Mar 2, 2014 - This trend is a result of the increasing avail- ability of commercial ... novel developments in terms of applications and services based on radar ...
INDUSTRIAL PROFILES Alexander Kaptein, Jürgen Janoth, OLIVER LANG, and Noemie Bernede Airbus Defence and Space, Geo-Intelligence
Trends in Commercial Radar Remote Sensing Industry
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he last two decades have seen an unprecedented development in the satellite-based Earth observation industry. The combination of an increasing number of operational satellites, the higher resolution of the acquired data and the advances in the processing techniques have enabled a wider adoption of satellite data and the development of a diverse range of products and applications. Although the market is still strongly biased toward electro-optically derived imagery a rising tide of acceptance and usage of satellite derived Synthetic Aperture Radar (SAR) data can be noticed over the last few years. This trend is a result of the increasing availability of commercial SAR satellite data, development of sophisticated processing and analysis tools and industry driven training effort conducted to familiarize image analysts with the specifics of SAR imagery, its interpretation and its utility. Intuitively the colored imagery derived from electro-optical systems provides the human eyes with familiar representations of the Earth’s surface. However, the user community is increasingly recognizing that there is much more than meets the eye in blackand-white SAR data and imagery. The most obvious SAR advantage is the weather and daylight independence of radar systems, which ensures a guaranteed acquisition of the area of interest. This however is just one side of the coin. The real advantages of SAR unfold when the data is processed and analyzed in an appropriate manner. Many unique effects of SAR satellite data (such as phase information) can be exploited to extract information from the imagery that is not detectable through visual interpretation only. SAR imagery can for instance be used to detect and even quantify the motion of objects on both land and sea or to monitor subtle changes to the surface conditions.
The current operational SAR missions have proven that commercial radar remote sensing has a considerable commercial potential. The demand from both institutional and commercial data users continues to drive advances in sensor technology and processing techniques to ensure another leap ahead in regards to data quality and availability. In the next decade over 360 Earth observation satellites are expected to be launched by government and commercial operators1 across 42 countries (36 are SAR satellite), enabling the development of improved and novel space-based applications as well as the advancement of existing applications. The SAR data market is growing particularly fast increasing from 93 Mio € in 2013 to 226 Mio € in 2021 (CAGR 2011–2021: 9.76%). According to the Northern Sky Research Study “Satellite based Earth Observation, 5th Edition” the high-resolution SAR data market represented 3% of the total data market in 2012, the medium-resolution data segment was worth 6% of the total data market in 2012. The growth for radar data is driven by public budgets and procurement mechanisms that are implemented by the defence sector and by consumer driven applications. Primary applications for radar data are defense and maritime applications such as border surveillance, oil spill, ship and ice monitoring. SAR data is also used for land applications (geology, agriculture) and infrastructure management (e.g. surface movement monitoring). Used in combination with optical data, radar data provides advanced opportunities regarding information content. An integrated use of radar and optical sensors can support timely change identification through analysis of the weather-independent radar image and then subsequent identification of changes using the optical sensors.
Digital Object Identifier 10.1109/MGRS.2014.2304632 Date of publication: 8 April 2014
1Satellite-Based Earth Observation, Market Prospects to 2022,
Euroconsult 2013.
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Demands and requirements from novel applications and increased uptake of SAR imagery are the key drivers to technology and service developments. Satellite builders, operators and data providers continuously strive to upgrade their space and ground infrastructures to meet the increasing demands of data users both in the institutional and the commercial market sectors. A few major trends in regards to advances in the SAR sensor technology and novel developments in terms of applications and services based on radar data are highlighted in the following. Platforms Tailored to Respective User Requirements A first distinct trend of the last years is the growing interest of small and developing nations in the use of space systems and applications for the benefit of their socio-economic development. Since the 1990’s, various developed and emerging countries have drafted their own national space plan. From 2001 to 2011, the number of nations with space programmes has grown from 26 to 492. In addition to other space programs (e.g. in the satcom domain), these nations are increasingly thriving to establish their own remote sensing satellite capabilities. The main rationale is usually to establish an independent data acquisition capacity to improve civil security and quality of live. For these newcomers it is challenging to enter this domain as the countries need to leverage high development/operation costs, the long-term dimension of programs, the limited experience with identification of requirements and priorities as well as the expected return on investment. For these reasons, the first systems with which these nations enter the spaceborne remote sensing domain are usually low-cost systems that can be launched quickly. Such systems enable the nations to start building knowledge of space programs and provide a direct return at economic and social level. Data acquired by these systems is mainly used for disaster management, monitoring of natural resources and mapping applications. In addition to the application-based benefits such systems foster the technology transfer into these developing nations and enable them to gain experience in the operation and exploitation of space systems. On a next level emerging space nations obtain highend instruments to enhance platforms that are integrated based on proprietary technology in the country. An example would be the recently launched KOMPSAT-5 satellite, developed and managed by the Korean Aerospace Research Center KARI. The design, development and integration of the satellite bus are led by KARI supported by the national aerospace industry. Experiences from previous programs (KOMPSAT-1/KOMPSAT-2/KOMPSAT-3) are exploited to enhance the new satellite bus. The X-Band 2Euroconsult, 2012, Profiles of Government Space Programs.
