Use of measured aerosol optical depth and precipitable water to model clear sky irradiance

Abstract The authors present a new algorithm to retrieve aerosol optical depth (AOD) over a desert using the window channels centered at 8.7, 10.8, and 12.0 μm of the Spinning Enhanced Visible and Infrared Imager (SEVIRI) instrument on board the Meteosat Second Generation satellite. The presence of dust aerosols impacts the longwave outgoing radiation, allowing the aerosols over the desert surfaces to be detected in the thermal infrared (IR) wavelengths. To retrieve the aerosol properties over land, the surface contribution to the satellite radiance measured at the top of the atmosphere has to be taken into account. The surface radiation depends on the surface temperature, which is characterized by a strong diurnal variation over the desert, and the surface emissivity, which is assumed to be constant over a time span of 24 h. The surface emissivity is based on clear-sky observations that are corrected for atmospheric absorption and emission. The clear-sky image is a composite of pixels that is characterized by the highest brightness temperature (BT) of the SEVIRI channel at 10.8 μm, and by a negative BT difference between the channels at 8.7 and 10.8 μm. Because of the lower temperatures of clouds and aerosols compared to clear-sky conditions, the authors assume that the selected pixel values are obtained for a clear-sky day. A forward model is used to simulate the thermal IR radiation transfer in the dust layer. The apparent surface radiation for the three window channels in the presence of aerosols is calculated as a function of the surface emissivity and the surface temperature, the aerosol layer temperature, and the AOD for different aerosol loadings. From these simulations two emissivity ratios, which are stored in lookup tables (LUT), are calculated. The retrieval algorithm consists of processing the clear-sky image and computing the surface emissivity, processing the instantaneous image, and computing the apparent surface radiation for the three window channels. The two emissivity ratios are computed using the radiances at 8.7 and 10.8 μm and at 8.7 and 12.0 μm, respectively. The SEVIRI AOD is obtained by the inversion of these emissivity ratios using the corresponding LUT. The algorithm is applied to a minor dust event over the Sahara between 19 and 22 June 2007. For the validation the SEVIRI AOD is compared with the AOD from the Cloud Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) along the satellite track.

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Validation of satellite and model aerosol optical depth and precipitable water vapour observations with AERONET data over Pune, India

International Journal of Remote Sensing ◽

10.1080/01431161.2018.1476789 ◽

2018 ◽

Vol 39 (21) ◽

pp. 7643-7663 ◽

Cited By ~ 2

Author(s):

K. Vijayakumar ◽

P. C. S. Devara ◽

David M. Giles ◽

Brent N. Holben ◽

S. Vijaya Bhaskara Rao ◽

...

Keyword(s):

Water Vapour ◽

Aerosol Optical Depth ◽

Optical Depth ◽

Precipitable Water ◽

Precipitable Water Vapour ◽

Model Aerosol

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Comparison of MODIS 3 km and 10 km resolution aerosol optical depth retrievals over land with airborne sunphotometer measurements during ARCTAS summer 2008

Atmospheric Chemistry and Physics ◽

10.5194/acp-14-2015-2014 ◽

2014 ◽

Vol 14 (4) ◽

pp. 2015-2038 ◽

Cited By ~ 26

Author(s):

J. M. Livingston ◽

J. Redemann ◽

Y. Shinozuka ◽

R. Johnson ◽

P. B. Russell ◽

...

Keyword(s):

