Mathieu Quatrevalet

Optical parametric oscillators and amplifiers for airborne and spaceborne active remote sensing of CO2 and CH4

Carbon dioxide (CO2) and methane (CH4) are the most important of the greenhouse gases that are directly influenced by human activities. The Integrated Path Differential Absorption (IPDA) lidar technique using hard target reflection in the near IR (1.57μm and 1.64μm) to measure the column-averaged dry air mixing ratio of CO2 and CH4 with high precision and low bias has the potential to deliver measurements from space and air that are needed to understand the sources and sinks of these greenhouse gases. CO2 and CH4 IPDA require tunable laser sources at 1.57 μm and 1.64 μm that coincide with appropriate absorption lines of these species having high pulse energy and average power as well as excellent spectral and spatial properties. Within this study we have realized more than 50mJ of pulse energy in the near IR coincident with appropriate absorption lines using an injection-seeded optical parametric oscillator-amplifier system pumped at 100 Hz. At the same time this device showed excellent spectral and spatial properties. Bandwidths of less than 100 MHz with a high degree of spectral purity (> 99.9 %) have been achieved. The frequency stability was likewise excellent. The M2-factor was better than 2.3. Owing to these outstanding properties optical parametric devices are currently under investigation for the CH4 lidar instrument on the projected French-German climate satellite MERLIN. A similar device is under development at DLR for the lidar demonstrator CHARM-F which will enable the simultaneous measurement of CO2 and CH4 from an airborne platform.

Pseudo-Random Single Photon Counting for space-borne atmospheric sensing applications

The ability to accurately observe the Earths carbon cycles from space gives scientists an important tool to analyze climate change. Current space-borne Integrated-Path Differential Absorption (IPDA) lidar concepts have the potential to meet this need. They are mainly based on the pulsed time-of-flight principle, in which two high energy pulses of different wavelengths interrogate the atmosphere for its transmission properties and are backscattered by the ground. In this paper, feasibility study results of a Pseudo-Random Single Photon Counting (PRSPC) IPDA lidar are reported. The proposed approach replaces the high energy pulsed source (e.g. a solid-state laser), with a semiconductor laser in CW operation with a similar average power of a few Watts, benefiting from better efficiency and reliability. The auto-correlation property of Pseudo-Random Binary Sequence (PRBS) and temporal shifting of the codes can be utilized to transmit both wavelengths simultaneously, avoiding the beam misalignment problem experienced by pulsed techniques. The envelope signal to noise ratio has been analyzed, and various system parameters have been selected. By restricting the telescopes field-of-view, the dominant noise source of ambient light can be suppressed, and in addition with a low noise single photon counting detector, a retrieval precision of 1.5 ppm over 50 km along-track averaging could be attained. We also describe preliminary experimental results involving a negative feedback Indium Gallium Arsenide (InGaAs) single photon avalanche photodiode and a low power Distributed Feedback laser diode modulated with PRBS driven acoustic optical modulator. The results demonstrate that higher detector saturation count rates will be needed for use in future spacebourne missions but measurement linearity and precision should meet the stringent requirements set out by future Earth-observing missions.

INNOSLAB-based single-frequency MOPA for airborne lidar detection of CO2 and methane

For the CO2 and CH4 IPDA lidar CHARM-F two single frequency Nd:YAG based MOPA systems were developed. Both lasers are used for OPO/OPA-pumping in order to generate laser radiation at 1645 nm for CH4 detection and 1572 nm for CO2 detection. By the use of a Q-switched, injection seeded and actively length-stabilized oscillator and a one-stage INNOSLAB amplifier about 85 mJ pulse energy could be generated for the CH4 system. For the CO2 system the energy was boosted in second INNOSLAB-stage to about 150 mJ. Both lasers emit laser pulses of about 30 ns pulse duration at a repetition rate of 100 Hz.

Analysis of a random modulation single photon counting differential absorption lidar system for space-borne atmospheric CO 2 sensing

The ability to observe the Earths carbon cycles from space provides scientists an important tool to analyze climate change. Current proposed systems are mainly based on pulsed integrated path differential absorption lidar, in which two high energy pulses at different wavelengths interrogate the atmosphere sequentially for its transmission properties and are back-scattered by the ground. In this work an alternative approach based on random modulation single photon counting is proposed and analyzed; this system can take advantage of a less power demanding semiconductor laser in intensity modulated continuous wave operation, benefiting from a better efficiency, reliability and radiation hardness. Our approach is validated via numerical simulations considering current technological readiness, demonstrating its potential to obtain a 1.5 ppm retrieval precision for 50 km averaging with 2.5 W average power in a space-borne scenario. A major limiting factor is the ambient shot noise, if ultra-narrow band filtering technology could be applied, 0.5 ppm retrieval precision would be attainable.

Investigations on Frequency and Energy References for a Space-borne Integrated Path Differential Absorption Lidar

For a prediction of the rate of climate change during the 21st century, there is an urgent need to better understand the global carbon cycle, in particular the processes that control the carbon flows between the various reservoirs, and their interactions with the climate system. Atmospheric carbon dioxide (CO2) represents the main atmospheric phase of this biogeochemical cycle. Due to human activities, the concentration of this most important of the Earth’s greenhouse gases has grown from a pre-industrial average atmospheric mole fraction of about 280 parts per million volume (ppm) to 390.5 ppm in 2011 which is an increase of 40%. CO2 contributes to ~63% to the overall global radiative forcing.