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Figure 1. Surface movement monitoring using TerraSAR-X radar satellite data for an underground construction project in Budapest, Hungary. © 2011 Airbus Defence and Space/Infoterra GmbH.
SAR payload however was subcontracted to Thales Alenia Space of Italy. At the other end of the scale mature space nations are expanding their space programs and improve the quality and exploitation of their space systems. Depending on the respective space strategies, the countries follow different implementation roads to achieve their strategic goals. These countries increasingly implement complex mission concepts such as different constellation approaches or even formation flights (e.g. the world’s first operational very close formation flight was implemented with the German TerraSAR-X and TanDEM-X satellites that fly at distances of down to a few hundred meters). Another development are novel schemes to finance the Earth observation programs, such as commercialisation of the data (as done in the TerraSAR-X program) or dual use missions such as Cosmo-Skymed. Another way for nations to satisfy their increasing demand for spaceborne data and leverage limited financial budgets are Government-toGovernment bartering agreements. By this, nations can substitute capabilities that are not available in-country through in-kind exchanges with other nations, benefiting from possibly advanced technologies available elsewhere and getting access to state-of-the-art data sources that they would not be able to finance themselves. A further increase of SAR data usage can be expected from the Sentinel-1 satellites, to be launched in the upcoming years. As part of the European Copernicus programme these satellites will provide free mediumresolution SAR satellite data. On the one hand, this will stimulate SAR data exploitation, but it also entails, that commercial data providers will have to adapt to this new situation and identify niche markets (e.g. very-high resolution data provision) that cannot be serviced by the Sentinel satellites. 43
TerraSAR-X Image - 07 Dec 2011
TerraSAR-X Image - 01 Nov 2012
Detected Damage
SPOT 5 Image - 11 Jan 2003 © CNES 2003 Distribution Astrium Services/Spot Image S.A.
Amplitude Change Detection - 07 Dec 2011 vs. 01 Nov 2012
Figure 2. Change analysis based on EO and SAR satellite data following Hurricane Sandy in Long Island, New York, USA. © 2013 Airbus Defence and Space/Infoterra GmbH.
Technology Developments Technological development is key to the increased use and exploitation of radar remote sensing systems. Increasingly sophisticated requirements for complex applications such as high-frequency automated change detection or accurate wide-area monitoring drive the innovation on the technology side. a) High-Resolution Wide-Swath (HRWS) Capabilities One advanced concept that directly answers the widespread user need for large area coverage (e.g. for maritime monitoring) is the development of High-Resolution Wide-Swath (HRWS) capabilities. While current phasedarray SAR systems offer flexibility regarding operational modes, e.g. StripMap, SpotLight, ScanSAR, users often have to accept a trade-off between ground resolution and ground coverage, i.e. a decision between acquisitions of smaller scenes with high resolution vs. large area surveillance modes providing medium to low resolution. SAR systems of the future, such as the HRWS concept by Airbus Defence and Space, will introduce Digital Beam-forming techniques to overcome these restrictions. The SAR antenna will be partitioned in flight (azimuth) and height (elevation) direction, related to independent radar channels. By this, multiple signals are received for each radar transmit pulse, allowing for the reduction of the physical pulse repetition frequency, facilitating wide swath coverage maintaining high resolution. In effect, 44
the azimuth resolution can be much finer than the wellknown relation “azimuth resolution equals approximately half the antenna length”. Elevation Digital Beamforming can be used to improve instrument sensitivity by real-time focusing of the antenna beam to the current target on the ground. Enhanced concepts carry these techniques further, e.g. by multi-beam modes or by the option to process the same data with respect to different applications, e.g. imaging versus moving target detection. Ultimately HRWS will allow a much greater flexibility when defining acquisition modes. Thus facilitating the optimization of image geometry for the respective application requirements. b) Multi-Polarimetry Another technological advancement is the increased adoption of multi-polarimetry. Multi-polarized SAR data allows the user to measure the polarization properties of a target and not simply the backscatter at a single polarization. Usage of polarimetric-data can be divided into variety of land cover or target recognition categories, such as agriculture, forest land cover, ice-classification, maritime research (ship detection, wind speed, sea-cover (oil)), vehicle detection or urban land cover. The propagation planes of radar signals at different polarizations (vertical (V) and horizontal (H)) interact dissimilarly with target structures of different dielectric properties. Thus the combination of the polarimetric responses results in a false color image, which provides improved ieee Geoscience and remote sensing magazine
