Search results for "Radiance"
showing 10 items of 284 documents
A New Method for Determining the Ångström Turbidity Coefficient from Broadband Filter Measurements
2000
Abstract In this work, a new method for determining Angstrom turbidity coefficients is presented. This method is based on broadband filter irradiance measurements. By combining measurements obtained with different filters it is possible to obtain a single value of the turbidity coefficient representative of the whole measurement range of the pyrheliometer. The results provided by this new method are compared with the original Angstrom method and turbidity coefficient values derived by spectroradiometric measurements. The results reproduce the actual values, as measured by a spectroradiometer, better than the previous best correlation did, thus demonstrating the advantage of analyzing the op…
Study of erythemal, UV (A + B) and global solar radiation in Valencia (Spain)
2008
Although ultraviolet B radiation (UVB), the solar radiation band between 280 and 315 nm, is only a small fraction of the extraterrestrial solar radiation, it accounts for 80% of the harmful effects of exposure to the sun. In this work values of erythemal solar irradiance (UVER) measured in Valencia on a horizontal plane in the period between June 2003 and June 2005 are analysed and compared with measures of UV (A+B) and global irradiances on a horizontal plane. UV erythemal (UVER) irradiance has been measured using a YES-UVB-1 broadband radiometer; UV (A+B) irradiance has been measured using a TUVR Eppley radiometer with spectral response between 290 and 385 nm and global irradiance on a ho…
Comparing irradiance fields derived from Moderate Resolution Imaging Spectroradiometer airborne simulator cirrus cloud retrievals with solar spectral…
2007
[1] During the Cirrus Regional Study of Tropical Anvils and Cirrus Layers–Florida Area Cirrus Experiment, the Moderate Resolution Imaging Spectroradiometer (MODIS) airborne simulator (MAS) and the solar spectral flux radiometer (SSFR) operated on the same aircraft, the NASA ER-2. While MAS provided two-dimensional horizontal fields of cloud optical thickness and effective ice particle radius, the SSFR measured spectral irradiance in the visible to near-infrared wavelength range (0.3–1.7 μm). The MAS retrievals, along with vertical profiles from a combined radar/lidar system on board the same aircraft were used to construct three-dimensional cloud fields, which were input into Monte Carlo ra…
A new method to retrieve the aerosol layer absorption coefficient from airborne flux density and actinic radiation measurements
2010
A new method is presented to derive the mean value of the spectral absorption coefficient of an aerosol layer from combined airborne measurements of spectral net irradiance and actinic flux density. While the method is based on a theoretical relationship of radiative transfer theory, it is applied to atmospheric radiation measurements for the first time. The data have been collected with the Spectral Modular Airborne Radiation Measurement System (SMARTA¢ÂÂAlbedometer), the Solar Spectral Flux Radiometer (SSFR), and the Actinic Flux Spectroradiometer (AFSR) during four field campaigns between 2002 and 2008 (the Saharan Mineral Dust Experiment (SAMUM), the Influence of Clouds on the Spectra…
Ground-based measured and calculated spectra of actinic flux density and downward UV irradiance in cloudless conditions and their sensitivity to aero…
2003
Ground-based spectral measurements of actinic flux density (300–660 nm wavelength) and downward UV irradiance (300–324 nm) under cloudless conditions have been compared with the results of one-dimensional radiative transfer calculations employing concurrent airborne vertical profile measurements of aerosol particle size distributions. Good agreement (within ±10%) between measured and calculated spectra was found. The remaining differences were explained by uncertainties inherent in the aerosol particle microphysical input data and the column ozone content. A respective sensitivity analysis of the calculated spectra, which was based on the observed variability of microphysical properties, ha…
Influence of ice crystal shape on retrieval of cirrus optical thickness and effective radius: A case study
2009
Airborne measurements of spectral upwelling radiances (350A¢Â�Â�2200 nm) reflected by cirrus using the Spectral Modular Airborne Radiation measurement sysTem (SMART)-Albedometer were made over land and water surfaces. Based on these data, cloud optical thickness tau and effective radius Reff of the observed cirrus were retrieved. By using different crystal shape assumptions (hexagonal plates, solid and hollow columns, rough aggregates, planar and spatial rosettes, ice spheres, and a mixture of particle habits) in the retrieval, the influence of crystal shape on the retrieved tau and Reff was evaluated. With relative differences of up to 70%, the influence of particle habit on t is larger th…
Data flow of spectral UV measurements at Sodankylä and Jokioinen
2016
Abstract. The data flow involved in a long-term continuous solar spectral UV irradiance monitoring program is investigated and structured to provide an overall view on the multiphase process from data acquisition to the final products. The program employing Brewer spectrophotometers as measuring instruments is maintained by the Finnish Meteorological Institute (FMI) ever since the 1990s at two sites in Finland: Sodankylä (67° N) and Jokioinen (61° N). It is built upon rigorous operation routines, processing procedures, and tools for quality control (QC) and quality analysis (QA) under continuous development and evaluation. Three distinct levels of data emerge, each after certain phase in th…
Approaches to partitioning the global UVER irradiance into its direct and diffuse components in Valencia, Spain
2012
[1] The paper explores methods of partitioning the hourly average UV erythemal flux into its direct and diffuse components for Valencia, Spain. It is shown that the cloud modification factor, the ratio of measured to cloudless erythemal flux relates linearly to the fraction of the measured irradiance that is diffuse. This relationship was developed further into two simple models- a linear and nonlinear one. The models are characterized by an effective cloud cover to partition the global erythemal flux. The diffuse fraction increases linearly with cloud cover in the linear model, but exponentially in the nonlinear one. The models may be used to partition the direct and diffuse irradiance wit…
Intercomparison of spectroradiometers and Sun photometers for the determination of the aerosol optical depth during the VELETA-2002 field campaign
2006
In July 2002 the VELETA-2002 field campaign was held in Sierra Nevada (Granada) in the south of Spain. The main objectives of this field campaign were the study of the influence of elevation and atmospheric aerosols on measured UV radiation. In the first stage of the field campaign, a common calibration and intercomparison between Licor-1800 spectroradiometers and Cimel-318 Sun photometers was performed in order to assess the quality of the measurements from the whole campaign. The intercomparison of the Licor spectroradiometers showed, for both direct and global irradiances, that when the comparisons were restricted to the visible part of the spectrum the deviations were within the instrum…
On the direct and semidirect effects of Saharan dust over Europe: A modeling study
2007
[1] On the basis of a new regional dust model system, the sensitivity of radiative forcing to dust aerosol properties and the impact on atmospheric dynamics were investigated. Uncertainties in optical properties were related to uncertainties in the complex spectral refractive index of mineral dust. The climatological-based distribution of desert-type aerosol in the radiation scheme of the nonhydrostatic regional model LM was replaced by dust optical properties from spectral refractive indices, derived from in situ measurements, remote sensing, bulk measurements, and laboratory experiments, employing Mie theory. The model computes changes in the solar and terrestrial irradiance from a spatia…