Sat nav signals enlisted to measure ocean wind and waves

Sat nav signals enlisted to measure ocean wind and waves

It's rarely a problem to tell how rough the sea is when you're afloat on it. But gauging conditions from a distance and across a wider area has always proved much harder.
Now scientists have pioneered a way to use signals from satellites in navigation systems like Global Positioning System (GPS) or Galileo to measure the intensity and direction of ocean wind and waves from space.

GPS signals are found constantly everywhere in the world, and if properly interpreted could dramatically improve our ability to monitor the oceans, providing a large amount of data on conditions at sea to marine scientists and meteorologists. This would help improve advance warning of storms and weather forecasts.

Specialised satellites can already provide data on wind speed and direction, but the global coverage is daily at best. Taking advantage of GPS signals could give scientists access to far more measurements closer to real-time.

The researchers hail from the National Oceanography Centre, Southampton (NOCS), private company Surrey Satellite Technology Ltd and the University of Sannio in Italy.

Surrey Satellite Technology developed a small, lightweight instrument that can be installed on a satellite in low Earth orbit to measure the signals bouncing off the planet from the network of GPS satellites orbiting far above. The researchers' findings appear in Geophysical Research Letters.

'This is a great achievement as it demonstrates the capability of this low-cost technology to provide ocean roughness data', says Dr Christine Gommenginger, a specialist in exploiting satellite data for oceanography who supervised the project at NOCS, adding that this information is expected to complement rather than replace the data gained from dedicated Earth observation satellites.

The technique involves detecting signals from global navigation satellites after they are reflected from the ocean's surface. The idea, known as Global Navigation Satellite System-Reflectometry, or GNSS-R, was first proposed in 1993 but its spaceborne implementation is only now becoming a reality.

Satellites of opportunity

'The GNSS-R instrument doesn't need to generate its own sounding signals; it can therefore be very small and has low power requirements, so it could piggy-back on any satellite,' adds Gommenginger.

'In the future we would like to be able to put this kind of Earth observation payload on commercial satellites, such as telecommunication satellites, taking advantage of these as platforms of opportunity in space in the same way as in oceanography we now gather data with instruments on ships of opportunity.'

One such opportunity could have been on the Iridium NEXT constellation of telecommunications satellites, which was seeking Earth Observation instruments to include in their payload, but the timescale proved too short to make this a reality.

Work is now underway to build the next generation of GNSS-R receivers with improved performance in a project funded by the Centre for Earth Observation Instrumentation led by SSTL. The team hope that such a GNSS-R receiver will be included in the payload of the follow-on to the European Space Agency's Soil Moisture and Ocean Salinity (SMOS) mission - SMOSOps.

Researchers first proved the concept from space in 2005, but this early work gave information only on ocean roughness; the new work establishes for the first time that reflected navigation signals can also provide information about the direction of roughness.

Navigation satellites orbit around 20,000 kilometres above the ground. For this research their signals bounced off the sea surface and were collected by a receiver on Surrey Satellite Technology's UK-DMC satellite, which orbits at just 680 kilometres. The UK-DMC satellite was part of the SSTL Disaster Monitoring Constellation, which main function is global imaging primarily for disaster monitoring purposes.

Just one second's worth of GNSS-R data gives the scientists the information needed to build a picture of conditions at the sea surface. As well as directional wind and wave information, the reflected signals could also be mined for information about the mean sea level to perform ocean altimetry.

The researchers compared the satellite results with model predictions and against in situ wave data from the US National Data Buoy Center. Earlier research had collected reflected navigation satellite signals over the Mediterranean using a receiver on an aircraft, but the technique needed to be demonstrated from satellites which make it possible to achieve global coverage and does not depend on a time-limited aircraft mission to take measurements

WEATHER NOTE

Volcano Hazards Program Observatories and Centers

Monitoring and research at the five volcano observatories in conjunction with the Menlo Science Center in Menlo Park helps advance our understanding of active volcanism and allows the Volcano Hazards Program to provide warnings of impending eruptions in the United States. We monitor earthquake activity, ground deformation, gas chemistry, and other geophysical and hydrologic conditions before, during, and after eruptions.