Aerosol Optical Depth ◽

Optical Depth ◽

Retrieval Algorithm ◽

Grid Cells ◽

Data Set ◽

Clear Sky ◽

Modis Aod ◽

Research Aircraft ◽

Bright Surface ◽

Moderate Resolution Imaging Spectroradiometer

Abstract. Airborne sunphotometer measurements acquired by the NASA Ames Airborne Tracking Sunphotometer (AATS-14) aboard the NASA P-3 research aircraft are used to evaluate dark-target over-land retrievals of extinction aerosol optical depth (AOD) from spatially and temporally near-coincident measurements by the Moderate Resolution Imaging Spectroradiometer (MODIS) during the summer 2008 Arctic Research of the Composition of the Troposphere from Aircraft and Satellites (ARCTAS) field campaign. The new MODIS Collection 6 aerosol data set includes retrievals of AOD at both 10 km × 10 km and 3 km × 3 km (at nadir) resolution. In this paper we compare MODIS and AATS AOD at 553 nm in 58 10 km and 134 3 km retrieval grid cells. These AOD values were derived from data collected over Canada on four days during short time segments of five (four Aqua and one Terra) satellite overpasses of the P-3 during low-altitude P-3 flight tracks. Three of the five MODIS–AATS coincidence events were dominated by smoke: one included a P-3 transect of a well-defined smoke plume in clear sky, but two were confounded by the presence of scattered clouds above smoke. The clouds limited the number of MODIS retrievals available for comparison, and led to MODIS AOD retrievals that underestimated the corresponding AATS values. This happened because the MODIS aerosol cloud mask selectively removed 0.5 km pixels containing smoke and clouds before the aerosol retrieval. The other two coincidences (one Terra and one Aqua) occurred during one P-3 flight on the same day and in the same general area, in an atmosphere characterized by a relatively low AOD (< 0.3), spatially homogeneous regional haze from smoke outflow with no distinguishable plume. For the ensemble data set for MODIS AOD retrievals with the highest-quality flag, MODIS AOD agrees with AATS AOD within the expected MODIS over-land AOD uncertainty in 60% of the retrieval grid cells at 10 km resolution and 69% at 3 km resolution. These values improve to 65 % and 74%, respectively, when the cloud-affected case with the strongest plume is excluded. We find that the standard MODIS dark-target over-land retrieval algorithm fails to retrieve AOD for thick smoke, not only in cloud-contaminated regions but also in clear sky. We attribute this to deselection, by the cloud and/or bright surface masks, of 0.5 km resolution pixels that contain smoke.

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Aerosol properties and aerosol–radiation interactions in clear sky conditions over Germany

10.5194/acp-2021-517 ◽

2021 ◽

Author(s):

Jonas Witthuhn ◽

Anja Hünerbein ◽

Florian Filipitsch ◽

Stefan Wacker ◽

Stefanie Meilinger ◽

...

Keyword(s):

Radiative Transfer ◽

Aerosol Optical Depth ◽

Optical Depth ◽

Kernel Method ◽

Detection Algorithm ◽

Surface Energy Budget ◽

Radiative Effect ◽

Clear Sky ◽

Observational Network ◽

Level Of Agreement

Abstract. The clear-sky radiative effect of aerosol-radiation interactions is of relevance for our understanding of the climate system. The influence of aerosol on the surface energy budget is of high interest for the renewable energy sector. In this study, the radiative effect is investigated in particular with respect to seasonal and regional variations for the region of Germany and the year 2015 at the surface and top of atmosphere using two complementary approaches. First, an ensemble of clear-sky models which explicitly consider aerosols is utilized to retrieve the aerosol optical depth and the surface direct radiative effect of aerosols by means of a clear sky fitting technique. For this, short-wave broadband irradiance measurements in the absence of clouds are used as a basis. A clear sky detection algorithm is used to identify cloud free observations. Considered are measurements of the shortwave broadband global and diffuse horizontal irradiance with shaded and unshaded pyranometers at 25 stations across Germany within the observational network of the German Weather Service (DWD). Clear sky models used are MMAC, MRMv6.1, METSTAT, ESRA, Heliosat-1, CEM and the simplified Solis model. The definition of aerosol and atmospheric characteristics of the models are examined in detail for their suitability for this approach. Second, the radiative effect is estimated using explicit radiative transfer simulations with inputs on the meteorological state of the atmosphere, trace-gases and aerosol from CAMS reanalysis. The aerosol optical properties (aerosol optical depth, Ångström exponent, single scattering albedo and assymetrie parameter) are first evaluated with AERONET direct sun and inversion products. The largest inconsistency is found for the aerosol absorption, which is overestimated by about 0.03 or about 30 % by the CAMS reanalysis. Compared to the DWD observational network, the simulated global, direct and diffuse irradiances show reasonable agreement within the measurement uncertainty. The radiative kernel method is used to estimate the resulting uncertainty and bias of the simulated direct radiative effect. The uncertainty is estimated to −1.5 ± 7.7 and 0.6 ± 3.5 W m−2 at the surface and top of atmosphere, respectively, while the annual-mean biases at the surface, top of atmosphere and total atmosphere are −10.6, −6.5 and 4.1 W m−2, respectively. The retrieval of the aerosol radiative effect with the clear sky models shows a high level of agreement with the radiative transfer simulations, with an RMSE of 5.8 W m−2 and a correlation of 0.75. The annual mean of the REari at the surface for the 25 DWD stations shows a value of −12.8 ± 5 W m−2 as average over the clear sky models, compared to −11 W m−2 from the radiative transfer simulations. Since all models assume a fixed aerosol characterisation, the annual cycle of the aerosol radiation effect cannot be reproduced. Out of this set of clear sky models, the largest level of agreement is shown by the ESRA and MRMv6.1 models.

