Solid Plan for Continuity
from Spot Image
First Sub-meter Satellite for Spot Image:
EDITOR'S NOTE This article is one in a series of the high-resolution commercial satellite companies.
The SPOT remote sensing satellite program is poised to add an important new chapter to its 23-year story of successful commercial operations. In 2010, the Spot Image Group will launch the first of two sub-meter imaging satellites, known as Pleiades, marking the program's first foray into the very high-resolution Earth observation market and adding new capabilities to an already robust constellation of existing satellites.
"The demand for high-quality imagery with spatial resolution in the 50-cm range for urban, defense, insurance and mapping applications is nearly limitless," said Antoine de Chassy, President and CEO of Spot Image Corp. (Chantilly, Va.). "We will serve this market with the same combination of advanced imaging technologies and innovative product delivery mechanisms that is the hallmark of the SPOT program."
De Chassy is quick to add that the Spot Image Group has no intention of abandoning the enormous mid- to high-resolution satellite imagery market that it created with the launch of SPOT-1 in 1986. Early in 2008, the Spot Image Group started the SPOT-5 follow-on program, with SPOT-6 and -7, ensuring continuity of the SPOT line of satellites well into the next decade. See Figure 1 of the SPOT constellation. The funding for these two satellites will be private; the final financial package is expected to be finalized soon. This will be an industry first, as no other Earth observation satellite of this scope has been financed by the operator and private funds.
Figure 1 An illustration of the SPOT constellation of satellites – SPOT-2, -4 and -5: Imagery from the SPOT satellites range from 20-m B&W to 2.5-m color. Spot Image compliments this constellation with 2-m imagery from FORMOSAT-2 and 1-m imagery from KOMPSAT-2.
The Spot Image Group, led by Spot Image SA of Toulouse, France, currently operates three commercial satellites, SPOT-2, -4 and -5. Plans call for SPOT-6 and -7 to be launched in 2012 and 2013, respectively. Joining the SPOT constellation next year will be Pleiades-1 followed by Pleiades-2, in 2011. In addition, the group maintains distribution rights to imagery from the Taiwanese FORMOSAT-2 satellite and the South Korean KOMPSAT-2 satellite.
"Our growing constellation of satellites, complemented by distribution arrangements with other system operators, provides an impressive selection of spatial detail, spectral information and revisit capability to meet the needs of end-user applications in every segment of the commercial geospatial industry," said de Chassy.
Planning the Pleiades Constellation
Development of the Pleiades satellites began in 2001 with funding from the governments of France and other European nations. The first Pleiades, which is scheduled for delivery to the launch pad in French Guyana later this year, and its twin will offer several new capabilities designed to complement, and to distinguish themselves from, the SPOT satellites. The most notable differences will be the resolving power of the imaging sensors and addition of a blue band for natural color imaging. See Figure 2.
Figure 2 An illustration depicting one of the two identical Pleiades satellites to be launched beginning in February 2010. Pleiades will deliver a standard 50-cm orthorectified color product and will be equipped with direct tasking capabilities that will enable the satellite to be tasked up to 40 minutes before acquisition.
"We entered the 1-m market with KOMPSAT-2 last year," says Nicolas Stussi, Director of Services and Business Development at Spot Image Corp. "We will make another major leap forward next year with the launch of our first Pleiades satellite, when we will be able to offer 50-cm color products on a worldwide scale."
With 95 percent of their imaging capacity—over 1 million km2/day for the two satellites—dedicated to commercial clients, each Pleiades satellite can deliver 0.5-m color products in 20x20 km scenes. The standard product will be a 50-cm ortho-rectified color image combining the ground detail from the panchromatic sensor with the spectral information from the multispectral bands. The customer will receive the complete set of bands: blue, red, green and near-infrared. Thanks to precise knowledge of satellite pointing and high-quality digital terrain models extracted from stereo pairs, location accuracy of ortho-image products is expected to be around three meters without the need for ground control points.
The Pleiades satellites were designed and built together to function as their own mini-constellation providing daily revisit, which is an extremely important capability for many very high-resolution imagery applications. When Pleiades-2 joins the first in space by mid-2011, the two satellites will travel in offset orbits to image the same point on the Earth's surface every two days at the equator and less than 24 hours at points above 45 degrees of latitude.
The frequent revisit cycle of Pleiades is in part due to the agility of the satellite. Each satellite will benefit from four Control Moment Gyroscopes (CMG) that will allow the satellites to pitch and roll forward, backward, and side-to-side up to 45 degrees, while preferably remaining within 30 degrees to keep the pixel size better than 1 meter. The ability to do this quickly means the satellite can acquire a multitude of separate or contiguous point targets covering up to 5,000 km2/minute in a single pass. Alternatively, each satellite can acquire long strips of imagery with 20-km-wide swaths.
