scholarly journals Aerosol optical depth determination in the UV using a four-channel precision filter radiometer

2016 ◽  
Author(s):  
Thomas Carlund ◽  
Natalia Kouremeti ◽  
Stelios Kazadzis ◽  
Julian Gröbner
Keyword(s):  
Aerosol Optical Depth ◽  
Optical Depth ◽  
Spectral Response ◽  
Wavelength Region ◽  
Measuring Instruments ◽  
Response Functions ◽  
Total Column Ozone ◽  
Total Uncertainty ◽  
Air Mass ◽  
Filter Radiometer

Abstract. The determination of aerosol properties, especially the aerosol optical depth (AOD) in the UV wavelength region is of great importance to understand the climatological variability of UV radiation. However, operational retrievals of AOD at the biological most harmful wavelengths in the UVB are currently only made at very few places. This paper reports on the UVPFR sunphotometer, a stable and robust instrument that can be used for AOD retrievals at four UV wavelengths. Instrument characteristics and results of Langley calibrations at a high altitude site were presented. It was shown that due to the relatively wide spectral response functions of the UVPFR, the calibration constants (V0) from Langley plot calibrations underestimate the true extra-terrestrial signals. Accordingly, correction factors were introduced. In addition, the instrument spectral response functions also result in an apparent airmass dependent decrease in ozone optical depth used in the AOD determinations. An adjusted formula for the calculation of AOD, with a correction term dependent on total column ozone amount and ozone air mass, was therefore developed. Langley calibrations performed 13–14 months apart resulted in sensitivity changes of ≤ 1.1 %, indicating good instrument stability. Comparison with a standard PFR, measuring AOD at 368–862 nm wavelengths with high accuracy, showed consistent results. Also very good agreement was achieved comparing the UVPFR with AOD at UVB wavelengths derived with a Brewer spectrophotometer, which was calibrated against the UVPFR at an earlier date. Mainly due to non-instrumental uncertainties connected with ozone optical depth, the total uncertainty of AOD in the UVB are higher than the ones reported from UVA and visible AOD measuring instruments. However, the precision can be high between instruments using harmonized algorithms for ozone and Rayleigh optical depth as well as for air mass terms. For several months of comparison measurements with the UVPFR and a Brewer the root mean squared AOD differences were

scholarly journals Aerosol optical depth determination in the UV using a four-channel precision filter radiometer

2017 ◽  
Vol 10 (3) ◽  
pp. 905-923 ◽  
Author(s):  
Thomas Carlund ◽  
Natalia Kouremeti ◽  
Stelios Kazadzis ◽  
Julian Gröbner
Keyword(s):  
Aerosol Optical Depth ◽  
Optical Depth ◽  
Correction Term ◽  
Spectral Response ◽  
Wavelength Region ◽  
Response Functions ◽  
Total Column Ozone ◽  
Total Uncertainty ◽  
Air Mass ◽  
Filter Radiometer

Abstract. The determination of aerosol properties, especially the aerosol optical depth (AOD) in the ultraviolet (UV) wavelength region, is of great importance for understanding the climatological variability of UV radiation. However, operational retrievals of AOD at the biologically most harmful wavelengths in the UVB are currently only made at very few places. This paper reports on the UVPFR (UV precision filter radiometer) sunphotometer, a stable and robust instrument that can be used for AOD retrievals at four UV wavelengths. Instrument characteristics and results of Langley calibrations at a high-altitude site were presented. It was shown that due to the relatively wide spectral response functions of the UVPFR, the calibration constants (V0) derived from Langley plot calibrations underestimate the true extraterrestrial signals. Accordingly, correction factors were introduced. In addition, the instrument's spectral response functions also result in an apparent air-mass-dependent decrease in ozone optical depth used in the AOD determinations. An adjusted formula for the calculation of AOD, with a correction term dependent on total column ozone amount and ozone air mass, was therefore introduced. Langley calibrations performed 13–14 months apart resulted in sensitivity changes of ≤ 1.1 %, indicating good instrument stability. Comparison with a high-accuracy standard precision filter radiometer, measuring AOD at 368–862 nm wavelengths, showed consistent results. Also, very good agreement was achieved by comparing the UVPFR with AOD at UVB wavelengths derived with a Brewer spectrophotometer, which was calibrated against the UVPFR at an earlier date. Mainly due to non-instrumental uncertainties connected with ozone optical depth, the total uncertainty of AOD in the UVB is higher than that reported from AOD instruments measuring in UVA and visible ranges. However, the precision can be high among instruments using harmonized algorithms for ozone and Rayleigh optical depth as well as for air mass terms. For 4 months of comparison measurements with the UVPFR and a Brewer, the root mean squared AOD differences were found < 0.01 at all the 306–320 nm Brewer wavelengths.

