Fabien Gibert | Centre National de la Recherche Scientifique / French National Centre for Scientific Research (original) (raw)

Papers by Fabien Gibert

Applied Optics, 2008

A 2 μm wavelength, 90 mJ, 5 Hz pulsed Ho laser is described with wavelength control to precisely ... more A 2 μm wavelength, 90 mJ, 5 Hz pulsed Ho laser is described with wavelength control to precisely tune and lock the wavelength at a desired offset up to 2:9 GHz from the center of a CO 2 absorption line. Once detuned from the line center the laser wavelength is actively locked to keep the wavelength within 1:9 MHz standard deviation about the setpoint. This wavelength control allows optimization of the optical depth for a differential absorption lidar (DIAL) measuring atmospheric CO 2 concentrations. The laser transmitter has been coupled with a coherent heterodyne receiver for measurements of CO 2 concentration using aerosol backscatter; wind and aerosols are also measured with the same lidar and provide useful additional information on atmospheric structure. Range-resolved CO 2 measurements were made with < 2:4% standard deviation using 500 m range bins and 6:7 min (1000 pulse pairs) integration time. Measurement of a horizontal column showed a precision of the CO 2 concentration to < 0:7% standard deviation using a 30 min (4500 pulse pairs) integration time, and comparison with a collocated in situ sensor showed the DIAL to measure the same trend of a diurnal variation and to detect shorter time scale CO 2 perturbations. For vertical column measurements the lidar was setup at the WLEF tall tower site in Wisconsin to provide meteorological profiles and to compare the DIAL measurements with the in situ sensors distributed on the tower up to 396 m height. Assuming the DIAL column measurement extending from 153 m altitude to 1353 m altitude should agree with the tower in situ sensor at 396 m altitude, there was a 7:9 ppm rms difference between the DIAL and the in situ sensor using a 30 min rolling average on the DIAL measurement.

Journal of Quantitative Spectroscopy & Radiative Transfer, 2008

A diode laser spectrometer was used in the Groupe de Spectrométrie Moléculaire et Atmosphérique o... more A diode laser spectrometer was used in the Groupe de Spectrométrie Moléculaire et Atmosphérique of Reims (France) to study CO2 line intensities, self-broadening coefficients and air-pressure-broadening coefficients near 2.063 μm. The spectral region ranging from ...

Journal of Atmospheric and Oceanic Technology, 2010

The vertical profiling of CO 2 turbulent fluxes in the atmospheric boundary layer (ABL) is invest... more The vertical profiling of CO 2 turbulent fluxes in the atmospheric boundary layer (ABL) is investigated using a coherent differential absorption lidar (CDIAL) operated nearby a tall tower in Wisconsin during June 2007. A CDIAL can perform simultaneous range-resolved CO 2 DIAL and velocity measurements. The lidar eddy covariance technique is presented. The aims of the study are (i) an assessment of performance and current limitation of available CDIAL for CO 2 turbulent fluxes and (ii) the derivation of instrument specifications to build a future CDIAL to perform accurate range-resolved CO 2 fluxes. Experimental lidar CO 2 mixing ratio and vertical velocity profiles are successfully compared with in situ sensors measurements. Time and space integral scales of turbulence in the ABL are addressed that result in limitation for time averaging and range accumulation. A first attempt to infer CO 2 fluxes using an eddy covariance technique with currently available 2-mm CDIAL dataset is reported.

Journal of Geophysical Research, 2007

1] The present paper deals with a boundary layer budgeting method which makes use of observations... more 1] The present paper deals with a boundary layer budgeting method which makes use of observations from various in situ and remote sensing instruments to infer regional average net ecosystem exchange (NEE) of CO 2 . Measurements of CO 2 within and above the atmospheric boundary layer (ABL) by in situ sensors, in conjunction with a precise knowledge of the change in ABL height by lidar and radiosoundings, enable to infer diurnal and seasonal NEE variations. Near-ground in situ CO measurements are used to discriminate natural and anthropogenic contributions of CO 2 diurnal variations in the ABL. The method yields mean NEE that amounts to 5 mmol m À2 s À1 during the night and À20 mmol m À2 s À1 in the middle of the day between May and July. A good agreement is found with the expected NEE accounting for a mixed wheat field and forest area during winter season, representative of the mesoscale ecosystems in the Paris area according to the trajectory of an air column crossing the landscape. Daytime NEE is seen to follow the vegetation growth and the change in the ratio diffuse/direct radiation. The CO 2 vertical mixing flux during the rise of the atmospheric boundary layer is also estimated and seems to be the main cause of the large decrease of CO 2 mixing ratio in the morning. The outcomes on CO 2 flux estimate are compared to eddy-covariance measurements on a barley field. The importance of various sources of error and uncertainty on the retrieval is discussed. These errors are estimated to be less than 15%; the main error resulted from anthropogenic emissions. Citation: Gibert, F., M. Schmidt, J. Cuesta, P. Ciais, M. Ramonet, I. Xueref, E. Larmanou, and P. H. Flamant (2007), Retrieval of average CO 2 fluxes by combining in situ CO 2 measurements and backscatter lidar information,

