This paper, “ALADIN: an atmospheric laser Doppler wind lidar instrument for wind velocity measurements from space," was presented as part of International Conference on Space Optics—ICSO 1997, held in Toulouse, France.
Methane is one of the strongest anthropogenic greenhouse gases. It contributes by its radiative forcing significantly to the global warming. For a better understanding of climate changes, it is necessary to apply precise space-based measurement techniques in order to obtain a global view on the complex processes that control the methane concentration in the atmosphere. The MERLIN mission is a joint French-German cooperation, on a micro satellite mission for space-based measurement of spatial and temporal gradients of atmospheric methane columns on a global scale. MERLIN will be the first Integrated Path Differential Absorption LIDAR for greenhouse gas monitoring from space. In contrast to passive methane missions, the LIDAR instrument allows measurements at alllatitudes, all-seasons and during night.
The Methane Remote Sensing LIDAR Mission (MERLIN) is a joint French-German cooperation on the development, launch and operation of a climate monitoring satellite, executed by the French Space Agency CNES and the German Space Administration DLR.
Methane is a powerful greenhouse gas. The radiative forcing caused by methane contributes significantly to the warming
of the atmosphere. To better understand the complex global Methane Cycle, it is necessary to apply space-based
measurements techniques in order to obtain global coverage at high precision
The Methane Remote Sensing Lidar Mission (MERLIN) is a joint French-German cooperation on a micro satellite
mission for space-based measurement of spatial and temporal gradients of atmospheric methane columns on a global
scale. MERLIN will be the first Integrated Path Differential Absorption LIDAR for methane monitoring from space. In
contrast to passive methane missions, the LIDAR instrument allows to retrieve methane fluxes at all-latitudes, allseasons
and during night as it is not relying on sunlight. First scientific studies show a substantial reduction of the prior
methane flux uncertainties in key observational regions when using synthetic MERLIN observations in the flux inversion
experiments. Furthermore, MERLIN observations can help to quantify and verify in scientific credible way national
emission reduction scenarios as formulated in the Kyoto protocol.
This paper reports on the present status of MERLIN and gives an overview on the joint mission concept with the German
LIDAR on the French satellite platform MYRIADE.
We report on a novel 2 μm laser transmitter for CO2 DIAL, based on a nanosecond parametric master oscillator-power
amplifier architecture. The master oscillator is an entangled-cavity, doubly resonant, optical parametric oscillator, based
on a type-II periodically poled Lithium Niobate nonlinear crystal. This device provides single-longitudinal-mode
radiation, with a high frequency stability and high beam quality, with no need of an additional seeding source. The 2.05
μm signal emission is amplified by multi-stage parametric amplifiers to generate more than 10 mJ. After amplification,
both the spectral purity and beam quality are maintained: we demonstrate single-longitudinal-mode emission with a
frequency stability better than 3 MHz rms, within a nearly diffraction limited beam, with a M2 quality factor close to 1.5.
The unique performances of this parametric architecture make this device a relevant transmitter for CO2 differential-absorption
LIDAR. Such approach could be readily duplicated for the detection of other greenhouse gases.
We report the development of a 355-nm lidar system for short-range wind speed measurements, using a fringe-imaging Michelson interferometer as a spectral analyzer. The instrument principle is to deduce the wind speed from the phase variations of the two-wave interference pattern provided by the interferometer. A laboratory demonstrator has been realized, which was designed in an original way to minimize the sensitivity to phase fluctuations caused by thermo-mechanical disturbances and laser drifts. An accurate signal processing has been developed, providing with estimates of five fringe parameters: intensity, contrast, periodicity, angular orientation, and phase. It is implemented in two steps: the first step uses a Fourier transform analysis and the second step a maximum-likelihood estimator. To validate the instrument principle, measurement method and signal processing alltogether, a calibrated speed measurement experiment has been performed on hard target, for which the results are shown.
