© 2014 Airbus Defence and Space – All rights reserved. The reproduction, distribution and utilization of this document as well as the communication of its contents to others without express authorization is prohibited. Offenders will be held liable for the payment of damages. All rights reserved in the event of the grant of a patent, utility model or design. The Ocean Surface Current Mission (OSCM) Earth Observation for Ocean Atmosphere Interactions Science, ESRIN, Frascati, Italy 28th-31st of October 2014 Benjamin Dobke – Airbus Defence & Space, ESA OSCM Study

© 2014 Airbus Defence and Space – All rights reserved. The reproduction, distribution and utilization of this document as well as the communication of its contents to others without express authorization is prohibited. Offenders will be held liable for the payment of damages. All rights reserved in the event of the grant of a patent, utility model or design. Ocean Surface Current Mission (OSCM) Study Outline  Aim: to give an overview of some of the issues and options within and Ocean Surface Current Mission (OSCM)  Science Motivation  Measurement Principle  Key Mission Drivers  Key Sensitivities  Instrument Configuration Options  Orbital Options and Regions-of-Interest  Data Processing and Downlinking Options  Estimated Performance  Mass, Power and Launcher  Summary

© 2014 Airbus Defence and Space – All rights reserved. The reproduction, distribution and utilization of this document as well as the communication of its contents to others without express authorization is prohibited. Offenders will be held liable for the payment of damages. All rights reserved in the event of the grant of a patent, utility model or design. Ocean Surface Current Mission (OSCM) Study Science Motivation  Have known for centuries the large scale ocean currents that traverse the world  Have also known about smaller surface currents (~1-100 km) called the mesoscale and sub-meso scale.  Unable to measure currents globally  Eddies, jets, fronts and filaments are ubiquitous and account for over 50% of the oceans’ kinetic energy  OSCM is a science mission, but could also help inform multiple users, e.g. global shipping routes. MotivationMeasurementDriversSensitivitiesInstrumentOrbit/DataPerformanceLauncher

© 2014 Airbus Defence and Space – All rights reserved. The reproduction, distribution and utilization of this document as well as the communication of its contents to others without express authorization is prohibited. Offenders will be held liable for the payment of damages. All rights reserved in the event of the grant of a patent, utility model or design. Ocean Surface Current Mission (OSCM) Study Measurement Principle  The focus of the OSCM will be to attain Total Surface Current Velocites (TSCV)  This is performed by measuring phase differences in via Along Track Interferometry (ATI)  Area of ocean is illuminated with a radar swath at time t=0, and later at t=1.  All else being constant, the phase difference between the two received signals will be due to ocean currents T = 0T = 1 MotivationMeasurementDriversSensitivitiesInstrumentOrbit/DataPerformanceLauncher

© 2014 Airbus Defence and Space – All rights reserved. The reproduction, distribution and utilization of this document as well as the communication of its contents to others without express authorization is prohibited. Offenders will be held liable for the payment of damages. All rights reserved in the event of the grant of a patent, utility model or design. Ocean Surface Current Mission (OSCM) Study Key Mission Drivers  Key mission drivers, or requirements, broadly fall into four catagories: MeasurementInstrumentOrbitalSystem 5 cm/s accuracy Wind removal Try to provide raw data 200km swath (split/non-split) Ambiguity control 2-10 day repeat Global coverage VEGA class LV Size, mass, power Sufficient data downlinking Baseline control  A number of these requirements are being re-informed by the OSCM studies MotivationMeasurementDriversSensitivitiesInstrumentOrbit/DataPerformanceLauncher

© 2014 Airbus Defence and Space – All rights reserved. The reproduction, distribution and utilization of this document as well as the communication of its contents to others without express authorization is prohibited. Offenders will be held liable for the payment of damages. All rights reserved in the event of the grant of a patent, utility model or design. Ocean Surface Current Mission (OSCM) Study Key Sensitivites  We measure the phase, which can be related to the baseline, the surface current velocity, and the velocity of the satellite  When measuring phase, the unknown position and lengths of the baseline can introduce phase errors that dominate the signal you try to measure in diffferent ways.  Putting in representative numbers show that the across-track is negligable, the alongtrack is important, but that the line-of-sight dominates. dx dβdβ B B’ MotivationMeasurementDriversSensitivitiesInstrumentOrbit/DataPerformanceLauncher

© 2014 Airbus Defence and Space – All rights reserved. The reproduction, distribution and utilization of this document as well as the communication of its contents to others without express authorization is prohibited. Offenders will be held liable for the payment of damages. All rights reserved in the event of the grant of a patent, utility model or design. Ocean Surface Current Mission (OSCM) Study Instrument Configuration Options  For the ESA OSCM study, we are focusing on single platform solutions.  The focus is also exclusively on ATI rather than XTI (i.e. sea surface heights)  Implies two high-level configuration restrictions. 1.A transmitter and receiver pair that must be separated by a significant distance (of the order of 10m) 2.A single, medium-sized platform  Due to the VEGA class launcher, will most likely need a folding antenna to achieve acceptable performance MotivationMeasurementDriversSensitivitiesInstrumentOrbit/DataPerformanceLauncher

