Satellite use growing to monitor facilities, map spills

Nov. 1, 2010
As the petroleum industry examines the lessons learned from the Deepwater Horizon disaster, one positive takeaway is the success with which remote sensing technologies were deployed to map the extent of the oil spill and track its movements in the Gulf of Mexico.

Bud Pope
Spatial Energy
Boulder, Colo.

Adrian McCardle
3v Geomatics Inc.
Vancouver, BC

As the petroleum industry examines the lessons learned from the Deepwater Horizon disaster, one positive takeaway is the success with which remote sensing technologies were deployed to map the extent of the oil spill and track its movements in the Gulf of Mexico.

From just a few days after the explosion up until the present, BP and the US government have relied on numerous imaging satellites and aircraft to determine how much oil spilled, where it reached shore, and which beaches might be hit next.

Although remote sensing has been utilized by the petroleum industry for decades in exploration and logistics applications, this technology is increasingly being called upon to routinely monitor production facilities for seeps and leaks and help prioritize emergency response efforts when disasters do occur.

While aircraft still play key roles in mapping and surveillance, commercial earth observation satellites are rapidly gaining market share due to their ability to quickly and economically map large areas, especially in remote regions. Surveillance from aircraft can be costly, is limited to smaller areas, and can be restricted due to weather.

Satellite images aid in classification of multiyear ice. Image copyright European Space Agency-distribution Sarcom, courtesy of 3v Geomatics.

Thirty years ago, petroleum geologists could choose any satellite imagery they wanted—as long as it was from Landsat. Today the story is much different. Although the US government still operates Landsat satellites, the program spawned a commercial remote sensing industry with a multitude of observation systems in orbit and more on the drawing board. These satellites collect imagery spanning a wide range of spectral wavelengths, spatial resolutions, revisit cycles and coverage areas.

Many of these satellites have the imaging capabilities needed to identify seeps, slicks, and leaks—onshore or off—before they become major spills. Thanks to the ever-growing commercial market for satellite imagery and value-added services, there is a data set available to meet the requirements of nearly any geographic, environmental, or weather condition. More importantly, the large constellation of satellites means at least one is positioned to capture an image over a specific area of interest on a given day, making it possible to track rapidly changing situations anywhere in the world with little advance notice.

From a technical perspective, most imaging satellites are now divided into two categories: optical and radar. Similar to Landsat, the optical satellites carry digital sensors capable of measuring energy reflected off the Earth's surface in the visible and infrared portions of the spectrum. Most optical satellites capture panchromatic (black-and-white) imagery covering one broad spectral band as well as multispectral imagery in several individual narrow bands.

The other category of imaging system is synthetic aperture radar (SAR). These active radar sensors emit their own sources of surface illumination in the form of microwave beams, which enables them to operate day or night in any weather condition including clouds and rain. Unlike optical systems with fixed spatial resolutions, SAR satellites can adjust their imaging configurations at the command of ground controllers to vary their spatial resolutions and fields of view to meet the needs of specific mapping projects.

Used together or individually, this diverse array of spaceborne observation systems can perform a variety of planned and unplanned monitoring functions for exploration and production operators. Choosing the right imaging system for a particular assignment depends on the location and environment of the features being monitored.

Routine offshore monitoring

Operators of petroleum production and transmission facilities that currently subscribe to remote sensing monitoring services use them most as oil spill early warning systems.

These services can be deployed for both on- and offshore operations. For monitoring open water around drilling platforms and shipping terminals, radar satellites are preferred because they differentiate oil on water more effectively than optical satellites and can be relied upon to capture images when weather conditions limit optical satellites.

Most commercial SAR systems operate in the C- or X-band portion of the microwave spectrum. The wavelengths of these radar beams are long enough to penetrate clouds and short enough to discern centimeter differences in patterns on the surface of water. When oil floats on water, it dampens the capillary waves on the ocean surface creating a smoother reflection pattern in the resulting imagery that differs from the surrounding water.