Figure 3 A simulated image of the Cannes, France, seashore as it will be seen by Pleiades. 95 percent of Pleiades’s resources will be dedicated to the commercial market, allowing more users access to sub-meter imagery.
Each Pleiades satellite also will offer a strip mapping capability, expanding the collection swath up to 140 km, by acquiring several contiguous data strips on a single pass. This mode of collection will allow acquisition of contiguous areas up to 21,000 km2. See Figure 3 for sample image.
The Pleiades ground segment has been designed to accommodate better the needs of very high-resolution imagery users. In particular, time elapsed between request and delivery will be counted in hours and not in days, especially in times of emergency. To achieve this, Pleiades' tasking plan will be refreshed three times a day—every eight hours. This quick tasking is expected to be greeted enthusiastically by clients whose applications involve incidents and events that occur on short notice, such as natural or man-made disasters.
Spot Image will also offer a direct tasking capability for Pleiades, providing the ability, in case of emergency, to directly task the two satellites. "With the direct tasking capability, we will put the joystick into the hands of our customers, allowing them to task each satellite up to 40 minutes before the actual pass," says Stussi. Up-load of the tasking plan to the satellite will be done either by SPOT Image's main ground receiving station, or directly by the user's ground receiving station. The user will benefit from having a better knowledge of local weather and cloud conditions right before scheduling a collect, which will enable them to adjust the satellite pointing accordingly.
Thanks to the high agility of the satellite, Pleiades will also have the ability to collect same-pass stereo and tri-stereo imagery. Digital Elevation Models derived from such stereo data will prove to be even more precise and accurate than the already highly accurate 3D products Spot Image is currently offering with its Reference3D DTED Level 2 product.
"While the Pleiades satellites have been developed to work in tandem with each other, they have also been designed to complement the SPOT constellation as a whole," said Stussi. "A multi-satellite constellation of remote sensing platforms operating at different spatial resolutions is a very powerful asset. We are already seeing great interest from our clients in acquiring mid-resolution SPOT imagery over broad areas combined with half-meter scenes over specific targets—all in a single project or application."
More SPOT Sats Coming
The SPOT satellite program is widely credited with igniting the commercial satellite imaging revolution more than two decades ago. Today, these satellites continue to be critical for high-quality imagery, digital elevation models, wide-area mosaics and other geospatial information products derived from mid- to high-resolution satellite data. SPOT imagery has become the mainstay data set in environmental, natural resource, agricultural, forestry, urban planning and other applications that benefit from a rich combination of spatial detail and spectral information content.
Launched in 2002, the SPOT-5 satellite was considered a breakthrough, high-resolution imaging platform providing 2.5-m spatial resolution and 10-m multispectral data in the green, red, near- and mid-infrared bands. Setting SPOT-5 apart from its predecessors is the High Resolution Stereoscopy (HRS) sensor, an instrument dedicated to collection of stereo pairs on a single pass.
Reference3D is SPOT's premier product developed from HRS stereo pairs. Reference3D combines a Digital Elevation Model, a 5-m ortho-rectified image and eight quality masks to provide users with a complete geospatial base product. This product has been utilized by many Ministries of Defense around the world, including the U.S. government, to fill in data gaps in the Shuttle Radar Topography Mission global elevation data set, which sought to map surface elevations for the entire Earth. SPOT-5 has collected more than 110 million km2 of cloud-free stereo pairs ready for processing into Reference3D products, and over 35 million km2 of off-the-shelf DEMs are ready for delivery.
SPOT-2 and -4 continue to collect data for commercial applications. Their spatial resolution is 10-m panchromatic and 20-m multispectral, and their 60x60-km scene size is identical to SPOT-5. With the 60-km-wide swath, the SPOT program seems to have found the ideal scene size for mid-resolution applications. The scene is considered large enough for many regional geologic, environmental and natural resource uses, while remaining small enough to be cost-effective for localized logistical applications.
According to Stussi, the foremost goal of the SPOT program dating back two decades has been to develop the commercial market for satellite imagery. "Our main focus is now to ensure a continuity of service for the 2- to 10-m resolution market we have being developing over the past 23 years. With SPOT-6 and -7, we will ensure continuity of services to our customers up to at least 2020."
Design of the two new SPOT satellites began last year in France by EADS Astrium, which obtained an 81 percent majority stake in Spot Image SA by purchasing shares formerly held by CNES, the French Space Agency. Along with its 60-km swath, SPOT-6 and -7 will offer an improved 2-m spatial and 8-m multispectral resolution. Clients can also expect to see enhanced positional accuracy in the SPOT-6 and -7 data sets, including a greater revisit rate and improved collection capacity worldwide.
