0000000000033905
AUTHOR
Roberto Pedrós
showing 34 related works from this author
Measurement and correction of atmospheric effects in O<inf>2</inf>-B and O<inf>2</inf>-A absorption bands in the context of s…
2014
Under sun-light illumination, the shape of the atmospheric oxygen bands (O 2 -B, 687 nm and O 2 -A, 760 nm) of the vegetation radiance is modified by chlorophyll fluorescence. However for far-range measurements, atmospheric effects also modify this shape. In this study, measurements in O 2 -A and O 2 -B absorption bands have been performed at different altitudes up to 3123 m over bare soil and wheat fields. It is observed that bands depth increase significantly with altitude. In O 2 -B band, the total magnitude of variation is of the same order of magnitude as the change induced by vegetation fluorescence, while it is much greater in O 2 -A band. We used MODTRAN 4 to correct measurements fr…
Design of a sun tracker for the automatic measurement of spectral irradiance and construction of an irradiance database in the 330-1100 nm range
2007
Abstract An automatic global and direct solar spectral irradiance system has been designed based on two LICOR spectroradiometers equipped with fibre optics and remote cosine sensors. To measure direct irradiance a sun tracker based on step motors has been developed. The whole system is autonomous and works continuously. From the measurements provided by this system a spectral irradiance database in the 330–1100 nm range has been created. This database contains normal direct and global horizontal irradiances as well as diffuse irradiance on a horizontal plane, together with total atmospheric optical thickness and aerosol optical depth.
AEROgui: A graphical user interface for the optical properties of aerosols
2014
Atmospheric aerosols have an uncertain effect on climate and serious impacts on human health. The uncertainty in the aerosols' role on climate has several sources. First, aerosols have great spatial and temporal variability. The spatial variability arises from the fact that aerosols emitted in a certain place can travel thousands of kilometers, swept by the winds to modify the destination region's climate. The spatial variability also means that aerosols are inhomogeneously distributed in the vertical direction, which can lead to a differential effect on the energy balance depending on the aerosols' altitude. On the other hand, aerosols experience physical and chemical transformations in th…
Aerosol optical characteristics from a summer campaign in an urban coastal Mediterranean area
2001
The authors present a preliminary study of some optical properties of atmospheric aerosols over the area of Valencia, Spain, a coastal Mediterranean city. Measurements of spectral direct irradiance in the 300-1100 nm range were taken simultaneously at three sites: rural-continental, rural-coastal, and urban-coastal, all located within a 50 km radius of the city of Valencia. The irradiance measurements were obtained using three Li-cor 1800 spectroradiometers provided with radiance limiting tubes with field of views (FOVs) of 4.7/spl deg/. The measurements were made under clear sky conditions during a field campaign carried out in the summer of 1998. In order to avoid the uncertainties associ…
Column-integrated aerosol optical properties in Sodankylä (Finland) during the Solar Induced Fluorescence Experiment (SIFLEX-2002).
2006
[1] A study has been made of the column aerosols using solar irradiance extinction measurements at ground level in a boreal region (Sodankyla, Finland) during spring 2002. The aerosol properties have been related to air mass origin. In general, the aerosol levels were observed to be very low, independent of the air mass origin, with an aerosol optical depth (AOD) value at 500 nm of less than 0.09 ± 0.03. Two characteristic patterns were observed depending on whether the air masses originated in the north and west or from the south and east. In the first case (north and west origins) the aerosol load was very small, with very low optical depths in the range 0.03 ± 0.02 to 0.09 ± 0.03 for 500…
Analysis of four years of ceilometer-derived aerosol backscatter profiles in a coastal site of the western Mediterranean
2018