Cloud altitude measurements by a 532nm backscatter Lidar and time lapsed digital photography are combined to monitor the cloud velocity profile. The cloud images are recorded in time steps of two seconds by a Nikon D100 digital camera through a 63° solid angle while the Lidar was measuring the cloud altitude. The images are recorded in 8 bits gray scale JPG format in an array of 2240×1488 pixels. To measure the angular displacement of different parts of the cloud, each image is meshed into an array of 44×29 cells, each cell contains 50×50 pixels. The grayscale density cross correlations between similar cells of successive images are computed using a MATLAB code developed by us for this application. The output products are the direction and the amount of displacement of each cell, in pixels. combining the results on cloud displacement with Lidar measurements enable to calculate the velocity vector in each cell. The resolution in velocity is about 1 ms-1 and 2° in direction. The calculation technique also is tested by simulating the cloud motion by moving the image pixels with a computer generated Gaussian velocity distribution.
The lidar systems contribute with privileged information to study environmental pollution due to its capacity to discriminate different atmospheric parameters in time and space. In this work, three of those system were developed at CEILAP laboratory in Argentina (34° 33' S, 58° 30' W): 1) a Multiwavelength lidar to characterized the atmospheric boundary layer and tropospheric aerosols using a Nd:YAG laser (10 Hz, 650 mJ @ 1064 nm); 2) a Raman lidar to measure night-time water vapor profiles, useful as a tracer of air parcel and in understanding energy transport within the atmosphere. This system utilizes an excimer laser (XeCl) (100 Hz, 300 mJ @ 308 nm), and 3) a differential absorption lidar (DIAL) to measure the stratospheric ozone profile. Two laser are used, the same excimer laser of Raman lidar and a Nd:YAG laser (30 Hz, 950 mJ @ 1064 nm). Complementary in situ measurements are also performed with a sun-photometer (AERONET-NASA); UVA, UVB and GUV radiometers (Argentina Solar Monitoring Network), pyranometer and a pyrgeometer. Recent results and the synergy between the actives and passives instruments are showed.
The speckle pattern in the image plane of the burst illumination imaging lidar system is characterized by the intensity correlation function. This speckle pattern, specific to coherent laser light, has two origins: the target roughness and the turbulence perturbation. We propose a model which takes into account both of them. For a non turbulent atmosphere, we find the classic speckle pattern given by Goodman. With a turbulent atmosphere, the perturbation along the forward and backward paths may be coupled or independent. In the coupled turbulence perturbation case, the collected intensity is amplified and the target scintillation is filtered by the receiver. For the independent turbulence perturbation case, the analysis is restricted here to a diffraction-limited atmosphere-lens system and two limiting cases are distinguished: the far-field and near-field assumptions.
An analysis of aerosols optical parameters is made using the sun photometer measurements taken at CEILAP in 2000. The sun photometer deployed in the Buenos Aires suburb is part of AERONET. Using the present data set, time series of key optical parameters such as the optical depth at 500 nm and Angstrom coefficient of the wavelength scaling law are derived. Clustering the observations by mean of a statistical analysis we can infer the pollution episodes in the Buenos Aires area. They can be either of local or regional origins, depending on the meteorological conditions prevailing over central Argentina.
Christian Werner, Pierre Flamant, Oliver Reitebuch, Friedrich Koepp, Juergen Streicher, Stephan Rahm, Engelbert Nagel, Michael Klier, H. Herrmann, Claude Loth, P. Delville, Ph. Drobinski, B. Romand, Ch. Boitel, D. Oh, M. Lopez, Mireille Meissonnier, Didier Bruneau, Alain Dabas
Pierre Flamant, Christian Werner, Friedrich Koepp, Claude Loth, P. Delville, Oliver Reitebuch, Ch. Boitel, Didier Bruneau, Ph. Drobinski, R. Haering, H. Herrmann, Michael Klier, M. Lopez, Mireille Meissonnier, Engelbert Nagel, B. Romand, L. Sauvage, M. Schrecker, Juergen Streicher, Guenter Wildgruber
An airborne coherent Doppler Lidar to retrieve mesoscale wind fields has been developed in the frame of the Franco- German WIND project. The instrument is based on a pulsed CO2 laser transmitter, heterodyne detection and wedge scanner. The performance of the instrument operating on the ground and in the aircraft is reported.
