REMOTE SENSING: Norway Enhances Oil Spill Detection with RADARSAT
Tromso Satellite Station uses SAR data to direct surveillance aircraft toward oil slicks.
By Kevin P. Corbley

As one of the world's leading producers of offshore crude oil, Norway faces the constant threat of oil spills polluting its valuable fisheries and fouling its extensive shoreline. Approximately 600 spills are reported each year in Norway, and as many as five to 10 of those require organized containment and clean-up operations.
      Accidental spills are unavoidable hazards of offshore production, which has compelled Norway to develop sophisticated procedures for identifying and tracking floating oil slicks. The most promising of these involves the combined use of surveillance aircraft and synthetic aperture radar (SAR) images acquired by the Canadian RADARSAT satellite.
      Troms¿ Satellite Station (TSS), a private receiving facility in Troms¿, Norway, spearheaded development of the detection technique in 1991 using SAR imagery acquired by the European ERS-1 satellite. The program received funding from the European Space Agency, oil companies and the Norwegian Space Centre with technical support from the Norwegian Defense Research Establishment and several offshore producers.
      In its pre-operational phase, the goal of the project was to provide the Norwegian Pollution Control Authority (SFT) with coordinates of possible oil spills in less than two hours after satellite overpass. SFT is a government agency responsible for contingency requirements, monitoring pollution and taking the lead in containment and remediation efforts.
      This mandate for quick turnaround required a ground system that could process and analyze SAR data for rapid delivery to end users such as SFT and offshore operators so they could contain the oil. Two Norwegian high-tech companies, Spacetec and Informasjonkontroll, developed a near-real time SAR processing system, known as CESAR, which is capable of generating radar images within 10 minutes of reception by the station.
      This ground system capability was further upgraded in 1995 when Telenor R&D, the research arm of the Norwegian telephone company, developed a service for quick distribution of processed images. Called SARA, it is a PC-based technology that enables TSS to transmit digital satellite images to its end-users as simple file attachments to standard e-mail messages.
      With the ground system in place, TSS began transitioning the oil spill detection program from its R&D phase in 1994 to an operational mode with eventual plans for a fully commercial program. The launch of RADARSAT in late 1995 provided a technological boost to the program's development schedule. TSS was one of the first international ground stations to receive RADARSAT data, and they are also licensed to process and distribute RADARSAT data.
      "RADARSAT offers improved spatial and temporal coverage," said Jan Petter Pedersen, director of marketing at TSS. "It provides an important data source to bring the project another step closer to operational status."
      As an operationally oriented satellite, RADARSAT supplies consistent coverage over Norway, acquiring scenes as requested by TSS - something the experimental ERS satellites could not guarantee. And the broader swath width provided by RADARSAT has dramatically increased the coverage area, frequency and timeliness of the imagery.
      TSS is now starting to use RADARSAT images to make the initial sightings of potential slicks so that an aircraft can be directed to the area for closer inspection. This combination of satellite and aerial remote sensing is now responsible for detecting nearly one-third of oil slicks in Norwegian waters.
      Offshore producers are excited by the technology. Several operating companies, such as Statoil and Shell, are examining some unexplained oil slicks as possible clues to locations of natural oil seeps at the ocean bottom. These seeps can be used to target new drilling sites.

SAR is Norway's Only Option
Norway had used aircraft since 1981 to patrol its 48,000 kilometers of shoreline and vast ocean areas, searching for oil spilled by drilling rigs or discharged illegally by tankers. But the unfavorable economics of airborne surveillance over large areas and disruption of flight schedules by poor weather impeded operational application of the technology.
      Satellite-based SAR solved both problems. Weather poses no difficulty to SAR image acquisition. Radar is an active imaging system whose signals penetrate clouds, rain, haze, and darkness to capture images regardless of weather or light conditions.
      "In Norway, SAR is really the only choice for monitoring open seas due to the year-round clouds and half-year of darkness," said Pedersen.
      Introduction of SAR satellites improved the economics of monitoring activities versus aircraft because a satellite covers thousands of square kilometers in a single overpass. Although aircraft must still be used to verify slicks first spotted by satellite, TSS has calculated that the costs of an oil spill monitoring service could be reduced by 30 percent using a combination of satellite SAR and aircraft, instead of airplanes alone.
      SAR offers another distinct advantage in detecting oil slicks. When oil floats on water, it slightly flattens the water surface and dampens wave action. SAR is extremely sensitive to surface roughness, which means that flattened water surfaces appear as anomalies, or dark patches, in the imagery.
      "We developed some automatic processing routines to pick out anomalies that are consistent with the size and shape of oil slicks," said Pedersen, "but we have found that human interpretation still works best."

