Averaging bias correction for the future space-borne methane IPDA lidar mission MERLIN

The CNES (French Space Agency) and DLR (German Space Agency) project MERLIN is a future integrated path differential absorption (IPDA) lidar satellite mission that aims at measuring methane dry-air mixing ratio columns (XCH4) in order to improve surface flux estimates of this key greenhouse gas. To reach a 1&thinsp;% relative random error on XCH4 measurements, MERLIN signal processing performs an averaging of data over 50&thinsp;km along the satellite trajectory. This article discusses how to process this horizontal averaging in order to avoid the bias caused by the non-linearity of the measurement equation and measurements affected by random noise and horizontal geophysical variability. Three averaging schemes are presented: averaging of columns of XCH4, averaging of columns of differential absorption optical depth (DAOD) and averaging of signals. The three schemes are affected both by statistical and geophysical biases that are discussed and compared, and correction algorithms are developed for the three schemes. These algorithms are tested and their biases are compared on modelled scenes from real satellite data. To achieve the accuracy requirements that are limited to 0.2&thinsp;% relative systematic error (for a reference value of 1780&thinsp;ppb), we recommend performing the averaging of signals corrected from the statistical bias due to the measurement noise and from the geophysical bias mainly due to variations of methane optical depth and surface reflectivity along the averaging track. The proposed method is compliant with the mission relative systematic error requirements dedicated to averaging algorithms of 0.06&thinsp;% (±1&thinsp;ppb for XCH4 = 1780 ppb) for all tested scenes and all tested ground reflectivity values.</p

The dual developmental origin of spinal cerebrospinal fluid-contacting neurons gives rise to distinct functional subtypes.

Chemical and mechanical cues from the cerebrospinal fluid (CSF) can affect the development and function of the central nervous system (CNS). How such cues are detected and relayed to the CNS remains elusive. Cerebrospinal fluid-contacting neurons (CSF-cNs) situated at the interface between the CSF and the CNS are ideally located to convey such information to local networks. In the spinal cord, these GABAergic neurons expressing the PKD2L1 channel extend an apical extension into the CSF and an ascending axon in the spinal cord. In zebrafish and mouse spinal CSF-cNs originate from two distinct progenitor domains characterized by distinct cascades of transcription factors. Here we ask whether these neurons with different developmental origins differentiate into cells types with different functional properties. We show in zebrafish larva that the expression of specific markers, the morphology of the apical extension and axonal projections, as well as the neuronal targets contacted by CSF-cN axons, distinguish the two CSF-cN subtypes. Altogether our study demonstrates that the developmental origins of spinal CSF-cNs give rise to two distinct functional populations of sensory neurons. This work opens novel avenues to understand how these subtypes may carry distinct functions related to development of the spinal cord, locomotion and posture

The mobile Water vapor Aerosol Raman LIdar and its implication in the framework of the HyMeX and ChArMEx programs: application to a dust transport process

International audienceThe increasing importance of the coupling of water and aerosol cycles in environmental applications requires observation tools that allow simultaneous measurements of these two fundamental processes for climatological and meteorological studies. For this purpose, a new mobile Raman lidar, WALI (Water vapor and Aerosol LIdar), has been developed and implemented within the framework of the international HyMeX and ChArMEx programs. This paper presents the key properties of this new device and its first applications to scientific studies. The lidar uses an eye-safe emission in the ultraviolet range at 354.7 nm and a set of compact refractive receiving telescopes. Cross-comparisons between rawinsoundings performed from balloon or aircraft and lidar measurements have shown a good agreement in the derived water vapor mixing ratio (WVMR). The discrepancies are generally less than 0.5 g kg −1 and therefore within the error bars of the respective instruments. A detailed study of the uncertainty of the WVMR retrieval was conducted and shows values between 7 and 11 %, which is largely constrained by the quality of the lidar calibration. It also proves that the lidar is able to measure the WVMR during daytime over a range of about 1 km. In addition the WALI system provides measurements of aerosol optical properties such as the lidar ratio (LR) or the particulate depolarization ratio (PDR). An important example of scientific application addressing the main objectives of the HyMeX and ChArMEx programs is then presented, following an event of desert dust aerosols over the Balearic Islands in October 2012. This dust intrusion may have had a significant impact on the intense pre-cipitations that occurred over southwestern France and the Spanish Mediterranean coasts. During this event, the LR and PDR values obtained are in the ranges of ∼ 45-63 ± 6 and 0.10-0.19 ± 0.01 sr, respectively, which is representative of dust aerosols. The dust layers are also shown to be associated with significant WVMR, i.e., between 4 and 6.7 g kg −1

