HMS Magpie tests groundbreaking software to rapidly map the seabed

Radar shoreline map of Plymouth Sound, 

a byproduct of the software used for the survey (Royal Navy)

 View of Plymouth Sound with the GeoGarage platform (UKHO raster map)

From Royal Navy

The Royal Navy has tested cutting-edge software to map the seabed close to shore in hours – not days or weeks.

Survey vessel HMS Magpie was able to chart the waters around Plymouth purely using regular radar installed on shipping the world over and a specialist computer program which measures wave height.

Using that data and information about currents, the software can produce a detailed profile of the seabed in a matter of hours – without the ship or boat having to physically sail over the area being surveyed.

All the system needs is wind and a swell to generate waves – plus computing power.

 

HMS Magpie off Portsmouth (Royal Navy)

It is not as detailed as the scans Magpie or other Royal Navy survey vessels can produce with their hi-tech sonar suites – and it only works close to shore.

But the method – known as radar bathymetry and developed by scientists from the National Oceanography Centre in Liverpool and MOD experts from Defence Science and Technology Laboratory – could be vital in times of peace or war when time is critical.

 

“By analysing the sea clutter images of waves visible on standard marine radars a bathymetric profile (that's the depth) and surface current assessment is created,” explained the lead project scientist at the National Oceanography Centre, Paul Bell.
“This technique could allow the remote charting of both shallow water and currents from a standoff distance of several nautical miles and could be employed by all Royal Navy Ships using the navigation radars that are already fitted with.”

Given her size, Magpie doesn’t carry the standard navigational radar used by the rest of the Fleet, so one was temporarily installed on a roof rack.

It would take the ship perhaps a fortnight to map the ocean floor on the approaches to Plymouth naval base and the Sound with her sonar.

It took the software just hours to do the same – and one by-product was an accurate composite map of the area’s coastline.

Time could be the difference between life and death in the aftermath of a natural disaster with a possible shifting seabed preventing the usual access to harbours or beaches or an amphibious landing on or evacuation from poorly/uncharted shores.

At present the software is still in development, but the goal is to integrate it with the Royal Navy’s existing navigational radar and systems – no new equipment would be required in most cases, just upgraded software – to provide accurate, real-time seabed maps.

“The Royal Navy is continually looking to employ new up-to-date technologies,” said Lieutenant Commander Mark White, HMS Magpie’s Commanding Officer.
“The beauty of this concept is that it uses the existing radars already fitted to our ships.
“It was excellent to work alongside the National Oceanography Centre to trial and develop these new and exciting techniques that could have a wide range of use in the Royal Navy.”

More regular duties are in store for Magpie shortly.

Having just emerged from her annual winter overhaul, the ship is due to head up the East Coast to conduct traditional survey work of ports and harbours.

SailGrib Android mobile app & GeoGarage

SailGrib Android on GooglePlay

SailGrib (version 6.0, March 8th) is compatible with the GeoGarage nautical chart platform

Tutorial (in English)

see SailGrib FAQ :  FR / US

Note : Weather4D R&N iOS users already having a GeoGarage account can use their GeoGarage account with SailGrib Android, and vice-versa

Norse goddess reveals seabed secrets

From NIWA

A large, orange Scandinavian robot gives NIWA’s marine geologists an in-depth look at changes to the seafloor off Kaikōura.

The 2016 earthquake left an all-too-visible trail of destruction across Kaikōura’s landscape.

Buildings were shattered, road and rail links severed, and massive scars cut across hillsides and coastal terraces alike.

What wasn’t so immediately obvious was the impact the 7.8 magnitude quake had on the deep underwater canyon just hundreds of metres off the coast.

 localization with the GeoGarage platform (Linz nautical raster chart)

 

The Kaikōura Canyon starts less than a kilometre out from land, as the seabed plunges to depths of more than 600m, and eventually to 2000m, creating a formation of channels and ravines which fan 60km out into the Pacific Ocean.

Cold currents rising from the deep bring nutrient-rich waters into the canyon system, helping to create a uniquely productive habitat nourishing organisms ranging from small seafloor invertebrates through to the region’s iconic dolphins and whales.

Marine geoscientist Dr Joshu Mountjoy describes the canyon as the bridge between the land and the ocean, connecting sedimentary systems, capturing carbon and supporting rich ecosystems.

Multibeam seabed surveys carried out by NIWA’s research vessels Tangaroa and Ikatere after the 2016 quake revealed dramatic changes.

Huge amounts of mud and sediment, estimated at 850 million tonnes, were shaken from the canyon rim, flowing down the underwater channels and out into the Pacific.

The AUV’s high resolution mapping technology reveals huge boulder ridges running across the seafloor more than a kilometre below the surface.

This massive submarine sediment flow, tracked at least 700km to the north, instantly turned the canyon floor from a biodiversity hotspot full of marine life into a barren, almost uninhabited seascape.

Late last year Mountjoy led another team of researchers back to the waters off the Kaikōura coast aboard Tangaroa.