RADARSAT Enhances Detection Program
The availability of RADARSAT has had a greater positive impact on the project than TSS anticipated. The design of the Canadian satellite differs significantly from the ERS satellites, most notably related to incidence angle and beam modes. Both ERS-1 and -2 have fixed 23 degree incidence angles and 100-kilometer swath widths, which have been adequate for oil detection, but researchers were unsure what advantages RADARSAT's multiple beam modes and variable incidence angle would offer.
      RADARSAT's incidence angle can be adjusted between 10 and 59 degrees from vertical, providing shallow or steep angled views of the Earth's surface. Ground controllers can also vary the power of its transmission signal to acquire images with horizontal ground resolution ranging from 8 to 100 meters, and swath widths varying from 50x50 kilometers to 500x500 kilometers.
      The RADARSAT advantage was quickly identified when researchers in Norway contributing to the oil spill service development discovered they could locate oil slicks in RADARSAT's ScanSAR Narrow beam images, which cover a 300x300 kilometer area. TSS analysts had been anxious to confirm that slicks could be found in these wide-area scenes because they have relatively low costs per square kilometer and further enhance program economics.
      Use of RADARSAT ScanSAR scenes also offers an operational benefit to the program. At Norway's latitude, ScanSAR can acquire images of the national territorial waters nearly once a day - a tremendous advantage in locating and containing a spill before it can do serious damage.

A Day's Work
In a typical application of the oil spill detection system, TSS works closely with SFT to coordinate activities between satellite and aircraft to minimize unnecessary overlapping of coverage.
      "We use satellite-based SAR data as a daily planning tool for aerial surveillance missions," said J¿rn Harald Andersen, a SFT senior executive officer. "Our dedicated Merlin Fairchild IIIB aircraft is guided by possible oil spills in SAR images."
      At its operational headquarters in Horten, 100 kilometers south of Oslo, SFT receives information from a variety of sources. The national weather service provides oil trajectory prognoses that will help SFT chart a slick's movement once it is found. Offshore platform operators have to notify the agency before performing rig operations that may inadvertently spill oil.
      SFT also tries to coordinate the aircraft's flight plan, on a given day, with the satellite overpass area so the airplane is relatively close by without overlapping areas, unless requested. In addition, TSS will adjust the analysis according to the aircraft flight pattern.
      Experts at TSS analyze every SAR image available from the service coverage area, and if a possible oil spill is identified within Norwegian national waters, a SARA message is sent to Horten in less than one hour after data acquisition. The SARA message contains slick information plus a quick look image to illustrate the observation. TSS also contacts the surveillance aircraft directly and provides it with the observation information.
      The aircraft, which carries Side-Looking Airborne Radar (SLAR), infrared and ultraviolet scanners, video cameras and human observers, is diverted to the site to positively identify the slick and its source. Based on this aerial observation, SFT decides how to handle the situation.
      "Satellite SAR data is particularly useful when possible oil spills are not observed at remote oil platform locations," said Andersen. "This 'no pollution' confirmation by satellite allows us to re-allocate flight time to areas not covered by the satellite."

Developing a Commercial Program
"TSS has proven the oil spill detection concept and overseen the development of state-of-the-art ground technology to apply it," said Adrian Bohane, director of sales in Europe, Africa and the Middle East for RADARSAT International (RSI), the Canadian company responsible for worldwide marketing and distribution of RADARSAT data.
      TSS plans to make the program more commercially attractive by finding ways to reduce operating expenses. RSI is looking to assist in this and other coastal monitoring projects, by developing RADARSAT products and services to better meet the demands of users. Initially, TSS will offer the detection program as a service to pollution control agencies throughout northern Europe, especially in countries bordering the North and Baltic Seas.
      Offshore petroleum producers are expected to purchase oil spill information from TSS on a per-project basis. Often they know when they have spilled oil, and several producers have already approached TSS to obtain images for use in managing clean-ups of known spills.
      Another important source of potential business for TSS is on the exploration side of petroleum recovery. When TSS finds a slick that appears to be unrelated to any kind of existing offshore operations, the technicians can analyze the slick to determine if it could result from a natural oil seep. In those cases, the station plans to aggressively market the information to exploration companies working the area.
      "This program really has enormous commercial potential," said Pedersen.

About the Author:
Kevin Corbley is a freelance writer specializing in remote sensing, GPS and GIS. He lives in Denver and may be reached at 303-987-3979 or by e-mail at [email protected]

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