Abstract We present the analysis of four years of measurements by a CL51 ceilometer in Burjassot (39.51 N, 0.42 W), a research station in the western Mediterranean coast. The 1-min resolution profiles of the CL51 are corrected, calibrated, grouped and cloud-screened to create a 1-h resolution database of aerosol backscatter profiles at 910 nm (βa) spanning from July 2013 to August 2017. A total of 21,247 βa profiles are obtained, covering 58% of the considered period. The analysis of the βa profiles as a function of the main aerosol in the atmosphere reveals that dust arrives at Burjassot mainly in the form of elevated layers, with a highest impact between 1 and 4 km. The βa profiles obtain…
Remote sensing of sunlight-induced chlorophyll fluorescence and reflectance of Scots pine in the boreal forest during spring recovery
2005
A measurement campaign to assess the feasibility of remote sensing of sunlight-induced chlorophyll fluorescence (ChlF) from a coniferous canopy was conducted in a boreal forest study site (Finland). A Passive Multi-wavelength Fluorescence Detector (PMFD) sensor, developed in the LURE laboratory, was used to obtain simultaneous measurements of ChlF in the oxygen absorption bands, at 687 and 760 nm, and a reflectance index, the PRI (Physiological Reflectance Index), for a month during spring recovery. When these data were compared with active fluorescence measurements performed on needles they revealed the same trend. During sunny days fluorescence and reflectance signals were found to be str…
Relationship between UVB and broadband solar radiation in Spain
2014
The daily values of UVB irradiation (290–315 nm), IUVB, and the broadband total irradiation (300–2800 nm), IT, measured on a horizontal plane have been correlated for the period 2000–2008 at 16 measurement sites in Spain. The results have been compared with the daily experimental values registered at the same sites during the period 2009–2011. The coefficients of determination R2 obtained by applying a linear regression are higher than 0.88 for all sites and increase to 0.94 when using a quadratic regression. When all data are considered together, the values of R2 are 0.91 and 0.97 for the linear and quadratic regressions, respectively. Three different clearness indices, which are dimension…
Characterization of the atmosphere during SEN2FLEX 2005 field campaign
2008
The European Space Agency carried out the Sentinel-2 and Fluorescence Experiment (SEN2FLEX) campaign in Barrax (Spain) during the summer of 2005, with the main objective of observe solar induced fluorescence signal using the AirFLEX airborne instrument over different vegetation targets in order to verify signal suitability for observations from space as proposed in the FLEX mission. A highly precise atmospheric correction is mandatory for adequate measurements of the AirFLEX instrument; thus a complete characterization of the atmosphere was programmed in SEN2FLEX in order to document the presence of atmospheric aerosols above the experimental area, as their effects represent the major sourc…
Intercomparison of spectroradiometers for global and direct solar irradiance in the visible range.
2003
This paper presents the results of the analysis of the spectral, global, and direct solar irradiance measurements in the visible range (400–700 nm) that were made in the framework of the first Iberian UV–visible (VIS) instruments intercomparison. The instruments used in this spectral range were four spectroradiometers: three Licor 1800s equipped with different receiver optics and one Optronic 754. For the direct solar irradiance measurements the spectroradiometers were equipped with collimators with different fields of view. Parallel studies have been carried out with the data given by the spectroradiometers with their original calibration file and with the same data that is corrected, foll…
La evaluación y seguimiento del estudiante de forma telemática: el proyecto Cuestionarios
2011
En la mayor parte de las ciencias, los ejercicios practicos son la mejor manera de adquirir y evaluar, tanto conocimientos cientificos como las habilidades y competencias necesarias para su aplicacion. Es un entrenamiento que, como en el mundo del deporte, resulta imprescindible y mejora el rendimiento. La resolucion de problemas exige una gran dedicacion del profesorado y, en este aspecto, la utilizacion de cuestionarios on-line puede ser de gran ayuda. Sin embargo, este tipo de cuestionarios tambien presentan una dificultad, que es el esfuerzo inicial necesario. Para reducir esta dificultad se planteo la elaboracion de una base de datos de cuestiones y un protocolo de exportacion.