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classification information of e.g. vegetation classes. Full polarimetry can furthermore support target identification and improve accuracy of urban area mapping applications. Future SAR systems such as Cosmo Skymed Second Generation and TerraSAR-X Next Generation will feature such full polarimetry capabilities. c) Increased Bandwidth Another development currently under way is the intended extension of the chirp bandwidth for X-Band SAR from 600 MHz to 1200 MHz. The pursued extension of the ITU bandwidth allocation to 1,200 MHz bandwidth, necessary to achieve very high resolution, has been adopted as topic for approval on the agenda of the next World Radio Conference in 2015. This will enable the acquisition of X-band SAR imagery with a resolution down to 25 cm—a quantum leap in image quality. The improved resolution facilitates the more intuitive analysis of the imagery as even small scaled objects are recognizable and identifiable easily. Near-Real-Time Service Capabilities A key requirement for many SAR applications is the timely availability and delivery of data to the end user. Particularly monitoring applications such as Open Ocean Surveillance and disaster management require instant data availability to take full advantage of remote sensing data. The timeliness of the data is influenced by two factors, firstly the rapid access to the target area and secondly the instant download and delivery of the data to the end user. Various strategies are pursued to achieve an increased temporal resolution and an expansion of Near-Real-Time (NRT) service capabilities. a) Satellite Constellations Depending on the number of satellites and their orbit positions satellite constellations enable daily and even intra-daily revisit capacities to any point on Earth. The only currently operational commercial SAR constellation is Cosmo-Skymed with four identical satellites in orbit. However, for the next generation of Radarsat and TerraSAR-X constellation approaches are foreseen to provide for reduced revisit times and enhanced acquisition capacities worldwide. An alternative to a full constellation approach is offered by Coordinated Constellation Concepts. Such a concept entails the sharing of risks and benefits of implementing space systems between various partners, each of whom owns and operates a part of the constellation. While the ownership of the space assets remains with the respective companies, the partners have access to the capacities of the entire fleet. Such a Coordinated Constellation Concept is currently implemented for the German satellite formation TerraSAR-X/TanDEM-X (commercial data provider: Airbus Defence and Space) together with the Spanish PAZ satellite (owner and operator: Hisdesat). The owner commarch 2014
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Figure 3. Comparison between current imaging capabilities (left) and the future enhanced capabilities of TerraSAR-X Next Generation (center and right). © 2013 Airbus Defence and Space/Infoterra GmbH, DLR.
panies of the respective systems retain complete control of their satellites, while they implement a harmonised ground and service segment. This integration includes harmonised acquisition modes as well as coordinated acquisition planning, satellite tasking, ordering and delivery procedures. Operating the virtually identical satellites in a constellation affords Airbus Defence and Space and Hisdesat with a more flexible capacity management of their systems. Data users will benefit from significantly reduced revisit times, enhanced acquisition capacities and easy ordering and delivery processes. The constellation approach also provides for enhanced applications such as improved SAR capabilities for precise monitoring and detection of surface movement phenomena. b) Expansion of Ground Station Networks The most commonly pursued approach to improve data delivery times is the expansion of the ground station network. In the vicinity of the ground stations an immediate
Figure 4. SpaceDataHighway architecture. © ESA.
