An algorithm for the Sun photometer calibration

2002 ◽  
Author(s):  
A.M. Ignatov ◽  
I.L. Dergileva ◽  
S.M. Sakerin ◽  
D.M. Kabanov
Keyword(s):  
The Sun ◽  
Sun Photometer ◽  
Photometer Calibration

scholarly journals Improving Langley calibrations by reducing diurnal variations of aerosol Ångström parameters

2012 ◽  
Vol 5 (5) ◽  
pp. 6479-6492
Author(s):  
A. Kreuter ◽  
S. Wuttke ◽  
M. Blumthaler
Keyword(s):  
Monte Carlo ◽  
Monte Carlo Method ◽  
Aerosol Optical Depth ◽  
State Of The Art ◽  
Diurnal Variations ◽  
The Sun ◽  
Calibration Constant ◽  
Solar Noon ◽  
Sun Photometer ◽  
Photometer Calibration

Abstract. Errors in the sun photometer calibration constant lead to artificial diurnal variations, symmetric around solar noon, of the retrieved Aerosol Optical Depth (AOD) and the associated Ångström exponent α and its curvature γ. We show in simulations that within the uncertainty of state-of-the-art Langley calibrations, these diurnal variations of α and γ can be significant in low AOD conditions, while those of AOD are negligible. We implement a weighted Monte-Carlo method of finding an improved calibration constant by minimizing the diurnal variations in α and γ and apply the method to sun photometer data of a clear day in Innsbruck, Austria. The results show that our method can be used to improve the calibrations in two of the four wavelength channels by up to a factor of 3.6.

scholarly journals Improving Langley calibrations by reducing diurnal variations of aerosol Ångström parameters

2013 ◽  
Vol 6 (1) ◽  
pp. 99-103 ◽  
Author(s):  
A. Kreuter ◽  
S. Wuttke ◽  
M. Blumthaler
Keyword(s):  
Monte Carlo ◽  
Monte Carlo Method ◽  
Aerosol Optical Depth ◽  
State Of The Art ◽  
Diurnal Variations ◽  
The Sun ◽  
Calibration Constant ◽  
Solar Noon ◽  
Sun Photometer ◽  
Photometer Calibration

Abstract. Errors in the sun photometer calibration constant lead to artificial diurnal variations, symmetric around solar noon, of the retrieved aerosol optical depth (AOD) and the associated Ångström exponent α and its curvature γ. We show in simulations that within the uncertainty of state-of-the-art Langley calibrations, these diurnal variations of α and γ can be significant in low AOD conditions, while those of AOD are negligible. We implement a weighted Monte Carlo method of finding an improved calibration constant by minimizing the diurnal variations in α and γ and apply the method to sun photometer data of a clear day in Innsbruck, Austria. The results show that our method can be used to improve the calibrations in two of the four wavelength channels by up to a factor of 3.6.

scholarly journals Evaluation of the MODIS Aerosol Retrievals over Ocean and Land during CLAMS

2005 ◽  
Vol 62 (4) ◽  
pp. 974-992 ◽  
Author(s):  
R. C. Levy ◽  
L. A. Remer ◽  
J. V. Martins ◽  
Y. J. Kaufman ◽  
A. Plana-Fattori ◽  
...  
Keyword(s):  
Atmospheric Correction ◽  
Radiant Energy ◽  
Solar Spectrum ◽  
Lookup Table ◽  
Aerosol Size Distribution ◽  
The Sun ◽  
Satellite Platform ◽  
Validation Experiment ◽  
Modis Aod ◽  
Sun Photometer

Abstract The Chesapeake Lighthouse Aircraft Measurements for Satellites (CLAMS) experiment took place from 10 July to 2 August 2001 in a combined ocean–land region that included the Chesapeake Lighthouse [Clouds and the Earth’s Radiant Energy System (CERES) Ocean Validation Experiment (COVE)] and the Wallops Flight Facility (WFF), both along coastal Virginia. This experiment was designed mainly for validating instruments and algorithms aboard the Terra satellite platform, including the Moderate Resolution Imaging Spectroradiometer (MODIS). Over the ocean, MODIS retrieved aerosol optical depths (AODs) at seven wavelengths and an estimate of the aerosol size distribution. Over the land, MODIS retrieved AOD at three wavelengths plus qualitative estimates of the aerosol size. Temporally coincident measurements of aerosol properties were made with a variety of sun photometers from ground sites and airborne sites just above the surface. The set of sun photometers provided unprecedented spectral coverage from visible (VIS) to the solar near-infrared (NIR) and infrared (IR) wavelengths. In this study, AOD and aerosol size retrieved from MODIS is compared with similar measurements from the sun photometers. Over the nearby ocean, the MODIS AOD in the VIS and NIR correlated well with sun-photometer measurements, nearly fitting a one-to-one line on a scatterplot. As one moves from ocean to land, there is a pronounced discontinuity of the MODIS AOD, where MODIS compares poorly to the sun-photometer measurements. Especially in the blue wavelength, MODIS AOD is too high in clean aerosol conditions and too low under larger aerosol loadings. Using the Second Simulation of the Satellite Signal in the Solar Spectrum (6S) radiative code to perform atmospheric correction, the authors find inconsistency in the surface albedo assumptions used by the MODIS lookup tables. It is demonstrated how the high bias at low aerosol loadings can be corrected. By using updated urban/industrial aerosol climatology for the MODIS lookup table over land, it is shown that the low bias for larger aerosol loadings can also be corrected. Understanding and improving MODIS retrievals over the East Coast may point to strategies for correction in other locations, thus improving the global quality of MODIS. Improvements in regional aerosol detection could also lead to the use of MODIS for monitoring air pollution.