Aerosol closure study by lidar, sun photometry, and airborne optical counters during DAMOCLES field campaign at El Arenosillo sounding station, Spain
2011
We present a comparison of aerosol properties derived from in situ and remote sensing instruments during DAMOCLES campaign, aimed at investigating the equivalence between the instrumentation and methodologies employed by several Spanish groups to study atmospheric aerosols at a regional background site. The complete set of instruments available during this closure experiment allowed collecting a valuable high-resolution aerosol measurement data set. The data set was augmented with airborne in situ measurements carried out in order to characterize aerosol particles during the midday of 29 June 2006. This work is focused on aerosol measurements using different techniques of high-quality instr…
Climatology of the aerosol extinction-to-backscatter ratio from sun-photometric measurements
2010
The elastic lidar equation contains two unknown atmospheric parameters, namely, the particulate optical extinction and backscatter coefficients, which are related through the lidar ratio (i.e., the particulate-extinction-to-backscatter ratio). So far, independent inversion of the lidar signal has been carried out by means of Raman lidars (usually limited to nighttime measurements), high-spectral-resolution lidars, or scanning elastic lidars under the assumption of a homogeneously vertically stratified atmosphere. In this paper, we present a procedure to obtain the lidar ratio at 532 nm by a combined Sunphotometer– aerosol-model inversion, where the viability of the solution is largely reinf…
Operational considerations to improve total ozone measurements with a Microtops II ozone monitor
2012
A Microtops II "ozone monitor" with UV channels centered at 305.5, 312.5, and 320 nm has been used routinely in six experimental campaigns carried out in several geographic locations and seasons, covering latitudes from 35 to 68° N during the last ten years (2001–2011). The total ozone content is retrieved by Microtops II by using different combinations (Channel I, 305.5/312.5 nm; Channel II, 312.5/320 nm; and Channel III, 305.5/312.5/320 nm) of the signals at the three ultraviolet wavelengths. The long-term performance of the total ozone content determination has been studied taking into account the sensitivities to the calibration, airmass, temperature and aerosols. When a calibration was…
Aerosol size distributions and air mass back trajectories over a Mediterranean coastal site
2004
In this paper we present the results obtained from ground-based measurements using a CIMEL sunphotometer during selected clear days corresponding to the winter and summer periods of 2002 in Valencia, an urban coastal Mediterranean site. From the direct solar extinction data the spectral aerosol optical depth (AOD) has been retrieved. This spectral AOD has been used to obtain the size distribution function from the King inversion algorithm. The results show the great dependence of the optical aerosol characteristics on the dominant winds in this area. This location is subject to winds which have either a land or Mediterranean origin which frequently mask the aerosols coming from the Atlantic…
A multi-instrument approach for characterizing the atmospheric aerosol optical thickness during the STAAARTE/DAISEX-99 campaign
2002
This work deals with the retrieval of the aerosol optical thickness (AOT) needed to carry out the atmospheric correction of remote sensing data measured in Barrax (Spain) on 4 June 1999 in the framework of 1999 Digital Airbone Imaging Spectrometer Experiment (DAISEX'99). The AOT was estimated through three approaches based on: spectral extinction of direct solar irradiance at ground level, airborne nephelometer measurements at different altitudes, and backscatter lidar in the lower troposphere. We found extremely low AOT values due to a cold Atlantic front that swept across the Iberian Peninsula from west to east producing light rain over the test area on 2 June 1999. The results were solar…
FluorMODleaf: A new leaf fluorescence emission model based on the PROSPECT model
2010
International audience; A new model of chlorophyll a fluorescence emission by plant leaves, FluorMODleaf, is presented. It is an extension of PROSPECT, a widely used leaf optical properties model that regards the leaf as a pile of N absorbing and diffusing elementary plates. In FluorMODleaf, fluorescence emission of an infinitesimal layer of thickness dx is integrated over the entire elementary plate. The fluorescence source function is based on the excitation spectrum of diluted isolated thylakoids and on the emission spectra of isolated photosystems, PSI and PSII, which are the main pigment–protein complexes involved in the initial stages of photosynthesis. Scattering within the leaf is p…
Analysis of a strong wildfire event over Valencia (Spain) during Summer 2012 – Part 1: Aerosol microphysics and optical properties
2013
Abstract. The most intense wildfire experienced in Eastern Spain since 2004 happened in Valencia during summer 2012. Although the fire was mostly active during days 29–30 June, a longer temporal period (from 24 June to 4 July) was selected for this analysis. Column-integrated, vertical resolved and surface aerosol observations were performed continuously at the Burjassot station throughout the studied period. The aerosol optical depth at 500 nm shows values larger than 2 for the most intense part of the wildfire and an extremely high maximum of 8 was detected on 29 June. The simultaneous increase of the Ångström exponent was also observed, indicating the important contribution of small part…
Aerosol Lidar Intercomparison in the Framework of SPALINET—The Spanish Lidar Network: Methodology and Results
2009
