scholarly journals Technical Note: Improved total atmospheric water vapour amount determination from near-infrared filter measurements with sun photometers

2007 ◽  
Vol 7 (17) ◽  
pp. 4613-4623 ◽  
Author(s):  
F. Mavromatakis ◽  
C. A. Gueymard ◽  
Y. Franghiadakis
Keyword(s):  
Radiative Transfer ◽  
Water Vapour ◽  
Near Infrared ◽  
Solar Spectrum ◽  
Theoretical Data ◽  
Precipitable Water ◽  
Technical Note ◽  
Residual Effects ◽  
Response Curves ◽  
Absolute Level

Abstract. In this work we explore the effect of the contribution of the solar spectrum to the recorded signal in wavelengths outside the typical 940-nm filter's bandwidth. We employ gaussian-shaped filters as well as actual filter transmission curves, mainly AERONET data, to study the implications imposed by the non-zero out-of-band contribution to the coefficients used to derive precipitable water from the measured water vapour band transmittance. Published parameterized transmittance functions are applied to the data to determine the filter coefficients. We also introduce an improved, three-parameter, fitting function that can describe the theoretical data accurately, with significantly less residual effects than with the existing functions. The moderate-resolution SMARTS radiative transfer code is used to predict the incident spectrum outside the filter bandpass for different atmospheres, solar geometries and aerosol optical depths. The high-resolution LBLRTM radiative transfer code is used to calculate the water vapour transmittance in the 940-nm band. The absolute level of the out-of-band transmittance has been chosen to range from 10−6 to 10−4, and typical response curves of commercially available silicon photodiodes are included into the calculations. It is shown that if the out-of-band transmittance effect is neglected, as is generally the case, then the derived columnar water vapour is mainly underestimated by a few percents. The actual error depends on the specific out-of-band transmittance, optical air mass of observation and water vapour amount. Further investigations will use experimental data from field campaigns to validate these findings.

scholarly journals Improved total atmospheric water vapour amount determination from near-infrared filter measurements with sun photometers

2007 ◽  
Vol 7 (3) ◽  
pp. 6113-6141
Author(s):  
F. Mavromatakis ◽  
C. A. Gueymard ◽  
Y. Franghiadakis
Keyword(s):  
Radiative Transfer ◽  
Water Vapour ◽  
Near Infrared ◽  
Solar Spectrum ◽  
Theoretical Data ◽  
Precipitable Water ◽  
Residual Effects ◽  
Response Curves ◽  
Absolute Level ◽  
Actual Filter

Abstract. In this work we explore the effect of the contribution of the solar spectrum to the recorded signal in wavelengths outside the typical 940-nm filter's bandwidth. We use gaussian-shaped filters as well as actual filter transmission curves to study the implications imposed by the non-zero out-of-band contribution to the coefficients used to derive precipitable water from the measured water vapour band transmittance. The moderate-resolution SMARTS radiative transfer code is used to predict the incident spectrum outside the filter bandpass for different atmospheres, solar geometries and aerosol optical depths. The high-resolution LBLRTM radiative transfer code is used to calculate the water vapour transmittance in the 940 nm band. The absolute level of the out-of-band transmittance has been chosen to range from 10−6 to 10−4, and typical response curves of commercially available silicon photodiodes are included into the calculations. It is shown that if the out-of-band transmittance effect is neglected, as is generally the case, then the derived columnar water vapour is systematically underestimated by a few percents. The actual error depends on the specific out-of-band transmittance, optical air mass of observation and water vapour amount. We apply published parameterized transmittance functions to determine the filter coefficients. We also introduce an improved, three-parameter, fitting function that can describe the theoretical data accurately, with significantly less residual effects than with the existing functions. Further investigations will use experimental data from field campaigns to validate these findings.

scholarly journals Technical Note: A novel parameterization of the transmissivity due to ozone absorption in the <i>k</i>-distribution method and correlated-<i>k</i> approximation of Kato et al. (1999) over the UV band

2015 ◽  
Vol 15 (13) ◽  
pp. 7449-7456 ◽  
Author(s):  
W. Wandji Nyamsi ◽  
A. Arola ◽  
P. Blanc ◽  
A. V. Lindfors ◽  
V. Cesnulyte ◽  
...  
Keyword(s):  
Radiative Transfer ◽  
Solar Spectrum ◽  
Ground Level ◽  
Technical Note ◽  
Radiative Transfer Model ◽  
Transfer Model ◽  
Spectral Interval ◽  
Computationally Efficient ◽  
Ozone Absorption ◽  
Distribution Method

