[Show abstract][Hide abstract] ABSTRACT: This contribution evaluates an approach using an extended Kalman filter (EKF) to estimate the planetary boundary layer height (PBLH) from lidar measurements obtained in the framework of the European Aerosol Research LIdar NETwork (EARLINET) at 12 UTC ± 30-min for a 7-year period (2007-2013) under different synoptic flows over the complex geographical area of Barcelona, Spain. PBLH diagnosed with the EKF technique are compared with classic lidar methods and radiosounding estimates. Seven unique synoptic flows are identified using cluster analysis of 5756 HYSPLIT (HYbrid Single Particle Lagrangian Integrated Trajectory) three-day backtrajectories for a 16-year period (1998-2013) arriving at 0.5 km, 1.5 km, and 3 km, to represent the lower PBL, upper PBL, and low free troposphere, respectively. Regional recirculations are dominant with 54% of the annual total at 0.5 km and 57% of the total lidar days at 1.5 km, with a clear preference for summertime (0.5 km: 36% and 1.5 km: 29%). PBLH retrievals using the EKF method range from 0.79 - 1.6 km asl. The highest PBLHs are observed in southwest flows (15.2% of total) and regional recirculations from the east (34.8% of total), mainly caused by the stagnant synoptic pattern in summertime over the Iberian Peninsula. The lowest PBLHs are associated with north (19.6% of total) and northeast (4.3% of total) synoptic flows, when fresh air masses tend to lower PBLH. The adaptive nature of the EKF technique allows retrieval of reliable PBLH without the need for long time averaging or range smoothing, as typical with classic methods.
[Show abstract][Hide abstract] ABSTRACT: An improvement of the estimation of mineral dust longwave, direct radiative forcing is presented. It is based on recent developments that combine sun-photometer and multi-wavelength lidar data to retrieve range-resolved coarse- and fine-mode extinction coefficients. The forcings are calculated separately for each mode and their sum is compared to the classical approach in which only the total extinction is considered. The results of four cases of mineral dust intrusion in Barcelona, Spain, show that when the coarse mode predominates the longwave forcings calculated with the classical approach are underestimated up to 20 % near the surface. In all cases the strong coarse mode predominance near the surface has also an effect on the forcing in the upper layers.
[Show abstract][Hide abstract] ABSTRACT: The planetary boundary-layer (PBL) is defined as the height of the inversion level separating the free troposphere from the boundary-layer [Stull, 1988]. PBL height is an important parameter in applications ranging from climate studies to air quality modeling. Lidars with high spatial (< 30 m) and temporal (< 5 min) resolutions can be employed to monitor the PBL height using aerosols as tracers.
This study evaluates an approach using an Extended Kalman Filter (EKF) to estimate the PBL height in different atmospheric situations over Barcelona, Spain. PBL heights estimated by the EKF method are compared with classic methods (gradient, Haar wavelet, radiosondes, etc.) under 7 atmospheric conditions.
Atmospheric situations are selected using a cluster analysis of 2-day backtrajectories from the NOAA HYSPLIT model.
[Show abstract][Hide abstract] ABSTRACT: Pesticide spray drift entails a series of risks and costs in terms of human, animal and environmental well-being. A proper understanding of this phenomenon is essential to minimise these risks. However, most conventional methods used in drift measurement are based on point collectors which are unable to obtain information concerning the temporal or spatial evolution of the pesticide cloud. Such methods are also costly, labour-intensive, and require a considerable amount of time. The aim of this paper is to propose a method to measure the spray drift based on lidar (LIght Detection And Ranging) and to prove that it can be an alternative to passive collectors. An analytical model is proposed to relate the measurements obtained through passive collectors and those obtained with lidar systems considering several spray application and meteorological parameters. The model was tested through an experimental campaign involving multiple ground spray tests. A lidar system and two types of passive collectors (nylon strings and water-sensitive paper) were used simultaneously to measure the drift. The results showed for each test a high coefficient of determination (R2 ≈ 0.90) between the lidar signal and the tracer mass captured by the nylon strings. This coefficient decreased (R2 = 0.77) when all tests were considered together. Lidar measurements were also used to study the evolution of the pesticide cloud with high range (1.5 m) and temporal resolution (1 s) and to estimate its velocity. Furthermore, a very satisfactory adjustment (R2 = 0.89) was observed between the tracer mass collected by the nylon lines and the coverage on water-sensitive paper sheets. These results are in accordance with the proposed analytical model and allow the conclusion that the application and meteorological parameters can be considered spatially invariant for a given test but are not invariant for different tests.