Spectrochimica Acta Part A-molecular and Biomolecular Spectroscopy, 2009

Remote sensing and in situ instruments are presented and compared in the same location for accura... more Remote sensing and in situ instruments are presented and compared in the same location for accurate CO(2) mixing ratio measurements in the atmosphere: (1) a 2.064 microm Heterodyne DIfferential Absorption Lidar (HDIAL), (2) a field deployable infrared Laser Diode Spectrometer (LDS) using new commercial diode laser technology at 2.68 microm, (3) LICOR NDIR analyzer and (4) flasks. LDS, LICOR and flasks measurements were made in the same location, LICOR and flasks being taken as reference. Horizontal HDIAL measurements of CO(2) absorption using aerosol backscatter signal are reported. Using new spectroscopic data in the 2 microm band and meteorological sensor measurements, a mean CO(2) mixing ratio is inferred by the HDIAL in a 1 km long path above the 15m height location of the CO(2) in situ sensors. We compare HDIAL and LDS measurements with the LICOR data for 30 min of time averaging. The mean standard deviation of the HDIAL and the LDS CO(2) mixing ratio results are 3.3 ppm and 0.89 ppm, respectively. The bias of the HDIAL and the LDS measurements are -0.54 ppm and -0.99 ppm, respectively.

Journal of Geophysical Research, 2008

Boundary-layer Meteorology, 2008

A network of remote and in-situ sensors was deployed in a Paris suburb in order to evaluate the m... more A network of remote and in-situ sensors was deployed in a Paris suburb in order to evaluate the mesoscale evolution of the daily cycle of CO2 and related tracers in the atmospheric boundary layer (ABL) and its relation to ABL dynamics and nearby natural and anthropogenic sources and sinks. A 2-μm heterodyne Doppler differential absorption lidar, which combines measurements of, (1) structure of the atmosphere, (2) radial velocity, and (3) CO2 differential absorption was a particularly unique element of the observational array. We analyse the differences in the diurnal cycle of CO, CO2, lidar reflectivity (a proxy for aerosol content) and H2O using the lidar, airborne measurements in the free troposphere and ground-based measurements made at two sites located few kilometres apart. We demonstrate that vertical mixing dominates the early morning drawdown of CO and aerosol content trapped in the former nocturnal layer but not the H2O and CO2 mixing ratio variations. Surface fluxes, vertical mixing and advection all contribute to the ABL CO2 mixing ratio decrease during the morning transition, with the relative importance depending on the rate and timing of ABL rise. We also show evidence that when the ABL is stable, small-scale (0.1-km vertical and 1-km horizontal) gradients of CO2 and CO are large. The results illustrate the complexity of inferring surface fluxes of CO2 from atmospheric budgets in the stable boundary layer.

Journal of Geophysical Research, 2007

1] The present paper deals with a boundary layer budgeting method which makes use of observations... more 1] The present paper deals with a boundary layer budgeting method which makes use of observations from various in situ and remote sensing instruments to infer regional average net ecosystem exchange (NEE) of CO 2 . Measurements of CO 2 within and above the atmospheric boundary layer (ABL) by in situ sensors, in conjunction with a precise knowledge of the change in ABL height by lidar and radiosoundings, enable to infer diurnal and seasonal NEE variations. Near-ground in situ CO measurements are used to discriminate natural and anthropogenic contributions of CO 2 diurnal variations in the ABL. The method yields mean NEE that amounts to 5 mmol m À2 s À1 during the night and À20 mmol m À2 s À1 in the middle of the day between May and July. A good agreement is found with the expected NEE accounting for a mixed wheat field and forest area during winter season, representative of the mesoscale ecosystems in the Paris area according to the trajectory of an air column crossing the landscape. Daytime NEE is seen to follow the vegetation growth and the change in the ratio diffuse/direct radiation. The CO 2 vertical mixing flux during the rise of the atmospheric boundary layer is also estimated and seems to be the main cause of the large decrease of CO 2 mixing ratio in the morning. The outcomes on CO 2 flux estimate are compared to eddy-covariance measurements on a barley field. The importance of various sources of error and uncertainty on the retrieval is discussed. These errors are estimated to be less than 15%; the main error resulted from anthropogenic emissions. Citation: Gibert, F., M. Schmidt, J. Cuesta, P. Ciais, M. Ramonet, I. Xueref, E. Larmanou, and P. H. Flamant (2007), Retrieval of average CO 2 fluxes by combining in situ CO 2 measurements and backscatter lidar information,

Journal of Quantitative Spectroscopy & Radiative Transfer, 2011

Atmospheric carbon dioxide (CO 2 ) is one of the main contributors to the greenhouse effect. A gl... more Atmospheric carbon dioxide (CO 2 ) is one of the main contributors to the greenhouse effect. A global monitoring of CO 2 from space is foreseen as a key issue to quantify its sources and sinks at a regional scale and to better predict future levels of CO 2 and their effect on climate change. Differential Absorption Lidar (DiAL) is a promising and novel spectroscopic technique for remote sensing CO 2 spatial and temporal concentration distribution with a high level of accuracy. However, a precise knowledge of spectroscopic parameters of CO 2 molecular transitions and their dependence with temperature and pressure is required for reducing the uncertainty on DiAl measurements. Hence, to support remote sensing of carbon dioxide in the troposphere, we report on the accurate determination of air pressure-induced shift coefficients for eight absorption lines belonging to the R branch of (20 0 1) III '(00 0 0) I band of CO 2 at 2.05 mm. Purposely, a high-resolution tunable diode laser absorption spectrometer (TDLAS) coupled to a cryogenically cooled optical cell was implemented. From these measurements, we have further determined the temperature-dependencies of the air pressure-induced shift coefficients.

