A new measurement approach for validating satellite-based above-cloud aerosol optical depth

Abstract. The retrieval of aerosol parameters from passive satellite instruments in cloudy scenes is challenging, partly because clouds and cloud-related processes may significantly modify aerosol optical depth (AOD) and particle size, a problem that is further compounded by 3D radiative processes. Recent advances in retrieval algorithms such as the “color ratio” method, which utilizes the measurements at a shorter (470 nm) and a longer (860 nm) wavelength, have demonstrated the simultaneous derivation of AOD and cloud optical depth (COD) for scenes in which absorbing aerosols are found to overlay low-level cloud decks. This study shows simultaneous retrievals of above-cloud aerosol optical depth (ACAOD) and aerosol-corrected cloud optical depth (COD) from airborne measurements of cloud-reflected and sky radiances using the color ratio method. These airborne measurements were taken over marine stratocumulus clouds with NASA's Cloud Absorption Radiometer (CAR) during the SAFARI 2000 field campaign offshore of Namibia. The ACAOD is partitioned between the AOD below-aircraft (AOD_cloudtop) and above-aircraft AOD (AOD_sky). The results show good agreement between AOD_sky and sun-photometer measurements of the above-aircraft AOD. The results also show that the use of aircraft-based sun-photometer measurements to validate satellite retrievals of the ACAOD is complicated by the lack of information on AOD below aircraft. Specifically, the CAR-retrieved AOD_cloudtop captures this “missing” aerosol layer caught between the aircraft and cloud top, which is required to quantify above-cloud aerosol loading and effectively validate satellite retrievals. In addition, the study finds a strong anticorrelation between the AOD_cloudtop and COD for cases in which COD < 10 and a weaker anticorrelation for COD > 10, which may be associated with the uncertainties in the color ratio method at lower AODs and CODs. The influence of 3D radiative effects on the retrievals is examined, and the results show that at cloud troughs, 3D effects increase retrieved ACAOD by about 3 %–11 % and retrieved COD by about 25 %. The results show that the color ratio method has little sensitivity to 3D effects at overcast stratocumulus cloud decks. These results demonstrate a novel airborne measurement approach for assessing satellite retrievals of aerosols above clouds, thereby filling a major gap in global aerosol observations.

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A new measurement approach for validating satellite-based above cloud aerosol optical depth

10.5194/amt-2020-246 ◽

2020 ◽

Author(s):

Charles K. Gatebe ◽

Hiren Jethva ◽

Ritesh Gautam ◽

Rajesh Poudyal ◽

Tamas Várnai

Keyword(s):

Aerosol Optical Depth ◽

Optical Depth ◽

Ratio Method ◽

Cloud Optical Depth ◽

Airborne Measurements ◽

Radiative Processes ◽

Color Ratio ◽

Satellite Retrievals ◽

3D Effects ◽

Measurement Approach

Abstract. The retrieval of aerosol parameters from passive satellite instruments in cloudy scenes is challenging partly because clouds and cloud-related processes may significantly modify aerosol optical depth (AOD) and particle size, a problem that is further compounded by the 3D radiative processes. Recent advances in retrieval algorithms such as the “color ratio” method which utilizes the measurements at a shorter (470 nm) and a longer (860 nm) wavelength have demonstrated the simultaneous derivation of AOD and cloud optical depth (COD) for scenes where absorbing aerosols are found to overlay low-level cloud decks. This study shows simultaneous retrievals of above-cloud aerosol optical depth (ACAOD) and aerosol-corrected cloud optical depth (COD) from airborne measurements of cloud-reflected and sky radiances using the color ratio method. These airborne measurements were taken over marine stratocumulus clouds with NASA's Cloud Absorption Radiometer (CAR) during SAFARI 2000 field campaign offshore of Namibia. The ACAOD is partitioned between the AOD below aircraft (AOD_cloudtop) and above aircraft AOD (AOD_sky). The results show good agreement between AOD_sky and sunphotometer measurements of the above aircraft AOD. The results also show that the use of aircraft-based sunphotometer measurements to validate satellite retrievals of the ACAOD is complicated by the lack of information on AOD below aircraft. Specifically, the CAR-retrieved AOD_cloudtop captures this “missing” aerosol layer caught between the aircraft and cloud top, which is required to quantify above cloud aerosol loading and effectively validate satellite retrievals. In addition, the study finds a strong anticorrelation between the AOD_cloudtop and COD for cases where COD 10, which may be associated with the uncertainties in the color ratio method at lower AODs and CODs. The influence of 3D radiative effects on the retrievals is examined and the results show that at cloud troughs, 3D effects increase retrieved ACAOD by about 3–10 % and retrieved COD by about 25 %. The results show that the color ratio method has little sensitivity to 3D effects at overcast stratocumulus cloud decks. These results demonstrate a novel airborne measurement approach for assessing satellite retrievals of aerosols above clouds, thereby filling a major gap that exists in the global aerosol observations.

