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 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

A systematic multi-technique comparison of luminescence characteristics of two reference quartz samples

MB did the experiments using the equipment belonging to the Centre for Modern Interdisciplinary Technologies, Nicolaus Copernicus University in Torun, ul. Wilenska 4, 87–100 Torun, Poland (e-mail: [email protected]) and has been financed by the grant of the National Science Centre, Poland, No. 2018/31/B/ST10/03917.International audienceFurther developments in luminescence dating, dosimetry and temperature-sensing require a deep understanding of luminescence processes and their driving parameters. Natural quartz is one of the most widely used minerals for these purposes. Still, poor reproducibility of results often hampers comparability and credibility of findings in the literature. We identified the lack of suitable natural reference samples as a pivotal problem impeding significant progression. Ideally, basic investigations involve several laboratories working on well-characterised reference quartz samples with different characteristics. Investigations should include multiple complementing methods to analyse luminescence properties and mineralogical and geochemical composition.Here, we present such a multi-technique luminescence comparison of two natural quartz samples. Next to the recently introduced Fontainebleau (FB) reference quartz, we propose another reference sample derived from the ‘Silver Sands of Morar’ (lab code ‘MR’; Scotland, UK). Our experiments confirm that both quartz samples behave fundamentally different in terms of signal composition and sensitivity. The comparative characterisation of both samples targeted electron traps via thermoluminescence (TL) and optically stimulated luminescence (OSL) techniques and luminescence centres via radioluminescence and time-resolved OSL spectrometry. In summary, we conclude that all observed differences are likely the results of divergent defect concentrations rather than variances in defects' composition (nature). The measurement data of our study are accessible open-access for inspection by others

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

Middle and Late Pleistocene environmental history of the Marsworth area, south-central England

To elucidate the Middle and Late Pleistocene environmental history of south-central England, we report the stratigraphy, sedimentology, palaeoecology and geochronology of some deposits near the foot of the Chiltern Hills scarp at Marsworth, Buckinghamshire. The Marsworth site is important because its sedimentary sequences contain a rich record of warm stages and cold stages, and it lies close to the Anglian glacial limit. Critical to its history are the origin and age of a brown pebbly silty clay (diamicton) previously interpreted as weathered till. The deposits described infill a river channel incised into chalk bedrock. They comprise clayey, silty and gravelly sediments, many containing locally derived chalk and some with molluscan, ostracod and vertebrate remains. Most of the deposits are readily attributed to periglacial and fluvial processes, and some are dated by optically stimulated luminescence to Marine Isotope Stage (MIS) 6. Although our sedimentological data do not discriminate between a glacial or periglacial interpretation of the diamicton, amino-acid dating of three molluscan taxa from beneath it indicates that it is younger than MIS 9 and older than MIS 5e. This makes a glacial interpretation unlikely, and we interpret the diamicton as a periglacial slope deposit. The Pleistocene history reconstructed for Marsworth identifies four key elements: (1) Anglian glaciation during MIS 12 closely approached Marsworth, introducing far-travelled pebbles such as Rhaxella chert and possibly some fine sand minerals into the area. (2) Interglacial environments inferred from fluvial sediments during MIS 7 varied from fully interglacial conditions during sub-stages 7e and 7c, cool temperate conditions during sub-stage 7b or 7a, temperate conditions similar to those today in central England towards the end of the interglacial, and cool temperate conditions during sub-stage 7a. (3) Periglacial activity during MIS 6 involved thermal contraction cracking, permafrost development, fracturing of chalk bedrock, fluvial activity, slopewash, mass movement and deposition of loess and coversand. (4) Fully interglacial conditions during sub-stage 5e led to renewed fluvial activity, soil formation and acidic weathering

Retinal vessel diameters and reactivity in diabetes mellitus and/or cardiovascular disease

Background: Retinal vessel calibre and vascular dilation/constriction in response to flicker light provocation may provide a measure distinguishing patients suffering from diabetes mellitus and/or cardiovascular disease. Methods: One hundred and sixteen age and sex matched patients with diabetes mellitus (DM), cardiovascular disease (CVD) and both DM and CVD (DM+CVD) underwent systemic and intraocular pressure measurements. Retinal vessel calibres were assessed using a validated computer-based program to compute central retinal artery and vein equivalents (CRVE) from monochromatic retinal images. Vessel dilation and constriction responses to flicker light provocation were assessed by continuous retinal vessel diameter recordings. Plasma endothelial markers von Willebrand factor (vWf) and soluble E selectin (sEsel) were measured by ELISA. Results: Retinal vessel calibres were comparable across groups but CRVE correlated significantly with disease duration in DM patients (r=0.57, p<0.001). Patients suffering DM only exhibited reduced arterial vasomotion at rest and reduced arterial constriction following flicker light induced vessel dilation compared to patients with CVD and those suffering both CVD+DM (p=0.030). Patients suffering from CVD+DM exhibited significant differences between each flicker cycle in regards to arterial maximum constriction (p=0.006) and time needed to reach arterial maximum dilation (p=0.004), whereas the other two groups did not show such inconsistencies between individual flicker cycles. vWf was raised in CVD+DM compared to the other two groups (p≤0.02), whilst sEsel was raised in CVD+DM compared to DM alone (p=0.044). Conclusions: Dynamic retinal vascular calibres as obtained by continuous diameter measurements using flicker light provocation can reveal subtle differences between groups suffering from CVD with and without DM. This difference in reaction pattern and lack of arterial constriction in DM may provide a suitable marker to monitor progression