GEO-OCULUS: A MISSION FOR REAL-TIME MONITORING THROUGH HIGH RESOLUTION IMAGING FROM GEOSTATIONARY ORBIT

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1 GEO-OCULUS: A MISSION FOR REAL-TIME MONITORING THROUGH HIGH RESOLUTION IMAGING FROM GEOSTATIONARY ORBIT Ulrich Schull, Thiemo Knigge Astrium GmbH, Friedrichshafen, Germany Contact: Ulrich Schull; Ulrich.Schull@astrium.eads.net; Tel.: +49 (0) Abstract Geo-Oculus is a mission with the objective to enable observations of the Earth combining high resolution and real-time monitoring. Among the wealth of Earth observation activities on and international level, the Space Agency has identified the lack of this capability. Therefore the Geo-Oculus study performed under ESA contract investigates the user needs and analyses at Phase-0 level the feasibility of an agile satellite in geostationary orbit offering a high to medium resolution ( m) in a spectral range from UV to infrared. NEW CLASS OF EARTH-OBSERVATION MISSIONS So far, satellites for Earth-Observation (EO) specialise on high performance either in the temporal domain or in the spatial domain. Today's missions to geostationary orbit feature real-time access, short revisit times and fast data dissemination while providing rather coarse spatial resolution. High spatial resolution is linked to a low Earth orbit. In the near future a new class of EO-missions will be possible that combine both high resolution imaging and real-time imaging, and therefore will open up room for new fields of applications not feasible today. ESA has identified the lack of this capability and class of EO-missions and initiated a dedicated study named Geo-Oculus. This study is focussed on a survey of preliminary mission objectives and the system design to identify concepts to handle the technological challenges. In the following the key features are detailed, then the survey for mission objectives, the preliminary mission objectives and derived requirements are described. Representative operational scenarios and preliminary system design is followed by a conclusion. KEY FEATURES For Geo-Oculus numerous technological challenges have to be mastered. The instrument requires a very large aperture and a precise optical characterisation that allows for image deconvolution techniques to be applied. Very large detectors with high dynamic range and fast readouts are a premise for this mission. As for the instrument also the satellite system and the ground segment are faced to stringent requirements that demand the implementation of new concepts and technologies. Defining a new class of Earth observation missions, Geo-Oculus is characterised by its unique combination of features: High Spatial Resolution A very large aperture of about 1.5 m combined with image deconvolution techniques to restore MTF gain a spatial resolution of 20 m with a panchromatic channel and about 50 m for super-spectral channels in the UV to NIR in Europe (52 N). This is in particular suited for disaster monitoring because it requires the high resolution in a panchromatic channel to analyse impact and severity for mitigation efforts. For applications with heterogenic topology like coastal zones monitoring such resolution significantly reduces parasitic signal from adjacent spots.

2 Real-Time Control Geostationary orbit and permanent up- and downlink allow for real-time control of the system to command observations immediately with the arrival of a request by users. Furthermore optimisation of observation for regularly cloud covered areas becomes possible by e.g. the integration of now-casting information derived by Meteosat data. Agile Satellite The satellites attitude control system supports rapid pointing manoeuvres to access every commanded area of observation within about 1 min, depending of distance from previous site. This time also includes a tranquilisation period to settle vibrations that were induced by the attitude manoeuvre within the solar array and structure. Real-Time Data Transmission Through the permanent contact to the ground station the data transmission starts immediately after acquisition and essential onboard processing. Raw data become available at the ground station within few seconds after actual image take. Further on-ground processing to higher level products for delivery to the users is the dominating portion of the overall timeliness that is required to be e.g. 15 min for fire monitoring and 1 hour for disaster monitoring. Rapid Revisit Capability The agility, real-time control and real-time data transmission allow for a rapid revisit capability of the system that can be as low as two minutes for a full set of spectral channels when no other observations are conducted in parallel. While running a routine background mission, e.g. coastal zones monitoring with three complete cycles, the system is capable of three additional missions with a revisit of 10 min and six with a revisit of one hour. Very short time-scale processes in various fields of applications can be studied at unprecedented detail in both, temporal and spatial resolution, which is reflected in Figure 1. Figure 1: Comparison of Geo-Oculus with existing EO-missions in revisit, resolution and timeliness.