Development and First Results of a new Near-IR Airborne Greenhouse Gas Lidar

An airborne lidar system has been developed to measure the two most important anthropogenic greenhouse gases, carbon dioxide and methane. The instrumental setup and first results onboard the German research aircraft HALO are discussed.

High-brightness all semiconductor laser at 1.57 μm for space-borne lidar measurements of atmospheric carbon dioxide: device design and analysis of requirements

The availability of suitable laser sources is one of the main challenges in future space missions for accurate measurement of atmospheric CO2. The main objective of the European project BRITESPACE is to demonstrate the feasibility of an all-semiconductor laser source to be used as a space-borne laser transmitter in an Integrated Path Differential Absorption (IPDA) lidar system. We present here the proposed transmitter and system architectures, the initial device design and the results of the simulations performed in order to estimate the source requirements in terms of power, beam quality, and spectral properties to achieve the required measurement accuracy. The laser transmitter is based on two InGaAsP/InP monolithic Master Oscillator Power Amplifiers (MOPAs), providing the ON and OFF wavelengths close to the selected absorption line around 1.57 μm. Each MOPA consists of a frequency stabilized Distributed Feedback (DFB) master oscillator, a modulator section, and a tapered semiconductor amplifier optimized to maximize the optical output power. The design of the space-compliant laser module includes the beam forming optics and the thermoelectric coolers. The proposed system replaces the conventional pulsed source with a modulated continuous wave source using the Random Modulation-Continuous Wave (RM-CW) approach, allowing the designed semiconductor MOPA to be applicable in such applications. The system requirements for obtaining a CO2 retrieval accuracy of 1 ppmv and a spatial resolution of less than 10 meters have been defined. Envelope estimated of the returns indicate that the average power needed is of a few watts and that the main noise source is the ambient noise.

Atmospheric CO

We propose an integrated path differential absorption (IPDA) lidar system based on a hybrid master oscillator power amplifier (MOPA) and single photon counting detection for column-averaged measurements of atmospheric CO2. The random modulated continuous wave (RM-CW) approach has been selected as the best suited to the average output power obtained from hybrid and monolithically integrated MOPAs. A compact RM-CW IPDA lidar instrument has been designed and fabricated. High-sensitivity and low-noise single photon counting has been used for the receiver. Colocated 2-km horizontal trial path experiments with a pulsed system and in situ measurements were performed for comparison. The RM-CW IPDA lidar instrument shows a relative accuracy of the order of about ±10% or ±40 parts per million CO2 concentration in absolute terms. The measurements qualitatively demonstrate the feasibility of CO2 IPDA measurements with an RM-CW system.

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We propose an integrated path differential absorption lidar system based on all-semiconductor laser sources and single photon counting detection for column-averaged measurements of atmospheric CO2. The Random Modulated Continuous Wave (RM-CW) approach has been selected as the best suited to semiconductor lasers. In a RM-CW lidar, a pseudo random sequence is sent to the atmosphere and the received signal reflected from the target is correlated with the original sequence in order to retrieve the path length. The transmitter design is based on two monolithic Master Oscillator Power Amplifiers (MOPAs), providing the on-line and off-line wavelengths close to the selected absorption line around 1.57 µm. Each MOPA consists of a frequency stabilized distributed feedback master oscillator, a bent modulator section, and a tapered amplifier. This design allows the emitters to deliver high power and high quality laser beams with good spectral properties. An output power above 400 mW with a SMSR higher than 45 dB and modulation capability have been demonstrated. On the side of the receiver, our theoretical and experimental results indicate that the major noise contribution comes from the ambient light and detector noise. For this reason narrow band optical filters are required in the envisioned space-borne applications. In this contribution, we present the latest progresses regarding the design, modeling and characterization of the transmitter, the receiver, the frequency stabilization unit and the complete system.

Sensing with a Random Modulation Continuous Wave Integrated Path Differential Absorption Lidar

Emissions from strong point sources, primarily large power plants, are a major portion of the total CO2 emissions. International climate agreements will increasingly require their independent monitoring. A satellite-based, double-pulse, direct detection Integrated Path Differential Absorption (IPDA) Lidar with the capability to actively target point sources has the potential to usefully complement the current and future GHG observing system. This initial study uses simple approaches to determine the required Lidar characteristics and the expected skill of spaceborne Lidar plume detection and emission quantification. A Gaussian plume model simulates the CO2 or CH4 distribution downstream of the sources. A Lidar simulator provides the instrument characteristics and dimensions required to retrieve the emission rates, assuming an ideal detector configuration. The Lidar sampling frequency, the footprint distance to the emitting source and the error of an individual measurement are of great importance. If wind speed and direction are known and environmental conditions are ideal, an IPDA Lidar on a 500-km orbit with 2 W average power in the 1.6 µm CO2 absorption band, 500 Hz pulse repetition frequency, 50 m footprint at sea level and 0.7 m telescope diameter can be expected to measure CO2 emission rates of 20 Mt/a with an average accuracy better than 3% up to a distance of 3 km away from the source. CH4 point source emission rates can be quantified with comparable skill if they are larger than 10 kt/a, or if the Lidar pulse repetition frequency is augmented.