Passive microwave radiometers have been operated in space for nearly four decades. The sensors have provided key climatological indicators of the Earth System, in particular over Arctic areas, where reduction in sea ice extent observed by these sensors provides one of the most striking examples of effects of global climate change [1]. However, for many operational applications, present passive microwave sensors are hampered by the inherent coarse resolution of the sensors, which is typically in the order of tens of kilometers. Moreover, the continuity of the observational time series, crucial for climatological analyses, is presently under threat with the termination of key satellite programmes.

The Copernicus Space Component (CSC) Expansion programme includes six High Priority Candidate Missions (HPCM) for future new Sentinel satellites identified as priorities to be implemented in the coming years. One of the candidate missions is the Copernicus Imaging Microwave Radiometer (CIMR) mission [2]. CIMR is expected to deliver continuity and improvement on observations of key sea ice parameters (including sea ice extent, sea ice concentration, and ice drift) and sea surface temperature (SST). In order to meet these goals, CIMR would provide observations of brightness temperatures at C-, X, Ku- and Ka-bands at high spatial resolution using a large real-aperture antenna (>7 m). An additional L-band channel is under consideration, which amongst other applications would provide ability to estimate thin sea ice thickness. Compared to e.g. the Advanced Microwave Scanning Radiometer 2 (AMSR2), CIMR observations from C- to Ka-bands would be delivered at unprecedented spatio-temporal resolution and accuracy, while the considered L-band observations would provide continuity to present experimental L-band sensors on board the Soil Moisture and Ocean Salinity (SMOS) and Soil Moisture Active Passive (SMAP) missions.

In order to support CIMR geophysical retrieval algorithm development and to aid tradeoff analyses in instrument design, ESA has initiated the CIMR Arctic Airborne Campaign (CIMREx). CIMREx is designed to provide quantitative reference information to help study trade-offs regarding the resolution of the space-borne system and mission complexity and cost. It will support CIMR end-to-end simulation activities by providing realistic reference brightness temperature measurements over large areas of the Arctic at CIMR frequencies, finally enabling to document the total signal at spaceborne resolutions in terms of sub-pixel scale components. In order to achieve this, CIMREx will operate airborne radiometers at 6.8, 10.65 and 18.7 GHz over the Arctic Ocean, capturing a variety of sea ice and ocean conditions. The study region north of Svalbard and along the East Greenland Current includes different ice types and snow conditions. A heritage instrument, the multi-frequency, dual polarization Helsinki University of Technology Radiometer (HUTRAD) has been refurbished and refitted on a de Havilland Canada DCH-6 Twin Otter aircraft for the campaign. The aircraft sensor complement includes also a camera, a lidar system and a high-definition thermal imaging instrument, providing quantitative reference of ice conditions.

CIMREx is planned for February 2019. We present the preliminary results of the airborne campaign, as well as the performance of newly refurbished airborne radiometer system. CIMREx is a joint initiative by the Finnish Meteorological Institute, the Danish National Space Institute, University of Bremen, Aalto University and Harp Technologies Ltd.


[1] Serreze, M., M. M. Holland, and J. Stroeve., 2007. Perspectives on the Arctic’s Shrinking sea-ice cover. Science 315, 1533.

[2] Kilic, L., Prigent, C., Aires, F., Boutin, J., Heygster, G., Tonboe, R. T. et al., 2018. Expected performances of the Copernicus Imaging Microwave Radiometer (CIMR) for an all‐weather and high spatial resolution estimation of ocean and sea ice parameters. Journal of Geophysical Research: Oceans, 123. https://doi.org/10.1029/2018JC014408

DRIFT4SKIM is a multi-platform, multi-sensor, campaign designed to study near-surface currents and surface waves, scheduled to take place in November 2018. The main objectives of the campaign are to develop a relationship between in situ physical conditions and airborne remote sensing observations in support of the proposed SKIM satellite mission. The campaign consists of two major components; an airborne component, using instrumentation designed to simulate key aspects of the proposed SKIM sensors, and a ship-based component to make in situ geophysical measurements. This seminar will discuss results from the ship-based measurements.