Comparison of IASI water vapor retrieval with H 2 O-Raman lidar in the framework of the Mediterranean HyMeX and ChArMEx programs

International audienceThe Infrared Atmospheric Sounding Interferom-eter (IASI) is a new generation spaceborne passive sensor mainly dedicated to meteorological applications. Operational Level-2 products have been available via the European Organisation for the Exploitation of Meteorological Satellites (EUMETSAT) for several years. In particular, vertical profiles of water vapor measurements are retrieved from infrared radiances at the global scale. Nevertheless, the robustness of such products has to be checked because only a few validations have been reported. For this purpose, the field experiments that were held during the HyMeX and ChArMEx international programs are a very good opportunity. A H 2 O-Raman lidar was deployed on the Balearic island of Menorca and operated continuously for ∼ 6 and ∼ 3 weeks during fall 2012 (Hydrological cycle in the Mediterranean eXperiment-HyMeX) and summer 2013 (Chemistry-Aerosol Mediter-ranean Experiment-ChArMEx), respectively. It measured simultaneously the water vapor mixing ratio and aerosol optical properties. This article does not aim to describe the IASI operational H 2 O inversion algorithm, but to compare the vertical profiles derived from IASI onboard (meteorolog-ical operational) MetOp-A and the ground-based lidar measurements to assess the reliability of the IASI operational product for the water vapor retrieval in both the lower and middle troposphere. The links between water vapor contents and both the aerosol vertical profiles and the air mass origins are also studied. About 30 simultaneous observations, performed during nighttime in cloud free conditions, have been considered. For altitudes ranging from 2 to 7 km, root mean square errors (correlation) of ∼ 0.5 g kg −1 (∼ 0.77) and ∼ 1.1 g kg −1 (∼ 0.72) are derived between the operational IASI product and the available lidar profiles during HyMeX and ChArMEx, respectively. The values of both root mean square error and correlation are meaningful and show that the operational Level-2 product of the IASI-derived vertical water vapor mixing ratio can be considered for meteorological and climatic applications, at least in the framework of field campaigns

Lidar profiling of aerosol optical properties from Paris to Lake Baikal (Siberia)

International audienceIn June 2013, a ground-based mobile lidar performed the ∼ 10 000 km ride from Paris to Ulan-Ude, near Lake Baikal, profiling for the first time aerosol optical properties all the way from western Europe to central Siberia. The instrument was equipped with N 2-Raman and depolarization channels that enabled an optical speciation of aerosols in the low and middle troposphere. The extinction-to-backscatter ratio (also called lidar ratio or LR) and particle depolar-ization ratio (PDR) at 355 nm have been retrieved. The LR in the lower boundary layer (300-700 m) was found to be 63 ± 17 sr on average during the campaign with a distribution slightly skewed toward higher values that peaks between 50 and 55 sr. Although the difference is small, PDR values observed in Russian cities (> 2 %, except after rain) are systematically higher than the ones measured in Europe (< 1 %), which is probably an effect of the lifting of terrige-nous aerosols by traffic on roads. Biomass burning layers from grassland or/and forest fires in southern Russia exhibit LR values ranging from 65 to 107 sr and from 3 to 4 % for the PDR. During the route, desert dust aerosols originating from the Caspian and Aral seas regions were characterized for the first time, with a LR (PDR) of 43 ± 14 sr (23 ± 2 %) for pure dust. The lidar observations also showed that this dust event extended over 2300 km and lasted for ∼ 6 days. Measurements from the Moderate Resolution Imaging Spectrometer (MODIS) show that our results are comparable in terms of aerosol optical thickness (between 0.05 and 0.40 at 355 nm) with the mean aerosol load encountered throughout our route

