Frederic Fabre

The Airborne Demonstrator for the Direct-Detection Doppler Wind Lidar ALADIN on ADM-Aeolus. Part I: Instrument Design and Comparison to Satellite Instrument

Abstract The global observation of profiles of the atmospheric wind speed is the highest-priority unmet need for global numerical weather prediction. Satellite Doppler lidar is the most promising candidate to meet the requirements on global wind profile observations with high vertical resolution, precision, and accuracy. The European Space Agency (ESA) decided to implement a Doppler wind lidar mission called the Atmospheric Dynamics Mission Aeolus (ADM-Aeolus) to demonstrate the potential of the Doppler lidar technology and the expected impact on numerical weather forecasting. An airborne prototype of the instrument on ADM-Aeolus was developed to validate the instrument concept and retrieval algorithms with realistic atmospheric observations before the satellite launch. It is the first airborne direct-detection Doppler lidar for atmospheric observations, and it is operating at an ultraviolet wavelength of 355 nm. The optical design is described in detail, including the single-frequency pulsed laser and th...

Canopy height estimation in French Guiana with LiDAR ICESat/GLAS data using principal component analysis and random forest regressions

Estimating forest canopy height from large-footprint satellite LiDAR waveforms is challenging given the complex interaction between LiDAR waveforms, terrain, and vegetation, especially in dense tropical and equatorial forests. In this study, canopy height in French Guiana was estimated using multiple linear regression models and the Random Forest technique (RF). This analysis was either based on LiDAR waveform metrics extracted from the GLAS (Geoscience Laser Altimeter System) spaceborne LiDAR data and terrain information derived from the SRTM (Shuttle Radar Topography Mission) DEM (Digital Elevation Model) or on Principal Component Analysis (PCA) of GLAS waveforms. Resultsshow that the best statistical model for estimating forest height based on waveform metrics and digital elevation data is a linear regression of waveform extent, trailing edge extent, and terrain index (RMSE of 3.7 m). For the PCA based models, better canopy height estimation results were observed using a regression model that incorporated both the first 13 principal components (PCs) and the waveform extent (RMSE = 3.8 m). Random Forest regressions revealed that the best configuration for canopy height estimation used all the following metrics: waveform extent, leading edge, trailing edge, and terrain index (RMSE = 3.4 m). Waveform extent was the variable that best explained canopy height, with an importance factor almost three times higher than those for the other three metrics (leading edge, trailing edge, and terrain index). Furthermore, the Random Forest regression incorporating the first 13 PCs and the waveform extent had a slightly-improved canopy height estimation in comparison to the linear model, with an RMSE of 3.6 m. In conclusion, multiple linear regressions and RF regressions provided canopy height estimations with similar precision using either LiDAR metrics or PCs. However, a regression model (linear regression or RF) based on the PCA of waveform samples with waveform extent information is an interesting alternative for canopy height estimation as it does not require several metrics that are difficult to derive from GLAS waveforms in dense forests, such as those in French Guiana.

ALADIN: the lidar instrument for the AEOLUS mission

The ALADIN Instrument is a Doppler Wind Lidar, which will be launched in 2007 aboard the ESA Core Explorer Aeolus Mission. The main purpose of this payload is the measurement of tropospheric wind profiles on a global scale. The concept is based on a solid-state Nd:YAG laser associated with a direct detection frequency receiver. Astrium-SAS is prime contractor for the development of ALADIN. This program includes in particular the development of a Pre Development Model for the critical parts of the instrument. This paper describes the flight instrument design and reviews the achievements of the PDM activities: this will cover in particular the development status of the engineering models of the CCD detectors, front-end units and spectrometers.