Abstract. The k-distribution method and the correlated-k approximation of Kato et al. (1999) is a computationally efficient approach originally designed for calculations of the broadband solar radiation at ground level by dividing the solar spectrum in 32 specific spectral bands from 240 to 4606 nm. Compared to a spectrally resolved computation, its performance in the UV band appears to be inaccurate, especially in the spectral intervals #3 [283, 307] nm and #4 [307, 328] nm because of inaccuracy in modeling the transmissivity due to ozone absorption. Numerical simulations presented in this paper indicate that a single effective ozone cross section is insufficient to accurately represent the transmissivity over each spectral interval. A novel parameterization of the transmissivity using more quadrature points yields maximum errors of respectively 0.0006 and 0.0143 for intervals #3 and #4. How to practically implement this new parameterization in a radiative transfer model is discussed for the case of libRadtran (library for radiative transfer). The new parameterization considerably improves the accuracy of the retrieval of irradiances in UV bands.

scholarly journals Variation of aerosol optical thickness with atmospheric water vapour : A case study over a continental station Mysore, India

MAUSAM ◽  
2021 ◽  
Vol 62 (3) ◽  
pp. 441-448
Author(s):  
K.E. GANESH ◽  
T.K. UMESH ◽  
B. NARASIMHAMURTHY
Keyword(s):  
Water Vapour ◽  
Optical Thickness ◽  
Near Infrared ◽  
Solar Spectrum ◽  
Aerosol Optical Thickness ◽  
Infrared Range ◽  
Atmospheric Water ◽  
Atmospheric Measurements ◽  
Precipitable Water Vapour ◽  
Atmospheric Water Vapour

Atmospheric measurements in a continental, low latitude station Mysore (12.3° N) has been carried out, for the period December 2003 to June 2006. Measurements were made using a sunphotometer with five bands in the visible and near-infrared range of the solar spectrum. To bring out the wavelength dependence of Aerosol Optical Thickness (AOT) on atmospheric water vapour, typically two wavelength channels are being used, one at 500 nm and the other at 1020 nm. A linear dependence between AOT and water vapour on meteorologically calm days is the important observation made. Growth rate of AOT is found to be larger at shorter wavelength (500 nm) than that of the longer wavelength (1020 nm). A mass-plot representation is followed on monthly basis, which is nothing but the graphical plot of spectral AOT versus water vapour of the scans for all the clear sky days of a particular month. Further investigations reveal that some months exhibit a single trend of growth of AOT with water vapour whereas double trend is the scenario for other months. These results provide insight into the changes in the atmospheric aerosol characteristics with precipitable water vapour, which is the subject matter of this paper.

scholarly journals Technical Note: A new discrete ordinate first-order rotational Raman scattering radiative transfer model – implementation and first results

2011 ◽  
Vol 11 (20) ◽  
pp. 10471-10485 ◽  
Author(s):  
A. Kylling ◽  
B. Mayer ◽  
M. Blumthaler
Keyword(s):  
Radiative Transfer ◽  
Raman Scattering ◽  
Solar Spectrum ◽  
Technical Note ◽  
Radiative Transfer Model ◽  
Transfer Model ◽  
Discrete Ordinate ◽  
First Order ◽  
Spectral Interpolation ◽  
First Results

Abstract. Rotational Raman scattering in the Earth's atmosphere explains the filling-in of Fraunhofer lines in the solar spectrum. A new model including first-order rotational Raman scattering has been developed, based on a reimplementation of the versatile discrete ordinate radiative transfer (DISORT) solver in the C computer language. The solver is fully integrated in the freely available libRadtran radiative transfer package. A detailed description is given of the model including the spectral resolution and a spectral interpolation scheme that considerably speeds up the calculations. The model is used to demonstrate the effect of clouds on top and bottom of the atmosphere filling-in factors and differential optical depths. Cloud effects on vertical profiles of the filling-in factor are also presented. The spectral behaviour of the model is compared against measurements under thunderstorm and aerosol loaded conditions.

scholarly journals Photometry and performance of SPECULOOS-South

2020 ◽  
Vol 495 (2) ◽  
pp. 2446-2457 ◽  
Author(s):  
C A Murray ◽  
L Delrez ◽  
P P Pedersen ◽  
D Queloz ◽  
M Gillon ◽  
...  
Keyword(s):  
Water Vapour ◽  
Near Infrared ◽  
Precipitable Water ◽  
Correction Method ◽  
Light Curves ◽  
Precipitable Water Vapour ◽  
Correction Technique ◽  
Robotic Telescopes ◽  
Differential Photometry ◽  
And Performance