scholarly journals Results from the Fourth WMO Filter Radiometer Comparison for aerosol optical depth measurements

2018 ◽  
Vol 18 (5) ◽  
pp. 3185-3201 ◽  
Author(s):  
Stelios Kazadzis ◽  
Natalia Kouremeti ◽  
Henri Diémoz ◽  
Julian Gröbner ◽  
Bruce W. Forgan ◽  
...  
Keyword(s):  
Water Vapor ◽  
Individual Differences ◽  
Aerosol Optical Depth ◽  
Optical Depth ◽  
High Accuracy ◽  
Measured Data ◽  
Air Mass ◽  
Filter Radiometer ◽  
The World ◽  
Near Future

Abstract. This study presents the results of the Fourth Filter Radiometer Comparison that was held in Davos, Switzerland, between 28 September and 16 October 2015. Thirty filter radiometers and spectroradiometers from 12 countries participated including reference instruments from global aerosol networks. The absolute differences of all instruments compared to the reference have been based on the World Meteorological Organization (WMO) criterion defined as follows: 95% of the measured data has to be within 0.005 ± 0.001∕m (where m is the air mass). At least 24 out of 29 instruments achieved this goal at both 500 and 865 nm, while 12 out of 17 and 13 out of 21 achieved this at 368 and 412 nm, respectively. While searching for sources of differences among different instruments, it was found that all individual differences linked to Rayleigh, NO2, ozone, water vapor calculations and related optical depths and air mass calculations were smaller than 0.01 in aerosol optical depth (AOD) at 500 and 865 nm. Different cloud-detecting algorithms used have been compared. Ångström exponent calculations showed relatively large differences among different instruments, partly because of the high calculation uncertainty of this parameter in low AOD conditions. The overall low deviations of these AOD results and the high accuracy of reference aerosol network instruments demonstrated a promising framework to achieve homogeneity, compatibility and harmonization among the different spectral AOD networks in the near future.

scholarly journals Results from the 4<sup>th</sup> WMO Filter Radiometer Comparison for aerosol optical depth measurements

2017 ◽  
Author(s):  
Stelios Kazadzis ◽  
Natalia Kouremeti ◽  
Henri Diémoz ◽  
Julian Gröbner ◽  
Bruce W. Forgan ◽  
...  
Keyword(s):  
Water Vapor ◽  
Individual Differences ◽  
Aerosol Optical Depth ◽  
Optical Depth ◽  
High Accuracy ◽  
Measured Data ◽  
Air Mass ◽  
Filter Radiometer ◽  
The Absolute ◽  
Near Future

Abstract. This study presents the results of the 4th Filter Radiometer Comparison that was held in Davos, Switzerland, between September 28 and October 16, 2015. Thirty filter radiometers and spectroradiometers from 12 countries participated including reference instruments from global aerosol networks. The absolute differences of all instruments compared to the reference have been based on the WMO criterion defined as 95 % of the measured data has to be within 0.005 ± 0.001/m (where m is the air mass). At least 24 out of 29 instruments achieved this goal at both 500 and 865 nm, while 12 out of 17 and 13 out of 21 achieved this at 368 and 412 nm, respectively. While searching for sources of differences among different instruments, it was found that all individual differences linked to Rayleigh, NO2, ozone, water vapor calculations and related optical depths and air mass calculations were smaller than 0.01 in AOD at 500 and 865 nm. Different cloud detecting algorithms used have been compared. Ångström exponent calculations showed relatively large differences among different instruments partly because of the sensitivity of this parameter at low AOD conditions. The overall low deviations of these AOD results and the high accuracy of reference aerosol network instruments demonstrated a promising framework to achieve homogeneity, compatibility and harmonization among the different spectral AOD networks in the near-future.