[Show abstract][Hide abstract] ABSTRACT: The depth of the planetary boundary-layer (PBL) is defined as the height of the inversion level separating the free troposphere (FT) from the boundary-layer (Stull, 1988). Reliable representation of PBL height is important in applications ranging from climate studies to air quality modeling. Convective turbulent mixing processes are dominant in the mixing layer of the PBL and have a major influence on the growth and transport of atmospheric pollutants. In recent years, lidar (laser radar) has proven to be a useful operational tool for nearly continuous monitoring of the lowest levels of the atmosphere with high spatial (~ 3.75 m) and temporal (< 5 min) resolutions. Four Raman-elastic multi-wavelength lidar stations from EARLINET (European Aerosol Research Lidar Network) conducted a 72-hr campaign of continuous observations over Spain (Barcelona, Granada, Madrid) and Portugal (Evora) in early July 2012. This study systematically exploits 1-min averaged, range-squared-corrected lidar signals (RSCS) from the 532 nm analog reception channel of the instruments. Several methods that have been applied in previous literature to derive PBL height from vertical aerosol backscatter profiles are compared. Most widely used are derivative techniques such as the gradient method (GM), inflection point method (IPM), and logarithm gradient method (LGM) and covariance techniques such as the wavelet covariance transform (WCT) method using a Haar wavelet. The methods function by detecting steep gradients in the aerosol backscatter profile, a proxy for the transition zone between the PBL and FT. It is found that all the methods provide comparable results. However, it is determined that WCT is an optimal method as it is more computationally efficient than the derivative techniques. In summer, PBL heights over the Iberian Peninsula are typically between 1-3 km. In addition, spatial patterns and diurnal variation of the PBL height and an analysis of the meteorological situation over the study area are also conducted. Backward trajectories from the NOAA HYSPLIT model indicate aerosols arrived from tropical maritime origins over the eastern Atlantic Ocean in the previous 24-48 hours of the campaign. Overall, it is shown that lidar can be an effective means of obtaining accurate PBL heights on a nearly continuous basis.
2013 Fall Meeting of the American Geophysical Union, San Francisco, CA, USA; 12/2013
[Show abstract][Hide abstract] ABSTRACT: A solution based on a Kalman filter to trace the evolution of the atmospheric boundary layer (ABL) sensed by a ground-based elastic-backscatter tropospheric lidar is presented. An erf-like profile is used to model the mixing-layer top and the entrainment-zone thickness. The extended Kalman filter (EKF) enables to retrieve and track the ABL parameters based on simplified statistics of the ABL dynamics and of the observation noise present in the lidar signal. This adaptive feature permits to analyze atmospheric scenes with low signal-to-noise ratios (SNRs) without the need to resort to long-time averages or range-smoothing techniques, as well as to pave the way for future automated detection solutions. First, EKF results based on oversimplified synthetic and experimental lidar profiles are presented and compared with classic ABL estimation quantifiers for a case study with different SNR scenarios.