Journal of Quantitative Spectroscopy & Radiative Transfer, 2008

A diode laser spectrometer was used in the Groupe de Spectrométrie Moléculaire et Atmosphérique o... more A diode laser spectrometer was used in the Groupe de Spectrométrie Moléculaire et Atmosphérique of Reims (France) to study CO2 line intensities, self-broadening coefficients and air-pressure-broadening coefficients near 2.063 μm. The spectral region ranging from ...

Journal of Quantitative Spectroscopy & Radiative Transfer, 2011

Atmospheric carbon dioxide (CO 2 ) is one of the main contributors to the greenhouse effect. A gl... more Atmospheric carbon dioxide (CO 2 ) is one of the main contributors to the greenhouse effect. A global monitoring of CO 2 from space is foreseen as a key issue to quantify its sources and sinks at a regional scale and to better predict future levels of CO 2 and their effect on climate change. Differential Absorption Lidar (DiAL) is a promising and novel spectroscopic technique for remote sensing CO 2 spatial and temporal concentration distribution with a high level of accuracy. However, a precise knowledge of spectroscopic parameters of CO 2 molecular transitions and their dependence with temperature and pressure is required for reducing the uncertainty on DiAl measurements. Hence, to support remote sensing of carbon dioxide in the troposphere, we report on the accurate determination of air pressure-induced shift coefficients for eight absorption lines belonging to the R branch of (20 0 1) III '(00 0 0) I band of CO 2 at 2.05 mm. Purposely, a high-resolution tunable diode laser absorption spectrometer (TDLAS) coupled to a cryogenically cooled optical cell was implemented. From these measurements, we have further determined the temperature-dependencies of the air pressure-induced shift coefficients.

Boundary-layer Meteorology, 2007

We question the correlation between vertical velocity (w) on the one hand and the occurrence of c... more We question the correlation between vertical velocity (w) on the one hand and the occurrence of convective plumes in lidar reflectivity (i.e. range corrected backscatter signal Pz 2) and depolarization ratio (Δ) on the other hand in the convective boundary layer (CBL). Thermal vertical motion is directly investigated using vertical velocities measured by a ground-based Doppler lidar operating at 2 μm. This lidar provides also simultaneous measurements of lidar reflectivity. In addition, a second lidar 200 m away provides reflectivities at 0.53 and 1 μm and depolarization ratio at 0.53 μm. The time series from the two lidars are analyzed in terms of linear correlation coefficient (ρ). The main result is that the plume-like structures provided by lidar reflectivity within the CBL as well as the CBL height are not a clear signature of updrafts. It is shown that the lidar reflectivity within the CBL is frequently anti-correlated (ρ (w, Pz 2 )) with the vertical velocity. On the contrary, the correlation coefficient between the depolarization ratio and the vertical velocity ρ (w, Δ ) is always positive, showing that the depolarization ratio is a fair tracer of updrafts. The importance of relative humidity on the correlation coefficient is discussed.

Journal of Atmospheric and Oceanic Technology, 2011

The vertical profiling of CO 2 turbulent fluxes in the atmospheric boundary layer (ABL) is invest... more The vertical profiling of CO 2 turbulent fluxes in the atmospheric boundary layer (ABL) is investigated using a coherent differential absorption lidar (CDIAL) operated nearby a tall tower in Wisconsin during June 2007. A CDIAL can perform simultaneous range-resolved CO 2 DIAL and velocity measurements. The lidar eddy covariance technique is presented. The aims of the study are (i) an assessment of performance and current limitation of available CDIAL for CO 2 turbulent fluxes and (ii) the derivation of instrument specifications to build a future CDIAL to perform accurate range-resolved CO 2 fluxes. Experimental lidar CO 2 mixing ratio and vertical velocity profiles are successfully compared with in situ sensors measurements. Time and space integral scales of turbulence in the ABL are addressed that result in limitation for time averaging and range accumulation. A first attempt to infer CO 2 fluxes using an eddy covariance technique with currently available 2-mm CDIAL dataset is reported.

Applied Spectroscopy, 2007

An a posteriori corrective method based on photo-acoustic cell (PAC) information is proposed to c... more An a posteriori corrective method based on photo-acoustic cell (PAC) information is proposed to correct for laser transmitter spectral shift during atmospheric CO(2) measurements by 2 microm heterodyne differential absorption lidar (HDIAL) technique. The method for using the PAC signal to retrieve the actual atmospheric CO(2) absorption is presented in detail. This issue is tackled using a weighting function. The performance of the proposed corrective method is discussed and the various sources of error associated with the PAC signal are investigated. For 300 shots averaged and a frequency shift (from the CO(2) absorption line center) lower than the CO(2) absorption line half-width, the relative error on HDIAL CO(2) mixing ratio measurements is lower than 1.3%. The corrective method is validated in absolute value by comparison between HDIAL and in situ sensor measurements of CO(2).