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Validating MODIS above-cloud aerosol optical depth retrieved from “color ratio” algorithm using direct measurements made by NASA's airborne AATS and 4STAR sensors

Atmospheric Measurement Techniques ◽

10.5194/amt-9-5053-2016 ◽

2016 ◽

Vol 9 (10) ◽

pp. 5053-5062 ◽

Cited By ~ 10

Author(s):

Hiren Jethva ◽

Omar Torres ◽

Lorraine Remer ◽

Jens Redemann ◽

John Livingston ◽

...

Keyword(s):

Aerosol Optical Depth ◽

Optical Depth ◽

Field Experiments ◽

Ratio Method ◽

Cloud Optical Depth ◽

Color Ratio ◽

Direct Measurements ◽

Absorbing Aerosols ◽

Good Agreement

Abstract. We present the validation analysis of above-cloud aerosol optical depth (ACAOD) retrieved from the “color ratio” method applied to MODIS cloudy-sky reflectance measurements using the limited direct measurements made by NASA's airborne Ames Airborne Tracking Sunphotometer (AATS) and Spectrometer for Sky-Scanning, Sun-Tracking Atmospheric Research (4STAR) sensors. A thorough search of the airborne database collection revealed a total of five significant events in which an airborne sun photometer, coincident with the MODIS overpass, observed partially absorbing aerosols emitted from agricultural biomass burning, dust, and wildfires over a low-level cloud deck during SAFARI-2000, ACE-ASIA 2001, and SEAC4RS 2013 campaigns, respectively. The co-located satellite-airborne matchups revealed a good agreement (root-mean-square difference  <  0.1), with most matchups falling within the estimated uncertainties associated the MODIS retrievals (about −10 to +50 %). The co-retrieved cloud optical depth was comparable to that of the MODIS operational cloud product for ACE-ASIA and SEAC4RS, however, higher by 30–50 % for the SAFARI-2000 case study. The reason for this discrepancy could be attributed to the distinct aerosol optical properties encountered during respective campaigns. A brief discussion on the sources of uncertainty in the satellite-based ACAOD retrieval and co-location procedure is presented. Field experiments dedicated to making direct measurements of aerosols above cloud are needed for the extensive validation of satellite-based retrievals.

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Validating MODIS Above-cloud Aerosol Optical Depth Retrieved from "Color Ratio" Algorithm using Direct Measurements made by NASA’s Airborne AATS and 4STAR Sensors

10.5194/amt-2016-178 ◽

2016 ◽

Author(s):

Hiren Jethva ◽

Omar Torres ◽

Lorraine Remer ◽

Jens Redemann ◽

John Livingston ◽

...

Keyword(s):

Root Mean Square Error ◽

Aerosol Optical Depth ◽

Optical Depth ◽

Ratio Method ◽

Mean Square ◽

Airborne Measurements ◽

Color Ratio ◽

Direct Measurements ◽

Reflectance Measurements ◽

Good Agreement

Abstract. We present the first ever validation of above-cloud aerosol optical depth (ACAOD) retrieved from the "color ratio" method applied to MODIS cloudy-sky reflectance measurements using the limited direct measurements made by NASA's airborne AATS and 4STAR sensors. A thorough search of the airborne database collection revealed a total of five events in which airborne sunphotometer, coincident with the MODIS overpass, observed agricultural biomass burning, dust, and wildfire-emitted aerosols above a low-level cloud deck during SAFARI-2000, ACE-ASIA 2001, and SEAC4RS-2013 campaigns, respectively. The co-located satellite-airborne measurements revealed a good agreement (root-mean-square-error