© 2014 Airbus Defence and Space – All rights reserved. The reproduction, distribution and utilization of this document as well as the communication of its contents to others without express authorization is prohibited. Offenders will be held liable for the payment of damages. All rights reserved in the event of the grant of a patent, utility model or design. Ocean Surface Current Mission (OSCM) Study Orbital Options and Regions of Interest  There are specific highly dynamic regions that are of most interest to oceanographers.  Raw data and fast, good area coverage should prioritise these areas.  Open ocean can fill up remaining data allowance  Sun-Synchronous orbit performs best for coverage, thermal, and power  Fixed and drifting orbits at altitudes between km are being explored MotivationMeasurementDriversSensitivitiesInstrumentOrbit/DataPerformanceLauncher

© 2014 Airbus Defence and Space – All rights reserved. The reproduction, distribution and utilization of this document as well as the communication of its contents to others without express authorization is prohibited. Offenders will be held liable for the payment of damages. All rights reserved in the event of the grant of a patent, utility model or design. Ocean Surface Current Mission (OSCM) Study Data Processing and Downlinking Options  Depending on the number of polarisations used, data from a single receiver is of the order of 1.4Gbit/s  Depending on number of receivers and orbital duty cycle, total data per orbit can be ~5-10Tbits  A few downlinking options:  Relying solely on X-band implies that an OSCM would require fully compressed data.  Raw SLC data can be provided with K-band / EDRS. Assuming a likely 1 st generation K-band, ~3 minutes of raw data could be provided per orbit in selected areas  Lossless BAQ is also a help (factor of ~2), but could be is not ‘noiseless’ compression.  An on-board data compression could reduce data rate to 30kbit/s allowing high level of coverage at X-band MotivationMeasurementDriversSensitivitiesInstrumentOrbit/DataPerformanceLauncher

© 2014 Airbus Defence and Space – All rights reserved. The reproduction, distribution and utilization of this document as well as the communication of its contents to others without express authorization is prohibited. Offenders will be held liable for the payment of damages. All rights reserved in the event of the grant of a patent, utility model or design. Ocean Surface Current Mission (OSCM) Study Estimated Performance  Starlab Ltd. and Airbus DS have tools to help estimate expected performance.  Ongoing refininment in design understanding of the complexities of performance  Error on the current retrieval can be considered as two separate factors: 1.Bias errors: a fixed error dependant upon baseline and spacecraft attitude errors. Can be measured and removed by calibration although residual error will remain 2.Variance: error dependant upon instrument performance and surface decorrelation time  Working on making the performance as compliant as possible MotivationMeasurementDriversSensitivitiesInstrumentOrbit/DataPerformanceLauncher

© 2014 Airbus Defence and Space – All rights reserved. The reproduction, distribution and utilization of this document as well as the communication of its contents to others without express authorization is prohibited. Offenders will be held liable for the payment of damages. All rights reserved in the event of the grant of a patent, utility model or design. Ocean Surface Current Mission (OSCM) Study Mass, Power and Launcher  Mass, volume and power are other critical areas for the mission VEGA PSLV  Mass capacity reduces with altitude, power increases with altitude for the same SNR.  But performance not necessarily better at lower altitudes. Trade-off… MotivationMeasurementDriversSensitivitiesInstrumentOrbit/DataPerformanceLauncher

© 2014 Airbus Defence and Space – All rights reserved. The reproduction, distribution and utilization of this document as well as the communication of its contents to others without express authorization is prohibited. Offenders will be held liable for the payment of damages. All rights reserved in the event of the grant of a patent, utility model or design. Ocean Surface Current Mission (OSCM) Study Summary 1) Strong science motivation to measure un-observed global currents 5) Configuration will most likely need folding antenna. In an in-line ‘Sentinel-1’ style configuration 2) There are key mission drivers that influence mission design 6) Data rates are extremely large. X-band only enabled through compression, 1 st Gen K- band offers minutes of raw data 3) Errors in the phase are central to the instrument design issues and performance. Arrise due to baseline knowledge. 7) Performance is continually being refined. Bias dominate but calibration should be able to remove most. Low wind performance a challenge 4) Coverage will likely focus on key dynamic areas with open ocean coverage secondary 8) Launch dictates mass and size. Vega is prefered, PSLV can provide a higher mass alternative. MeasurementInstrumentOrbitalSystem