CO₂ DIAL activities conducted at IPSL and ESA to study biosphere-atmosphere processes and climate change issues

International audienceSince 2002, the Institut-Pierre-Simon-Laplace (IPSL) is involved in several projects addressing CO2 monitoring by Lidar for basic environmental science and spaceborne applications. The activity started with the development of a 2-µm CO2 heterodyne DIAL project. The first instrumental activity gave rise to two new programs to develop a transportable and an airborne CO2 DIAL. In 2006, "A-SCOPE" a proposal aiming at a spaceborne CO2 mission has been submitted to the European Space Agency (ESA) in response to a Call for Ideas in the framework of the Earth Explorer Mission program. A-SCOPE has been selected with 5 other missions for phase "0" study and preliminary feasibility assessments by 2 European industrial consortia. A-SCOPE and the 5 other potential missions will be presented in Lisbon and discussed by the Users Community during a meeting on 20-21 January 2009. The various steps will be presented at the conference to show explicitly the building phase of knowledge and expertise in innovative instrumentation that are requested to contribute to both basic environmental science and a new potential mission like "A-SCOPE"

CO₂ DIAL activities conducted at IPSL and ESA to study biosphere-atmosphere processes and climate change issues

International audienceSince 2002, the Institut-Pierre-Simon-Laplace (IPSL) is involved in several projects addressing CO2 monitoring by Lidar for basic environmental science and spaceborne applications. The activity started with the development of a 2-µm CO2 heterodyne DIAL project. The first instrumental activity gave rise to two new programs to develop a transportable and an airborne CO2 DIAL. In 2006, "A-SCOPE" a proposal aiming at a spaceborne CO2 mission has been submitted to the European Space Agency (ESA) in response to a Call for Ideas in the framework of the Earth Explorer Mission program. A-SCOPE has been selected with 5 other missions for phase "0" study and preliminary feasibility assessments by 2 European industrial consortia. A-SCOPE and the 5 other potential missions will be presented in Lisbon and discussed by the Users Community during a meeting on 20-21 January 2009. The various steps will be presented at the conference to show explicitly the building phase of knowledge and expertise in innovative instrumentation that are requested to contribute to both basic environmental science and a new potential mission like "A-SCOPE"

CO₂ DIAL activities conducted at IPSL and ESA to study biosphere-atmosphere processes and climate change issues

International audienceSince 2002, the Institut-Pierre-Simon-Laplace (IPSL) is involved in several projects addressing CO2 monitoring by Lidar for basic environmental science and spaceborne applications. The activity started with the development of a 2-µm CO2 heterodyne DIAL project. The first instrumental activity gave rise to two new programs to develop a transportable and an airborne CO2 DIAL. In 2006, "A-SCOPE" a proposal aiming at a spaceborne CO2 mission has been submitted to the European Space Agency (ESA) in response to a Call for Ideas in the framework of the Earth Explorer Mission program. A-SCOPE has been selected with 5 other missions for phase "0" study and preliminary feasibility assessments by 2 European industrial consortia. A-SCOPE and the 5 other potential missions will be presented in Lisbon and discussed by the Users Community during a meeting on 20-21 January 2009. The various steps will be presented at the conference to show explicitly the building phase of knowledge and expertise in innovative instrumentation that are requested to contribute to both basic environmental science and a new potential mission like "A-SCOPE"