Coupling potential of ICESat/GLAS and SRTM for the discrimination of forest landscape types in French Guiana

The Shuttle Radar Topography Mission (SRTM) has produced the most accurate nearly global elevation dataset to date. Over vegetated areas, the measured SRTM elevations are the result of a complex interaction between radar waves and tree crowns. In this study, waveforms acquired by the Geoscience Laser Altimeter System (GLAS) were combined with SRTM elevations to discriminate the five forest landscape types (LTs) in French Guiana. Two differences were calculated: (1) penetration depth, defined as the GLAS highest elevations minus the SRTM elevations, and (2) the GLAS centroid elevations minus the SRTM elevations. The results show that these differences were similar for the five LTs, and they increased as a function of the GLAS canopy height and of the SRTM roughness index. Next, a Random Forest (RF) classifier was used to analyze the coupling potential of GLAS and SRTM in the discrimination of forest landscape types in French Guiana. The parameters used in the RF classification were the GLAS canopy height, the SRTM roughness index, the difference between the GLAS highest elevations and the SRTM elevations and the difference between the GLAS centroid elevations and the SRTM elevations. Discrimination of the five forest landscape types in French Guiana was possible, with an overall classification accuracy of 81.3% and a kappa coefficient of 0.75. All forest LTs were well classified with an accuracy varying from 78.4% to 97.5%. Finally, differences of near coincident GLAS waveforms, one from the wet season and one from the dry season, were analyzed. The results showed that the open forest LT (LT12), in some locations, contains trees that lose leaves during the dry season. These trees allow LT12 to be easily discriminated from the other LTs that retain their leaves using the following three criteria: (1) difference between the GLAS centroid elevations and the SRTM elevations, (2) ratio of top energy in the wet season to top energy in the dry season, or (3) ratio of ground energy in the wet season to ground energy in the dry season.

Predevelopment of a direct detection Doppler wind lidar for ADM/AEOLUS mission

The Atmospheric Dynamics Mission (ADM-Aeolus) has been selected as the second of a series of Earth Explorer Core Missions. The payload aims at providing measurements of atmospheric wind profiles with global coverage. The key element of ADM-Aeolus is the Atmospheric Laser Doppler Lidar Instrument (ALADIN), a Direct Detection Doppler Lidar. The ALADIN instrument belongs to a completely new class of earth-observation lidar payloads with limited power requirements and high reliability over a three-year lifetime. Technological challenges are addressed in an early stage by the development of a Pre-Development Model (PDM), which is a functional representative model of the receiver of ALADIN. The PDM is being established to validate the technologies used in the ALADIN design, evaluate the flight-worthiness of its major subsystems and verify the instrument overall performances. The purpose of this paper is to present the latest results on the status of the ALADIN Pre-Development Model.

Results of the pre-development of ALADIN, the Direct Detection Doppler Wind Lidar for ADM/AEOLUS

Due for launch in late 2007, the Atmospheric Dynamics Mission (ADM-Aeolus) has been selected as the second Earth Explorer Core Missions within ESA Living Planet Programme. Its payload aims at providing measurements of atmospheric wind profiles with global coverage. The key elecment of ADM-Aeolus is the Atmospheric LAser Doppler Lidar INstrument (ALADIN), a Direct Detection Doppler Lidar in the ultra-violet spectral region operating with aerosol and molecular backscatter signals in parallel. The ALADIN instrument belongs to a completely new class of earth-observation payloads with limited power requirements and high reliability over a three-year lifetime. It will be the first European Lidar in space. Technological challenges are addressed in an early stage by a pre-development programme that consists of designing, manufacturing and testing a functional representative model of the receiver of ALADIN (the Pre-Development Model, PDM), and a breadboard of the transmitter. The pre-development programme is being established to validate the technologies used in the ALADIN design, evaluate the flight-worthiness of its major subsystems and verify the instrument overall performances. The purpose of this paper is to present the main achievements of the pre-development programme: environmental tests on the Pre-Development Model (thermal-vacuum and mechanical tests), development of the laser breadboards and assessment programme of the laser diodes.

