ICEWATCH - REAL-TIME SEA ICE MONITORING OF THE NORTHERN SEA ROUTE USING SATELLITE RADAR TECHNOLOGY
ICEWATCH is the first joint project in earth observation between Russian Space Agency (RKA) and European Space Agency (ESA). The overall objective of the project is to implement satellite monitoring by combined use of ESA ERS SAR, RKA Okean SLR and other remote sensing data to support ice navigation in the Northern Sea Route (NSR), offshore industry and environmental studies. ERS-1 SAR images have been used in ice monitoring of the NSR in several demonstration campaigns since 1991. The experience from use of SAR data onboard Russian icebreakers to assist in ice navigation is very positive although ERS-1 can only provide data in selected parts of the NSR with a limited swath width of 100 km. In the ICEWATCH project a concept for integrating ERS SAR data in the Russian ice monitoring service is demonstrated where Okean SLR data are included. The system is currently tested in pilot demonstration phase before it is planned to become operational. In addition to data acquisition and interpretation techniques for data integration, ice classification and data transmission techniques have been tested. Also user requirements have been investigated, suggesting that there are many new and potential users of SAR ice information in the NSR. In future other radar satellites will also be used such as ESA ENVISAT which will be launched in 1999. The first results of ICEWATCH were presented at the Second ERS Applications Workshop in London in December 1995 (Johannessen et al., 1996).
The rationale for the project is practical as well as scientific: Ships traversing the NSR along the Siberian coast need good knowledge of ice conditions from day to day as well as on long term basis for safe and efficient navigation. Oil exploration and production facilities in areas such as the Eastern Barents and Kara Sea areas will require both reliable design statistics and timely monitoring and forecasts of sea ice behavior. Fishing vessels need accurate ice maps updated daily in order to operate in ice edge regions throughout the year. Finally, monitoring of Arctic sea ice over many years is essential to provide an early indicator of global climate change which is predicted to become most severe in polar regions.
The NSR is the sailing route along the coast north of Russia between the Barents Sea and the Bering Strait. In ICEWATCH we have concentrated the studies to the western part of the NSR which includes the Barents and Kara Sea (Fig. 1). The ice conditions in this region restrict sea transportation which requires ice class vessels as well as icebreaker assistance throughout the year. In summer there is traffic in the whole sailing route, whereas in winter it is mainly the western part which is used serving the ports on the Yenisei River. An extensive ice monitoring and forecasting service has been built up in Russia over the last 50 years to serve the sea transportation and icebreaker operations in the NSR. The service is based on data collection from ice stations, coastal stations, vessels, aircraft and satellites. But use of spaceborne SAR has not been a routine part of this service.
The ice monitoring and forecasting service is organized under the Russian Hydro-Meteorological Committee and the Ministry of Transport. The key institutions operating the ice monitoring service are the Marine Operational Headquarters (MOH) located in Dikson (for the western part) and Pevek (for the eastern part). The MOHs operate the ice services in cooperation with Murmansk Shipping Company and the Arctic and Antarctic Research Institute.
The Nansen Environmental and Remote Sensing Center in Bergen, Norway first demonstrated use of ERS-1 SAR data for near real-time ice mapping in the NSR in August 1991, only a few weeks after the launch of the ERS-1 satellite. SAR derived sea ice maps were then sent by telefax to the French polar vessel LŽAstrolabe during her voyage through the Northeast Passage from Norway to Japan (Johannessen et al., 1992). This was the first civilian expedition through the NSR since the Russian revolution. This demonstration was evaluated as very interesting by the captains and sea ice experts onboard the Russian icebreakers which escorted L'Astrolabe through the ice-covered parts of the route.