Quarterly Journal of The Royal Meteorological Society, 2011

Generation of internal gravity waves in the boundary layer is investigated from observations. Sim... more Generation of internal gravity waves in the boundary layer is investigated from observations. Simultaneous measurements from a 2 µm Doppler lidar and a 0.5 µm backscatter lidar are combined to analyse the occurrence, or not, of internal gravity waves in the residual layer during the morning transition on two days, 10 and 14 June 2005. Three cases are studied for illustrating three different flow configurations in the residual layer: no wave, evanescent wave and propagating wave. Comparison of the three cases suggests two necessary conditions for the generation of gravity waves: a stably stratified residual layer and a convective boundary layer with mechanical forcing frequencies less than the Brunt-Va¨ısala frequency. The horizontal wind shear probably plays a role in the dynamics of the waves, but, in the cases analysed, it is not sufficient alone to generate the observed waves through the obstacle effect. In the case of wave propagation, the waves tilt upstream and against the wind shear, with a typical horizontal wavelength and a line phase direction with respect to the vertical of 2.4 km and 32 • , respectively. Unexpectedly, we found that measurements of the wave-associated vertical velocity and the displacement of tracers (0.5 µm depolarization ratio or 2 µm backcatter, both indicative of relative humidity fluctuations) are in phase. Possible explanations include: (i) aerosol particles are not passive with respect to temperature or water vapour fluctuations; or (ii) a nonlinear wave-turbulence interaction is at work and needs further investigation.

Applied Optics, 2006

A 2 m heterodyne differential absorption lidar (HDIAL) has been operated at the Instïtut Pierre S... more A 2 m heterodyne differential absorption lidar (HDIAL) has been operated at the Instïtut Pierre Simon Laplace, Laboratoire de Météorologie Dynamique (Paris) to monitor the CO 2 mixing ratio in absolute value at high accuracy in the atmospheric boundary layer. Horizontal measurements at increasing range are made to retrieve the optical depth. The experimental setup takes advantage of a heterodyne lidar developed for wind velocity measurements. A control unit based on a photoacoustic cell filled with CO 2 is tested to correct afterward for ON-line frequency drift. The HDIAL results are validated using in situ routine measurements. The Doppler capability is used to follow the change in wind direction in the Paris suburbs.

Boundary-layer Meteorology, 2007

We question the correlation between vertical velocity (w) on the one hand and the occurrence of c... more We question the correlation between vertical velocity (w) on the one hand and the occurrence of convective plumes in lidar reflectivity (i.e. range corrected backscatter signalPz 2 ) and depolarization ratio ( ) on the other hand in the convective boundary layer (CBL). Thermal vertical motion is directly investigated using vertical velocities measured by a ground-based Doppler lidar operating at 2 µm. This lidar provides also simultaneous measurements of lidar reflectivity. In addition, a second lidar 200 m away provides reflectivities at 0.53 and 1 µm and depolarization ratio at 0.53 µm. The time series from the two lidars are analyzed in terms of linear correlation coefficient (ρ). The main result is that the plume-like structures provided by lidar reflectivity within the CBL as well as the CBL height are not a clear signature of updrafts. It is shown that the lidar reflectivity within the CBL is frequently anti-correlated (ρ w, Pz 2 ) with the vertical velocity. On the contrary, the correlation coefficient between the depolarization ratio and the vertical velocityρ (w, ) is always positive, showing that the depolarization ratio is a fair tracer of updrafts. The importance of relative humidity on the correlation coefficient is discussed.

A Heterodyne Differential Absorption Lidar (HDIAL) for monitoring atmospheric CO 2 concentration ... more A Heterodyne Differential Absorption Lidar (HDIAL) for monitoring atmospheric CO 2 concentration is presented. The design of the lidar system is discussed including the 2.06-µm pulsed laser transmitter, heterodyne detection and signal processing. Moreover a numerical simulation in the time domain for HDIAL enables to evaluate the lidar performance for such measurements. Finally preliminary experimental results are presented and compared to the results of realistic simulations.

Journal of Geophysical Research, 2008

Applied Optics, 2006

A detailed study using both analytical and numerical calculations of direct and heterodyne differ... more A detailed study using both analytical and numerical calculations of direct and heterodyne differential absorption lidar (DIAL) techniques is conducted to complement previous studies. The DIAL measurement errors depend on key experimental parameters, some of which can be adjusted to minimize the statistical error. Accordingly, the pertinent criteria on optical thickness, the number of photons emitted at the on and off wavelengths, are discussed to reduce the relative error on the total column content or range-resolved measurements that rely on either hard target or atmospheric backscatter returns. In direct detection, the optimal optical thickness decreases from 1.3 to 0.8 when the background increases while the on-line-to-offline optimal energy ratio decreases from 3.6 to 2.7. In heterodyne detection, the minimum error is obtained for an optical thickness of 1.2 and an energy ratio of 4.3.