ABSTRACT SPECULOOS-South, an observatory composed of four independent 1-m robotic telescopes, located at ESO Paranal, Chile, started scientific operation in 2019 January. This Southern hemisphere facility operates as part of the Search for Habitable Planets EClipsing ULtra-cOOl Stars (SPECULOOS), an international network of 1-m-class telescopes surveying for transiting terrestrial planets around the nearest and brightest ultracool dwarfs (UCDs). To automatically and efficiently process the observations of SPECULOOS-South, and to deal with the specialized photometric requirements of UCD targets, we present our automatic pipeline. This pipeline includes an algorithm for automated differential photometry and an extensive correction technique for the effects of telluric water vapour, using ground measurements of the precipitable water vapour. Observing very red targets in the near-infrared can result in photometric systematics in the differential light curves, related to the temporally-varying, wavelength-dependent opacity of the Earth’s atmosphere. These systematics are sufficient to affect the daily quality of the light curves, the longer time-scale variability study of our targets and even mimic transit-like signals. Here we present the implementation and impact of our water vapour correction method. Using the 179 nights and 98 targets observed in the I + z′ filter by SPECULOOS-South since 2019 January, we show the impressive photometric performance of the facility (with a median precision of ∼1.5 mmag for 30-min binning of the raw, non-detrended light curves) and assess its detection potential. We compare simultaneous observations with SPECULOOS-South and TESS, to show that we readily achieve high-precision, space-level photometry for bright, UCDs, highlighting SPECULOOS-South as the first facility of its kind.

scholarly journals Modeling the influence of cloudiness on diffuse horizon-tal irradiation under various sky conditions in Nigeria

2017 ◽  
Vol 5 (2) ◽  
pp. 91 ◽  
Author(s):  
Samuel Nwokolo ◽  
Julie Ogbulezie
Keyword(s):  
Water Vapour ◽  
Performance Test ◽  
Solar Spectrum ◽  
Model Performance ◽  
Precipitable Water ◽  
High Water ◽  
Dew Point ◽  
Diffuse Fraction ◽  
Ecological Zones ◽  
Sky Conditions

In this study, modeling the influence of cloudiness on diffuse horizontal irradiation (DHI) in six tropical ecological zones in Nigeria (Latitude 4.75-13.067oN and Longitude 3.333-13.16oE) using 22-year data (July 1983- June 2005) was analysed for all sky and clear sky conditions. The result revealed that the absorption of DHI in the global horizontal irradiation (GHI) portion of the solar spectrum is greatly enhanced in the Southern tropical zones as a result of heavy presence of smog, cloudiness, and high water vapour parameters such as relative humidity, dew point temperature and precipitable water thereby increasing the diffuse fraction in the zone. However, in the Northern tropical zones, the absorption of DHI in the GHI portion of the solar spectrum lowered due to presence of low smog, cloudiness and low water vapour parameters thereby reducing the diffuse fraction in the region. The quadratic regression correlation model developed deeming from the model performance test indicates that the proposed model could be used to estimate DHI accurately over the six tropical ecological zones in Nigeria and other locations with comparable sky condition to Nigeria.

scholarly journals Technical Note: Cloud and aerosol effects on rotational Raman scattering: measurement comparisons and sensitivity studies

2010 ◽  
Vol 10 (10) ◽  
pp. 22515-22552 ◽  
Author(s):  
A. Kylling ◽  
B. Mayer ◽  
M. Blumthaler
Keyword(s):  
Radiative Transfer ◽  
Raman Scattering ◽  
Optical Depth ◽  
Solar Spectrum ◽  
Technical Note ◽  
New Model ◽  
Earth’S Atmosphere ◽  
Sensitivity Studies ◽  
Aerosol Effects ◽  
Scattering Measurement

Abstract. Rotational Raman scattering in the Earth's atmosphere explains the filling-in of Fraunhofer lines in the solar spectrum. Based on the versatile DISORT (Stamnes et al., 1988) radiative transfer solver, a new model including single rotational Raman scattering, has been developed and implemented into the freely available libRadtran radiative transfer package (Mayer and Kylling, 2005). The model is successfully compared against measurements of the differential optical depth for both optically thick clouds and aerosol loaded cases. Subsequently, the model is used for various sensitivity studies to investigate how clouds and aerosol affect the filling-in of the calcium K line.

Variability of radiosonde-observed precipitable water in the Baltic region*

2005 ◽  
Vol 36 (4-5) ◽  
pp. 423-433 ◽  
Author(s):  
E. Jakobson ◽  
H. Ohvril ◽  
O. Okulov ◽  
N. Laulainen
Keyword(s):  
Water Vapour ◽  
Precipitable Water ◽  
Linear Functions ◽  
Water Vapour Pressure ◽  
Baltic Region ◽  
Geographical Latitude ◽  
Linear Formula ◽  
Annual Means ◽  
The Baltic ◽  
Two Parameters

The total mass of columnar water vapour (precipitable water, W) is an important parameter of atmospheric thermodynamic and radiative models. In this work more than 60 000 radiosonde observations from 17 aerological stations in the Baltic region over 14 years, 1989–2002, were used to examine the variability of precipitable water. A table of monthly and annual means of W for the stations is given. Seasonal means of W are expressed as linear functions of the geographical latitude degree. A linear formula is also derived for parametrisation of precipitable water as a function of two parameters – geographical latitude and surface water vapour pressure.

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