DRIFT4SKIM will make Lagrangian measurements of near-surface currents using an array of more than 100 drifting buoys. The drifters are drogued at a variety of depths, between 15 cm and 15 m in order to capture vertical shear near the surface. This will be supported by two nearly-collocated moorings designed to measure air-sea fluxes, Eulerian currents, and surface waves. Additional drifting wave buoys are also planned. Two deployment locations have been selected; one in the centre of the Iroise Sea, with spatially uniform open-ocean conditions, and a second near the island of Ushant, more coastal conditions with strong tidally-driven current shear and mixing. Multiple deployments at each location are expected, and due to the late-season timing of the experiment, strongly forced conditions are probable.

Geophysical results of DRIFT4SKIM will be discussed in the broader context of air-sea exchanges, wave-driven upper-ocean flows, and wave-current interactions. Analysis will include, for example exploration of the links between atmospheric forcing, surface wave breaking, and near-surface currents and shear. A key aspect of this work is developing relationships between small-scale in situ process studies, large-scale airborne measurements, and global-scale satellite remote sensing. Links will be drawn between DRIFT4SKIM and future work including calibration and validation activities for CFOSAT and the atmosphere-ice-ocean studies planned as part of the ERC-WAAXT project.

Since preparing for the launch of the first CryoSat satellite, DTU Space has collaborated with ESA and various partners to collect airborne validation data for the mission in the so-called CryoSat Validation Experiments, CryoVEx. An airborne version of the CryoSat SIRAL instrument has been used to collect Ku- band radar altimetry together with near infrared laser scanner surface mapping. Further upgrades to the instrument package were done in 2016, with the addition of Ka-band radar altimeter (KAREN). The KAREN system was developed by MetaSensing on request by ESA to test concepts for observing Ka- and Ku-band altimetry on the same platform in support of a potential future dual-frequency satellite mission.
Three CryoVEx campaigns have been carried out with the dual-freqency radar altimetry concept in the Arctic in Fall 2016 and Spring 2017 followed by an Antarctica campaign in southern hemisphere Summer 2017/18. The airborne observations have been carried out from Twin-Otter aircrafts and the measurement system include besides the radar and laser altimeters; precise geodetic GNSS positioning, attitude control by inertial navigation, and cameras to support surface classification.
The campaigns were designed to align with satellite tracks from the missions CryoSat, SARAL/AltiKa, and Sentinel-3A along with an extensive in situ program for documenting overflown snow and ice properties, both on sea ice and land ice. This enables inter-comparison of essential snow and ice parameters on scales from local to regional. In addition, data were collected to continue time series at specific validation sites visited regularly since the early 2000s (e.g the EGIG line crossing the Greenland ice sheet and sea ice north of Greenland and Canada).
Here, we present an overview of the campaigns carried out with dual-frequency radar altimetry and show results from analysing the co-located airborne and in-situ observations from the campaigns both over land- and sea ice.

During the 2018 FLEX campaign several hundred flight lines across five European core sites were recorded with the high resolution airborne imaging spectrometer HyPlant_3, which has improved optical performance in comparison to the version flown the years before. HyPlant_3 was mounted with an aligned TASI sensor for thermal and a LIDAR sensor for 3-D surface mapping on board a Cessna aircraft. HyPlant consists of two modules one being a classical hyperspectral imaging module (380 - 2500 nm), while the second module resolves the red and far-red spectral window with very high resolution enabling the retrieval of solar-induced fluorescence (FWHM 0.24 nm in the window of 670 - 780 nm). Flight modes included low-altitude flights for high-resolution spatial mapping and high altitude for larger scale mapping. High altitude HyPlant images were acquired in synchrony with a constellation of Sentinel 3A and Sentinel 3B to better understand the influence of atmospheric properties onto fluorescence retrieval.
Because of the exceptional weather conditions in June and July 2018, which were characterized by abnormally high temperatures and dry conditions, we were able to record an unique data set of various stressed and non-stressed vegetation types. A flexible campaign planning enabled data acquisition under clear sky conditions at different sites in synchrony with various ground activities and other airborne platforms such as APEX and AVIRIS NG.
With this presentation, we give a first overview on the available data and we will present first maps of solar-induced fluorescence from HyPlant. For the first time we applied the spectral fitting method (SFM), which will be the nominal retrieval method for the FLEX satellite mission, for a larger set of HyPlant images. This retrieval method uses a carefully parameterized atmospheric correction and a retrieval of both fluorescence peaks around the oxygen absorption bands. Maps of solar-induced fluorescence are registered with images of land surface temperature, structural vegetation properties, and detailed ground-based measurements of the functional status of various vegetation types. The dynamic changes in the solar induced fluorescence and information that is contained in the two peak feature of fluorescence is discussed on the background of the diurnal, seasonal and stress-induced functional acclimation of vegetation, for which the summer months of 2018 provided ideal conditions.