3 High Performance in all Earth Observation aspects Its unique features position the Geo-Oculus mission in a previously unoccupied field of Earth observation, nevertheless are the shared performance characteristics at the edge of technology. The instrument will feature an extended set of channels with narrow bandwidth for ocean colour. New UV-channels gain potential for future applications such as oil slick detection or detection of toxicity of algal blooms. High signal to noise ratios are obtained for all channels including MWIR and TIR channels to e.g. retrieve accurate ocean constituent amounts and sea-surface temperatures. A highest resolution panchromatic channel with 10 m GSD at sub-satellite point with a high MTF is included. The SWIR, MWIR and TIR channels provide high dynamic range suitable for hightemperature events without clipping to determine e.g. fire temperatures and hot spots. SURVEY FOR MISSION OBJECTIVES A comprehensive analysis of user requirements, potential applications and the related product requirements identifies preliminary mission objectives. The scope of this survey covers the political framework in terms of ongoing or future initiatives, especially the Kopernikus initiative, as well as international treaties and and national directives, policies and protocols. Synergies with and international Earth observation systems and missions, like the Sentinels, GEOSS and EPS are identified and contribute to the identification of suitable applications for Geo-Oculus. Mission of choice The analysis of user requirements and potential applications is conducted with an open mind for user demands that will especially benefit from the mission characteristics in fields of e.g.: Ecological, economical and humanitarian incidents Rapidly evolving events Local to regional monitoring Instantaneous situation awareness Regions regularly covered with clouds The survey points out that Geo-Oculus is the 'mission of choice' for the above mentioned fields of applications. Yet, another finding is that only few applications already exist that require the specific features of Geo-Oculus to become possible. This is not due to missing interest but due to missing capability of existing missions. Nevertheless many existing applications are identified that can profit from Geo-Oculus, some can significantly profit or first become possible in an operational manner. Important synergies Geo-Oculus provides strong assets for synergies with current and planned EO-missions. The optimisation for cloud cover, which is considered as a central benefit of Geo-Oculus, is only possible with support data from Meteosat and EPS. On the other hand, Geo-Oculus can support other missions to improve quality of service. Some synergies, receiving and supportive, are listed below: Receiving synergies: Real-time cloud cover information from Meteosat and EPS Fire presence by any means Highest resolution support data e.g. for disaster monitoring from SPOT, Pleiades, Ikonos etc. Supportive synergies: Oil slick verification Gap filling due to cloud cover Fine scale and real-time spotlight support to meteorology, e.g. for severe weather events These synergies are considered as a prerequisite for the selection of mission objectives. Selection process In a preliminary selection process based on criteria like "Political Importance", the "Institutional / Non- Profit Importance", the "Commercial Importance" and the "Suitability of Geo-Oculus" a set of applications is selected and correspondent mission objectives are set. These are used for sizing of the

4 system. For that reason, only sufficiently elaborated applications with available technical requirements can be taken into consideration. PRELIMINARY MISSION OBJECTIVES Core Objectives The preliminary mission objectives for Geo-Oculus are subdivided in primary and secondary mission objectives, the latter can not become design drivers for the system. Table 1 gives the mission objectives: Mission Objectives Primary / Secondary Political Framework Service Regions Events Service items Disaster Fire Algal Bloom Detection & Water Quality with respect to Regulation Oil Slick Environmental Erosion & Sediment Transport on the Shoreline Primary Primary Primary Primary Secondary Secondary DG AIDCO All Europe, optional Africa, Middle East Flooding, large landslides, storms image acquisition before expected weather abnormally (storm, heavy rain), volcano eruption, int. crisis; mapping & monitoring of damages and recovery activities DG AGRI, DG ENV Forests, emphasis on Mediterranean area Forrest / Wildlife fires Fire temperature, area, FRP Table 1: Mission objectives and description. GSE MARCOAST coastlines up to 65 N, Mediterranea n Sea Algal blooms Position and extend, persistence, drift vector WFD, Maritime Policy, OSPAR coastlines up to 65 N, Mediterranean Sea Anomalies of water quality Chlorophyll concentration, suspended sediments, yellow substance, eutrophication indices, turbidity CleanSeaNet, EMSA coastlines up to 65 N, Mediterranean Sea Reported oil slicks, Secci depth, detection of surface structures of chlorophyll and SST patterns; false alarm identification WFD, TMAP, EEA coastlines up to 65 N, Mediterranean Sea River run-offs, floods, storm events Damage assessment, shoreline changes The mission objectives combine on-demand services, e.g. disaster monitoring, and routine services, e.g. water quality monitoring, within one mission. Despite this basic difference, have all the objectives in common to require an agile system with high spatial resolution and are predestine to profit significantly by Geo-Oculus. In the following the term marine applications is used and refers to Algal Bloom Detection and, Water Quality with respect to Regulation, Oil Slick Environmental and Erosion and Sediment Transport on the Shoreline. Growth Potential and new Applications Naturally, such a mission, which has a chance of implementation rather on the long term, can not be finally sized based on mission objectives that rely on applications for low Earth orbit missions and selection criteria which are based on today's political understanding. Once the opportunity of a geostationary near-real-time high resolution observation is offered possibly additional applications will be identified by the scientific communities not expressed today and also the political priorities might have changed. Relevance of Geo-Oculus for Meteorological Applications So far the identified applications are mainly related to the environmental activities supported by the Kopernikus (former GMES) framework. In addition emergency missions like fire or disaster monitoring are taken into account. For meteorological purposes currently the Meteosat satellites provide the only possibility for near real-time data with a resolution of up to 500 m if the third generation which is

