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Measuring water vapor (WV) in the troposphere, where almost the totality of WV is found, is a key point to understand atmospheric composition and dynamics.In particular, a critical problem is to perform systematic WV measurements in the lowest part of the troposphere (~5-6 km) on a global scale,which helps to improve both climate modeling and numerical weather prediction capabilities at short time scale. Recent studies proposed an innovative approach (the Normalized Differential Spectral Attenuation-NDSA) capable to retrieve the integrated water vapour (IWV) from attenuation measurements made in the Ku/K bands along microwave links crossing the troposphere, such as those connecting two low Earth orbiting (LEO) satellites. The NDSA is based on the estimate of a parameter (called spectral sensitivity, S) related to the differential attenuation undergone by a pair of tone signals separated by a fractional band of less than 2%.It was demonstrated that S can be then directly converted into IWV.Two ESA studies provided an exhaustive insight into all theoretical aspects of the NDSA technique applied to the case of two counter-rotating LEO satellites. The purpose of the 2-years long SWAMM project, started in 2016 and funded by Tuscany Region,is the implementation of a NDSA demonstrator. An instrument able to perform NDSA measurements at 19 GHz between a transmitter at ground and a receiver onboard a stratospheric platform will be designed and developed. The solutions devised for the instrument, as well as the retrieval algorithms and the expected results in weather prediction chains will be discussed. Possible configurations for deployment of the NDSA receiver (or transmitter) onboard HAPS in combination with a transmitter at ground, high altitude platform or satellite will be also discussed.Specific focus will be given on the synergy with satellites, not only with regard to the combined use of data, but also, and with special emphasis, on the possibility of joint operations.

The Earth's thermal emission to space covers the Far-to-near-infrared (100-3000) cm-1. The majority of this emission has been covered by various satellite instruments, most recently IASI-MetOp, but the far-IR component, 100-667 cm-1, which can be up to 40% of the outgoing energy, has been neglected. A recent proposal (FORUM) for a satellite mission to fill this lack of coverage has been submitted to the ESA Earth Explorer 9 call. The low polar orbit of the mission, if selected, offers unique science but additional observations from ground or high altitude platforms are still valuable. Deployment of far-IR observational capacity such as the REFIR-PAD instrument to Chile (balloon) and Antarctica (ground) has established continuous and autonomous measurements as routine. This readily lends itself to deployment on a Stratospheric High Altitude Pseudo-Satellite (SHAPS). Coupled with similar mid-IR instrumentation SHAPS offers a unique opportunity to cover the full spectral range of Earth's thermal emission from a single platform at minimal costs. Here, we propose the use of two new instruments, a FORUM-like (100-1600 cm-1) and an IASI-like (600-3000 cm-1) instrument on board the SHAPS. The altitudes and stable location of these platforms enable the continuous monitoring of water vapour and cirrus clouds and can revolutionise the measurement of FIR surface emissivity. These observations will enable more precise measurements of cirrus radiative properties. As well as offering new measurements in the FIR the thermal overlap with IASI leads directly to coincident measurement validation and improved parameterisation of cirrus within Earth system models. Additionally to IASI this proposed use of the SHAPS offers an exciting synergy with the future deployment of the IR sounder part of EUMETSAT geostationary MTG program. The SHAPS ability to mimic the view of a geostationary platform while resolving spatial structure will provide valuable validation and diagnostic information.

A general overview is provided of the Horizon 2020 project AURORA (Advanced Ultraviolet Radiation and Ozone Retrieval for Applications) funded by the European Union in the frame of the Call Space, EO22015: Stimulating wider research use of Copernicus Sentinel Data. The overarching objective of AURORA is to simulate the provision of synergistic data products for the vertical profile of atmospheric ozone and to assess their quality with respect to the one expected for the operational products of the geostationary (GEO) mission Sentinel 4 and of the Low Earth Orbit (LEO) mission as Sentinel5p and Sentinel5. The project addresses key scientific issues relevant for synergistic exploitation of data acquired in different spectral ranges by different instruments on board the atmospheric Sentinels. A novel approach, based on the assimilation of GEO and LEO fused products by application of an innovative algorithm to S4 and S5 synthetic data, is adopted to assess quality of the unique ozone vertical profile obtained in a context simulating the operational environment. First priority is then attributed to the lower atmosphere with calculation of tropospheric columns and UV surface radiation from the resulting ozone vertical distribution. In parallel, AURORA tackles the technological challenges of creating the infrastructure, exploiting virtual machines and cloud data sharing, to implement the data processing chain, including a geodatabase and webservices for data access. The infrastructure represents a best practice that plays a key role in ensuring wider use of Copernicus Sentinel data for academia, public agencies and industry. It is the basis for a market analysis for premarket applications and uptake in commercial communities. Strategic dissemination and exploitation is targeted to European level (academia, CAMS, GEOSS) and international level (potential synergies and data exchange will be investigated with TEMPO and GEMS, in USA and ASIA). This presentation offers a first introduction to the three years project AURORA (February 1st, 2016 - January 31st, 2019) and describes the scientific, technological and applicationoriented concepts acting as the pillars of the proposed research and development activities. The scope and objectives of the project, the work plan, the expected outcome, as well as the longterm perspectives, are illustrated in some details. In conclusion, the progress status, along with a summary of the results obtained in the preliminary and first phase of the program, is reported. Furthermore, it will be possible to follow the subsequent steps and the dissemination initiatives of AURORA by using the list of references and contact points indicated at the end of the overview.

