2022 |
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1. | R. Román; D. González-Fernández; C. Toledano; C. Emde; V. Cachorro; D. Mateos; S. Herrero-Anta; J. C. Antuña-Sánchez; R. González; J.C. Antuña-Marrero; B. Mayer; A. Calle; A.M. de Frutos Impact of clouds on cloud-free sky radiances in a partially cloudy scenario Conference International Radiation Symposium Thessaloniki, Greece, 2022. BibTeX | Tags: all-sky camera, clouds, GRASP, sky radiance @conference{Román2022b, |
2. | R. Román; J. C. Antuña-Sánchez; V. E. Cachorro; C. Toledano; B. Torres; D. Mateos; D. Fuertes; C. López; R. González; T. Lapionok; M. Herreras-Giralda; O. Dubovik; A.M. de Frutos Retrieval of Aerosol Properties with an all-sky Camera Conference International Radiation Symposium Thessaloniki, Greece, 2022. BibTeX | Tags: Aerosol Properties, all-sky camera, GRASP @conference{Román2022c, |
3. | J.C. Antuña-Sánchez; R. Román; J.L. Bosch; C. Toledano; D. Mateos; R. González; V.E. Cachorro; Ángel de Frutos ORION software tool for the geometrical calibration of all-sky cameras Journal Article In: PLoS ONE 17(3), 2022. Abstract | Links | BibTeX | Tags: all-sky camera, clouds, image analylis, polynomials, stars @article{Antuña-Sánchez2022, This paper presents the software application ORION (All-sky camera geOmetry calibRation from star positIONs). This software has been developed with the aim of providing geometrical calibration to all-sky cameras, i.e. assess which sky coordinates (zenith and azimuth angles) correspond to each camera pixel. It is useful to locate bodies over the celestial vault, like stars and planets, in the camera images. The user needs to feed ORION with a set of cloud-free sky images captured at night-time for obtaining the calibration matrices. ORION searches the position of various stars in the sky images. This search can be automatic or manual. The sky coordinates of the stars and the corresponding pixel positions in the camera images are used together to determine the calibration matrices. The calibration is based on three parameters: the pixel position of the sky zenith in the image; the shift angle of the azimuth viewed by the camera with respect to the real North; and the relationship between the sky zenith angle and the pixel radial distance regards to the sky zenith in the image. In addition, ORION includes other features to facilitate its use, such as the check of the accuracy of the calibration. An example of ORION application is shown, obtaining the calibration matrices for a set of images and studying the accuracy of the calibration to predict a star position. Accuracy is about 9.0 arcmin for the analyzed example using a camera with average resolution of 5.4 arcmin/pixel (about 1.7 pixels). |
4. | R. Román; J. C. Antuña-Sánchez; V. E. Cachorro; C. Toledano; B. Torres; D. Mateos; D. Fuertes; C. López; R. González; T. Lapionok; M. Herreras-Giralda; O. Dubovik; Á. M. Frutos Retrieval of aerosol properties using relative radiance measurements from an all-sky camera Journal Article In: Atmospheric Measurement Techniques, vol. 15, no. 2, pp. 407–433, 2022. Abstract | Links | BibTeX | Tags: aerosol, all-sky camera, GRASP, retrieval @article{Román2022, This paper explores the potential of all-sky cameras to retrieve aerosol properties with the GRASP code (Generalized Retrieval of Atmosphere and Surface Properties). To this end, normalized sky radiances (NSRs) extracted from an all-sky camera at three effective wavelengths (467, 536 and 605?nm) are used in this study. NSR observations are a set of relative (uncalibrated) sky radiances in arbitrary units. NSR observations have been simulated for different aerosol loads and types with the forward radiative transfer module of GRASP, indicating that NSR observations contain information about the aerosol type, as well as about the aerosol optical depth (AOD), at least for low and moderate aerosol loads. An additional sensitivity study with synthetic data has been carried out to quantify the theoretical accuracy and precision of the aerosol properties (AOD, size distribution parameters, etc.) retrieved by GRASP using NSR observations as input. As a result, the theoretical accuracy of AOD is within ±0.02 for AOD values lower than or equal to 0.4, while the theoretical precision goes from 0.01 to 0.05 