IEEE Transactions on Geoscience and Remote Sensing 09/2013; PP(99):1-12. · 3.47 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The problem of overlap factor (OVF) computation and its near-range
sensitivity for medium-size aperture (f/10, f/11) bi-axial tropospheric
lidar systems using ray-tracing simulation software is presented. The
method revisits both detector and fiber optics coupling alternatives at
the telescope focal-plane along with the insertion of a field lens. A
sensitivity analysis is carried out as a function of laser divergence,
field lens, and detector/fiber positions, detector size, and the fiber's
core diameter and numerical aperture. The ray-tracing approach presented
here is straightforward and a comparatively much simpler solution than
analytical-based methods. Parametric simulations are carried out to show
that both approaches are coincident. Insertion of a field lens proves to
be an elegant and low sensitivity solution for OVF enhancement,
particularly, in the near-range of the lidar.
[Show abstract][Hide abstract] ABSTRACT: Total backscatter-coefficient inversion error bounds for the two-component lidar inversion algorithm (so-called Fernald's or Klett-Fernald-Sasano's method) are derived in analytical form in response to the following three error sources: 1) the measurement noise; 2) the user uncertainty in the backscatter-coefficient calibration; and 3) the aerosol extinction-to-backscatter ratio. The following two different types of error bounds are presented: 1) approximate error bounds using first-order error propagation and 2) exact error bounds using a total-increment method. Both error bounds are formulated in explicit analytical form, which is of advantage for practical physical sensitivity analysis and computational implementation. A Monte Carlo approach is used to validate the error bounds at 355-, 532-, and 1064-nm wavelengths.
IEEE Transactions on Geoscience and Remote Sensing 11/2012; 50(11):4791-4803. · 3.47 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: This paper presents parameter design methodology and related optomechanical engineering of a 905-nm diode-laser biaxial, eye-safe lidar ceilometer prototype for cloud-height monitoring. Starting with a brief review of the state-of-the-art ceilometer technology, acceptable parameter ranges are identified for the key system parts. Parameter tuning is achieved by imposing goal criteria on the simulated signal-to-noise ratio and laser-telescope overlap factor. The system is based on a low-cost pulsed semiconductor laser, low-cost Fresnel-lens telescope, a low-noise-equivalent power avalanche-photodiode optoelectronic receiver, and collimating/focusing adjustable parts. Finally, preliminary test measurements are presented.
[Show abstract][Hide abstract] ABSTRACT: Although routinely monitored by ground based air quality networks, the particulate
matter distribution could be eventually better described with remote sensing techniques.
However, valid relationships between ground level and columnar ground based quantities
should be known beforehand. In this study we have performed a comparison between
particulate matter measurements at ground level at different cut sizes (10, 2.5 and 1.0 mm),
and the aerosol optical depth obtained by means of a ground based sunphotometer during
a multiinstrumental field campaign held in El Arenosillo (Huelva, Spain) from 28 June to
4 July 2006. All the PM fractions were very well correlated with AOD with correlation
coefficients that ranged from 0.71 to 0.81 for PM10, PM2.5 and PM1. Furthermore, the
influence of the mixing layer height in the correlations was explored. The improvement in
the correlation when the vertical distribution is taken into account was significant for days
with a homogeneous mixing layer. Moreover, the chemical analysis of the individual size
fractions allowed us to study the origin of the particulate matter. Secondary components
were the most abundant and also well correlated in the three size fractions; but for PM10
fraction, chemical species related to marine origin were best correlated. Finally, we obtained
a relationship between MODIS L3 AOD from collection 5.1 and the three PM cut sizes.
In spite of being a relatively clean environment, all the techniques were able to capture
similar day to day variations during this field campaign.
Journal of Geophysical Research Atmospheres 02/2012; 117(D04201). · 3.44 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The need of a multi-spectral lidar has widely been experienced in last few years with a view to invert the optical and microphysical properties of aerosols and their impact on the climate change. As a part of the EARLINET-GALION objectives, a joint effort has already been made by the European Aerosol Research Lidar Network (EARLINET). The EARLINET advanced standard of 3+2-channel configuration for lidar instruments (3+2 standing for 3 elastic channels and 2 respective Raman channels) enables retrieval of aerosol microphysical properties. An overview of the new RSLAB 3+2+1 multispectral lidar system, therefore, is presented in terms of power budget estimation for all the reception channels and overall system performance, that is, signal-to-noise ratio (SNR) and maximum sounding range achieved.