Applied Optics, 2008

A 2 μm wavelength, 90 mJ, 5 Hz pulsed Ho laser is described with wavelength control to precisely ... more A 2 μm wavelength, 90 mJ, 5 Hz pulsed Ho laser is described with wavelength control to precisely tune and lock the wavelength at a desired offset up to 2:9 GHz from the center of a CO 2 absorption line. Once detuned from the line center the laser wavelength is actively locked to keep the wavelength within 1:9 MHz standard deviation about the setpoint. This wavelength control allows optimization of the optical depth for a differential absorption lidar (DIAL) measuring atmospheric CO 2 concentrations. The laser transmitter has been coupled with a coherent heterodyne receiver for measurements of CO 2 concentration using aerosol backscatter; wind and aerosols are also measured with the same lidar and provide useful additional information on atmospheric structure. Range-resolved CO 2 measurements were made with < 2:4% standard deviation using 500 m range bins and 6:7 min (1000 pulse pairs) integration time. Measurement of a horizontal column showed a precision of the CO 2 concentration to < 0:7% standard deviation using a 30 min (4500 pulse pairs) integration time, and comparison with a collocated in situ sensor showed the DIAL to measure the same trend of a diurnal variation and to detect shorter time scale CO 2 perturbations. For vertical column measurements the lidar was setup at the WLEF tall tower site in Wisconsin to provide meteorological profiles and to compare the DIAL measurements with the in situ sensors distributed on the tower up to 396 m height. Assuming the DIAL column measurement extending from 153 m altitude to 1353 m altitude should agree with the tower in situ sensor at 396 m altitude, there was a 7:9 ppm rms difference between the DIAL and the in situ sensor using a 30 min rolling average on the DIAL measurement.

Journal of Quantitative Spectroscopy & Radiative Transfer, 2008

A diode laser spectrometer was used in the Groupe de Spectrométrie Moléculaire et Atmosphérique o... more A diode laser spectrometer was used in the Groupe de Spectrométrie Moléculaire et Atmosphérique of Reims (France) to study CO2 line intensities, self-broadening coefficients and air-pressure-broadening coefficients near 2.063 μm. The spectral region ranging from ...

Journal of Atmospheric and Oceanic Technology, 2010

The vertical profiling of CO 2 turbulent fluxes in the atmospheric boundary layer (ABL) is invest... more The vertical profiling of CO 2 turbulent fluxes in the atmospheric boundary layer (ABL) is investigated using a coherent differential absorption lidar (CDIAL) operated nearby a tall tower in Wisconsin during June 2007. A CDIAL can perform simultaneous range-resolved CO 2 DIAL and velocity measurements. The lidar eddy covariance technique is presented. The aims of the study are (i) an assessment of performance and current limitation of available CDIAL for CO 2 turbulent fluxes and (ii) the derivation of instrument specifications to build a future CDIAL to perform accurate range-resolved CO 2 fluxes. Experimental lidar CO 2 mixing ratio and vertical velocity profiles are successfully compared with in situ sensors measurements. Time and space integral scales of turbulence in the ABL are addressed that result in limitation for time averaging and range accumulation. A first attempt to infer CO 2 fluxes using an eddy covariance technique with currently available 2-mm CDIAL dataset is reported.

Journal of Geophysical Research, 2007

1] The present paper deals with a boundary layer budgeting method which makes use of observations... more 1] The present paper deals with a boundary layer budgeting method which makes use of observations from various in situ and remote sensing instruments to infer regional average net ecosystem exchange (NEE) of CO 2 . Measurements of CO 2 within and above the atmospheric boundary layer (ABL) by in situ sensors, in conjunction with a precise knowledge of the change in ABL height by lidar and radiosoundings, enable to infer diurnal and seasonal NEE variations. Near-ground in situ CO measurements are used to discriminate natural and anthropogenic contributions of CO 2 diurnal variations in the ABL. The method yields mean NEE that amounts to 5 mmol m À2 s À1 during the night and À20 mmol m À2 s À1 in the middle of the day between May and July. A good agreement is found with the expected NEE accounting for a mixed wheat field and forest area during winter season, representative of the mesoscale ecosystems in the Paris area according to the trajectory of an air column crossing the landscape. Daytime NEE is seen to follow the vegetation growth and the change in the ratio diffuse/direct radiation. The CO 2 vertical mixing flux during the rise of the atmospheric boundary layer is also estimated and seems to be the main cause of the large decrease of CO 2 mixing ratio in the morning. The outcomes on CO 2 flux estimate are compared to eddy-covariance measurements on a barley field. The importance of various sources of error and uncertainty on the retrieval is discussed. These errors are estimated to be less than 15%; the main error resulted from anthropogenic emissions. Citation: Gibert, F., M. Schmidt, J. Cuesta, P. Ciais, M. Ramonet, I. Xueref, E. Larmanou, and P. H. Flamant (2007), Retrieval of average CO 2 fluxes by combining in situ CO 2 measurements and backscatter lidar information,

