Francisco Molero

Aerosol closure study by lidar, Sun photometry, and airborne optical counters during DAMOCLES field campaign at El Arenosillo sounding station, Spain

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 instruments (ground-based remote sensing and aircraft in situ) and their comparisons to characterize the aerosol vertical profiles. Our results indicate that the variability between the detected aerosol layers was negligible in terms of aerosol optical properties and size distributions. Relative differences in aerosol extinction coefficient profiles were less than 20% at 355 and 532 nm and less than 30% at 1064 nm, in the region with high aerosol concentration. Absolute differences in aerosol optical depth (AOD) were below 0.01 at 532 and 1064 nm and less than 0.02 at 355 nm, less than the uncertainties assumed in the AOD obtained from elastic lidar. Columnar values of the lidar ratio revealed some discrepancies with respect to the in situ aircraft measurements, caused fundamentally by the lack of information in the lowest part of the boundary layer.

Aerosol Lidar Intercomparison in the Framework of SPALINET—The Spanish Lidar Network: Methodology and Results

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 aerosol 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 troposphere, i.e., either the atmospheric boundary layer or the aerosol layer just above it. Some groups did not pass the quality assurance criterion on the first attempt. Following modification and improvement to these systems, all systems met the quality criterion. The backscatter algorithm intercomparison consisted of processing lidar signal profiles simulated for two types of atmospheric conditions. Three stages with increasing knowledge of the input parameters were considered. The results showed that all algorithms work well when all inputs are known. They also showed the necessity to perform, when possible, additional measurements to attain better estimation of the lidar ratio, which is the most critical unknown in the elastic lidar inversion.

Atmospheric Components Determination From Ground-Level Measurements During the Spectra Barax Campaigns (SPARC) Field Campaigns

The surface processes and ecosystem changes through response analysis (SPECTRA) Barrax campaigns were validation campaigns developed in the framework of the SPECTRA mission in order to verify that the geophysical data products provided by satellite imagery are consistent with the measurements made by independent means. Two campaigns took place in Barrax, Spain, during the summers of 2003 and 2004. This paper presents the results of the characterization of the atmospheric composition from solar radiation, radiosoundings, and lidar measurements. Several potentially interesting situations involving atmospheric layers with different types of aerosols and water content are discussed. The presence of a residual layer capping the mixing layer during some days of the 2003 campaign and the arrival of a dust-rich air mass from the Sahara on the last two days of the 2004 campaign provide some relevant aerosol vertical profiles to test atmospheric correction algorithms. The study of the effects of these atmospheric situations on radiative transfer calculations is required in the development and validation of advanced atmospheric correction codes for the new generation of Earth observation systems.

Study of vertically resolved aerosol properties over an urban background site in Madrid Spain

This work presents a comparison of aerosol properties measured by in situ and remote-sensing instrumentation over an urban background site in Madrid (Spain) in autumn 2010. Aerosol size distribution was characterized at ground level by the combined use of two instruments and also in elevated layers by airborne in situ instrumentation. Simultaneously, vertically resolved lidar profiles provided information about the optical properties of aerosols present in the different layers observed. Backscatter-derived Ångström exponent, calculated using Mie theory with volume size distribution detected experimentally, yielded values lower than 0.5 near ground level, increasing to over 1.5 in elevated layers. The same trend was observed for values obtained using the lidar system. Size distribution measured at elevated layers indicated that the large exponents observed there are associated with size distribution, with a negligible contribution of coarse particles. The results are compromised by the major uncertainty associated with the backscatter-derived Ångström exponents, due to the low aerosol load detected in the elevated layers.

Aerosol optical and microphysical properties observed by the lidar technique from a forest-fire smoke event over Madrid

On 27 August 2012, a wildfire occurred in the western zone of the Madrid region. Consequently, a significant release of smoke and aerosols was injected into the free troposphere and advected by the synoptic circulation in trajectories that passed over the capital. This event was detected by the Centro de Investigaciones Energéticas, Medioambientales y Tecnológicas (CIEMAT; Research Centre for Energy, Environment and Technology), Madrid lidar station at about 5 km height. While the main aerosol plume did not pass over the lidar station, the eastern portion of the dispersed emissions did. No aerosol layers were detected by lidar in the free-troposphere for the next few days. Since few observations of fresh biomass burning aerosol have been carried out by lidar so far, this study contributes to previous studies on biomass burning aerosols, in particular regarding the first stages of the smoke transport. This article studies the optical and microphysical properties of the smoke aerosols retrieved by the lidar technique along with the recently developed Lidar/Radiometer Inversion Code (LiRIC), which combines both lidar and sun–sky photometer data. The sun–sky photometer data are provided by the Agencia Estatal de Meteorología (AEMET; Spanish Meteorological Agency) station close to the CIEMAT site. We suggest that the aerosol properties retrieved might be linked to the water uptake phenomenon in view of the fact that simultaneous water vapour lidar measurements exhibited a close relationship with backscatter coefficient profiles. This article is concerned not only with showing the capability of combining different remote-sensing techniques and the LiRIC code to provide aerosol vertical distribution for fine and coarse modes, but also with providing signs about the plausible interaction between aerosols and humidity that leads fresh biomass burning aerosols to act as cloud condensation nuclei. This key role, known as the indirect effect, remains the major source of uncertainty when the global radiation budget is assessed.