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Aerosol Optical Depth Estimate Using Ground-Measured Spectral Skylight Ratio Method

IGARSS 2020 - 2020 IEEE International Geoscience and Remote Sensing Symposium ◽

10.1109/igarss39084.2020.9324583 ◽

2020 ◽

Author(s):

Jing Nie ◽

Huazhong Ren ◽

Hui Zeng ◽

Jiaji Dong ◽

Jinxin Guo ◽

...

Keyword(s):

Aerosol Optical Depth ◽

Optical Depth ◽

Ratio Method ◽

Depth Estimate

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Retrieval of aerosol single-scattering albedo and polarized phase function from polarized sun-photometer measurements for Zanjan's atmosphere

Atmospheric Measurement Techniques ◽

10.5194/amt-6-2659-2013 ◽

2013 ◽

Vol 6 (10) ◽

pp. 2659-2669 ◽

Cited By ~ 12

Author(s):

A. Bayat ◽

H. R. Khalesifard ◽

A. Masoumi

Keyword(s):

Aerosol Optical Depth ◽

Optical Depth ◽

Atmospheric Aerosols ◽

Phase Function ◽

Single Scattering ◽

Single Scattering Albedo ◽

Angstrom Exponent ◽

Ångström Exponent ◽

Sun Photometer ◽

Ångstrom Exponent

Abstract. The polarized phase function of atmospheric aerosols has been investigated for the atmosphere of Zanjan, a city in northwest Iran. To do this, aerosol optical depth, Ångström exponent, single-scattering albedo, and polarized phase function have been retrieved from the measurements of a Cimel CE 318-2 polarized sun-photometer from February 2010 to December 2012. The results show that the maximum value of aerosol polarized phase function as well as the polarized phase function retrieved for a specific scattering angle (i.e., 60°) are strongly correlated (R = 0.95 and 0.95, respectively) with the Ångström exponent. The latter has a meaningful variation with respect to the changes in the complex refractive index of the atmospheric aerosols. Furthermore the polarized phase function shows a moderate negative correlation with respect to the atmospheric aerosol optical depth and single-scattering albedo (R = −0.76 and −0.33, respectively). Therefore the polarized phase function can be regarded as a key parameter to characterize the atmospheric particles of the region – a populated city in the semi-arid area and surrounded by some dust sources of the Earth's dust belt.

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Long-Term Comparison of Lidar Derived Aerosol Optical Depth Between Two Operational Algorithms and Sun Photometer Measurements for Thessaloniki, Greece

Perspectives on Atmospheric Sciences - Springer Atmospheric Sciences ◽

10.1007/978-3-319-35095-0_113 ◽

2016 ◽

pp. 789-794 ◽

Cited By ~ 1

Author(s):

K. Voudouri ◽

N. Siomos ◽

E. Giannakaki ◽

V. Amiridis ◽

G. D’Amico ◽

...

Keyword(s):

Aerosol Optical Depth ◽

Optical Depth ◽

Sun Photometer

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Influence of sun photometer filter function on retrieving aerosol optical depth

2009 IEEE International Geoscience and Remote Sensing Symposium ◽

10.1109/igarss.2009.5417639 ◽

2009 ◽

Cited By ~ 1

Author(s):

Hao Zhang ◽

Bing Zhang ◽

Dongchuan Yan ◽

Jun-Sheng Li ◽

Qian Shen ◽

...

Keyword(s):

Aerosol Optical Depth ◽

Optical Depth ◽

Filter Function ◽

Sun Photometer

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Evaluating Aerosol Optical Depth From Himawari‐8 With Sun Photometer Network

Journal of Geophysical Research Atmospheres ◽

10.1029/2018jd028599 ◽

2019 ◽

Vol 124 (10) ◽

pp. 5516-5538 ◽

Cited By ~ 14

Author(s):

Wei Wang ◽

Feiyue Mao ◽

Zengxin Pan ◽

Wei Gong ◽

Mayumi Yoshida ◽

...