Spectrochimica Acta Part A-molecular and Biomolecular Spectroscopy, 2009

Remote sensing and in situ instruments are presented and compared in the same location for accura... more Remote sensing and in situ instruments are presented and compared in the same location for accurate CO(2) mixing ratio measurements in the atmosphere: (1) a 2.064 microm Heterodyne DIfferential Absorption Lidar (HDIAL), (2) a field deployable infrared Laser Diode Spectrometer (LDS) using new commercial diode laser technology at 2.68 microm, (3) LICOR NDIR analyzer and (4) flasks. LDS, LICOR and flasks measurements were made in the same location, LICOR and flasks being taken as reference. Horizontal HDIAL measurements of CO(2) absorption using aerosol backscatter signal are reported. Using new spectroscopic data in the 2 microm band and meteorological sensor measurements, a mean CO(2) mixing ratio is inferred by the HDIAL in a 1 km long path above the 15m height location of the CO(2) in situ sensors. We compare HDIAL and LDS measurements with the LICOR data for 30 min of time averaging. The mean standard deviation of the HDIAL and the LDS CO(2) mixing ratio results are 3.3 ppm and 0.89 ppm, respectively. The bias of the HDIAL and the LDS measurements are -0.54 ppm and -0.99 ppm, respectively.

Journal of Geophysical Research, 2008

Boundary-layer Meteorology, 2008

A network of remote and in-situ sensors was deployed in a Paris suburb in order to evaluate the m... more A network of remote and in-situ sensors was deployed in a Paris suburb in order to evaluate the mesoscale evolution of the daily cycle of CO2 and related tracers in the atmospheric boundary layer (ABL) and its relation to ABL dynamics and nearby natural and anthropogenic sources and sinks. A 2-μm heterodyne Doppler differential absorption lidar, which combines measurements of, (1) structure of the atmosphere, (2) radial velocity, and (3) CO2 differential absorption was a particularly unique element of the observational array. We analyse the differences in the diurnal cycle of CO, CO2, lidar reflectivity (a proxy for aerosol content) and H2O using the lidar, airborne measurements in the free troposphere and ground-based measurements made at two sites located few kilometres apart. We demonstrate that vertical mixing dominates the early morning drawdown of CO and aerosol content trapped in the former nocturnal layer but not the H2O and CO2 mixing ratio variations. Surface fluxes, vertical mixing and advection all contribute to the ABL CO2 mixing ratio decrease during the morning transition, with the relative importance depending on the rate and timing of ABL rise. We also show evidence that when the ABL is stable, small-scale (0.1-km vertical and 1-km horizontal) gradients of CO2 and CO are large. The results illustrate the complexity of inferring surface fluxes of CO2 from atmospheric budgets in the stable boundary layer.

Journal of Geophysical Research, 2007

1] The present paper deals with a boundary layer budgeting method which makes use of observations... more 1] The present paper deals with a boundary layer budgeting method which makes use of observations from various in situ and remote sensing instruments to infer regional average net ecosystem exchange (NEE) of CO 2 . Measurements of CO 2 within and above the atmospheric boundary layer (ABL) by in situ sensors, in conjunction with a precise knowledge of the change in ABL height by lidar and radiosoundings, enable to infer diurnal and seasonal NEE variations. Near-ground in situ CO measurements are used to discriminate natural and anthropogenic contributions of CO 2 diurnal variations in the ABL. The method yields mean NEE that amounts to 5 mmol m À2 s À1 during the night and À20 mmol m À2 s À1 in the middle of the day between May and July. A good agreement is found with the expected NEE accounting for a mixed wheat field and forest area during winter season, representative of the mesoscale ecosystems in the Paris area according to the trajectory of an air column crossing the landscape. Daytime NEE is seen to follow the vegetation growth and the change in the ratio diffuse/direct radiation. The CO 2 vertical mixing flux during the rise of the atmospheric boundary layer is also estimated and seems to be the main cause of the large decrease of CO 2 mixing ratio in the morning. The outcomes on CO 2 flux estimate are compared to eddy-covariance measurements on a barley field. The importance of various sources of error and uncertainty on the retrieval is discussed. These errors are estimated to be less than 15%; the main error resulted from anthropogenic emissions. Citation: Gibert, F., M. Schmidt, J. Cuesta, P. Ciais, M. Ramonet, I. Xueref, E. Larmanou, and P. H. Flamant (2007), Retrieval of average CO 2 fluxes by combining in situ CO 2 measurements and backscatter lidar information,

Journal of Quantitative Spectroscopy & Radiative Transfer, 2011

Atmospheric carbon dioxide (CO 2 ) is one of the main contributors to the greenhouse effect. A gl... more Atmospheric carbon dioxide (CO 2 ) is one of the main contributors to the greenhouse effect. A global monitoring of CO 2 from space is foreseen as a key issue to quantify its sources and sinks at a regional scale and to better predict future levels of CO 2 and their effect on climate change. Differential Absorption Lidar (DiAL) is a promising and novel spectroscopic technique for remote sensing CO 2 spatial and temporal concentration distribution with a high level of accuracy. However, a precise knowledge of spectroscopic parameters of CO 2 molecular transitions and their dependence with temperature and pressure is required for reducing the uncertainty on DiAl measurements. Hence, to support remote sensing of carbon dioxide in the troposphere, we report on the accurate determination of air pressure-induced shift coefficients for eight absorption lines belonging to the R branch of (20 0 1) III '(00 0 0) I band of CO 2 at 2.05 mm. Purposely, a high-resolution tunable diode laser absorption spectrometer (TDLAS) coupled to a cryogenically cooled optical cell was implemented. From these measurements, we have further determined the temperature-dependencies of the air pressure-induced shift coefficients.