Since 1993 SAR ice monitoring demonstrations have been carried out by the Nansen Centers in Bergen and St. Petersburg on several Russian icebreakers. In all these demonstration experiments, a scientist from the Nansen Center in St. Petersburg stayed onboard the icebreakers and analyzed the SAR images in cooperation with the captain and ice pilots (Johannessen et al., 1994, 1995). In addition to supporting ice navigation these experiments also had scientific objectives to study various ice processes and phenomena and their SAR signature. Several hundred ERS SAR scenes have been obtained showing the different stages and conditions of ice in the NSR. Figure 2 shows an example of an annotated SAR image of different young and new ice types from the freeze-up season in the southern Kara Sea. The ICEWATCH project started officially in August 1995 after signature of agreement between ESA, Russian Space Agency and the participating institutes.
3. PROJECT TASKS
The six major tasks in ICEWATCH are 1. Study of ERS SAR backscatter characteristics of different ice types in the NSR; 2. Implementation and improvement of methods and algorithms for processing, classification and interpretation of radar data; 3. Development of techniques for combined processing and use of ERS SAR and Okean SLR data; 4. Development of a scheme for polar ice radar monitoring, including study of user requirements, infrastructure and necessary equipment installation; 5. Application demonstration of radar ice monitoring for Murmansk Shipping Company icebreakers including cost benefit assessment; and 6. Recommendation for a real-time operational information system using satellite radar data.
Task 1: Radar backscatter studies of sea in the NSR.
Examples of ERS SAR images were analyzed and interpreted for a number of characteristic ice conditions in the NSR. The ERS images demonstrated good capability to distinguish between the main ice types in the NSR such as multiyear ice, firstyear ice, young ice and new-frozen ice. Different classes, forms and features of ice can also be identified such as fast ice, drifting ice, river ice, shear zones, leads, polynyas, ice topography (ridges and hummocks) and ice edge processes. However, in many cases the SAR backscatter data are ambiguous and it is difficult to classify ice the types correctly without additional data. This is particularly the problem for identification of various stages of young ice and firstyear ice, for quantification of surface roughness and to distinguish ice and open water during melt conditions. In spite of some limitations, the ERS SAR has proven to be a very useful instrument which can provide quantitative data on most of the important ice parameters except ice thickness. The ERS SAR backscatter values for various ice types were compared to simultaneous OKEAN Side Looking Radar (SLR) data (Table 1).
Table 1. Okean-01 SLR parameters
The main results of Task 1 was that state-of-art methods in radar ice classification was reviewed and exchanged, and that ERS SAR ice classification was tested and assessed positively by Russian ice experts.
Task 2: Methods and algorithms for processing, classification and interpretation of radar data.
In Task 2 ERS SAR data and Okean SLR data were exchanged among the project partners, and methods for radiometric and geometric corrections as well as algorithms for derivation of ice parameters were documented. Necessary instrument and satellite parameters as well as software for data processing were exchanged. Simultaneous acquisition of SAR and SLR data were done for several cases, and data were exchanged between Nansen Center and NPO Planeta using ìftpî. SAR and SLR data were displayed in common map projection (polar stereographic projection). Both ERS SAR and Okean SLR data showed similar backscatter properties of multiyear, firstyear and young ice/new-frozen ice for the cases which have been studied.
Task 3: Techniques for combined processing and use of ERS SAR and Okean SLR data.
ERS SAR and Okean SLR data will have different but complementary roles in and ice monitoring system. Okean SLR stripes obtained within one week can be merged into a mosaic which can cover most of the sea ice in the NSR, as is shown by the SLR mosaic in Fig. 3. The SLR mosaics show the main features of the ice pack such as ice edge location, coastal polynyas, firstyear ice and multiyear ice at a resolution of 1.5 km which is sufficient for the regional ice mapping.
Table 2. Users of sea ice information in the Northern Sea Route
The main role of ERS SAR data is to cover smaller, selected areas with detailed images of the sea ice which are needed in practical applications such as ice navigation. With 100 m resolution in the ERS SAR images, most of the ice features important for navigation can be detceted. ERS SAR coverage maps can be superimposed on the SLR mosaics and the most interesting areas for SAR coverage can be selected, as shown in Fig. 3. The corresponding SAR image from the Yamal coast (Fig. 4) shows that there is a band of open water and lower ice concentration (7 - 9/10) outside of the landfast ice. This situation cannot be mapped with sufficient details in the SLR image. The main disadvantage of ERS SAR data (lack of full coverage of the sailing route) is eliminated by use of Okean SLR data. The main disadvantage of the SLR images (lack of sufficient details) is eliminated by use of ERS SAR data in the areas where high resolution is needed.