Abstract—A group of eight Spanish lidars was formed in order to extend the European Aerosol Research Lidar Network–Advanced Sustainable Observation System (EARLINET-ASOS)project. This study presents intercomparisons at the hardware and software levels. Results of the system intercomparisons are based on range-square-corrected signals in cases where the lidars viewed the same atmospheres. Comparisons were also made for aeros backscatter coefficients at 1064 nm (2 systems) and 532 nm (all systems), and for extinction coefficients at 532 nm (2 systems). In total, three field campaigns were carried out between 2006 and 2007. Comparisons were limited to the highest layer found before the free tr…
Physics demos for all UVEG degrees: a unique project in Spain
2016
Abstract The Physics Demo Project at the University of Valencia ( www.uv.es/fisicademos ) has developed a collection of physics demonstrations to be used during lectures. It consists of more than 130 experimental demos about different physics topics. More than 30 professors borrow them whenever they lecture on physics in any of our 40 courses in 17 different science or technical degrees, involving 246 ECTS and more than 3500 students. Each demo kit with a simple experimental set displays a particular physics phenomenon. An on-line user guide highlights the main physics principles involved, instructions on how to use it and advices of how to link it to the theoretical concepts or to technica…
The optimisation of the angle of inclination of a solar collector to maximise the incident solar radiation
1999
Abstract Irradiation data, recorded on vertical surfaces facing north, south, east and west and on a horizontal surface every ten minutes during daylight hours from January–December 1992 in Valencia, Spain, have been compared with estimated solar irradiation from inclined-surface models. Results show that Hays model most accurately reproduces the variation in irradiation on all vertical surfaces. Hays model has been used to find the hourly variation in the optimum tilt angle for a South-facing solar collector in Valencia, Spain, and also to calculate the yearly average of this angle. This method has been compared with the results provided by another model that uses average monthly values of…
Fluorescence explorer (FLEX): An optimised payload to map vegetation photosynthesis from space
2006
The FLuorescence EXplorer (FLEX) mission proposes to launch a satellite for the global monitoring of steady-state chlorophyll fluorescence in terrestrial vegetation. Fluorescence is a sensitive probe of photosynthetic function in both healthy and physiologically perturbed vegetation, and a powerful non-invasive tool to track the status, resilience, and recovery of photochemical processes and moreover provides important information on overall photosynthetic performance with implications for related carbon sequestration. The early responsiveness of fluorescence to atmospheric, soil and plant water balance, as well as to atmospheric chemistry and human intervention in land usage makes it an ob…
Measurement and analysis of broadband UVB solar radiation in Spain.
2012
Measurements of broadband UVB irradiance (290-315 nm) at 14 locations in Spain for the period 2000-2009 have been used to generate instantaneous, hourly and daily values of irradiance (W m(-2)) and radiant exposure (kJ m(-2)). These measurements, and its statistical indices, have been analyzed. For the UVB irradiance, the values corresponding to July (maximum) and December (minimum) have been analyzed as representative of the year during the whole period for all locations. For the UVB radiant exposure, the temporal evolution of daily values has been evaluated for all locations to estimate an average yearly behavior. The accumulated radiant exposure for an average year has also been studied …
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…
Values of broad band turbidity coefficients in a mediterranean coastal site
1999
Abstract The Angstrom turbidity coefficient, the Linke turbidity factor, and the Unsworth–Monteith coefficient have been determined and analysed based on measurements of normal direct irradiance and global horizontal irradiance taken in Valencia, Spain, between January 1990 and December 1996. The data, which were acquired automatically and continuously, have been filtered to select only those values corresponding to clear sky conditions. To determine the Angstrom turbidity coefficient the method proposed by Louche et al. has been used whilst the expression for δCDA proposed by Kasten was used to obtain the Linke turbidity coefficient. The Angstrom turbidity coefficient showed a minimum in w…
A comparison of Microtops II and satellite ozone measurements in the period 2001-2011
2013
Daily average total ozone Microtops measurements obtained during several campaigns conducted from 2001 to 2011 at latitudes from 31 to 68N and in different seasons are compared with satellite observations. The Microtops ozone is derived using different wavelength combinations (Channel I, 305.5/312.5. nm; Channel II, 312.5/320. nm; and Channel III, 305.5/312.5/320. nm). Satellite data from TOMS, OMI, GOME, and GOME-2 are used in the comparison. The three Microtops channels show a high correlation with the satellite retrievals. Channel I shows the best results and produces a mean bias deviation (MBD) less than 2.14% with respect to TOMS, OMI and GOME. The MBD increases to 3% in the comparison…
Measurements of integrated direct, diffuse and global ultraviolet-B radiation
2015
Abstract We present the first multiyear set of simultaneous measurements of the global ultraviolet-B radiation and its two components: direct and diffuse. The measurements have been taken with four YES-UVB-1 radiometers: two radiometers to measure the diffuse radiation, one provided with a shadow band and the other with a shadow disk on a Sun tracker; a radiometer to measure the global horizontal radiation; and a Sun-tracking radiometer to measure the direct radiation with an especially designed radiance collimator. The diffuse minute-values measured with both instruments agree within a coefficient correlation of 1.00. The diffuse component represents at least 50% of the global UVB (ultravi…
