The National Aeronautics and Space Administration (NASA) and the European Space Agency (ESA) signed in September 2010 a Formal Earth Science and Observation Framework for Cooperation. This included the setup of a joint NASA-ESA Earth Science Joint Program Planning Group (JPPG) to enhance cooperation in the area of Earth science observation and global climate change. In order to foster the cooperation, three sub-groups were established covering the domains of a) Mission and Technology, b) Cal/Val and Field Campaigns and c) Ground Segment and Data. The JPPG reports to ESA/NASA top executive management on an annual basis.

The key objectives of this collaboration include the identification, evaluation and initiation, as appropriate, of a broad suite of collaboration opportunities, ranging from the coordination for possible cooperation in future missions; the shared interests in technology and instrument development; and the identification of a major new mission that could only be addressed with substantial collaboration. An important aspect is the coordination of measurements from satellites and airborne platforms for calibration and validation to ensure enhanced science and mission return. Substantial efforts have been made in data exchange, defining technical interfaces for information sharing and improved interoperability, as well as, potential joint project on Science/Mission exploitation platforms. Finally, the cross-representation of key American and European experts in NASA Science Teams/Science Definition Teams and ESA Mission Advisory Groups is ensured and coordinated.

The NASA-ESA framework of cooperation in Earth observation will be presented, as well as, some of the major achievements obtained up until now in order to illustrate the benefits of such a coordinated approach for monitoring the Earth and its environment.

Changes in the distribution of mass within and between the Earth’s atmosphere, oceans, ground water, and ice sheets have been shown to be fundamental indicators of the changes in the Earth system. The NASA-ESA Joint Programme Planning Group initiated an activity to investigate ideas for observing mass transport from space in the future. An Interagency Gravity Science Working Group (IGSWG) was established in 2013 with four experts from the US and four from ESA member states. The group took into account the user needs document produced by representatives of a global user community under the umbrella of the IUGG. The working group finalized its activities in 2016 by delivering the report "Towards a sustained observing system for mass transport to understand global change and to benefit society". This report addresses the compatibility between user requirements, constellation concepts, and expected performance. In addition, a roadmap for implementation in the post-2020 timeframe is included. It is recognized that continuity of observations of global mass transport – extending the data record beyond 30 years in length – is of highest priority to continue unravelling long-term changes in Earth’s water cycle. Improved observation of global mass transport in terms of temporal and spatial resolution would benefit a diversity of Earth science domains (e.g. hydrology, oceanography, cryospheric sciences, solid Earth sciences, atmospheric sciences) for both scientific and application focused users, and are necessary to characterize in full diverse global change processes. ESA and NASA/JPL are currently reviewing opportunities for future concepts responding to documented user needs, and to the Decadal Survey in the US.

The scientific community is faced with a unique and immediate need for improved data sharing and collaboration due to the recent and upcoming launches of new satellite missions as well as the increased understanding of ecological processes. For the Earth sciences and carbon monitoring community, these missions specifically include the NASA-ISRO SAR (NISAR) mission [1], the NASA Global Ecosystem Dynamics Investigation (GEDI) mission [2], and the ESA Biomass mission [3]. While these missions and the corresponding research leading up to launch, which includes airborne, field, and calibration/validation data collection and analyses, provide a wealth of data and information relating to global biomass estimation, they also present data storing, processing and sharing challenges. The NISAR mission alone will produce around 40 petabytes of data per year. These large data volumes will place accessibility limits on the scientific community and may impact scientific progress.

In this context, the ESA-NASA multi-Mission Algorithm and Analysis Platform (MAAP) dedicated to the NISAR, GEDI and Biomass missions is currently under development. This analysis platform will be a virtual open and collaborative environment. The MAAP will provide a common platform with computing capabilities co-located with data as well as a set of tools and algorithms developed to support this specific field of research.
The goal for this platform is to establish a collaboration framework between ESA and NASA to share data, science algorithms and compute resources in order to foster and accelerate scientific research conducted by ESA and NASA EO data users.
The objectives of the MAAP for NISAR, GEDI and Biomass missions are to:
1) Enable researchers to easily discover, process, visualize and analyze large volumes of data from both agencies;
2) Provide a wide variety of data in the same coordinate reference frame to enable comparison, analysis, data evaluation, and data generation;
3) Provide a version-controlled science algorithm development environment that supports tools, co-located data and processing resources;
4) Address intellectual property and sharing issues related to collaborative algorithm development and sharing of data and algorithms.