Most of the technical preparations for combined use of ERS SAR and Ocean SLR data, such as radiometric and geometric corrections, choice of map projection, etc. were made in Task 2. The main effort in Task 3 was therefore to analyze several examples of SAR and SLR images which were obtained near simultaneously over the same area and assess how combined use of SAR and SLR data can be optimized for better ice classification and ice mapping.
Task 4. Scheme for polar ice radar monitoring, including study of user requirements
In order to design a system for polar ice monitoring it is essential to know the requirements from the main user categories, both from established users and new or potential users. A number of such users were contacted and asked about their requirements for ice information. More than 50 users were found who considered ERS SAR images to be useful in their activities. The user categories are summarized in Table 2.
The users can be divided into three main groups: 1. operational users which need ice information in near real-time; 2: consulting services which mainly need archived data and statistical information on ice conditions, and 3: scientific users who need data in research and development projects. The operational users are first of all Murmansk Shipping Companyís icebreaker fleet, other shipping companies operating in ice-covered seas and the Russian HydroMet Service. Oil companies and offshore industry currently need consulting services, but will become operational users when they start offshore operations. Consulting services are also required from engineering companies, consulting companies and transport institutions. Scientific users include universities, marine research institutions and other and environmental research institutes.
Task 5: Demonstration of real-time transmission of SAR images to icebreakers.
An important part of the ICEWATCH project is to develop methods for near real-time distribution of the high resolution, 100 m, ERS SAR images and maps to icebreakers operating in the NSR. Digital transfer of compressed images in near real-time have been successfully tested using the INMARSAT - A service. For example, on January 25 - 26 1996 the icebreaker Taymir was sailing from Dikson to Beliy Island (70° - 80° E) in 100 % ice. With a PC and modem connected to the INMARSAT station onboard, ERS-1 SAR images were received 5 hours after the satellite overpass (Fig. 5). In the image areas of rough ice and hummocks (brighter signature) could be clearly distinguished from smooth undeformed ice (darker signatures). Based on this information the icebreaker changed its course and selected a much quicker and safer sailing route. Occasional use of SAR data like this is interesting for demonstration of new technology, but there is a number of requirements which need to be satisfied before the SAR monitoring technology can become an operational tool, such as: selection of SAR coverage in strategic areas, real-time access to SAR data, data ordering procedure, interpretation of SAR images, quantitative ice parameters from SAR, linking ERS data to the Russian ice monitoring services, transmission of ice maps and images to ships and other end users.
The concept of optimal ice routing using SAR images is illustrated in Fig. 6. Characteristic icebreaker velocity along a straight line in 90 - 100 % ice concentration is typically 3 knots, while the velocity in open water between floes is 15 knots. There is gain factor of 5 of navigating in 2 m thick ice of concentration 90 - 100% if SAR data can be provided in real-time (N. Babich, pers. comm.).
Task 6. Recommendation of a near-real time operational information system using satellite radar data.
It is suggested to implement an operational radar ice monitoring system which will be included in the general Russian ice monitoring service. It will use Okean SLR data for large scale surveying and ERS SAR data for detailed observations in specific key area, which are identified as difficult for the navigation It is recommended to obtain weekly coverage of SLR for the whole Northern Sea Route, and 6 - 10 ERS SAR stripes of 2--5 scenes per week covering key areas in prioritized order as shown in Table 3:
Table 3. Priority areas for ERS SAR coverage
With one Okean satellite and one ERS operational satellite it is only possible to implement a limited operational system for the next 2 - 3 years. From 1999, with wide-swath ENVISAT SAR data available, and possibly also the new Russian SAR satellite Resurs Arctica, the system can be fully operational using SAR data ever day. This system also requires a SAR receiving station in Russia in order to have full SAR coverage of the NSR. The system will provide SAR and SLR products which will be distributed to a selection of users in near real time: such as icebreakers, the headquarters of Murmansk Shipping Company, and ice centers in Dikson and AARI. Offline products will be made available for offshore industry and environmental agencies. The system will be open to include also other users who need radar ice information.