Geoscience and Remote Sensing Symposium (IGARSS), 2012 IEEE International; 01/2012
[Show abstract][Hide abstract] ABSTRACT: A methodology aimed at validating elastic-channel optical power return and signal-to-noise ratio (SNR) levels estimated at the link-budget design stage of a tropospheric lidar against the measured ones is presented. A Rayleigh fit along with knowledge of the atmospheric aerosol transmittance and emission energy is used to theoretically estimate the net voltage responsivity. As a further refinement, when simultaneous analog and photon-counting acquisition is available, the method formulates a rough estimate of the optical losses in the receiving chain. Preliminary validation of the link-budget-assessed optical power and SNR levels for the 1064-nm channel of the Remote Sensing Lab. (RSLab) lidar is discussed.
Geoscience and Remote Sensing Symposium (IGARSS), 2012 IEEE International; 01/2012
[Show abstract][Hide abstract] ABSTRACT: A 6-channel dichroic-based polychromator is presented as the spectrally selective unit for the U.P.C. elastic/Raman lidar. Light emission is made at 355-nm (ultraviolet, UV), 532-nm (visible, VIS) and 1064-nm (near infrared, NIR) wavelengths. In reception, the polychromator is the spectral separation unit that separates the laser backscattered composite return into 3 elastic (355, 532, 1064-nm wavelengths) and 3 Raman channels (386.7, 607.4 and 407.5-nm (water-vapor) wavelengths). The polychromator houses photo-multiplier tubes (PMT) for all the channels except for the NIR one, which is avalanche photodiode (APD) based. The optomechanical design uses 1-inch optics and Eurorack standards. The APD-based receiver uses a XY-axis translation/elevation micro-positioning stage due to its comparatively small active area and motorised neutral density filters are used in all PMT-based channels to avoid detector saturation. The design has been specially optimized to provide homogeneous spatial light distribution onto the photodetectors and good mechanical repeatability. All channels are acquired in mixed analog and photon-counting mode using LicelÂ® transient recorders, which are controlled by means of a user friendly LabVIEWTM interface. The paper focuses on the main polychromator optical design parameters, that is, light collimation trade-offs, end-to-end transmissivity, net channel responsivity, light distribution and spot size onto the photodetectors. The polychromator along with the rest of the U.P.C. lidar system has successfully been tested during a recent lidar system intercomparison campaign carried out in Madrid (Spain) during Oct. 2010.
[Show abstract][Hide abstract] ABSTRACT: A method to estimate wind velocity using the backscatter lidar signals of transported aerosol particles is presented. The lidar signal is correlated along range and time dimensions for each line of sight in which the lidar is pointing. The method is based on the analysis of contours of these range-time auto-correlation functions. This analysis obtains ellipse curve parameters which are related to the radial velocity and to the square wind speed, locally retrieved for a given line of sight. The combination of data from several angular positions enables the wind direction retrieval. Two possible implementations of the method are considered and tested with an actual measurement with the lidar of the Universitat PolitÃ¨cnica de Catalunya (UPC).
[Show abstract][Hide abstract] ABSTRACT: The bidimensional auto-correlation for the lidar signal measured along a single line of sight (LOS) is spectrally analyzed to estimate the wind turbulence variance, while a correlation contour analysis retrieves the mean wind speed. A combined model of a turbulent wind field plus an isotropic gaussian aerosol concentration field is used to 1) estimate the wind field variance causing diffusion on the aerosol structures and 2) to extend the contour autocorrelation analysis to include the turbulence effect and correct the mean wind estimation. The present analysis is intended to be used on a single LOS sensing, that can provide an estimation of the relative turbulence.