Viability Statistics of GLAS/ICESat Data Acquired Over Tropical Forests

The Geoscience Laser Altimeter System (GLAS) onboard the Ice, Cloud, and land Elevation satellite (ICESat) provides a useful dataset for characterizing tropical forests. However, some GLAS data are not viable for science processing. This work aims at quantifying GLAS data viability at a global scale over all tropical forests and determining the parameters that affect this viability. The percentage of nonviable data was analyzed according to several parameters: latitude, longitude, transmitted energy, GLAS mission, local hour of acquisition, and cloud parameters. Results show that only 79.9% of all GLAS data acquired between 2003 and 2009 is viable for tropical forests characterization. By applying additional filters used by scientists in the GLAS data processing for forestry applications, only 32.8% of GLAS data acquired over tropical forests becomes exploitable. The percentage of nonviable data seems higher over the equator, for low transmitted energy, for acquisition time between 10 and 13 local hour, for high cloud humidity, and for some geographical areas. Finally, in a multifactor approach, the Random Forest regression method demonstrated that the parameters that most significantly influence the returned LiDAR signal are transmitted energy and cloud presence index.

ALADIN Doppler Wind Lidar : Recent advances

The Atmospheric Laser Doppler Instrument (ALADIN) is the payload of the ADM-Aeolus mission, which will provide direct measurements of global wind fields. It will determine the wind velocity component normal to the satellite velocity vector. The instrument is a direct detection Doppler Lidar operating in the UV, which will be the first of its kind in space. ALADIN comprises a high energy laser and a direct detection receiver operating on aerosol and molecular backscatter signals in parallel. The laser is all solid-state, based on Nd-YAG technology and high power laser diodes. The detector is a silicon CCD whose architecture allows on-chip accumulation of the returns, providing photon counting performance. The 1.5 m diameter telescope is lightweight, all made of silicon carbide. ALADIN is now in its final construction stage: the integration of the Flight Model is on-going. Most of the subsystems have been integrated; the payload performance and qualification test campaign will commence. This paper briefly describes the instrument design and provides insights on the development status and the results obtained so far. This regards in particular the receiver performance, the telescope development and the challenges of the laser. The Aeolus satellite is developed for the European Space Agency by EADS Astrium Satellites as prime contractor for the satellite and the instrument.

ALADIN: the first european lidar in space

The Atmospheric LAser Doppler INstrument (ALADIN) is the payload of the ESA’s ADMAEOLUS mission, which aims at measuring wind profiles as required by the climatology and meteorology users. ALADIN belongs to a new class of Earth Observation payloads and will be the first European Lidar in space. The instrument comprises a diode-pumped high energy Nd:YAG laser and a direct detection receiver operating on aerosol and molecular backscatter signals in parallel. In addition to the Proto- Flight Model (PFM)., two instrument models are developed: a Pre-development Model (PDM) and an Opto-Structure-Thermal Model (OSTM). The flight instrument design and the industrial team has been finalised and the major equipment are now under development. This paper describes the instrument design and performance as well as the development and verification approach. The main results obtained during the PDM programme are also reported. The ALADIN instrument is developed under prime contractorship from EADS Astrium SAS with a consortium of thirty European companies.

ADM-Aeolus follow-on missions

ADM-Aeolus is a dedicated satellite to provide global observations of vertical wind profiles. It will demonstrate the capability of a spaceborne Doppler wind lidar to accurately measure wind profiles. Thus the mission addresses one of the major deficiencies of the present Global Observing System. Simulations show that the wind profiles from Aeolus will improve Numerical Weather Prediction analyses and forecasts in the tropics and extra tropics. Aeolus is a precursor for an operational wind profiler system. It is under development for the European Space Agency with Astrium Satellites as prime contractor. Launch is planned in 2009 for a 3 year mission. There is likely to be a significant gap between the nominal end of life of Aeolus in late 2012, and the availability of wind profiles from post-EPS instruments in 2019 or later. The presentation will sketch a programme to fill this gap. It is based on copies of the present Aeolus satellite with minor modifications, such as finer vertical sampling, an alternative line-of-sight, and measures to increase lifetime. The programmatics required to fill the data gap will be discussed.