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Towards closure between measured and modelled UV under clear skies at four diverse sites

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-7-1507-2007 ◽

2007 ◽

Vol 7 (1) ◽

pp. 1507-1555 ◽

Cited By ~ 1

Author(s):

J. Badosa ◽

R. L. McKenzie ◽

M. Kotkamp ◽

J. Calbó ◽

J. A. González ◽

...

Keyword(s):

Aerosol Optical Depth ◽

Optical Depth ◽

Single Scattering ◽

Uv Spectra ◽

Atmospheric Composition ◽

Model Calculations ◽

Uv Index ◽

Mauna Loa ◽

Clear Sky ◽

One Year

Abstract. The purpose of this work is determine the extent of closure between measurements and models of UV irradiances at diverse sites using state of the art instruments, models, and the best available data as inputs to the models. These include information about aerosol optical depth (unfortunately not extending down as far into the UVB region as desirable because such information is not generally available), ozone column amounts, as well as vertical profiles of ozone and temperature. We concentrate on clear-sky irradiances, and report the results in terms of UV Index (UVI). Clear-sky data from one year of measurements at each of four diverse sites (Lauder – New Zealand, Mauna Loa Observatory – Hawaii, Boulder – Colorado, and Melbourne – Australia) have been analysed in detail, also taking account of different measurements of ozone, including satellite-derived values, as well as ground measured values, both from Dobson instruments and as retrieved from the UV spectra under study. Previous studies have generally focussed on data from a single site, and for shorter periods. Consequently, this study is the most comprehensive of its kind to date. At Lauder, which is the cleanest low altitude site, we obtained agreement between measurement and model at 5% level, which is consistent with the best agreement found previously. At Mauna Loa Observatory, similar agreement was achieved, but model calculations need to allow for reflections from cloud that are present below the observatory. At this site, there are occasional problems with using satellite-derived ozone. At Boulder, mean agreements were similar but the dispersion around the mean was slightly larger, corresponding to larger uncertainties in the aerosol inputs to the model. However, at Melbourne, which is the only non-NDACC (Network for the Detection of Atmospheric Composition Change) site, there remain unexplained discrepancies. The measured values are significantly lower than the calculated values. We investigate the extent to which this discrepancy can be explained by incomplete knowledge of aerosol extinctions in the UV at this site. We conclude that further information about aerosol optical depth and single scattering albedo in the UVB region is needed to resolve the issues. At the three NDACC sites, the closure provided by the study gives confidence in both the measurements and our ability to model them. The study revealed a limitation in the use of PTFE diffusers when temperatures are lower than approximately 20°C. It also documents the range of clear sky UVI values expected at these diverse sites.

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A 30-year climatology (1990-2020) of aerosol optical depth and total column water vapor and ozone over Texas

Bulletin of the American Meteorological Society ◽

10.1175/bams-d-21-0010.1 ◽

2021 ◽

pp. 1-22

Author(s):

Forrest M. Mims

Keyword(s):