5 currently under study is taken into account. High resolution data is only available from low earth satellites with a revisit capability of days. Geo-Oculus would provide to the users the opportunity to get data from weather events in near realtime and with a high repeat cycle of minutes. This could be suitable for the investigation of severe weather events and deliver data on e.g. cloud patterns or give warning of heavy precipitation. DERIVED MISSION REQUIREMENTS AND SYSTEM REQUIREMENTS The survey for mission objectives identified the products and product requirements from which the mission and system requirements are derived. These technical requirements are used as input for the system design. General System Requirements The following general system requirements have been provided by ESA: 10 years operational lifetime Geostationary orbit at position 10 E with no inclination Single satellite system No synthetic aperture techniques Observation Requirements The primary regions of observation are the main land, the coastlines and the Mediterranean Sea. Optional are observations in Africa and the western part of the Middle East. Performance requirements are applicable up to view zenith angles of 60, which corresponds to latitude 52.5 N at 10 E. Figure 2 shows the observation area for the marine applications, where the orange lines indicate the areas to be covered. VZA = 80 Area not observed during winter solstice (SZA <80 ) 0 h 3 h 4 h 5 h VZA = 60 6 h 7 h 8 h Figure 2: Observation areas for marine applications and oil slick and erosion missions; orange lines indicate the areas to be covered. The system shall provide short acquisition delay, short observation cycles and fast data dissemination (timeliness) as specified in Table 2.

6 Mission objective Acquisition delay after Request Observation cycle Timeliness Goal Threshold Goal Threshold Goal Threshold 1 - Disaster 1 hour 6 hours 1 hour 2 days 1 hour 6 hours 2 - Fire 10 min 1 hour 10 min 1 hour 15 min 2 hours 3 - Algal Bloom Detection / 4 - Water Quality 3 hours 1 day 1 day 3 days 1 hour 6 hours 3 hours 1 day 1 day 3 days 1 hour 6 hours 5 - Oil Slick 1 hour 1 hour 1 hour 6 hour 1 hour 2 hours 6 - Erosion / Sediment Transport 1 hour 1 hour 1 hour 6 hour 1 hour 2 hours Table 2: Acquisition delay, observation cycle and timeliness requirements. The agility of the system shall allow for optimisation of cloud obscured observations by adapted mission planning and real-time now-casting information. The field of view of the instrument shall be at least 100 x 100 km². The instrument shall provide 26 spectral channels in the UV, VIS, NIR, SWIR, MWIR and TIR as specified in Table 3. Some channels are duplicate due to specific requirements of different applications, e.g. ocean colour and fire monitoring where the dynamic range of the TIR channels are different. Channel ID Center Wavelength [nm] Bandwidth [nm] Ground Pixel Size IFOV [m] TYP Threshold Goal Threshold Goal UV1 317, UV VNIR VNIR VNIR VNIR VNIR VNIR VNIR VNIR8a VNIR8b VNIR9 681,25 7, VNIR VNIR , VNIR VNIR13a VNIR13b VNIR VNIR VNIR SWIR MWIRa MWIRb TIR1a TIR1b TIR2a TIR2b Table 3: Spectral channels, bandwidth, GSD and SNR requirements.