scholarly journals Aerosol optical depth retrievals at the Izaña Atmospheric Observatory from 1941 to 2013 by using artificial neural networks

2016 ◽  
Vol 9 (1) ◽  
pp. 53-62 ◽  
Author(s):  
R. D. García ◽  
O. E. García ◽  
E. Cuevas ◽  
V. E. Cachorro ◽  
A. Barreto ◽  
...  
Keyword(s):  
Neural Networks ◽  
Time Series ◽  
Artificial Neural Networks ◽  
Aerosol Optical Depth ◽  
Optical Depth ◽  
Mineral Dust ◽  
Dust Particles ◽  
Filter Radiometer ◽  
Artificial Neural

Abstract. This paper presents the reconstruction of a 73-year time series of the aerosol optical depth (AOD) at 500 nm at the subtropical high-mountain Izaña Atmospheric Observatory (IZO) located in Tenerife (Canary Islands, Spain). For this purpose, we have combined AOD estimates from artificial neural networks (ANNs) from 1941 to 2001 and AOD measurements directly obtained with a Precision Filter Radiometer (PFR) between 2003 and 2013. The analysis is limited to summer months (July–August–September), when the largest aerosol load is observed at IZO (Saharan mineral dust particles). The ANN AOD time series has been comprehensively validated against coincident AOD measurements performed with a solar spectrometer Mark-I (1984–2009) and AERONET (AErosol RObotic NETwork) CIMEL photometers (2004–2009) at IZO, obtaining a rather good agreement on a daily basis: Pearson coefficient, R, of 0.97 between AERONET and ANN AOD, and 0.93 between Mark-I and ANN AOD estimates. In addition, we have analysed the long-term consistency between ANN AOD time series and long-term meteorological records identifying Saharan mineral dust events at IZO (synoptical observations and local wind records). Both analyses provide consistent results, with correlations  >  85 %. Therefore, we can conclude that the reconstructed AOD time series captures well the AOD variations and dust-laden Saharan air mass outbreaks on short-term and long-term timescales and, thus, it is suitable to be used in climate analysis.

scholarly journals Aerosol optical depth retrievals in central Amazonia from a multi-filter rotating shadow-band radiometer calibrated on-site

2019 ◽  
Vol 12 (2) ◽  
pp. 921-934
Author(s):  
Nilton E. Rosário ◽  
Thamara Sauini ◽  
Theotonio Pauliquevis ◽  
Henrique M. J. Barbosa ◽  
Marcia A. Yamasoe ◽  
...  
Keyword(s):  
Aerosol Optical Depth ◽  
Optical Depth ◽  
Spectral Response ◽  
Monitoring Site ◽  
Direct Normal Irradiance ◽  
Central Amazonia ◽  
Long Term Monitoring ◽  
Term Monitoring ◽  
Band Radiometer

Abstract. Extraterrestrial spectral response calibration of a multi-filter rotating shadow band radiometer (MFRSR) under pristine Amazonian Forest atmosphere conditions was performed using the Langley plot method. The MFRSR is installed in central Amazonia as part of a long-term monitoring site, which was used in the context of the GoAmazon2014/5 experiment. It has been operating continuously since 2011 without regular extraterrestrial calibration, preventing its application to accurate monitoring of aerosol particles. Once calibrated, the MFRSR measurements were applied to retrieve aerosol particle columnar optical properties, specifically aerosol optical depth (AODλ) and Ångström exponent (AE), which were evaluated against retrievals from a collocated Cimel Sun photometer belonging to the AErosol RObotic NETwork (AERONET). Results obtained revealed that pristine Amazonian conditions are able to provide MFRSR extraterrestrial spectral response with relative uncertainty lower than 1.0 % in visible channels. The worst estimate (air mass =1) for absolute uncertainty in AODλ retrieval varied from ≈0.02 to ≈0.03, depending on the assumption regarding uncertainty for MFRSR direct normal irradiance measured at the surface. The obtained root mean square error (RMSE ≈0.025) from the evaluation of MFRSR retrievals against AERONET AODλ was, in general, lower than estimated MFRSR AODλ uncertainty, and close to the uncertainty of AERONET field Sun photometers (≈0.02).

