Until now, Toulouse-based CLS that has been working successfully on environmental surveillance, the sustainable management of marine resources, and maritime safety for more than twenty years outfitted all the boats participating in the major world races with Argos beacons, which locate the boats and transmit any request for assistance in case they overturn. For the famous Vendée Globe 2008-2009 (solo round-the-world yacht race), CLS has innovated, offering participating navigators an experimental iceberg detection and drift prediction tool via satellite. CLS uses ESA satellite Envisat radar to do so.
Using 250 Envisat Radar Images
Today the boat skippers in the major high sea races see more and more icebergs in southern waters around Antarctica. So, the dangerous zones have to be carefully monitored to avoid collisions. "After falling overboard, icebergs are the second greatest danger for skippers. In 2004, Sébastien Josse hit a slab of ice that, according to him, was the size of a Breton commode - a block of ice that destroyed the aft end of his boat. So, two years ago, we began to tackle this problem, with CLS General Manager Christophe Vassal, among others, to find a solution," summed up Vendée Globe Race Director Denis Horeau. The satellite and particularly the radar satellite for clear observation regardless of cloud cover and night darkness, turns out to be the only way to accomplish this. For this purpose, CLS engineers use radar images provided by ESA satellite Envisat. The 8.2-ton 'monster', which was launched in 2002, is the most complex Earth observation satellite ever launched, with 10 optical and radar instruments aboard.
For the 2008-2009 Vendée Globe, the Radar Applications Division, the young Brest-based branch of the Toulouse-based company, processed, analyzed and interpreted 250 radar images on the route taken by the race challengers. "We programmed three image acquisition phases. The first was last November, ten to fifteen days before the first skippers entered the Southern hemisphere. We wanted to acquire all the locations of the ice at the different safety "doors" the boats had to pass," explained CLS Radar Applications Manager Vincent Kerbaol. A second image acquisition phase was carried out in the passage zone, a few days before the race leader went through. Believing that is was important to adjust, modulate and fine-tune the programming during the entire race, CLS engineers defined the third phase. "The point was to take account of the actual advance of the challengers, and to give ourselves enough leeway to focus on the high-risk zones we had identified," he explained.
A Useful Solution for Skippers and Race Organizers
As they cannot be interpreted by an untrained eye, the raw Envisat satellite images covering a 400 x 400km area, specialized software called SARTool engineered by CLS Radar Division has to be used for detailed image analysis. The software automatically pre-detects icebergs. A radar analyst then validates each detection and confirms the presence of big icebergs whose size is usually over 150 meters. Areas with a high number of icebergs are then materialized and ranked according to size. "Once the high risk areas have been mapped, the map is transmitted to race HQ that makes the necessary decisions."
For instance, last December 2, after studying the maps generated by Thémis visualization software (also designed by CLS), CLS Vendée Globe Project Manager Louis Mesnier and Denis Horeau identified a class 3 iceberg (300 meters) called R005. Their report simply said that to connect door 1 to door 2 of the race, the skippers would choose the shortest route (the orthodromic track) and look for favorable southern winds, a route that would lead straight into the detected iceberg. So, the decision was made to shift door 2 far from the iceberg, and move it West to prevent the new route for the skippers from passing over the shallow waters of the Prince Edward Island Archipelago, an area where rough ocean conditions prevail.
Virtual Iceberg and Drift Model
Although it is important to detect and locate icebergs at a given time, where they are drifting is also an important fact. This means having information on the winds and currents that cause their drift and taking account of water temperature, the size and shape of each iceberg, to have an idea of how they will gradually break down. "Météo France (the French weather bureau) provides us with wind data. We deduct current flow mainly from the measurements taken by altimeter radar aboard the Jason and Envisat satellites. Combining the wind data, currents and iceberg characteristics then gives us a drift model," explained CLS Spatial Oceanography Manager Philippe Escudier.
Nevertheless, it is impossible to predict everything. That is why CLS engineers designed another tool, a model based on the principle of virtual icebergs. "As we have precisely identified the borders of the polar ice pack, we can generate pseudo-icebergs of every size, which we then let drift, taking account of currents and and winds in the area. This way we obtain a statistical limit to the high-risk areas for icebergs, and gain additional information," he underscored. Thanks to the set of tools engineers by CLS, the Vendée Globe skippers now receive a digital ice-report where the geographic position of icebergs is listed. They just have to open the file for the data to be integrated immediately into the mapping system of each challenger, who can then decide which route to take. "Granted, the tool does not locate 100% of the ice since navigators have run into icebergs that were not detected. Nevertheless, the tool has substantially increased the safety of the Vendée Globe challengers, by not sending them into an ice field," concluded Denis Horeau.
