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

International audienceIn 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

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

International audienceIn 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

Carbon nanotube/PEDOT:PSS electrodes for organic photovoltaics

High conductive and transparent thin films based on carbon nanotube – poly(3,4-ethylene-dioxythiophene)-poly(styrene sulfonate), PEDOT-PSS blends have been used to replace the conventional indium tin oxide (ITO) as the hole collecting electrode in organic photovoltaic cells. Using PEDOT:PSS as the host material, excellent dispersion of functionalized single wall carbon nanotubes can be achieved enhancing the polymer's conductivity, while maintaining its excellent optical transparency. Photovoltaic cells with Poly(3-hexylthiophene), P3HT and [6,6]-phenyl-C61 butyric acid methyl ester (PCBM as the electron donor and acceptor on respectively on polymer-nanotube substrates have been fabricated and characterized. A power conversion efficiency of 1.3%, with a fill factor of 0.4, an open-circuit voltage of 0.6 V and a short-circuit current of 5.6 mA/cm2 under 100 mW/cm2 white light illumination are reported. These values are close with the reference cells made on ITO glass substrates with the same device structure and fabrication process. The only drawback is on the fill factor which is considerably smaller due to the high resistance of the polymer-nanotube film. Nevertheless, the results indicate that the spin casted polymer-nanotubes thin films are a low cost alternative to ITO for organic electronics