Atmospheric transparency over central Yakutia from the sun photometer data in 2004—2014

2017 ◽  
Vol 42 (11) ◽  
pp. 700-704 ◽  
Author(s):  
M. S. Vasiliev ◽  
S. V. Nikolashkin ◽  
R. N. Boroyev
Keyword(s):  
The Sun ◽  
Atmospheric Transparency ◽  
Central Yakutia ◽  
Sun Photometer

scholarly journals Comparison of the aerosol optical properties and size distribution retrieved by Sun photometer with in-situ measurements at mid-latitude

2016 ◽  
Author(s):  
Aurélien Chauvigné ◽  
Karine Sellegri ◽  
Maxime Hervo ◽  
Nadège Montoux ◽  
Patrick Freville ◽  
...  
Keyword(s):  
Remote Sensing ◽  
In Situ Measurements ◽  
The Sun ◽  
Size Distributions ◽  
Particle Size Distributions ◽  
Near Surface ◽  
Atmospheric Column ◽  
Fine Mode ◽  
Sun Photometer

Abstract. Aerosols influence the Earth radiative budget through scattering and absorption of solar radiation. Several methods are used to investigate aerosol properties and thus quantify their direct and indirect impacts on climate. At the Puy de Dôme station, continuous high altitude near surface in-situ measurements and low altitude ground-based remote sensing atmospheric column measurements give the opportunity to compare the aerosol extinction measured with both methods over a one year period. To our knowledge, it is the first time that such a comparison is realized with continuous measurements of a high altitude site during a long term period. This comparison addresses to which extend near surface in-situ measurements are representative of the whole atmospheric column, the aerosol Mixing Layer (ML), or the Free Troposphere (FT). In particular, the impact of multi aerosol layers events detected using LIDAR backscatter profiles is analysed. A good correlation between in-situ aerosol extinction coefficient and Aerosol Optical Depth (AOD) measured by the Aerosol Robotic Network (AERONET) Sun photometer is observed with a correlation coefficient around 0.80, indicating that the in-situ measurements station is representative of the overall atmospheric column. After filtering for multilayer cases and correcting for each layer optical contribution (ML and FT), the atmospheric structure seems to be the main factor influencing the comparison between the two measurement techniques. When the site lies in the ML, the in-situ extinction represents 45 % of the Sun photometer ML extinction while when the site lies within the FT, the in-situ extinction is more than two times higher than the FT Sun photometer extinction. Remote sensing retrievals of the aerosol particle size distributions (PSD) from the Sun photometer observations are then compared to the near surface in-situ measurements, at dry and at ambient relative humidities. When in-situ measurements are considered at dry state, the in-situ fine mode diameters are 44 % higher than the Sun photometer-retrieved diameters and in-situ volume concentrations are 20 % lower than of the Sun photometer-retrieved fine mode concentration. Using a parametrised hygroscopic growth factor applied to aerosol diameters, the difference between in-situ and retrieved diameters grows larger. Coarse mode in-situ diameter and concentrations show a good correlation with retrieved particle size distributions from remote sensing.

scholarly journals Comparison of the aerosol optical properties and size distribution retrieved by sun photometer with in situ measurements at midlatitude

2016 ◽  
Vol 9 (9) ◽  
pp. 4569-4585 ◽  
Author(s):  
Aurélien Chauvigné ◽  
Karine Sellegri ◽  
Maxime Hervo ◽  
Nadège Montoux ◽  
Patrick Freville ◽  
...  
Keyword(s):  
Remote Sensing ◽  
High Altitude ◽  
In Situ Measurements ◽  
Aerosol Extinction ◽  
The Sun ◽  
Near Surface ◽  
Atmospheric Column ◽  
Fine Mode ◽  
Sun Photometer