Aerosol Optical Depth ◽

Optical Depth ◽

El Niño ◽

El Nino ◽

Southern Oscillation ◽

Precipitable Water ◽

Texas History ◽

Total Column Ozone ◽

Annual Cycles ◽

Total Column

AbstractA 30-year time series (4 Feb 1990 to 4 Feb 2020) of aerosol optical depth of the atmosphere (AOD), total precipitable water (TPW) and total column ozone has been conducted in Central Texas using simple, highly stable instruments. All three parameters in this ongoing measurement series exhibited robust annual cycles. They also responded to many atmospheric events, including the historic volcanic eruption of Mount Pinatubo (1991), a record El Niño (1998), an unprecedented biomass smoke event (1998) and the La Niña that caused the driest drought in recorded Texas history (2011). Reduced air pollution caused mean AOD to decline from 0.175 to 0.14. The AOD trend measured for 30 years by an LED sun photometer, the first of its kind, parallels the trend from 20 years of measurements by a modified Microtops II. While TPW responded to El Niño-Southern Oscillation conditions, TPW exhibited no trend over the 30 years. The TPW data compare favorably with 4.5 years of simultaneous measurements by a nearby NOAA GPS (r2 = 0.78). The 30 years of ozone measurements compare favorably with those from a series of NASA ozone satellites (r2 = 0.78). In 2016, 194 comparisons of Microtops II and world standard ozone instrument Dobson 83 at the Mauna Loa Observatory agreed within 1.9% (r2 = 0.81). The paper concludes by observing that students and citizen scientists can collect scientifically useful atmospheric data with simple sun photometers that use one or more LEDs as spectrally selective photodiodes.

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Analysis on the impact of aerosol optical depth on surface solar radiation in the Shanghai megacity, China

Atmospheric Chemistry and Physics ◽

10.5194/acp-11-3281-2011 ◽

2011 ◽

Vol 11 (7) ◽

pp. 3281-3289 ◽

Cited By ~ 22

Author(s):

J. Xu ◽

C. Li ◽

H. Shi ◽

Q. He ◽

L. Pan

Keyword(s):

Solar Radiation ◽

Aerosol Optical Depth ◽

Optical Depth ◽

Decadal Variation ◽

Surface Solar Radiation ◽

Atmospheric Transparency ◽

Clear Sky ◽

Term Variation ◽

Sky Conditions

Abstract. This study investigated the decadal variation of the direct surface solar radiation (DiSR) and the diffuse surface solar radiation (DfSR) during 1961–2008 in the Shanghai megacity as well as their relationships to Aerosol Optical Depth (AOD) under clear-sky conditions. Three successive periods with unique features of long term variation of DiSR were identified for both clear-sky and all-sky conditions: a "dimming" period from the late 1960s to the mid 1980s, a "stabilization"/"slight brightening" period from the mid 1980s to the mid 1990s, and a "renewed dimming" period thereafter. During the two dimming periods of DiSR, DfSR brightened significantly under clear-sky conditions, indicating that change in atmospheric transparency resulting from aerosol emission has an important role on decadal variation of surface solar radiation (SSR) over this area. The analysis on the relationship between the Moderate-resolution Imaging Spectroradiometer (MODIS) retrieved AOD and the corresponding hourly measurements of DiSR and DfSR under clear-sky conditions clearly revealed that AOD is significantly correlated and anti-correlated with DfSR and DiSR, respectively, both above 99% confidence in all seasons, indicating the great impact of aerosols on SSR through absorption and/or scattering in the atmosphere. In addition, both AOD and the corresponding DiSR and DfSR measured during the satellite passage over Shanghai show obvious weekly cycles. On weekends, AOD is lower than the weekly average, corresponding to higher DiSR and lower DfSR, while the opposite pattern was true for weekdays. Less AOD on weekends due to the reduction of transportation and industrial activities results in enhancement of atmospheric transparency under cloud free conditions so as to increase DiSR and decrease DfSR simultaneously. Results show that aerosol loading from the anthropogenic emissions is an important modulator for the long term variation of SSR in Shanghai.