when AOD at 467?nm varies from 0.1 to 0.5. NSR measurements recorded at Valladolid (Spain) with an all-sky camera for more than 2 years have been inverted with GRASP. The retrieved aerosol properties are compared with independent values provided by co-located AERONET (AErosol RObotic NETwork) measurements. AODs from both data sets correlate with determination coefficient (r2) values of about 0.87. Finally, the novel multi-pixel approach of GRASP is applied to daily camera radiances together by constraining the temporal variation in certain aerosol properties. This temporal linkage (multi-pixel approach) provides promising results, reducing the highly temporal variation in some aerosol properties retrieved with the standard (one by one or single-pixel) approach. This work implies an advance in the use of all-sky cameras for the retrieval of aerosol properties. |
5. | Juan Carlos Antuña Sánchez Universidad de Valladolid, 2022, (dirección: Roberto Román, Ángel M. de Frutos y Victoria E. Cachorro.). Abstract | Links | BibTeX | Tags: all-sky camera, atmospheric aerosols, sky radiance @phdthesis{Sánchez2021, Atmospheric aerosols, solid or liquid particles floating in the atmosphere, play an important role in the Earth's climate, since they scatter and absorb part of the solar radiation reaching the Earth. The aerosol properties are usually obtained by measuring the diffuse solar radiation incoming in different directions (sky radiance), which is partially formed by the scattering of aerosols. The sky radiance is usually measured with photometers. A cheaper alternative to these photometers are the all-sky cameras, which capture images of the whole sky. In this doctoral thesis we propose the use of all-sky cameras to retrieve atmospheric parameters like the sky radiance and some aerosol properties, which can be obtained from these radiances. In this work, the ORION application has been developed to calibrate geometrically the all-sky cameras through the position of the stars. These calibrations are essential to locate the pixels of the camera pointing to a specific direction, such as the directions in which the sky radiance will be extracted. An all-sky camera has been geometrically calibrated with ORION, but it also has been configured to capture images in RAW format at different exposure times. The multi-exposure configuration, in addition with a exhaustive characterization of the camera (effective wavelengths, linearity, read noise, etc.), has allowed to obtain a linear high dynamic range image of the sky applying a proposed methodology. The sky radiance is proportional to the linear image obtained, so a relative sky radiance can be obtained with this proposed methodology. Once the relative sky radiances have been obtained with the all-sky camera, they have been used as input parameter in the GRASP (Generalized Retrieval of Atmosphere and Surface Properties) inversion algorithm to obtain some aerosol properties. It has been studied, using synthetic data, what aerosol properties can be derived from the relative sky radiance measured by all-sky cameras. The aerosol properties obtained with real measurements on GRASP have been compared with those independently derived by an AERONET (AErosol RObotic NETwork) photometer. This work concludes that, if the methodologies developed in this doctoral thesis are applied, a properly configured all-sky camera can be used to calculate the sky radiance, at least in a relative way, and these radiances can be also used to retrieve aerosol properties. |
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2022 |
|
1. | Impact of clouds on cloud-free sky radiances in a partially cloudy scenario Conference International Radiation Symposium Thessaloniki, Greece, 2022. |
2. | Retrieval of Aerosol Properties with an all-sky Camera Conference International Radiation Symposium Thessaloniki, Greece, 2022. |
3. | ORION software tool for the geometrical calibration of all-sky cameras Journal Article In: PLoS ONE 17(3), 2022. |
4. | Retrieval of aerosol properties using relative radiance measurements from an all-sky camera Journal Article In: Atmospheric Measurement Techniques, vol. 15, no. 2, pp. 407–433, 2022. |
5. | Universidad de Valladolid, 2022, (dirección: Roberto Román, Ángel M. de Frutos y Victoria E. Cachorro.). |