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data download and re-tasking of satellites is possible. Satellite operators are thus increasingly leveraging the use of various ground station locations distributed across the globe. Polar stations can offer access to (almost) all orbits of polar orbiting LEO satellites, thus enabling the data download after completion of each orbit and also the timely re-tasking of the space systems. In addition mid-latitude stations offer complementary capacities for operators to improve data latency and coverage.
Furthermore, multi-polarization capability will enable new applications and services in a variety of domains. Another trend is the combination of SAR data with AIS data for maritime monitoring applications. AIS receivers as secondary payload on SAR satellites (as foreseen for TerraSAR-X Next Generation) will enable a synchronised acquisition and matching of SAR data and AIS information facilitating a rapid provision of information for Open Ocean Surveillance.
c) Space-based Data Transfer Systems In the future space-based data transfer systems will complement conventional data transmission functionalities. Such data transmission systems are able to extend the NRT product delivery capabilities from areas of interest with a direct receiving station to a Demands and truly global scale. requirements from The first commercial data novel applications transfer system, the SpaceDaand increased update taHighway3, is currently under of SAR imagery are implementation and will comthe key drivers of mence service provision in technology and 2015. A system of geostationservice developments. ary satellites will enable satellites to immediately transfer data to the ground instead of waiting until they pass over a ground station. The key technology of the SpaceDataHighway is its novel Laser Communication Terminal (LCT), which facilitates data transmission at up to 1.8 Gigabits per second. Routing data over the SpaceDataHighway will enable unprecedented performance options for satellite payload tasking and data downlinking—bringing a true meaning to the term near-real-time data. Actionable information can be made available within 10–15 minutes on a global scale. Thus applications such as Open Ocean Surveillance and defence missions will be able to benefit from enhanced reactivity and high volume surveillance capabilities outside of ground station vicinity.
The TerraSAR-X Next Generation Program A second generation of TerraSAR-X is currently under preparation. The development of the next generation mission is based on the experiences and lessons learned from more than five years of commercial SAR operations with TerraSAR-X/TanDEM-X and related user feedback. This TerraSAR-X Next Generation mission will benefit from an advanced SAR sensor technology allowing a spatial resolution of 0.5 m by utilizing the current ITU allowance for 600 MHz chirp bandwidth, and down to 0.25 m with a total sweep (chirp) bandwidth of 1,200 MHz, as will be considered under an agenda item 1.12 at the World Radio Conference in 2015. Services based on TerraSAR-X Next Generation will comprise heritage modes and products from the first generation as well as enhanced products and services, featuring improved signal to noise ratio, larger swaths and submeter resolution, polarimetry, and synchronous AIS data collection. The data dissemination concept of TerraSAR-X Next Generation will continue to support registered TerraSAR-X receiving stations. The TerraSAR-X Next Generation mission is intended to take TerraSAR-X data and service continuity well beyond 2025. The Space Segment, initially a single spacecraft, will be launched into the TerraSAR-X reference orbit while first generation TerraSAR-X systems will still be operational. A constellation concept called WorldSAR is envisaged for TerraSAR-X Next Generation. The objective of WorldSAR is to provide Near-Real-Time (NRT) remote sensing information—at a global scale. This will be achieved through a network of three to five TerraSAR-X Next Generation type satellites operated by entities in regulated partner nations in the frame of a Coordinated Constellation Concept (CCC). This establishes a weather independent high quality SAR satellite constellation with unrivalled NRT data access and high speed workflow/ processing capability for the benefit of the users. The WorldSAR constellation will use a network of main and external ground stations including polar stations to minimise the information latency at the regional levels. Complementing the conventional data transmission functionality with a Laser Communication Terminal (LCT) would enable the bi-directional optical communication via relay satellites (EDRS—SpaceDataHighway with potential extensions) and extend the NRT product delivery capabilities to a global scale.GRS
Enhancement of Applications The technological advancements and enhancement of service capabilities as described in the previous chapters will enable the improvement of various SAR-based applications. Sophisticated future systems will be able to provide a geolocation accuracy of even less than 20 cm. This facilitates enhanced 3D applications in urban areas and surface motion monitoring of small infrastructures. Particularly, very high resolution will increase the number of persistent scatters significantly, which will open the floor for highly precise interferometric and satellite based geodesy applications. 3The SpaceDataHighway Service is based on the European Data Relay System (EDRS) developed and implemented within a Public Private Partnership (PPP) between the European Space Agency (ESA) and Airbus Defence and Space.
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