“We were interested in understanding the physical process that had removed such a huge amount of sediment and rock from the canyon. It was also a chance to establish how the ecosystems were recovering after such a major event, and measure the amount of sediment re-entering the canyon,” Mountjoy says.
“Although we had done surveys before, we now needed a way to capture the extent of the post-earthquake changes at a much higher resolution.”

To get such a detailed picture of conditions almost two kilometres under the surface, Mountjoy recruited the help of the European marine research alliance, Eurofleets+. NIWA is the only southern hemisphere member of this 27-country alliance.

In October, Rán, a 6.5m autonomous underwater vehicle named after the Norse goddess of the sea, arrived in Wellington on loan from Sweden’s Gothenburg University.

Technicians reprogramme Rán as the AUV prepares for its next mapping mission off the Kaikōura coast.

[Photo: Lana Young, NIWA]

Fully equipped with its own suite of sensors for remotely scanning the seafloor and monitoring oceanographic conditions, Rán was also accompanied by two European technicians who both had to undergo full quarantine procedures prior to joining the voyage.

Pre-programmed and deployed from the stern of Tangaroa, Rán descended to the depths of the canyon floor, operating for up to 29 hours before needing to return to the research vessel.

It is the first time this type of technology has been used in New Zealand waters, and sweeping as low as 20m above the seabed, the AUV was able to map the entire canyon floor at resolutions 25 times higher than earlier surveys.

During Tangaroa’s research voyage, Rán completed a total of 14 dives, surveyed over 2,000km of seafloor at an average speed of 7km/h, and acquired a staggering 1.6 billion datapoints.

“The data has given us unprecedented insight into how submarine canyons are created,” says Mountjoy.
“The mid-lower canyon is dominated by giant gravel waves that are carving out the bedrock.
“We already knew that dunes 20m high and 200m across had shifted 500m down the canyon. But the data collected by the AUV now shows that these dunes are made of boulders up to 7m across."
“It is hard to imagine how much power is required to move rocks of that size, but that’s exactly what has happened in that area.”

The research team are currently working their way through the detailed data files recovered during Rán’s successful mission – a high-resolution treasure trove which Mountjoy believes will lead to a clearer international understanding of post-earthquake continental shelf processes.

Links :

• GeoGarage blog : Scientists detect huge fault rupture offshore from Kaikoura

Walker 'stunned' to see ship hovering high above sea off Cornwall

  A tanker appears to hover high above the surface of the sea off the Cornish coast. Photograph: David Morris/Apex

From The Guardian by Ian Sample

David Morris encounters rare optical illusion known as superior mirage while out on coastal stroll

There are only so many polite words that come to mind when one spots a ship apparently hovering above the ocean during a stroll along the English coastline.

David Morris, who captured the extraordinary sight on camera, declared himself “stunned” when he noticed a giant tanker floating above the water as he looked out to sea from a hamlet near Falmouth in Cornwall.

The effect is an example of an optical illusion known as a superior mirage.Such illusions are reasonably common in the Arctic but can also happen in UK winters when the atmospheric conditions are right, though they are very rare.

The illusion is caused by a meteorological phenomenon called a temperature inversion.

Normally, the air temperature drops with increasing altitude, making mountaintops colder than the foothills.

But in a temperature inversion, warm air sits on top of a band of colder air, playing havoc with our visual perception.

The inversion in Cornwall was caused by chilly air lying over the relatively cold sea with warmer air above.

 

Warm air over cold water can produce a 'superior' mirage

Guardian graphic. Source HyperPhysics, Georgia State University.

Note : vertical scale exaggerated

 
Because cold air is denser than warm air, it has a higher refractive index.

In the case of the “hovering ship”, this means light rays coming from the ship are bent downwards as it passes through the colder air, to observers on the shoreline.

This makes the ship appear in a higher position than it really is – in this instance, above the sea surface.

“Superior mirages occur because of the weather condition known as a temperature inversion, where cold air lies close to the sea with warmer air above it,” said David Braine, a BBC meteorologist. 

“Since cold air is denser than warm air, it bends light towards the eyes of someone standing on the ground or on the coast, changing how a distant object appears.”

He added: “Superior mirages can produce a few different types of images – here a distant ship appears to float high above its actual position, but sometimes an object below the horizon can become visible.”

Photographers around the world have captured striking images of ships, yachts and other vessels apparently hovering in mid-air thanks to superior mirages.

One potential clue that the sight is a mirage is the lack of any detail below the vessel’s waterline – for example a mirage of a “hovering” yacht lacked the lower hull and keel.

The latter effect is well known to sailors who can sometimes rely on refraction to spot ships that are geometrically beyond the horizon.

Sailors say such ships are “looming” over the horizon and sometimes report distortions that stretch or compress the images, making them “towering” or “stooping” mirages, respectively.

More familiar optical illusions are the “inferior mirages” that give rise to apparent oases in the desert and puddles on hot summer roads.

These mirages happen when cooler air sits on a layer of hot air, directly above a road, for example. When sunlight coming down from the sky approaches the air near the hot surface, it is bent back upwards to the observer’s eye, making the sky appear to be reflected on the road.

Links :

• The Guardian : Weatherwatch : castles in the air
  

Beneath the blue: dive into a dazzling ocean under threat – interactive

click on The Guardian