REFERENCES
[1] P.A. Rosen, S. Hensley, S. Shaffer, L. Veilleux, M. Chakraborty, T. Misra, R. Bhan, V. Raju Sagi and R. Satish, "The NASA-ISRO SAR mission - An international space partnership for science and societal benefit", IEEE Radar Conference (RadarCon), pp. 1610-1613, 10-15 May 2015.

[2] https://science.nasa.gov/missions/gedi

[3] T. Le Toan, S. Quegan, M. Davidson, H. Balzter, P. Paillou, K. Papathanassiou, S. Plummer, F. Rocca, S. Saatchi, H. Shugart and L. Ulander, “The BIOMASS Mission: Mapping global forest biomass to better understand the terrestrial carbon cycle”, Remote Sensing of Environment, Vol. 115, No. 11, pp. 2850-2860, June 2011.

On 22 August 2018, ESA has successfully launched the Doppler Wind Lidar Mission Aeolus, hosting the Atmospheric Laser Doppler Instrument (Aladin). First scientific analysis of the satellite and instrument health, as well as the processing chain to Level 2 and initial data quality were available within two weeks (see [1]) as a result of the thorough preparation of the mission, ground segment and science investigations. During the Aeolus mission definition and development, regular contact and scientific exchange was established and maintained between ESA and NASA. The exchange took place in particular via the Aeolus Mission Advisory Group and the US Wind Lidar Working Group, but also during scientific conferences and workshops. This collaboration and exchange continues for the mission’s Calibration/Validation program as well as for the scientific exploitation and preparation for future operational wind Lidar missions.

As stated by WMO over the past decades, a current deficit of the Global Observing System is the lack of global coverage of wind profile observations. Space-based Doppler Wind Lidars is a technology which can address this deficit. The cooperation between ESA and NASA in support of the Aeolus mission is amongst others founded on a common interest in the development and qualification of this technology for operational use from space. This is supported by the airborne wind Lidar technology demonstrator programs, including the ESA supported DLR Aladin Airbone Demonstrator (A2D) [2, 3], and the DLR 2µm Doppler Wind Lidar (DWL) reference system, the NASA DAWN [4], the NASA TWiLiTE, the Ball Aerospace OAWL [5] and GrOAWL [6] wind lidars. These airborne systems provide the opportunity for collaborative work on the Aeolus satellite Calibration/Validation, product quality and science impact assessments. The joint ESA-NASA WindVal-I/PolarWinds 2015 campaign in Iceland successfully collected measurements of NASA’s DAWN and TWiLiTE instruments together with the A2D and 2µm-DWL Lidars onboard the DLR Falcon in preparation of the Aeolus mission.

Currently NASA and ESA are in discussion on future joint post-launch Calibration and Validation activities supporting Aeolus as well as the operational and scientific atmospheric dynamics community. Two airborne campaigns are planned for 2019 in Central Europe and the Arctic, with operations centres at DLR in Southern Germany and Iceland. In June/July 2020 a campaign focussing on the Tropics is being planned from the Cape Verde Islands, providing opportunities to study the dynamics and microphysics related to the Saharan Air Layer, African Easterly Waves and Jets, Tropical Easterly Jet and deep convection in the ITCZ. In addition to the Cal/Val objectives, the campaign plans to address the understanding of tropical dynamics such as Kelvin and gravity waves, intensive storm development (e.g. hurricanes), heat exchange with the ocean, its impact on tropical weather and intense storm development. This campaign is an opportunity to join the US and European airborne wind Lidar systems addressing the Aeolus validation and providing the science community unique data to address the science questions while providing further insight into wind Lidar technologies supporting the development of future space borne Wind Lidar systems in Europe and the US. Indeed, the 2017 NASA Earth Science Decadal Survey [8] placed satellite wind observations in its competitive Explorer category for potential satellite observations in the next decade.

In addition to the airborne Lidar activities, NASA supported the preparation of the Aeolus mission through participation in ESA’s Mission Advisory Group. NASA has planned to assimilate Aeolus data into NASA’s global modelling system with the focus on the transport of atmospheric constituents and aerosols. Further, the joint activities of ESA and NASA scientists are key in providing impetus and coordination to the Doppler Wind Lidar community.

[1] Aeolus Laser Shines Light on Wind, ESA News, 05 September 2018 (https://www.esa.int/Our_Activities/Observing_the_Earth/Aeolus/Aeolus_laser_shines_light_on_wind)

[2] Reitebuch, O., Lemmerz, C., Nagel, E., Paffrath, U., Durand, Y., Endemann, M., Fabre, F., and Chaloupy, M. (2009): The airborne demonstrator for the direct-detection Doppler wind lidar ALADIN on ADM-Aeolus: I. Instrument design and comparison to satellite instrument. J. Atmos. Ocean. Tech., 26, 2501-2515.