Keyword(s):

Aerosol Optical Depth ◽

Optical Depth ◽

Sun Photometer

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A Multi Linear Regression Model to Derive Dust PM10 in the Sahel Using AERONET Aerosol Optical Depth and CALIOP Aerosol Layer Products

Remote Sensing ◽

10.3390/rs12183099 ◽

2020 ◽

Vol 12 (18) ◽

pp. 3099

Author(s):

Jean-François Léon ◽

Nadège Martiny ◽

Sébastien Merlet

Keyword(s):

Linear Regression ◽

Regression Model ◽

Aerosol Optical Depth ◽

Optical Depth ◽

Linear Regression Model ◽

Population Exposure ◽

Aerosol Layer ◽

Multi Linear Regression ◽

Sun Photometer ◽

The Impact

Due to a limited number of monitoring stations in Western Africa, the impact of mineral dust on PM10 surface concentrations is still poorly known. We propose a new method to retrieve PM10 dust surface concentrations from sun photometer aerosol optical depth (AOD) and CALIPSO/CALIOP Level 2 aerosol layer products. The method is based on a multi linear regression model that is trained using co-located PM10, AERONET and CALIOP observations at 3 different locations in the Sahel. In addition to the sun photometer AOD, the regression model uses the CALIOP-derived base and top altitude of the lowermost dust layer, its AOD, the columnar total and columnar dust AOD. Due to the low revisit period of the CALIPSO satellite, the monthly mean annual cycles of the parameters are used as predictor variables rather than instantaneous observations. The regression model improves the correlation coefficient between monthly mean PM10 and AOD from 0.15 (AERONET AOD only) to 0.75 (AERONET AOD and CALIOP parameters). The respective high and low PM10 concentration during the winter dry season and summer season are well produced. Days with surface PM10 above 100 μg/m3 are better identified when using the CALIOP parameters in the multi linear regression model. The number of true positives (actual and predicted concentrations above the threshold) is increased and leads to an improvement in the classification sensitivity (recall) by a factor 1.8. Our methodology can be extrapolated to the whole Sahel area provided that satellite derived AOD maps are used in order to create a new dataset on population exposure to dust events in this area.

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Detailed Aerosol Optical Depth Intercomparison between Brewer and Li-Cor 1800 Spectroradiometers and a Cimel Sun Photometer

Journal of Atmospheric and Oceanic Technology ◽

10.1175/2009jtecha1217.1 ◽

2009 ◽

Vol 26 (8) ◽

pp. 1558-1571 ◽

Cited By ~ 6

Author(s):

V. E. Cachorro ◽

A. Berjón ◽

C. Toledano ◽

S. Mogo ◽

N. Prats ◽

...

Keyword(s):

Aerosol Optical Depth ◽

Optical Depth ◽

Reasonable Agreement ◽

Detailed Comparison ◽

Normal Operation ◽

Data Series ◽

Operational Conditions ◽

Sun Photometer ◽

Level Of Agreement ◽

Uv Range

Abstract Aerosol optical depth (AOD) using different instruments during three short and intensive campaigns carried out from 1999 to 2001 at El Arenosillo in Huelva, Spain, are presented and compared. The specific aim of this study is to determine the level of agreement between three different instruments running in operational conditions. This activity, however, is part of a broader objective to recover an extended data series of AOD in the UV range obtained from a Brewer spectroradiometer. This instrument may be used to obtain AOD at the same five UV wavelengths used during normal operation for ozone content determination. As part of the validation of the Brewer AOD data, a Cimel sun photometer and another spectroradiometer, a Li-Cor 1800, were used. A detailed comparison of these three instruments is carried out by means of near-simultaneous measurements, with particular emphasis on examining diurnal AOD variability. Absolute AOD uncertainties range from 0.02 for the Cimel to 0.08 for the Brewer, with intermediate values for the Li-Cor 1800. All data during the comparison are in reasonable agreement, when taking into account the different performance characteristics of each instrument. The comparison also demonstrates current deficiencies in the Brewer data and thus the difficulty to determine AOD values with low errors.

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