Daytime aerosol extinction profiles from the combination of CALIOP profiles and AERONET products
2018
Abstract. The solar background illumination has a strong effect on CALIOP (Cloud-Aerosol Lidar with Orthogonal Polarization) measurements, leading to a decrease in the signal-to-noise ratio of the lidar signal. Because of this, CALIOP level 2 data algorithms might be limited in the retrieval of the properties of the aerosols in the atmosphere. In this work, we present a methodology that combines CALIOP level 1 data with AERONET (Aerosol RObotic NETwork) measurements to retrieve aerosol extinction profiles and lidar ratios in daytime conditions. In this way, we fulfill a two-fold objective: first, we obtain more accurate daytime aerosol information; second, we supplement column integrated me…
Impact of dust and smoke mixing on column-integrated aerosol properties from observations during a severe wildfire episode over Valencia (Spain)
2017
The most destructive wildfire experienced in Spain since 2004 occurred close to Valencia in summer 2012. A total of 48.500ha were affected by two wildfires, which were mostly active during 29-30 June. The fresh smoke plume was detected at the Burjassot measurement station simultaneously to a severe dust episode. We propose an empirical method to evaluate the dust and smoke mixing and its impact on the microphysical and optical properties. For this, we combine direct-sun measurements with a Cimel CE-318 sun-photometer with an inversion methodology, and the Mie theory to derive the column-integrated size distribution, single scattering albedo (SSA) and asymmetry parameter (g). The mixing of d…
A Preliminary Estimation of the Direct Ultraviolet Spectral Irradiance in Valencia (Spain): Comparison with Measured Values
2000
UVSPEC and SMARTS2 models have been used to estimate the UV spectral irradiance values in Valencia, Spain, and the results of these estimations have been compared with experimental measurements of direct irradiance at normal incidence obtained using an Optronic OL 754 in the 300-400 nm range. The relative RMSD and MBD parameters have been used to estimate the deviations of the modelled values with respect to the experimental values. The results indicate that the deviations are smaller when the SMARTS2 model is used with the appropriate aerosol coefficients.
Chlorophyll fluorescence emission spectrum inside a leaf
2008
International audience; Chlorophyll a fluorescence can be used as an early stress indicator. Fluorescence is also connected to photosynthesis so it can be proposed for global monitoring of vegetation status from a satellite platform. Nevertheless, the correct interpretation of fluorescence requires accurate physical models. The spectral shape of the leaf fluorescence free of any re-absorption effect plays a key role in the models and is difficult to measure. We present a vegetation fluorescence emission spectrum free of re-absorption based on a combination of measurements and modelling. The suggested spectrum takes into account the photosystem I and II spectra and their relative contributio…
Column aerosol characterization in a semi‐arid region around Marrakech during the WATERMED 2003 campaign
2008
In the framework of the WATERMED (WATer use efficiency in natural vegetation and agricultural areas by Remote sensing in the MEDiterranean basin) project, an experimental field campaign was carried out in a semi‐arid region near Marrakech, Morocco, during March 2003. This work focused on the columnar aerosol characterization from spectroradiometric and photometric measurements of direct solar irradiance and sky radiance at ground level. The results show a high dependence of the aerosol optical properties on the air masses present in the area. Two periods with different aerosol loads were observed in the campaign. In the first, Atlantic‐origin aerosols showed a marine particle accumulation m…
Column-integrated aerosol optical properties from ground-based spectroradiometer measurements at Barrax (Spain) during the Digital Airborne Spectrome…
2003
[1] The Digital Airborne Imaging Spectrometer Experiment (DAISEX) was carried out for the European Space Agency (ESA) in order to develop the potential of spaceborne imaging spectroscopy for a range of different scientific applications. DAISEX involved simultaneous data acquisitions using different airborne imaging spectrometers over test sites in southeast Spain (Barrax) and the Upper Rhine valley (Colmar, France, and Hartheim, Germany). This paper presents the results corresponding to the columnintegrated aerosol optical properties from ground-based spectroradiometer measurements over the Barrax area during the DAISEX campaign days in the years 1998, 1999, and 2000. The instruments used f…
Analysis of Desert Dust Outbreaks Over Southern Europe Using CALIOP Data and Ground-Based Measurements
2016
Saharan dust outbreaks are one of the major aerosol sources in Southern Europe. Dust affects the radiative balance of the Earth–atmosphere system and impacts health. The assessment of Saharan outbreaks requires information about the vertical distribution of dust in the atmosphere, usually obtained from lidar measurements, such as the ones performed by the spaceborne Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) sensor. In this paper, we have used CALIOP level-1 daytime data in combination with aerosol optical depth (AOD) measurements from Aerosol Robotic Network (AERONET) ground-based photometers to obtain aerosol profiles during 23 dust outbreaks over Southern Europe. These pro…