The increase of atmospheric CO2 concentration [CO2] has a direct effect on photosynthesis and plant production. To study the effect of predicted [CO2] increase in the field Free Air CO2 Enrichment (FACE) experiments have been developed. These FACE experiments typically control [CO2] around 550 ppm and have measured plant performance in diverse ecosystems. In the agricultural ecosystems FACE experiments have shown often a significant increase in yield whereas quality may decrease.

Yield and quality are key traits to select for new varieties by breeders but they are breeding under lower [CO2] then when new varieties will be released under current [CO2] increasepredictions. To test (new) variety performance the BREEDFACE was set up by IBG-2 plant science in Campus Klein-Altendorf Germany. This FACE experiment allows growth of crops combined with quantifying plant traits with a large range of field phenotyping techniques.

In August 2018 around and at the day of the BREEDFACE overpass of the passive fluorescence sensor ‘Hyplant’ ground measurements were performed. Active and passive ground fluorescence (phenotyping) sensors were used to study two to four soybean varieties grown under elevated and ambient [CO2]. These varieties were chosen out of 18 varieties because of their contrasting photosynthetic efficiency (Fq’/Fm’) performance under elevated [CO2] measured in July 2018. To understand the contrasting response under of growth under elevated [CO2] measurements were taken at leaf level for active fluorescence by MiniPam, MoniPAm and Fluorpen and for passive fluorescence by the Fluowat. At canopy level the LIFT and FLOX were used for passive and active measurements, respectively.
Also for passive fluorescence two varieties differed when grown under elevated [CO2] in August. In this presentation these results will be compared to the active measurements at leaf and canopy level for plants grown under different [CO2]. Moreover we further investigated the direct response of canopy fluorescence by turning on and off CO2 supply in the field every half hour during one afternoon resulting in [CO2] from ambient to about 600 ppm for plants normally grown under elevated [CO2]. Combined these data show acclimation and direct response of photosynthesis to elevated [CO2] in soybean measured by active and passive fluorescence sensors.

The Sentinel-3A and -3B satellites carry the Sea and Land Surface Temperature Radiometer (SLSTR), the latest evolution of the (A)ATSR series of instruments carried onboard the ERS and ENVISAT series. SLSTR incorporates the functionality of AATSR alongside many new features, including two dedicated 'fire' channels (F1 and F2) specifically designed to provide unsaturated spectral radiance observations over high temperature targets in the midwave and longwave infrared spectral bands. The Sentinel-3 SLSTR Active Fire Product is planned to become operational in 2019, and uses data from both the ‘F1’ fire channel and the SLSTR ‘standard’ channels spanning the visible to longwave infrared regions to first detect sub-pixel high temperature targets, and then to characterise their radiative power output. Landscape fires are the main target, alongside gas flares and volcanoes. The fire radiative power (FRP) measures produced by the algorithm from landscape fires burning around the planet will be used to estimate fire emissions of trace gases and aerosols, for example within the Copernicus Atmospheric Monitoring Service (CAMS). Evaluation of the algorithm and prototype processor for the SLSTR Active Fire Products has been informed by a dedicated airborne campaign flown above wildfires in northern Ontario and conducted during the Sentinel Tandem Mission. The airborne campaign deployed both imaging spectrometers and broadband thermal imaging imagers on a UK research aircraft operated by NERC. These instruments covered the visible to longwave infrared spectral region using a total of nine imaging sensors. Supported by ESA, the aircraft flights were timed to overfly boreal wildfires exactly at the time of the Sentinel-3A and -3B overpass, both day and night. Here we will discuss the data captured during the airborne campaign, describe its pre-processing, and use it to illustrate the performance of the prototype Sentinel-3 SLSTR Active Fire Product, including differences seen in the two almost contemporaneously generated datasets from Sentinel-3A and -3B related, for example, to the different sub-pixel location of the fires within the Level 1b data coming from each imager.