  
David M. Winker ◽  
...  
Keyword(s):  
Stratospheric Aerosol ◽  
Influential Factor ◽  
Orthogonal Polarization ◽  
Polar Regions ◽  
Marine Aerosols ◽  
Preliminary Validation ◽  
Tropospheric Aerosol ◽  
Lidar Ratio ◽  
Selection Algorithms ◽  
Level 2

Abstract. The Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) version 4.10 (V4) level 2 aerosol data products, released in November 2016, include substantial improvements to the aerosol subtyping and lidar ratio selection algorithms. These improvements are described along with resulting changes in aerosol optical depth (AOD). The most fundamental change in the V4 level 2 aerosol products is a new algorithm to identify aerosol subtypes in the stratosphere. Four aerosol subtypes are introduced for stratospheric aerosols: polar stratospheric aerosol (PSA), volcanic ash, sulfate/other, and smoke. The tropospheric aerosol subtyping algorithm was also improved by adding the following enhancements: (1) all aerosol subtypes are now allowed over polar regions, whereas the version 3 (V3) algorithm allowed only clean continental and polluted continental aerosols; (2) a new “dusty marine” aerosol subtype is introduced, representing mixtures of dust and marine aerosols near the ocean surface; and (3) the “polluted continental” and “smoke” subtypes have been renamed “polluted continental/smoke” and “elevated smoke”, respectively. V4 also revises the lidar ratios for clean marine, dust, clean continental, and elevated smoke subtypes. As a consequence of the V4 updates, the mean 532 nm AOD retrieved by CALIOP has increased by 0.044 (0.036) or 52 % (40 %) for nighttime (daytime). Lidar ratio revisions are the most influential factor for AOD changes from V3 to V4, especially for cloud-free skies. Preliminary validation studies show that the AOD discrepancies between CALIOP and AERONET–MODIS (ocean) are reduced in V4 compared to V3.

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