Since 1996 a lidar station is operated routinely at CEILAP (CITEFA-CONTCET), located in Buenos Aires suburb. The scientific objectives are related to environmental and atmospheric radiative budget studies. Two backscatter lidars operating at 532 nm and 308 nm are used to document the atmospheric boundary layer dynamics, and cirrus clouds and tropospheric aerosols radiative properties. The lidar measurements are made in conjuction with visible radiometer measurements on the same site and radiosoundings made twice daily at the nearby meteorological station. Atmospheric boundary layer measurements during daytime are conducted since 1996 on a regular basis using the backscatter lida.r operating at 532 nm, and more recently using a second lidar on the same site operating at 308 nm. Similarly, cirrus clouds and tropospheric aerosols measurements are conducted during clear days (e.g. without low clouds) since 1996 using the backscatter lidars. Since the late 1997 more interest is given to urban ABL dynamics in connection with pollution events, and biomass burning taking place in the tropical South America. It happened that such plumes can be frequently transported over the Buenos Aires area by large scale circulation
A feasibility study for simultaneous range resolved measurements of minor species concentration by the differential absorption lidar (DIAL) technique and wind velocity using a pulsed carbon-dioxide HCLR is addressed. The LMD heterodyne coherent laser radar (HCLR) is used to investigate the statistical properties of the distributed aerosols backscattered power and Doppler frequency shift estimation as a function of range gate. We derive a trade off between accuracy for wind velocity and species concentration. We determine an optimal pulse bandwidth accounting for pulse duration and frequency chirp to fulfill the requirements on measurement accuracies, range resolution and time resolution. We show that for accurate concentration estimations, an accumulation on a few tens shots is required. We introduce a detector array in order to improve the performances with respect to statistical distribution.
AEROSPATIALE, leading a European team, has just conducted a successful study, under ESA contract, to demonstrate the feasibility of a spaceborne Doppler wind lidar instrument meeting the scientific requirements of wind velocity measurements from space with high spatial resolution. A first parametric investigation, based upon the initial set of mission requirements, and supported by dedicated models and detailed trade-off studies, took account of capabilities of most promising signal processing algorithms and calibration/validation constraints: it yielded a large conically scanned instrument deemed technologically risky. A risk analysis was then carried out to propose a less challenging instrument meeting most key mission requirements. The fixed line-of-sight concept with return signal accumulation appeared as most attractive. A second set of requirements agreed upon by scientific users was therefore issued, with relaxed constraints mainly on horizontal resolution, keeping roughly the same level of wind velocity measurement accuracy. A second instrument and subsystem trade-off was then performed to eventually produce an attractive instrument concept based upon a pair of small diameter telescopes each one associated to one scanning mirror rotating stepwise around the telescope axis, which drastically reduces the detection bandwidth. Following the main contract, studies of accommodation on the International Space Station have been performed, confirming the interest of such an instrument for wind measurements from space.
Gerard Brogniez, Helene Chepfer, Yves Fouquart, Jean-Francois Gayet, Pierre Flamant, Rene Valentin, Jacques Pelon, Vincent Trouillet, Cyril Flamant, Franck Albers
The Intensive Field Observation of E1TCREX 94. (EUropean Cloud and Radiation EXperiment)
held in April 1994 in Brest, France. was a three-aircraft and ground-based experiment dedicated
to the development and the validation of algorithms to derive relations between cirrus radiative
properties and cirrus microstructure from remote sensing measurements. A niultiangular visible
radiometer with polarization capabilities called 1OLDER (POLarization and Directionality of
Earth Reflectances) was installed doviiward. on-board the instrumented German Falcon of the
DLR. This aircraft was also equipped with upwar(l and downward pyra.nometers and pyrgeometers
and with PMS probe. The second instrumented aircraft was the ARAT (French Fokker 27 of
INSU). It was equipped with the upward lidar LEANDRE (\ = O.53jtm), with a photometer
POLDER looking downward, an(1 with upward and downward infrared radiometers
(;\ E [9.5gm - 11.5um]) and upward and downward pyraliometers and pyrgeometers. During
the upward and downward observations of the Fokker under cirrus, the Falcon performed optical
measurements above and microphysical measurements i uside clouds. A ground-based station with
Lidar, infrared radiometric and sunphol.omet.er measurenients w'as also operating during the same
time. The third aircraft was specially devoted to the low level clouds and was equipped with a
Fast FSSP, upward and downw'ard pyia noiieters and pvrgeometers and upward and downward
infrared radiometers.