Journal of Quantitative Spectroscopy & Radiative Transfer, 2008

A diode laser spectrometer was used in the Groupe de Spectrométrie Moléculaire et Atmosphérique o... more A diode laser spectrometer was used in the Groupe de Spectrométrie Moléculaire et Atmosphérique of Reims (France) to study CO2 line intensities, self-broadening coefficients and air-pressure-broadening coefficients near 2.063 μm. The spectral region ranging from ...

Journal of Quantitative Spectroscopy & Radiative Transfer, 2011

Atmospheric carbon dioxide (CO 2 ) is one of the main contributors to the greenhouse effect. A gl... more Atmospheric carbon dioxide (CO 2 ) is one of the main contributors to the greenhouse effect. A global monitoring of CO 2 from space is foreseen as a key issue to quantify its sources and sinks at a regional scale and to better predict future levels of CO 2 and their effect on climate change. Differential Absorption Lidar (DiAL) is a promising and novel spectroscopic technique for remote sensing CO 2 spatial and temporal concentration distribution with a high level of accuracy. However, a precise knowledge of spectroscopic parameters of CO 2 molecular transitions and their dependence with temperature and pressure is required for reducing the uncertainty on DiAl measurements. Hence, to support remote sensing of carbon dioxide in the troposphere, we report on the accurate determination of air pressure-induced shift coefficients for eight absorption lines belonging to the R branch of (20 0 1) III '(00 0 0) I band of CO 2 at 2.05 mm. Purposely, a high-resolution tunable diode laser absorption spectrometer (TDLAS) coupled to a cryogenically cooled optical cell was implemented. From these measurements, we have further determined the temperature-dependencies of the air pressure-induced shift coefficients.

Boundary-layer Meteorology, 2007

We question the correlation between vertical velocity (w) on the one hand and the occurrence of c... more We question the correlation between vertical velocity (w) on the one hand and the occurrence of convective plumes in lidar reflectivity (i.e. range corrected backscatter signal Pz 2) and depolarization ratio (Δ) on the other hand in the convective boundary layer (CBL). Thermal vertical motion is directly investigated using vertical velocities measured by a ground-based Doppler lidar operating at 2 μm. This lidar provides also simultaneous measurements of lidar reflectivity. In addition, a second lidar 200 m away provides reflectivities at 0.53 and 1 μm and depolarization ratio at 0.53 μm. The time series from the two lidars are analyzed in terms of linear correlation coefficient (ρ). The main result is that the plume-like structures provided by lidar reflectivity within the CBL as well as the CBL height are not a clear signature of updrafts. It is shown that the lidar reflectivity within the CBL is frequently anti-correlated (ρ (w, Pz 2 )) with the vertical velocity. On the contrary, the correlation coefficient between the depolarization ratio and the vertical velocity ρ (w, Δ ) is always positive, showing that the depolarization ratio is a fair tracer of updrafts. The importance of relative humidity on the correlation coefficient is discussed.

Journal of Atmospheric and Oceanic Technology, 2011

The vertical profiling of CO 2 turbulent fluxes in the atmospheric boundary layer (ABL) is invest... more The vertical profiling of CO 2 turbulent fluxes in the atmospheric boundary layer (ABL) is investigated using a coherent differential absorption lidar (CDIAL) operated nearby a tall tower in Wisconsin during June 2007. A CDIAL can perform simultaneous range-resolved CO 2 DIAL and velocity measurements. The lidar eddy covariance technique is presented. The aims of the study are (i) an assessment of performance and current limitation of available CDIAL for CO 2 turbulent fluxes and (ii) the derivation of instrument specifications to build a future CDIAL to perform accurate range-resolved CO 2 fluxes. Experimental lidar CO 2 mixing ratio and vertical velocity profiles are successfully compared with in situ sensors measurements. Time and space integral scales of turbulence in the ABL are addressed that result in limitation for time averaging and range accumulation. A first attempt to infer CO 2 fluxes using an eddy covariance technique with currently available 2-mm CDIAL dataset is reported.

Applied Spectroscopy, 2007

An a posteriori corrective method based on photo-acoustic cell (PAC) information is proposed to c... more An a posteriori corrective method based on photo-acoustic cell (PAC) information is proposed to correct for laser transmitter spectral shift during atmospheric CO(2) measurements by 2 microm heterodyne differential absorption lidar (HDIAL) technique. The method for using the PAC signal to retrieve the actual atmospheric CO(2) absorption is presented in detail. This issue is tackled using a weighting function. The performance of the proposed corrective method is discussed and the various sources of error associated with the PAC signal are investigated. For 300 shots averaged and a frequency shift (from the CO(2) absorption line center) lower than the CO(2) absorption line half-width, the relative error on HDIAL CO(2) mixing ratio measurements is lower than 1.3%. The corrective method is validated in absolute value by comparison between HDIAL and in situ sensor measurements of CO(2).