[3] Weissmann, M., Busen, R., Dörnbrack, A., Rahm, S., and Reitebuch, O. (2005): Targeted Observations with an Airborne Wind Lidar. J. Atmos. Ocean. Tech., 22, 1706-1719.

[4] Kavaya, M. J., J. Beyon, G. J. Koch, M. Petros, P. J. Petzar, U. Singh, B. Trieu, and J. Yu (2014), The Doppler Aerosol Wind Lidar (DAWN) Airborne, Wind-Profiling, Coherent-Detection Lidar System: Overview, Flight Results, and Plans, J. Atmos. Oceanic Technol., 34, 826-842, doi:10.1175/JTECH-D-12-00274.1.

[5] Sara C. Tucker, Carl S. Weimer, Sunil Baidar, and R. Michael Hardesty. (2018) The Optical Autocovariance Wind Lidar. Part I: OAWL Instrument Development and Demonstration. Journal of Atmospheric and Oceanic Technology 35:10, 2079-2097.

[6] S. Baidar, S. C. Tucker, M. Beaubien, and R. M. Hardesty. (2018) The Optical Autocovariance Wind Lidar. Part II: Green OAWL (GrOAWL) Airborne Performance and Validation. Journal of Atmospheric and Oceanic Technology 35:10, 2099-2116.

[7] National Academies of Sciences, Engineering, and Medicine. 2018. Thriving on Our Changing Planet: A Decadal Strategy for Earth Observation from Space. Washington, DC: The National Academies Press. https://doi.org.10.17226/24938.

The ESA BIOMASS mission was selected in 2013 as the 7th Earth Explorer mission. BIOMASS will provide estimates of forest biomass and height with full coverage over the tropical areas exploiting the penetration capabilities of P-band. In order to further support the BIOMASS mission development, especially concerning the mission concept verification and the development of geophysical algorithms, ESA funded the P-band AfriSAR campaign following the previous INDREX-II (Indonesia, 2004) and TropiSAR (French Guiana, 2009). AfriSAR has been carried out in Gabon by ONERA (SETHI system, July 2015, dry season) and DLR (F-SAR system, February 2016, wet season). In addition NASA was joining the team with the UAV SAR and LVIS instrument.
From ESA site four different test sites (Lopè, Mondah, Rabi and Mabounie) have been chosen including different physical forest structure types, biomass levels, growth stages, and different levels and kinds of disturbance. Key AfriSAR objectives are: (i) to assess penetration conditions, (ii) to evaluate the performance in forest height and biomass estimation in the 100-300 t/ha range, (iii) to quantify temporal decorrelation, (iv) to evaluate the temporal variability of polarimetric signatures and vertical reflectivity estimates in two seasons (wet and dry). To reach these objectives, in all of the four test sites, fully polarimetric multibaseline data sets are being acquired in order to allow the application of polarimetric (Pol-SAR), polarimetric interferometric (PolInSAR) and tomographic (TomoSAR) techniques. The Pol-InSAR baselines (2 to 3 depending on the test site) have been optimized in order to provide the necessary sensitivity for forest height inversion. Besides, the TomoSAR baselines (7 to 9) have been designed to provide a vertical Rayleigh resolution between 10 and 15m. The selected area in the Lope national park will be definitely the most covered in space and time due to the large biomass range (from 60 to 600 t/ha), structural diversity (mosaic of savannah and dense primary forest) and terrain slope variation. Beyond the TomoSAR stack, two additional data sets with a reduced number of tracks (3-4) will be collected with 4 days revisit time to quantify temporal decorrelation effects over PolInSAR parameter inversion. Furthermore, the same baselines will also be acquired with different headings to evaluate the effect of topography.
In this contribution, all the partners are showing their contribution to the AfriSAR campaigns in terms of data collected and results obtained.

ESA has been successfully collaborating with NASA-Operation Ice Bridge (OIB) since 2011 in the form of joint NASA-ESA flights underflying CryoSat-2 overpasses and joint ground measurements which amongst other activities have included week-long Arctic sea-ice camps and coordinated OIB and CryoVEx campaign flight activities in support of CryoSat-2 (and more recently Sentinel-3A) validation activities.

In view of the ICESat-2 successful launch in September 2018, the Campaigns section is preparing a CryoVEx/ICESat2 campaign in spring 2019 over the Arctic sea ice still supporting the long-term CryoSat-2 validation and with the new component of IceSat-2 validation. This new collaboration centred around the IceSat-2 validation will follow the same approach as previous campaigns where simultaneous joint underflights of ICESat-2 will be coordinated between ESA and NASA over selected portions of interest in the Arctic region.