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Atmospheric effect on the ground-based measurements of broadband surface albedo

Atmospheric Measurement Techniques ◽

10.5194/amt-5-2675-2012 ◽

2012 ◽

Vol 5 (11) ◽

pp. 2675-2688 ◽

Cited By ~ 12

Author(s):

T. Manninen ◽

A. Riihelä ◽

G. de Leeuw

Keyword(s):

Aerosol Optical Depth ◽

Optical Depth ◽

Surface Albedo ◽

Test Site ◽

Empirical Method ◽

Atmospheric Conditions ◽

Atmospheric Effect ◽

Clear Sky ◽

Using Data ◽

Sky Conditions

Abstract. Ground-based pyranometer measurements of the (clear-sky) broadband surface albedo are affected by the atmospheric conditions (mainly by aerosol particles, water vapour and ozone). A new semi-empirical method for estimating the magnitude of the effect of atmospheric conditions on surface albedo measurements in clear-sky conditions is presented. Global and reflected radiation and/or aerosol optical depth (AOD) at two wavelengths are needed to apply the method. Depending on the aerosol optical depth and the solar zenith angle values, the effect can be as large as 20%. For the cases we tested using data from the Cabauw atmospheric test site in the Netherlands, the atmosphere caused typically up to 5% overestimation of surface albedo with respect to corresponding black-sky surface albedo values.

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Ship borne rotating shadow band radiometer observations for the determination of multi spectral irradiance components and direct sun products for aerosol

10.5194/amt-2016-297 ◽

2016 ◽

Author(s):

Jonas Witthuhn ◽

Hartwig Deneke ◽

Andreas Macke ◽

Germar Bernhard

Keyword(s):

Aerosol Optical Depth ◽

Optical Depth ◽

Precipitable Water ◽

Gas Absorption ◽

Spectral Irradiance ◽

Total Uncertainty ◽

Direct Beam ◽

Sun Photometer ◽

Beam Transmittance ◽

Band Radiometer

Abstract. The 19 channel rotating shadow band radiometer GUVis-3511 built by Biospherical Instruments is introduced as an instrument which is able to provide automated ship borne measurements of the direct, diffuse and global spectral irradiance components without a requirement for stabilization. Several direct sun products, including spectral direct beam transmittance, aerosol optical depth, Angström exponent, and precipitable water can be derived from these observations. The individual steps of the data analysis are described, and the different sources of uncertainty are discussed. The total uncertainty of the observed direct beam transmittances is estimated to be 4.24 % at 95 % CI for ship borne operation. The calibration is identified as the dominating contribution to the total uncertainty. A comparison of direct beam transmittance with those obtained from a Cimel sun photometer at a land site and a manually operated Microtops II sun photometer on a ship is presented, yielding relative deviations of less than 3 % and 4 % on land and on ship, respectively, for most channels and in agreement with our previous uncertainty estimate. These numbers demonstrate that the instrument is well suited for ship borne operation, and the applied methods for motion correction work accurately. Based on spectral direct beam transmittance, aerosol optical depth at 510 nm can be retrieved with an uncertainty of 0.0032 for a 95 % CI. Only minor deviations occur due to the different methods used for estimating Rayleigh scattering and gas absorption optical depths, as implemented by AERONET and in our processing. Relying on the cross-calibration of the 940 nm water vapor channel with the Cimel sun photometer, the column amount of precipitable water has been estimated with an uncertainty of +−0.034 cm. More research is needed to estimate the accuracy of the instrument for low sun (solar zenith angles larger than 70°) and during periods with strong swell.

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Using Sun Fits images for calculation of terrestrial aerosol optical depth (AOD) and Ångström turbidity parameters in countryside of Kufa district

Journal of Kufa Physics ◽

10.31257/2018/jkp/2020/120203 ◽

2020 ◽

Vol 12 (02) ◽

pp. 33-38

Author(s):

Hayder Hasan Jawad ◽

◽

Aref Saleh Baron

Keyword(s):

Aerosol Optical Depth ◽

Optical Depth ◽

The Other ◽

Solar Telescope ◽

Laptop Computer ◽

Clear Sky ◽

Matlab Code

Since there are no previous studies conducted for calculating Kufa turbidity parameters considering that the urban pollutions is less than that of the Kufa city. For this The prior location of the Faculty of science telescope was chosen to make such observation using a 60 mm solar telescope Coronado of Hα filter equipped with CCD DSI III pro connected to laptop computer . Sun Fits images were captured under a clear sky as well as dusty conditions. Two types of images were classified, one in the clear sky and the other in dusty weather. Matlab code was used to estimate sun intensities in order to calculate aerosol optical depth and Ångström turbidity parameters from sun images. These values are expressing the normality behavior with nearer places in territorial region.

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