Quarterly Journal of The Royal Meteorological Society, 2011

Generation of internal gravity waves in the boundary layer is investigated from observations. Sim... more Generation of internal gravity waves in the boundary layer is investigated from observations. Simultaneous measurements from a 2 µm Doppler lidar and a 0.5 µm backscatter lidar are combined to analyse the occurrence, or not, of internal gravity waves in the residual layer during the morning transition on two days, 10 and 14 June 2005. Three cases are studied for illustrating three different flow configurations in the residual layer: no wave, evanescent wave and propagating wave. Comparison of the three cases suggests two necessary conditions for the generation of gravity waves: a stably stratified residual layer and a convective boundary layer with mechanical forcing frequencies less than the Brunt-Va¨ısala frequency. The horizontal wind shear probably plays a role in the dynamics of the waves, but, in the cases analysed, it is not sufficient alone to generate the observed waves through the obstacle effect. In the case of wave propagation, the waves tilt upstream and against the wind shear, with a typical horizontal wavelength and a line phase direction with respect to the vertical of 2.4 km and 32 • , respectively. Unexpectedly, we found that measurements of the wave-associated vertical velocity and the displacement of tracers (0.5 µm depolarization ratio or 2 µm backcatter, both indicative of relative humidity fluctuations) are in phase. Possible explanations include: (i) aerosol particles are not passive with respect to temperature or water vapour fluctuations; or (ii) a nonlinear wave-turbulence interaction is at work and needs further investigation.

Applied Optics, 2006

A 2 m heterodyne differential absorption lidar (HDIAL) has been operated at the Instïtut Pierre S... more A 2 m heterodyne differential absorption lidar (HDIAL) has been operated at the Instïtut Pierre Simon Laplace, Laboratoire de Météorologie Dynamique (Paris) to monitor the CO 2 mixing ratio in absolute value at high accuracy in the atmospheric boundary layer. Horizontal measurements at increasing range are made to retrieve the optical depth. The experimental setup takes advantage of a heterodyne lidar developed for wind velocity measurements. A control unit based on a photoacoustic cell filled with CO 2 is tested to correct afterward for ON-line frequency drift. The HDIAL results are validated using in situ routine measurements. The Doppler capability is used to follow the change in wind direction in the Paris suburbs.

Boundary-layer Meteorology, 2007

We question the correlation between vertical velocity (w) on the one hand and the occurrence of c... more We question the correlation between vertical velocity (w) on the one hand and the occurrence of convective plumes in lidar reflectivity (i.e. range corrected backscatter signalPz 2 ) and depolarization ratio ( ) on the other hand in the convective boundary layer (CBL). Thermal vertical motion is directly investigated using vertical velocities measured by a ground-based Doppler lidar operating at 2 µm. This lidar provides also simultaneous measurements of lidar reflectivity. In addition, a second lidar 200 m away provides reflectivities at 0.53 and 1 µm and depolarization ratio at 0.53 µm. The time series from the two lidars are analyzed in terms of linear correlation coefficient (ρ). The main result is that the plume-like structures provided by lidar reflectivity within the CBL as well as the CBL height are not a clear signature of updrafts. It is shown that the lidar reflectivity within the CBL is frequently anti-correlated (ρ w, Pz 2 ) with the vertical velocity. On the contrary, the correlation coefficient between the depolarization ratio and the vertical velocityρ (w, ) is always positive, showing that the depolarization ratio is a fair tracer of updrafts. The importance of relative humidity on the correlation coefficient is discussed.

A Heterodyne Differential Absorption Lidar (HDIAL) for monitoring atmospheric CO 2 concentration ... more A Heterodyne Differential Absorption Lidar (HDIAL) for monitoring atmospheric CO 2 concentration is presented. The design of the lidar system is discussed including the 2.06-µm pulsed laser transmitter, heterodyne detection and signal processing. Moreover a numerical simulation in the time domain for HDIAL enables to evaluate the lidar performance for such measurements. Finally preliminary experimental results are presented and compared to the results of realistic simulations.

Journal of Geophysical Research, 2008

Applied Optics, 2006

A detailed study using both analytical and numerical calculations of direct and heterodyne differ... more A detailed study using both analytical and numerical calculations of direct and heterodyne differential absorption lidar (DIAL) techniques is conducted to complement previous studies. The DIAL measurement errors depend on key experimental parameters, some of which can be adjusted to minimize the statistical error. Accordingly, the pertinent criteria on optical thickness, the number of photons emitted at the on and off wavelengths, are discussed to reduce the relative error on the total column content or range-resolved measurements that rely on either hard target or atmospheric backscatter returns. In direct detection, the optimal optical thickness decreases from 1.3 to 0.8 when the background increases while the on-line-to-offline optimal energy ratio decreases from 3.6 to 2.7. In heterodyne detection, the minimum error is obtained for an optical thickness of 1.2 and an energy ratio of 4.3.