7 OPERATIONAL SCENARIOS The operational scenarios for Geo-Oculus are most dominantly characterised by maximum flexibility. Despite having a precomputed plan the actual observations will be coordinated in real-time, taking into account all constraints and actual meteorological information and, of course, requests for on-demand observations. As for the sizing case that is considered during this study, the system will have a background mission, e.g. coverage of the coastlines for the marine applications, and, in case of incidents, one or more on-demand missions. The considered scenario is iterated with the present system design and represents a feasible approach. Background and On-demand Missions The marine applications form the background mission and require daily coverage of the coastlines and the entire Mediterranean Sea and hourly updates for algal blooms. With the FOV of 300 x 300 km² for the ocean colour channels, which is in line with the instrument design, this corresponds to about 70 images for full coverage. In order to preserve sufficient resources for cloud cover optimisation and algal bloom observation, threefold coverage is assumed; hence 210 images are planned. In parallel to the background mission, the system is capable to handle the following on-demand missions, three disaster missions with a revisit of one hour, three fire missions with a revisit of 10 minutes and two oil spill missions with a revisit of one hour. Figure 4 depicts a possible observation pattern where the marine missions (blue) are interleaved by disaster (green) and fire (orange) missions. fire disaster Figure 4: Representative observation pattern. marine Observation Constraints In contrast to LEO missions Geo-Oculus has a varying view zenith angle that is for observations in Europe in the range of about 40 to 80 depending on latitude. This raises the concern on air mass in the light path, which reduces accuracy of atmospheric correction when increased. Today's algorithms for atmospheric correction are tailored for Nadir viewing geometry and become less accurate for large view zenith angles. It is assumed that future optimisation of these algorithms will allow for more extreme viewing geometry, as for today a restriction to 60 also for solar zenith angle is set where the specified performance can be reached. A SHORT SUMMARY OF A PRELIMINARY SYSTEM DESIGN The main items of the system design are given below; the key mission facts are given in Table 4. Instrument A single instrument is chosen to provide both the 300 x 300 km² field for marine applications as well as the 100 x 100 km² field for high resolution imaging. A Korsch optical system (see Figure 4) with ~1.5 m aperture images via beam splitters on six focal planes. Filter wheels are used for the spectral channels. In order to gain the high required SNRs post-integration is used to reduce smear by residual slew.

8 M3 Optional SWIR detector M1 MWIR detector Field correction & focal length adjustment M2 TIR detector & filter wheel UV-blue detector & filter wheel Panchro VHR detector Red-NIR detector & filter wheel Figure 4: Preliminary instrument design. Spacecraft The spacecraft design a platform based on a standard telecommunications satellite bus accommodating the large optical instrument. The step and stare observation is performed via spacecraft pointing which utilizes magnetic bearing wheel as actuators to minimize the disturbances induced by the wheels on the spacecraft. The propulsion system consists of a four tank bi-propellant chemical system that performs the orbit acquisition and station keeping manoeuvres as well as the wheel desaturation. Optional application of an electrical propulsion system either for attitude control or manoeuvres is under investigation. Ground Segment Stringent requirements are set for the ground segment to achieve the overall performance in timeliness and real-time control as well as optimised mission planning. Interfaces to users, the space segment and the cooperative missions have to be streamlined. Table 4: Key mission facts. Key Mission Facts Launch: ~2015 with Soyuz from Kourou Lifetime: ~10 years Transfer: GTO-GEO with liquid apogee engine Platform: ~ 2.5 x 2.6 x 2.2 m³ Payload: ~ 3.5 x 2.3 x 2.3 m³ Mass (wet): ~ 3 tons Power: ~ 1.9 kw Orbit: GEO i~0, 10 E Data rate: X-Band ~230 MBit/s Instrument: Korsch telescope, ø ~1,5m FOV: ~300 x 300 km² (100 x 100 km² for HR) GSD: ~10m at SSP for HR (30 m for others) Coverage area: Europe (full disk capability) CONCLUSION The Geo-Oculus study unveiled significant potential for high resolution and real-time monitoring from geostationary orbit and demonstrated the technological feasibility for this new class of EO-missions. A sound scenario of mission objectives, mission operation and embedding into the framework of Earth observation has been identified. Technological response for the challenging requirements has been elaborated and proven feasibility. Nevertheless, it was found that the applications that will foster the unique features of Geo-Oculus the most have yet to be defined. This is due to the lack of capabilities of current systems while distinct interest for Geo-Oculus was perceived. Users are called to identify and develop new applications which are now in range of Earth observation missions.