Pseudo-random single photon counting for space-borne atmospheric sensing applications

The ability to accurately observe the Earth's carbon cycles from space gives scientists an important tool to analyze climate change. Current space-borne Integrated-Path Differential Absorption (IPDA) Iidar concepts have the potential to meet this need. They are mainly based on the pulsed time-offlight 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 solidstate 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 Earthobserving missions

Determination of the emission rates of CO2 point sources with airborne lidar

We report on CO2 emissions of a coal-fired power plant derived from flight measurements performed with the IPDA lidar CHARM-F during the CoMet campaign in spring 2018. Despite the results being in broad agreement with reported emissions, we observe strong variations between successive flyovers. Using a high-resolution large eddy simulation, we identify strong atmospheric turbulence as the cause for the variations and recommend more favorable measurement conditions for future campaign planning

Random-modulation differential absorption lidar based on semiconductor lasers and single photon counting for atmospheric CO2 sensing

Carbon dioxide (CO2) is the major anthropogenic greenhouse gas contributing to global warming and climate change. Its concentration has recently reached the 400-ppm mark, representing a more than 40 % increase with respect to its level prior to the industrial revolution. However, the exchanges of CO2 between the atmosphere and the natural or anthropogenic sources/sinks at the Earth’s surface are still poorly quantified. A better understanding of these surface fluxes is required for appropriate policy making. At present, the concentrations of CO2 are mainly measured in-situ at a number of surface stations that are unevenly distributed over the planet. Air-borne and spaceborne missions have the potential to provide a denser and better distributed set of observations to complement this network. In addition to passive measurement techniques, the integrated path differential absorption (IPDA) lidar technique [1] has been found to be potentially suited for fulfilling the stringent observational requirements. It uses strong CO2 absorption lines in the 1.57 or in the 2 μm region and the backscatter from the ground or a cloud top to measure the column averaged CO2 mixing ratio (XCO2) with high precision and accuracy. The European Space Agency (ESA), has studied this concept in the frame of the Advanced Space Carbon and Climate Observation of Planet Earth (A-SCOPE) mission in 2006. Although a lack of technological readiness prevented its selection for implementation, recommendations have been formulated to mature the instrument concept by pursuing technological efforts [2]. During the last years, a tremendous effort in the assessment of the optimal CO2 active sensing methodology is being performed in the context of NASA mission Active Sensing of CO2 Emissions over Nights, Days, and Season (ASCENDS

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

High brightness semiconductor lasers as transmitters for space lidar systems

High brightness semiconductor lasers are potential transmitters for future space lidar systems. In the framework of the European Project BRITESPACE, we propose an all-semiconductor laser source for an Integrated Path Differential Absorption lidar system for column-averaged measurements of atmospheric CO2 in future satellite missions. The complete system architecture has to be adapted to the particular emission properties of these devices using a Random Modulated Continuous Wave approach. We present the initial experimental results of the InGaAsP/InP monolithic Master Oscillator Power Amplifiers, providing the ON and OFF wavelengths close to the selected absorption line around 1572 nm

Atmospheric CO2 Sensing with a Random Modulation Continuous Wave Integrated Path Differential Absorption Lidar

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. Co-located 2 km horizontal trial path experiments with a pulsed system and insitu measurements were performed for comparison. The RM-CW IPDA lidar instrument shows a relative accuracy of the order of about 10% or 40 ppm CO2 concentration in absolute terms. The measurements qualitatively demonstrate the feasibility of CO2 IPDA measurements with a RM-CW system

LIDAR System based on a High Brightness Semiconductor Laser and Single Photon Counting Detection for Space -borne Atmospheric CO2 Monitoring

We theoretically investigate a dynamical regime, experimentally observed in monolithically integrated master oscillator power amplifiers emitting at 1.5 7 μm, consisting in large emission wavelength jumps of the device from the Bragg wavelength to that of the gain peak. Our analysis is based on numerical simulations by means of a travelling wave model that incorporates spatial effects such as spatial hole burning and coupled-cavity effects. Thermal effects are included by considering the optical response of the quantum well active medium within the quasi-equilibrium approximation at finite temperature, with a phenomenological description of the redshift of the gain peak and the changes in the background material refractive index by means of self- and cross-heating coefficients for both sections. We find that whereas the thermally-induced index changes are the responsible of the modal jumps between consecutive modes, the carrier-induced refractive index changes are the responsible of the jumps occurring between the Bragg wavelength and the gain peak

The French-German Climate Monitoring Initiative on global observations of atmospheric CH4

Knowledge of concentrations and fluxes of the most important long-lived greenhouse carbon dioxide (CO2) and methane (CH4) is a key element of climate change research. We report on the status of the French-German Climate Monitoring Initiative which aims on global observations of atmospheric methane. This mission which has recently been selected for joint Phase0/A studies at CNES and DLR is intended to improve our understanding of the Global Methane Cycle and the exploration of the nature of the processes which govern the exchange of methane between atmosphere and biosphere. As a novel feature, the observational instrument of this mission will be an Integrated Path Differential-Absorption (IPDA) lidar system embarked on the French spacecraft MYRIADE for the measurement of the column-weighted dry-air mixing ratio of CH4. This data will be provided by the lidar technique with no bias due to particles scattering in the light path and can directly be used as input for flux inversion calculation. Other geophysical quantities which can be derived from the measurements comprise information on vegetation height, cloud layers, and surface retro-reflectance

Towards a greenhouse gas lidar in space

Highly accurate measurements of atmospheric carbon dioxide (CO2) and methane (CH4) by a space-borne lidar will help to substantially improve knowledge of greenhouse gas fluxes. The method of integrated-path differential-absorption lidar for total column measurements has proven to be a suitable means for CH4 detection in natural gas leak surveillance and active remote sensing of CO2. This pioneering work facilitated the instrument development of an advanced greenhouse gas lidar on HALO and set the stage for the development of a CH4-lidar in space instrument foreseen in the Franco-German climate mission MERLIN