The exploitation of the synergy between infrared and mm-wave limb sounding measurements is one of the key strength of the scientific payload proposed for the PREMIER mission candidate to the Core Missions of ESA Earth Explorer 7. As part of the preparatory activities of PREMIER, the PremierEx campaign was conducted in the Arctic region (Kiruna, Sweden) with the high altitude research aircraft M-55 Geophysica in March 2010. In this work, we discuss the synergistic use of MARSCHALS and MIPAS-STR data acquired during the Premier Ex scientific flight conducted on March 10, 2010 by using an innovative approach to the problem of atmospheric data fusion. We compare the quality of synergistic and individual retrieval products and present our conclusions on the potential of combined exploitation of the information associated to infrared and mm-wave limb observations of the UTLS. The cloud coverage (low clouds in the first part, no clouds in the central part and high tropospheric clouds at the end) observed along the flight provided representative test cases to evaluate the synergy in three different cloudy scenarios.

International audience; Numerous vertical ozone profile data records collected over the past decades from space-based platforms have the potential to allow the ozone and climate communities to tackle a variety of research questions. A prime topic is the study and documentation of long-term changes in the vertical distribution of atmospheric ozone, as targeted by the recent SPARC/IO3C/IGACO-O3/NDACC Initiative (SI2N) and WMO’s ozone assessment. Such studies typically require data records with documented mutual consistency in terms of bias and long-term stability. Ground-based networks play a pivotal role in evaluating which satellite records comply with end-user requirements and are fit for their purpose. They provide high-quality, independent measurements on a pseudo- global scale from the ground up to the stratosphere.Here, we present an assessment of the long-term stability and mutual consistency of fourteen limb/occultation ozone profile data records, using NDACC/GAW/SHADOZ ozonesonde and NDACC lidar network data as reference standards. We show how a harmonized analysis framework and robust statistical methods allow us to derive reliable estimates of the drift, bias, and short-term variability of each satellite data record. We examine the dependence of these parameters on altitude and, whenever feasible, on latitude and season. The analysis is furthermore performed in four different ozone profile representations, as it turns out that auxiliary data used for unit and representation conversions can impact data quality. We discuss the mutual consistency and compliance of satellite data sets with respect to specific user requirements from GCOS and from climate research groups. We conclude by reflecting on the implication of our results for trend assessments on recently merged ozone profile records (Ozone_CCI, GOZCARDS, SWOOSH, ...)

An overview of the results obtained by the MARSCHALS (Millimetre-wave Airborne Receivers for Spectroscopic CHaracterisation in Atmospheric Limb Sounding) instrument during Premier-Ex (March 2010, Kiruna, Sweden) and ESSenCe 2011 (December 2011, Kiruna, Sweden) aircraft Arctic campaigns is presented. The two campaigns were part of the activities conducted as preparatory studies for PREMIER (Process Exploration through Measurements of Infrared and millimeter-wave Emitted Radiation), one of the three candidate core missions of ESA Earth Explorer 7. The primary objective of PREMIER is to gain a better understanding of the processes that are linking atmospheric chemistry and dynamics with climate. PREMIER will achieve this by observing the Upper Troposphere / Lower Stratosphere (UTLS) - a region of particular importance in the study of climate change - with unprecedented spatial and temporal resolution. PREMIER combines the complementary capabilities of two limb-sounders in the infrared and millimeter-wave spectral regions and MARSCHALS was developed as an airborne demonstrator of the PREMIER millimeter-wave spectrometer. In the frame of the two Arctic campaigns, MARSCHALS sampled the Arctic UTLS retrieving vertical profiles of its main atmospheric targets (T, H2O, O3, HNO3, N2O, CO). The obtained vertical profiles have been used to investigate chemical and dynamical processes taking place in the Arctic atmosphere. In particular, we found the presence of filaments of vortex air during the Premier-Ex campaign and of re-nitrification or HNO3 redistribution due to sedimentation followed by evaporation of Polar Stratospheric Cloud (PSC) particles during the ESSenCe campaign. Furthermore, the results of the comparisonbetween MARSCHALS and MIPAS-STR products as well as the state of the atmosphere during the ESSenCe campaign simulated by theCLaMS (Chemical Lagrangian Model of the Stratosphere) and EMAC (ECHAM/MESSy Atmospheric Chemistry) models will be presented.