Spot Image predicts that the majority investment in Spot Image by EADS Astrium Services is a precursor of new opportunities to come for the Spot Image Group and its clients in the next few years, leading up to SPOT-6 and -7. In the past two years, SPOT has focused efforts on delivering a variety of new services based on the satellite-derived information, most notably leveraging the Google Earth viewing environment. With a services company now the majority owner, SPOT is expected to place an even greater emphasis on finding new and innovative ways to deliver data more quickly to customers in formats that are easier to use.
FORMOSAT-2 and KOMPSAT-2
In terms of overall value to specific applications, the spatial and spectral resolving capabilities of an imaging satellite are followed closely by its revisit cycle. Rapidly changing events such as environmental disasters—floods and wildfires, for example—require frequent monitoring so that emergency personnel can respond accordingly and deploy assets where they are needed most. Because no single satellite can be everywhere at once, catastrophic situations highlight the advantages of a multi-satellite constellation.
"There are certain events where clients want data every time our satellites pass overhead, even if spatial resolutions are different," said Drew Hopwood, Project Manager for Spot Image Corp.
Figure 4 In October 2007, as wildfires wreaked havoc in southern California, Spot Image acquired this image with SPOT-5, embedded it within Google Earth and distributed it to emergency responders to help them locate and access the fire damage.
Hopwood cited the devastating 2007 California wildfires as an example of using FORMOSAT-2 (F2) imagery (see Figure 4). The commanders of fire crews needed to have multiple images of fires spread over large areas every day to try and keep their teams ahead of the flames. They called on Spot Image Corp. to bring all of its resources to bear on the situation. Anticipating needs such as this, Spot Image had already made arrangements to back up its own three satellites with marketing and distribution agreements involving other remote sensing operators.
In North America, Spot Image Corp. has exclusive distribution rights to imagery from the Taiwanese FORMOSAT-2 satellite. Launched in 2004, F2 has 2-m panchromatic and 8-m multispectral imaging capabilities. Because the satellite is designed to provide daily coverage over Taiwan, its orbit does not allow image acquisition worldwide. But for those areas it does overpass—such as the East and West Coasts of the United States—daily acquisition is the rule. Another interesting difference F2 offers is a 9:30 a.m. equatorial crossing, which enables it to capture morning imagery before the clouds gather in some tropical zones.
Figure 5 High-resolution imagery and daily revisit capabilities make FORMOSAT-2 an ideal solution for change detection applications. This image of Kuwait City, taken on Sept. 17, 2005, is an example of the high quality 2-m imagery FORMOSAT-2 provides.
Figure 6 Along The Strip in Las Vegas, NV, huge hotels and casinos rival each other with their bold architectural designs as seen in this KOMPSAT-2 image acquired on Feb. 20, 2007. KOMPSAT-2 with 1-m imagery is a very high resolution solution for civilian and commercial markets.
Figure 7 This KOMPSAT-2 image of the beautiful city of Putrajayan, Malaysia, was taken on Apr. 21, 2007. KOMPSAT-2 combines 1-m imagery in 15-km swaths with a large acquisition and storage capacity to make it an ideal solution for mapping of large and small areas.
In addition to calling on F2 during the California wildfires, SPOT has tasked the satellite to acquire imagery for agricultural and coastal monitoring. Hopwood also noted that SPOT offers a cost-effective, turn-key monitoring service in which F2 acquires continuous images over a target specified by a client that wants to detect some type of change in surface conditions or features over time. The client can check the images via a dedicated web portal and purchase only the images that contain the information they want. Figure 5 shows Kuwait City, taken by F2.
To further supplement and complement its existing constellation of satellites, Spot Image Corp. recently obtained distribution rights to the South Korean KOMPSAT-2 satellite. This satellite will enable SPOT to begin cultivating its market for very high-resolution imagery in anticipation of Pleiades. KOMPSAT-2 acquires 1-m panchromatic and 4-m multispectral in four bands (red, green, blue and near-infrared). Unlike most optical satellite platforms, it follows a south-to-north acquisition orbit.
"Most of the interest we have seen so far in KOMPSAT-2 data has been for urban applications where very small objects are being mapped in municipal environments," said Hopwood. See Figures 6 and 7.
To derive the most value from all available resources, Spot Image has developed an integrated collection management solution to support combined collections from SPOT-2, -4 and -5 as well as FORMOSAT-2 and KOMPSAT-2. SPOT ground receiving stations can also be equipped with a standard, turn-key hardware and software solution to acquire and utilize imagery from all available platforms.
Summarizing the ability of the Spot Image Group to meet the needs of a diverse base of current and future geospatial information customers, de Chassy said, "With five healthy satellites in orbit and four more under development, SPOT will be serving the mid- to very high-resolution imagery markets with an unprecedented combination of frequent revisit and large-area coverage well into the next decade."