Intercomparison of spanish advanced lidars in the framework of EARLINET

To extend and reinforce the action of the EARLINET- ASOS project, a nucleus of Spanish advanced lidars was created. Four systems were intercompared satisfactorily in terms of backscatter coefficients at two elastic wavelengths.

Comparison of aerosol size distributions measured at ground level and calculated from inversion of solar radiances

Ground-based sunphotometry measurements can be used to investigate atmospheric aerosol optical properties, such as the volume size distribution, an important parameter in the study of the effect of aerosol on atmospheric processes. Most inversion algorithms assume constant aerosol optical characteristics over the whole air column. In this work we present observational evidence of the limitations of this simplifying assumption in cases where the aerosol vertical structure is highly inhomogeneous. During the field campaign VELETA 2002, carried out in Granada (Spain), a quite complete characterization of the atmospheric aerosol was obtained by simultaneously measuring the columnar aerosol characteristics, by means of CIMEL C318 sun-tracking photometers, the size-segregated near-surface aerosol mass concentration by a GRIMM 1108 dust monitor and the aerosol vertical profiles by a lidar system. During the last days of the campaign, a dust-rich air mass from the Sahara reached the site, producing a multilayered structure on the aerosol vertical profile. The ground level size distributions can be compared with the columnar ones using retrieved scale height values from a lidar extinction coefficient profiles, corresponding to the altitude where the integrated extinction is equal to 1-e-1 of the AOD. Comparisons of the column-integrated and the modified ground-level aerosol size distributions show a good agreement in the days previous to the arrival of the Saharan intrusion, when the aerosols are homogeneously distributed in a well-mixed boundary layer. But, when the vertical homogeneity is reduced due to elevated layers containing desert dust, the column properties clearly deviates from the surface properties. This indicates the importance of verifying the vertical distribution of aerosol in order to correctly relate column and ground-level optical properties.

Coordinated lidar observations of Saharan dust over Europe in the frame of EARLINET-ASOS project during CALIPSO overpasses: A strong dust case study analysis with modeling support

Coordinated lidar observations of Saharan dust over Europe are performed in the frame of the EARLINET-ASOS (2006-2011) project, which comprises 25 stations: 16 Raman lidar stations, including 8 multi-wavelength (3+2 station) Raman lidar stations, are used to retrieve the aerosol microphysical properties. Since the launch of CALIOP, the two-wavelength lidar on board the CALIPSO satellite (June 2006) our lidar network has been performing correlative aerosol measurements during CALIPSO overpasses over the individual stations. In our presentation, we report on the correlative measurements obtained during Saharan dust intrusions in the period from June 2006 to June 2008. We found that the number of dust events is generally greatest in late spring, summer and early autumn periods, mainly in southern and south-eastern Europe. A measurement example is presented that was analyzed to show the potential of a ground based lidar network to follow a dust event over a specific study area, in correlation with the CALIOP measurements. The dust transport over the studied area was simulated by the DREAM forecast model. Cross-section analyses of CALIOP over the study area were used to assess the model performance for describing and forecasting the vertical and horizontal distribution of the dust field over the Mediterranean. Our preliminary results can be used to reveal the importance of the synergy between the CALIOP measurement and the dust model, assisted by ground-based lidars, for clarifying the overall transport of dust over the European continent.

New inversion algorithm for raman lidar without derivative of the inelastic signal

A new algorithm for extracting the backscattering coefficient profiles from elastic and inelastic lidar signals is presented. It re-formulate the Raman lidar equation, provided by the interaction of the laser light with the atmospheric nitrogen, in order to obtain the exponential of the integral of the extinction coefficient at the elastic wavelength instead of the extinction coefficient profile, as it is traditionally made, assuming the usual wavelength-dependent relationship between the Raman and Elastic extinction coefficients, and then substitutes that quantity into the elastic lidar equation to obtain the backscattering profile. That circumvents the calculation of the derivative of the noisy inelastic lidar signal with the main advantage of the extraction of backscattering coefficient profiles, one of the final products, without requiring any smoothing or filtering of the original signals. Several examples of the new method applied to profiles obtained with the CIEMAT lidar system, located in Madrid (SPAIN), are analyzed and the results are compared with other algorithm calculations. In conclusion, an improvement of the reliability and accuracy of the retrieved data was observed in the cases analyzed.

Aerosol optical depth derived from lidar measurements during VELETA-2002 campaign

We present measurements of the vertical structure of the aerosol extinction coefficient in the lower troposphere, up to five kilometers. Lidar profiles were collected at Armilla (680 m asl) and Pitres (1252 m asl) during the VELETA-2002 campaign, organized to analyze the effect of altitude and aerosols on ground-level UV spectral irradiance. Single-wavelength lidar signals are inverted to derive vertically resolved aerosol extinction coefficient and integrated to provide aerosol optical depth (AOD) at 532 nm. These results are compared with measurements of the aerosol optical depth at the same wavelength provided by Licor LI-1800 spectroradiometers located at several altitudes. Lidar traces show that most of the aerosol loading is present in the first 2.5 km layer before a high-dust Saharan air mass overflew the site. On the 17th of July evening, an elevated aerosol layer was detected between 2.5 and 3.5 km and during the following three days the aerosol vertical profile of the lower atmosphere showed Sahara dust layers, producing relatively high values for the optical depth.