Natural oil seeps occur in water bodies around the world and are often used as indicators that oil may be found below the ocean floor. These natural seeps, however, can be confused with leaks from drilling and production operations in the vicinity of offshore platforms. For this reason, most periodic monitoring programs start with the acquisition of a baseline image of the project area to identify and map the natural seeps in advance.

Monitoring open water for oil seeps, slicks, spills, and leaks involves a tradeoff between spatial resolution and total project area when selecting imagery. It is important to keep in mind, therefore, that as swath width and overall coverage size increase, spatial resolution decreases, which means that small objects and features will not be distinguishable in the resulting imagery (Table 1).

SAR images covering large areas are economically attractive because of their low cost per square kilometer, but their spatial resolution is relatively low, which means only large objects and features can be identified. High-resolution imagery, on the other hand, costs the most per square kilometer and covers the smallest field of view but it is capable of identifying smaller objects and features. When small objects and features must be identified and mapped, the cost may be justified (Table 2).

To provide baseline monitoring of offshore facilities, the most effective strategy is to select SAR products that cover an entire project area with resolution sufficient to detect floating oil. A spatial resolution of 150 m is typically considered the minimum required for this task. Fortunately, there are now four major commercial SAR satellite systems with beam modes capable of covering large areas at this level of detail: the Canadian Radarsat, European ENVISAT, Italian COSMO-SkyMed, and German TerraSAR-X. Of these, Radarsat covers more than 250,000 sq km at 100-m resolution in one pass.

Operators with numerous offshore platforms spread across several blocks typically select the lower resolution image products covering large areas to get the most economical coverage. The large coverage gives the added benefit of identifying spills and seeps beyond the immediate area of interest.

Oil slick image generated from radar data. Image copyright European Space Agency-distribution Sarcom, courtesy of 3v Geomatics.

The frequency of monitoring programs can range from biweekly to near daily acquisitions depending on the user requirements. Imagery from multiple satellites can be acquired to increase revisit time and is particularly beneficial in emergency situations.

Closer to shore, where tankers dock at terminals, the area of interest can be much smaller. The higher resolution SAR beam modes are often called into service on a weekly or monthly basis to identify potential leaks emanating from vessels or from the terminals themselves. A spatial resolution of 30 m is considered the threshold for this type of monitoring. The RADARSAT-2, COSMO-SkyMed, and TerraSAR-X satellites are able to pinpoint the locations of leak sources with amazing accuracy using their high-resolution modes.

An economic advantage lies in establishing a periodic monitoring schedule for remote facilities (Table 2). Most satellite operators and third-party value-added vendors charge less to acquire and process imagery on a planned schedule than they do for unplanned, fast-turnaround products in emergency situations.

Finding leaks onshore

Onshore facilities have traditionally been monitored directly by personnel on foot, in vehicles, or aircraft, but optical multispectral satellites are becoming more prevalent for these duties, especially when underground pipelines and storage tanks are involved.

The first sign of an underground oil leak is often distress in the surrounding vegetation. The multispectral bands on modern optical sensors, specifically the near- and mid-infrared, can detect this stress before the human eye does, providing early notice that oil is leaking into the underground root system.

The most prominent commercial optical systems are operated by GeoEye and DigitalGlobe, both US companies, the French SPOT Image, and the German RapidEye. In the world of optical satellites, high-resolution is considered less than one meter, medium-resolution ranges from one to 20 m, and low or coarse resolution is usually above 20 m. Landsat is still the premier provider of coarse-resolution multispectral imagery although its panchromatic band offers 15-m resolution (Table 3).

Of the commercial satellites, the SPOT and RapidEye satellites are the most economical for monitoring large onshore areas because they cover relatively large surface areas at resolution sufficient for vegetative health mapping. The SPOT 4 and 5 satellites capture near- and mid-infrared multispectral imagery at 20 and 10-m resolutions, respectively, over an area of 3,600 sq km. The German RapidEye system consists of five satellites that capture 6.5-m resolution multispectral imagery with a daily capacity of up to 4 million sq km.