Abstract. Aerosols influence the Earth radiative budget through scattering and absorption of solar radiation. Several methods are used to investigate aerosol properties and thus quantify their direct and indirect impacts on climate. At the Puy de Dôme station, continuous high-altitude near-surface in situ measurements and low-altitude ground-based remote sensing atmospheric column measurements give the opportunity to compare the aerosol extinction measured with both methods over a 1-year period. To our knowledge, it is the first time that such a comparison is realised with continuous measurements of a high-altitude site during a long-term period. This comparison addresses to which extent near-surface in situ measurements are representative of the whole atmospheric column, the aerosol mixing layer (ML) or the free troposphere (FT). In particular, the impact of multi-aerosol layers events detected using lidar backscatter profiles is analysed. A good correlation between in situ aerosol extinction coefficient and aerosol optical depth (AOD) measured by the Aerosol Robotic Network (AERONET) sun photometer is observed with a correlation coefficient around 0.80, indicating that the in situ measurements station is representative of the overall atmospheric column. After filtering for multilayer cases and correcting for each layer optical contribution (ML and FT), the atmospheric structure seems to be the main factor influencing the comparison between the two measurement techniques. When the site lies in the ML, the in situ extinction represents 45 % of the sun photometer ML extinction while when the site lies within the FT, the in situ extinction is more than 2 times higher than the FT sun photometer extinction. Moreover, the assumption of a decreasing linear vertical aerosol profile in the whole atmosphere has been tested, significantly improving the instrumental agreement. Remote sensing retrievals of the aerosol particle size distributions (PSDs) from the sun photometer observations are then compared to the near-surface in situ measurements, at dry and at ambient relative humidities. When in situ measurements are considered at dry state, the in situ fine mode diameters are 44 % higher than the sun-photometer-retrieved diameters and in situ volume concentrations are 20 % lower than those of the sun-photometer-retrieved fine mode concentration. Using a parameterised hygroscopic growth factor applied to aerosol diameters, the difference between in situ and retrieved diameters grows larger. Coarse mode in situ diameters and concentrations show a good correlation with retrieved PSDs from remote sensing.

scholarly journals The STARTWAVE atmospheric water database

2006 ◽  
Vol 6 (8) ◽  
pp. 2039-2056 ◽  
Author(s):  
J. Morland ◽  
B. Deuber ◽  
D. G. Feist ◽  
L. Martin ◽  
S. Nyeki ◽  
...  
Keyword(s):  
Water Vapour ◽  
Microwave Radiometer ◽  
Measurement Techniques ◽  
The Sun ◽  
Qualitative Comparison ◽  
Radiosonde Station ◽  
The Alps ◽  
Sun Photometer ◽  
Microwave Radiometers ◽  
Stratospheric Water Vapour

Abstract. The STARTWAVE (STudies in Atmospheric Radiative Transfer and Water Vapour Effects) project aims to investigate the role which water vapour plays in the climate system, and in particular its interaction with radiation. Within this framework, an ongoing water vapour database project was set up which comprises integrated water vapour (IWV) measurements made over the last ten years by ground-based microwave radiometers, Global Positioning System (GPS) receivers and sun photometers located throughout Switzerland at altitudes between 330 and 3584 m. At Bern (46.95° N, 7.44° E) tropospheric and stratospheric water vapour profiles are obtained on a regular basis and integrated liquid water, which is important for cloud characterisation, is also measured. Additional stratospheric water vapour profiles are obtained by an airborne microwave radiometer which observes large parts of the northern hemisphere during yearly flight campaigns. The database allows us to validate the various water vapour measurement techniques. Comparisons between IWV measured by the Payerne radiosonde with that measured at Bern by two microwave radiometers, GPS and sun photometer showed instrument biases within ±0.5 mm. The bias in GPS relative to sun photometer over the 2001 to 2004 period was –0.8 mm at Payerne (46.81° N, 6.94° E, 490 m), which lies in the Swiss plains north of the Alps, and +0.6 mm at Davos (46.81° N, 9.84° E, 1598 m), which is located within the Alps in the eastern part of Switzerland. At Locarno (46.18° N, 8.78° E, 366 m), which is located on the south side of the Alps, the bias is +1.9 mm. The sun photometer at Locarno was found to have a bias of –2.2 mm (13% of the mean annual IWV) relative to the data from the closest radiosonde station at Milano. This result led to a yearly rotation of the sun photometer instruments between low and high altitude stations to improve the calibrations. In order to demonstrate the capabilites of the database for studying water vapour variations, we investigated a front which crossed Switzerland between 18 November 2004 and 19 November 2004. During the frontal passage, the GPS and microwave radiometers at Bern and Payerne showed an increase in IWV of between 7 and 9 mm. The GPS IWV measurements were corrected to a standard height of 500 m, using an empirically derived exponential relationship between IWV and altitude. A qualitative comparison was made between plots of the IWV distribution measured by the GPS and the 6.2 µm water vapour channel on the Meteosat Second Generation (MSG) satellite. Both showed that the moist air moved in from a northerly direction, although the MSG showed an increase in water vapour several hours before increases in IWV were detected by GPS or microwave radiometer. This is probably due to the fact that the satellite instrument is sensitive to an atmospheric layer at around 320 hPa, which makes a contribution of one percent or less to the IWV.

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