The ENVISAT validation programme for the atmospheric instruments MIPAS, SCIAMACHY and GOMOS is based on a number of balloon-borne, aircraft, satellite and ground-based correlative measurements. In particular the activities of validation scientists were coordinated by ESA within the ENVISAT Stratospheric Aircraft and Balloon Campaign or ESABC. As part of a series of similar papers on other species [this issue] and in parallel to the contribution of the individual validation teams, the present paper provides a synthesis of comparisons performed between MIPAS CH4 and N2O profiles produced by the current ESA operational software (Instrument Processing Facility version 4.61 or IPF v4.61, full resolution MIPAS data covering the period 9 July 2002 to 26 March 2004) and correlative measurements obtained from balloon and aircraft experiments as well as from satellite sensors or from ground-based instruments. In the middle stratosphere, no significant bias is observed between MIPAS and correlative measurements, and MIPAS is providing a very consistent and global picture of the distribution of CH4 and N2O in this region. In average, the MIPAS CH4 values show a small positive bias in the lower stratosphere of about 5%. A similar situation is observed for N2O with a positive bias of 4%. In the lower stratosphere/upper troposphere (UT/LS) the individual used MIPAS data version 4.61 still exhibits some unphysical oscillations in individual CH4 and N2O profiles caused by the processing algorithm (with almost no regularization). Taking these problems into account, the MIPAS CH4 and N2O profiles are behaving as expected from the internal error estimation of IPF v4.61 and the estimated errors of the correlative measurements.

International audience; Launched on March 1st, 2002 on-board the polar orbiting ENVISAT satellite, the MIPAS (Michelson Interferometer for Passive Atmospheric Sounding) mid-infrared FT spectrometer performed limb emission measurements at high spectral resolution (0.025 cm-1) for about two years. Due to too frequent anomalies observed in the Interferometer Drive Unit, operations were suspended in March 2004 and finally resumed, in January 2005, in a new reduced resolution (0.01 cm-1) mode. Operational level 2 products for the complete set of target species (i.e. geo-located vertical profiles of Temperature and volume mixing ratio of H2O, O3, HNO3, CH4, N2O and NO2) were obtained during MIPAS full resolution mission, from July 6th, 2002 to March 26th, 2004. In this timeframe, several research groups involved in the ESA programme for geophysical validation of the ENVISAT Atmospheric Chemistry Instruments and in related national activities, carried out a variety of ground-based observations (ozone soundings, FT-IR, microwave radiometers, lidars) of the ozone vertical distribution and of in situ and remote sensing measurements from high altitude platforms, in close spatial and temporal coincidence with MIPAS overpasses. As a result, a comprehensive database of correlative measurements became available for a first inter-comparison of MIPAS O3 profiles with various datasets from coincident observations. A co-ordinated effort was finally conducted to bring together the individual outcomes of the different validation activities and to better exploit their redundant and complementary information. In the latter phase, special attention was paid to rigorous selection and use of correlative data, by adopting stringent coincidence criteria and by giving top priority to homogeneous and reliable validation data sources. Here we report a brief overview of the validation of MIPAS O3 data versions 4.61 and 4.62 (fully equivalent for validation purposes) by ground-based, balloon/aircraft and satellite measurements and discuss in details the resulting quality assessment of MIPAS O3 retrieved profiles.

Fourier transform spectrometers, thanks to their intrinsic advantages of high throughput, high spectral resolution and multiplex acquisition of spectral channels, offer a powerful tool for the characterization of the Earth's atmosphere. The use of photon noise limited detectors in FTS instruments operating in the middle/far infrared spectral region permits high sensitivity emission spectroscopy measurements, without the limitations arising from the use of an external radiation source. The wide operating spectral range of FTS instruments makes possible simultaneous detection of different atmospheric chemical species that show rotational and vibrational spectral bands in the middle/far infrared region. Spatially resolved measurements of the concentration of the interesting species are of fundamental interest in the study of local phenomena in atmospheric chemistry and physics, and can be obtained through the use of various observation and data inversion techniques. Among these, the best results in terms of vertical resolution are achieved through the limb sounding observation technique from airborne platform. As an example of possibilities offered by the above considered technique, results obtained from the SAFIRE/A (Spectroscopy of the Atmosphere using Far InfraRed Emission - Airborne) during the Antarctic campaign APE-GAIA (Airborne Polar Experiment - Geophysica Aircraft In Antarctica, Ushuaia, Argentina, September-October, 1999) are presented.