During this intensive field of observations. four well documented cirrus cases were observed from
aircraft and from the ground. Ana1ve of these observations is I)resented by comparison to a
radiative transfer calculations. These calculations are performed taking into account the optical
properties of hexagonal ice crystals obtained by a. ray-tracing method. All theses observations
allow to determine a. bulk Properties of cirrus clouds in particular a. ra.dia.t.ively equivalent microstructure.
AEROSPATIALE, leading a European team, has just conducted a successful study, under ESA contract, to demonstrate the feasibility of a spaceborne Doppler wind lidar instrument meeting the scientific requirements of wind velocity measurements from space with high spatial resolution. A first parametric investigation, based upon the initial set of mission requirements, and supported by dedicated models and detailed trade-off studies, took account of capabilities of the most promising signal processing algorithms and calibration/validation constrains: it yielded a large conically scanned instrument deemed technologically risky. A risk analysis was then carried out to propose a less challenging instrument meeting most key mission requirements. The fixed line-of-sight concept with return signal accumulation appeared as most attractive. A second set of requirements agreed upon by scientific users was therefore issued, with relaxed constraints mainly on horizontal resolution, keeping roughly the same level of wind velocity measurement accuracy. A second instrument and subsystem trade- off was then performed to eventually produce an attractive instrument concept based upon a pair of small diameter telescopes each one associated to one scanning mirror rotating stepwise around the telescope axis, which drastically reduces the detection bandwidth. Following the main contract, studies of accommodation on the International Space Station have been performed, confirming the interest of such an instrument for wind measurements from space.
In meteorological and climatological fields, the scientific community will increasingly need global measurements of key atmospheric parameters with high spatial resolution (horizontal as well as vertical): the spaceborne lidars are the most suitable instruments for those missions. While backscatter lidar (ATLID, currently studied as ESA) is presently first candidate for space deployment, the next generation of lidars will be DIAL and Doppler wind lidars, presenting a higher level of complexity, mainly due to the large power and complex signal processing required. The present considered wind lidars are based on CO2 lasers, whose space compliance still needs confirmation, while alexandrite lasers are considered for water vapor and temperature measurements, but they need flashlamp pumping which poses a lot of several thermal constraints and lifetime problems: on the other side, the recent developments achieved in solid-state technology allow to envisage diode pumping as most promising possibility for both previous applications.
Claude Loth, Alain Dabas, Pierre Flamant, D. Oh, J. Delume, B. Romand, Jacques Pelon, Didier Bruneau, J.-L. Zarader, Christian Werner, Friedrich Koepp, H. Herrmann, Michael Klier, W. Nagel, Stephan Rahm, Juergen Streicher, J. Wildgruber
WIND is a joint project between France (CNRS-CNES-Meteo France) and Germany (DLR) to develop an airborne wind Doppler lidar for meteorological applications. The instrument specifications are derived from the measurement objectives as well as the state-of-the-art in technology. Presently an operational airborne wind lidar can be designed around the CO2 laser technology, heterodyne detection, and a conical scanning of the lidar line-of-sight to sample the atmospheric wind field. The 10-micron spectral domain is suitable for long range measurements for it corresponds to an atmospheric window and an adequate backscatter coefficient in the troposphere. The first flights are scheduled early 1995 on board the Falcon 20 operated by DLR.
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