Monitoring of aboveground transmission pipelines remains one of the most common applications of remote sensing technologies, often required by government regulation. Aircraft perform this duty more often than satellites because fixed-wing airplanes and helicopters have the maneuverability to follow long pipeline corridors in a single flight and capture extremely high-resolution imagery from low altitude.

It should be noted, however, the new high-resolution satellites, GeoEye's GeoEye-1 and DigitalGlobe WorldView-1 and -2, have stunning agility. Their ability to swivel in orbit enables them to capture long stretches of linear features in a single pass. Each of these satellites captures 50-cm-resolution panchromatic imagery, which has expanded their applicability to inspect pipelines and other facilities at an incredible level of detail. In late 2010, SPOT Image will join the 50-cm imaging club with the launch of Pleiades-1.

Reservoir deformation monitoring of subsidence and uplift. Image courtesy of 3v Geomatics.

The eight multispectral bands on the new WorldView-2 satellite are currently undergoing vigorous testing and are anticipated to be especially well suited for vegetation change analysis.

Tracking emergencies

In open waters immediately following a large hurricane or storm, offshore platform operators often rely on SAR imagery to peer through the lingering clouds to determine if their facilities survived and to see if spills resulted.

Once damage to an offshore platform has been spotted, high-resolution satellites are often consulted for a second look to assess the extent of harm inflicted before crews are allowed to return.

Optical satellites are preferred to make these detailed assessments of structural damage due to the clarity of their imagery compared to SAR, but lingering clouds can make that impossible. In those cases when cloud cover persists and winds have died down, aircraft carrying extremely high-resolution imaging sensors are dispatched to photograph. In these instances, some aircraft have the advantage of being able to image from overhead and at oblique angles to view the sides of the floating platforms.

When oil does spill from a damaged offshore facility, the slick eventually reaches land. At this point, high-resolution optical satellites become the favored monitoring tool. The panchromatic bands of GeoEye-1 and WorldView-2 are usually capable of identifying oil that has washed onto beaches, while the mid-resolution multispectral bands of the SPOT satellites are adept at determining if larger wetlands and marshes have been inundated. In some recent cases, multispectral bands have been used to penetrate shallow water as deep as 5 m to locate oil floating just below the surface.

Following disasters such as the Deepwater Horizon spill, remote sensing systems are often applied in a tiered fashion. The broadest-swath satellites are used first to cover wide areas and find the floating spill or onshore damage. From there, higher resolution systems, either airborne or spaceborne, are called in to focus on the trouble spots and gather views as detailed as possible.

Benefits of commercial competition

The plethora of commercial imaging satellites has brought competition to the market.

Today, all satellite operators are fully aware the information contained in their imagery is time sensitive, and many can deliver it within hours in many cases.

Recent advancements in software, networks, data compression and new Web Mapping Services (WMS) technologies have allowed many suppliers to send geospatial information directly to key decision makers within the environments of online mapping systems such as Google Earth and Bing Maps, or visualization software common in the petroleum industry, such as ESRI ArcGIS and Global Energy Mapper.

In addition, an industry of value-added services companies has emerged to process the massive image files, extract information from them, and deliver GIS-ready vector layers or written reports, either as one-time projects or on a regular subscription basis. More importantly, these third-party vendors typically maintain data purchase agreements with numerous satellite operators, increasing the likelihood the vendor can obtain imagery from a satellite passing over an area of interest just when a client needs it.

The authors

Bud Pope is cofounder and president of Spatial Energy LLC, Boulder, Colo. He founded Spatial Energy in 2005 to provide satellite imagery to oil, gas, and mining companies worldwide, and most major and independent oil and gas companies are recurring customers. Pope previously was an executive in charge of the energy market for DigitalGlobe, the leading provider of commercial satellite data based in the US, and before that was vice-president of land products for ION Geophysical Corp. He is a CPA.
Adrian McCardle is president of 3v Geomatics Inc., Vancouver, BC. He specializes in advanced radar applications, data processing, and product development. He has extensive experience in the analysis and interpretation of satellite and airborne radar as well as optical imagery.

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