scholarly journals Aerosol Optical Depth retrievals in Central Amazonia from a Multi-Filter Rotating Shadow-band Radiometer on-site calibrated

2018 ◽  
Author(s):  
Nilton E. Rosário ◽  
Thamara Sauini ◽  
Theotonio Pauliquevis ◽  
Henrique M. J. Barbosa ◽  
Marcia A. Yamasoe ◽  
...  
Keyword(s):  
Aerosol Optical Depth ◽  
Optical Depth ◽  
Spectral Response ◽  
Monitoring Site ◽  
Direct Normal Irradiance ◽  
Central Amazonia ◽  
Mean Square Errors ◽  
Term Monitoring ◽  
Band Radiometer

Abstract. Extraterrestrial spectral response calibration of a Multi-Filter Rotating Shadow band Radiometer (MFRSR) under Amazonian Forest atmosphere pristine conditions using the Langley plot method was performed and evaluated. The MFRSR is installed in central Amazonia as part of a long-term monitoring site, which was used in the context of the GoAmazon2014/5 Experiment. It has been operating continuously since 2011 without regular extraterrestrial calibration, preventing its application to accurate monitoring of aerosol particles. Once calibrated, the MFRSR measurements were applied to retrieve aerosols particles columnar optical properties, specifically Aerosol Optical Depth (AODλ) and Ångström Exponent (AE), which were evaluated against retrievals from a collocated CIMEL sunphotometer belonging to the AErosol RObotic NETwork (AERONET). Results obtained revealed that Amazonian pristine conditions are able to provide MFRSR extraterrestrial spectral response with relative uncertainty lower than 1.0 % at visible channels. The worst estimate (air mass = 1) for absolute uncertainty in AODλ retrieval varied from ~ 0.02 to ~ 0.03, depending on the assumption regarding uncertainty for MFRSR direct-normal irradiance measured at the surface. Obtained Root Mean Square Errors (RMSE ~ 0.025) from the evaluation of MFRSR retrievals against AERONET AODλ were, in general, lower than estimate MFRSR AODλ uncertainties, and close to AERONET field sunphotometers (~ 0.02).

scholarly journals SPATIAL AND TEMPORAL CHANGES OF AEROSOL OPTICAL DEPTH AND ITS DRIVING FACTORS BASED ON MODIS IN JIANGSU PROVINCE

2018 ◽  
Vol XLII-3 ◽  
pp. 645-649
Author(s):  
C. Jiang ◽  
Q. Xu ◽  
Y. K. Gu ◽  
X. Y. Qian ◽  
J. N. He
Keyword(s):  
Spatial Distribution ◽  
Aerosol Optical Depth ◽  
Optical Depth ◽  
Temporal Changes ◽  
Jiangsu Province ◽  
Driving Factors ◽  
Air Mass ◽  
Spatial And Temporal Changes ◽  
Clear Point ◽  
Precipitation And Temperature

Aerosol Optical Depth (AOD) is of great value for studying air mass and its changes. In this paper, we studied the spatial-temporal changes of AOD and its driving factors based on spatial autocorrelation model, gravity model and multiple regression analysis in Jiangsu Province from 2007 to 2016. The results showed that in terms of spatial distribution, the southern AOD value is higher, and the high-value aggregation areas are significant, while the northern AOD value is lower, but the low-value aggregation areas constantly change. The AOD gravity centers showed a clear point-like aggregation. In terms of temporal changes, the overall AOD in Jiangsu Province increased year by year in fluctuation. In terms of driving factors, the total amount of vehicles, precipitation and temperature are important factors for the growth of AOD.

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

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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