SAR derived ice information has proven to be essential in ice monitoring of the NSR, both for navigation and off-shore operations. Near real-time use of SAR data onboard Russian icebreakers can improve the ship velocity considerably if the data are obtained over the critical areas at the right time. The main limitation of ERS data is that only selected parts of the NSR can be covered. A synergetic use of ERS SAR and Okean SLR data is considered to be the optimal scheme for real time ice monitoring. The SLR data will be used for regional mapping every week, whereas the ERS SAR data will be used only in the most critical areas where high resolution ice information is needed. A future operational monitoring system will first be based on ERS SAR and Okean SLR data. Later, ENVISAT ASAR data will be included, which will enable a much better SAR coverage in the NSR.
The project has been supported by European Space Agency, Russian Space Agency the Norwegian Research Council and Murmansk Shipping Company.
Johannessen, O.M. and S. Sandven,. ERS-1 SAR ice routing of "L'Astrolabe" through the Northeast Passage. NERSC technical report no. 56, February 1992b.
Johannessen, O. M., L. H. Pettersson, S. Sandven, V. V. Melentyev, M. Miles, K. Kloster, L. P. Bobylev, M. Stette, Ć. Drottning and K. Ya. Kondratyev. Real-time sea ice monitoring of the NSR using ERS-1 satellite radar images. Terra Orbit Technical Report no.1/94, Bergen, July 1994, 33 pp.
Johannessen, O. M., S. Sandven, K. Kloster, M. Miles, V. V. Melentyev and L. Bobylev. A Sea Ice Monitoring system for the NSR using ERS SAR data. NERSC Technical Report no. 103, September 1995, 50 pp.
Johannessen, O. M., S. Sandven, and V. Melentyev. ICEWATCH - Ice SAR Monitoring of the Northern Sea Route. Proceedings of the Second ERS Applications Workshop, London, UK, 6 - 8 December 1995. ESA SP-383, pp.291 - 296, 1996.
Figure 1. Map showing alternative sailing routes in the western part of the Northern Sea Route, between Murmansk, Dikson and Mathiessen Strait. The bold line is the most frequently used route if ice conditions permit.
Figure 2. Example of ERS SAR image from southern Kara Sea (11. November 1994) in the beginning of the ice season. The image is shown with annotation of ice types and colour code (green: land, blue: open water, various grey shades: various stages of new and young ice).
Figure 3. Okean Side Looking Radar (SLR) mosaic from 4 stripes obtained from 16 to 21 May 1996.The mosaic is superimposed on a polar stereographic projection with land contours. The Okean SLR images have a resolution of about 1.5 km. The two white rectangles indicate where ERS SAR images were obtained at the same time as the SLR image. The SAR image from the Yamal coast (in southern Kara Sea) is shown in Fig. 4. Copyright: NPO Planeta.
Figure 4. ERS SAR image from Yamal coast on 19 May 1996. The image shows open water (dark signature) between the landfast ice near the coast and 90 - 100 % concentration of firstyear ice further north. The SAR image shows details of the ice cover which are not shown in the Okean SLR image in Fig. 3. Copyright ESA/TSS 1996.
Figure 5. ERS SAR image of 26 January 1996. The image was transmitted to the icebreaker Taymyr in near real-time and was used by the captain to change the sailing route due to difficult ice conditions. The ship track with time markers are superimposed on the image. Copyright ESA/TSS 1996
Figure 6. Concept of optimal ice routing between ice floes in a 10 by 10 km area using SAR images (bold red line) compared with theoretical straight line between two waypoints (dashed green line).
Keywords: ESA European Space Agency - Agence spatiale europeenne, observation de la terre, earth observation, satellite remote sensing, teledetection, geophysique, altimetrie, radar, chimique atmospherique, geophysics, altimetry, radar, atmospheric chemistry
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