Observations are used to detect activity leading to an eruption, provide real-time emergency information about future and ongoing eruptions, identify hazardous areas around active and potentially active volcanoes, and improve our understanding of how volcanoes erupt and change our environment. The Volcano Disaster Assistance Program also assists other nations prepare for and respond to volcano emergencies.

Alaska Volcano Observatory (AVO): The Alaska Volcano Observatory monitors Alaskan volcanoes from its locations in Anchorage and Fairbanks, Alaska. It is supported by the U.S. Geological Survey, the Geophysical Institute of the University of Alaska Fairbanks, and the Alaska Division of Geological and Geophysical Surveys.

Cascades Volcano Observatory (CVO): The USGS Cascades Volcano Observatory monitors the U.S. Cascade volcanoes and is located in Vancouver, Washington. The USGS Volcano Disaster Assistance Program, which is headquartered at CVO, is supported by the USGS and the U.S. Agency for International Development's Office of Foreign Disaster Assistance.

Hawaiian Volcano Observatory (HVO): The USGS Hawaiian Volcano Observatory is located in Hawai`i Volcanoes National Park on the Big Island of Hawai`i.

Long Valley Observatory (LVO) The USGS Long Valley Observatory manages the monitoring efforts for the Long Valley Caldera from the USGS Western Region Headquarters in Menlo Park, California.

Yellowstone Volcano Observatory (YVO) The Yellowstone Volcano Observatory monitors and studies the active geologic processes and hazards of the Yellowstone Plateau volcanic field and its caldera. The Observatory is supported by the U.S. Geological Survey, University of Utah, and the Yellowstone National Park. Yellowstone National Park contains the largest and most diverse collection of natural thermal features in the world.

Worldwide Volcanology Sites

For worldwide volcano information, please see the Smithsonian Institution's Global Volcanism Program.

USGS Volcano Hazards Program Webcams

Below is a list of webcams of U.S. volcanoes. All webcams are operated by the USGS, unless otherwise noted. The images below are not the webcams but links to the webcams. The images were taken in the past by cameras and are meant to show the approximate area, not necessarily the view from the webcam.

Pu`u `O`o vent, Kilauea Volcano (HVO)

Halema`uma`u, Kilauea Volcano (HVO)

Summit caldera of Mauna Loa Volcano (HVO)

USDA Forest Service - Mount St. Helens Crater

Akutan, Alaska (AVO)

Augustine from Homer, Alaska (AVO)

Augustine Island, Alaska (AVO)

University of Alaska Geophysical Institute Augustine camp on the west side of the island, Alaska (AVO)

Near Infrared (NIR) Augustine, Alaska - best during low light (AVO)

Mount Cleveland, Alaska (AVO)

Fourpeaked Volcano, Alaska (AVO)

Katmai, Alaska (AVO)

Pavlof Volcano, Alaska (AVO)

Peulik, Alaska (AVO)

Mount Spurr, Alaska (AVO)

Mount Spurr, Alaska from station CKT (AVO)

Veniaminof Volcano, Alaska (AVO)

MARITIME NOTE

Amver Tanker Dispatched To Rescue French Yachtsman

Vendee Globe organizers lost all communications with French yachtsman Jean Le Cam after his sailboat capsized 200 miles off the coast of Cape Horn early Tuesday morning. An international effort, including a tanker dispatched by the Amver system, was underway to rescue the sailor.

Search and rescue authorities from Chile, France, and the United States Coast Guard Amver system are working together to coordinate the rescue.

Chilean authorities dispatched a rescue aircraft and, using data from the United States Coast Guard Amver program, requested the Bahamian flagged oil tanker Sonagol Kassenje to Cam's last known position.

Winds greater than 25 knots prevented the tanker crew from lowering their rescue boat. The Sonagol Kassenje, managed by Sonagol, remains on scene waiting for safer weather conditions. Cam remains trapped in the overturned hull of his sailboat but has been able to communicate with fellow racer Vincent Riou.

RS