Technology in focus: GNSS Receivers

Trimble Catalyst software defined receiver with an Android device

connected capable of RTK solutions.

Image courtesy: Trimble.

From Hydro Int. by Huibert-Jan Lekkerkerk

Evolution Towards Higher Accuracies

GNSS has now been operational in the surveying industry, and especially in hydrography, for more than 25 years.
Where the first receivers such as the Sercel NR103 (once the workhorse of the industry) boasted 10 parallel GPS L1 channels, current receiver technology has evolved to multi GNSS, multi-channel and multi-frequency solutions.
In this article, we will look at the current state of affairs and try to identify the areas where development can be expected in the years to come.

In hydrography, we can distinguish between ‘land use’ and ‘marine use’ of our GNSS receivers.
Especially in the dredging, nearshore and inshore domains both land survey as well as maritime receivers are employed.
They do not differ in their basic capabilities such as positioning accuracy of number of channels (and GNSS) they can receive.
The main differences lie in the form factor of the receiver (portable for land survey, rack mounted for marine survey) and the method of operation.
Whereas a land survey receiver is almost always combined with a separate controller running extensive data acquisition software, the marine receiver is more and more of the black box type with at most a minimal display (and sometimes none).
Setting of the pure marine receiver is done using a network interface with the computer browser whereas the positioning data is transported over the network (or if required RS232) connections to the data acquisition software.

 GNSS constellations, their associated frequencies and the number of satellites ultimately transmitting these signals.

Source: gsa.europa.eu

GNSS Signal Reception

If we look at the major developments over the last few years, then it is the continuous addition of systems to the satellite constellation such as Beidou and Galileo as well as the longer existing GPS and Galileo.
But even within the existing systems developments are ongoing, with new frequencies such as L1C, L2C and L5 being added to the spectrum of available signals.
Most receivers are ahead of actual GNSS operations and will supply their receivers prepared to receive all GNSS and the maximum number of satellites and signals available.
As a result, a modern receiver may boast over 400 channels with an average of around 200 channels in a receiver.
A single channel will receive a single frequency from a single satellite for a single GNSS.
Thus, current high-end receivers can track over 125 satellites at the same time! Be aware however that not all systems are currently at full operational capability (FOC).
GPS and Galileo are at FOC whereas both Beidou and Galileo have limited coverage.
Those working in the far East will benefit from Chinese Beidou, the Japanese QZSS and the Indian IRNSS as the local coverage is very stable.
However, elsewhere in the world Beidou coverage is still marginal and QZSS and IRNSS coverage non-existent due to their regional character.

 Percentage of GNSS receivers able to receive a certain constellation in 2016.

Image courtesy: gsa.europa.eu

Signal Processing

The processing of GNSS signals is still being improved although this is more evolutionary than revolutionary.
The availability of ever greater processing power allows the GNSS receiver to allow, for example, for a better multi-path rejection.
Also, receiving weak signals and being able to detect the direct signal from a confused set of GNSS signals is currently possible..
Better tracking and multi-path rejection is not only the result of higher processing power but also of developments in antenna design.
Thus, it becomes easier to move the GNSS in difficult situations whilst still keeping relatively stable and accurate positioning.
The increased computing power also makes it easier to implement algorithms that have an increased accuracy when processing multiple GNSS signals at the same time.
The increased processing power also makes it easier to integrate Precise Point Positioning (PPP) and heading solutions on a single receiver board making the units effectively smaller.

In general, the use of PPP seems to be increasing with major suppliers of correction signals now supplying PPP corrections for all four global GNSS.
Most professional receivers are now dual frequency receivers, but these are expected to be replaced by triple frequency systems as the Galileo commercial service becomes available and GPS will have introduced L5 in more satellites.
Triple frequency processing promises even more accurate RTK and PPP solutions with faster initialisation times.

A modern GNSS receiver will start within a minute even in situations where it has not been started for a while if connected to the internet such as in most land survey receivers.
Without assisted-GNSS start-up times can be longer for a cold start.
Re-acquisition times are now well below 15 seconds with the more high-end receivers boasting re-acquisition times of just a few seconds in most situations.

Software Defined Receiver

One of the latest developments is the low-cost software defined receiver.
Where a traditional receiver has all the processing power in a standalone device, the software defined receiver uses the computing power of an existing device.
This means that the actual receiver is reduced to an antenna and analogue-digital converter to allow the GNSS signals to be processed by the positioning device, for example, a tablet.
The lack of dedicated hardware means that the software defined receiver is relatively cheap and lightweight and can be integrated into existing applications that have direct access to the positioning system rather than to just the output.

Data Output

As stated earlier, most modern receivers employ internet connection to transmit their data to the survey computer.
Serial connection (RS232) is still available with modern receivers although the number of ports are being reduced in favour of the network connection.
The frequency of data output is becoming higher with less latency for the signals with a higher update rate.
While in the past the interpolation of ‘intermediate’ positions between the 1s formal output was very visible, modern GNSS receivers can output at relatively high frequencies without a significant degradation of positioning accuracy.
However, most manufacturers still advise using the 1 second output if the utmost accuracy is required in favour of update rates of 20 – 100Hz.
The main advantage of the higher update rates is that for applications where this high update rate is required such as in dynamic positioning it is available with a limited degradation of positioning accuracy, especially when operating in PPP.

Links :

• GeoGarage blog :  Superaccurate GPS chips coming to ... / New Air Force satellites launched to improve GPS / Europe's own satnav, Galileo, due to go live / Happy 20th Anniversary, GPS! / Behind the master controls of gps  ...

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The Soviet military program that secretly mapped the entire world

The Pentagon is visible at bottom left in this detail from a Soviet map of Washington, DC. printed in 1975.

ALL images from the Red Atlas: how the Soviet Union secretly mapped America, by John Davies and Alexander J. Kent, published by the University of Chicago press

From National Geographic by Greg Miller

The U.S.S.R. covertly mapped American and European cities—down to the heights of houses and types of businesses.

During the Cold War, the Soviet military undertook a secret mapping program that’s only recently come to light in the West.
Military cartographers created hundreds of thousands of maps and filled them with detailed notes on the terrain and infrastructure of every place on Earth.
It was one of the greatest mapping endeavors the world has ever seen.

San Francisco Bay area (1980)

Soviet maps of Afghanistan indicate the times of year certain mountain passes are free of snow and passable for travel.
Maps of China include notes on local vegetation and whether water from wells in a particular area is safe to drink.
The Soviets also mapped American cities in remarkable detail, including some military buildings that don’t appear on American-made maps of the same era.
These maps include notes on the construction materials and load-bearing capacity of bridges—things that would be near-impossible to know without people on the ground.

This Soviet map of lower Manhattan, printed in 1982, details ferry routes, subway stations, and bridges.

 New York Manhattan

Much of what’s known about this secret Soviet military project is outlined in a new book, The Red Atlas, by John Davies, a British map enthusiast who has spent more than a decade studying these maps, and Alexander Kent, a geographer at Canterbury Christ Church University.

The Red Atlas dives inside the secret Soviet mapping program.

Beginning in the 1940s, the Soviets mapped the world at seven scales, ranging from a series of maps that plotted the surface of the globe in 1,100 segments to a set of city maps so detailed you can see transit stops and the outlines of famous buildings like the Pentagon (see above).
It’s impossible to say how many people took part in this massive cartographic enterprise, but there were likely thousands, including surveyors, cartographers, and possibly spies.

A Soviet map of Boston printed in 1979.

Most of these maps were classified, their use carefully restricted to military officers.
Behind the Iron Curtain, ordinary people did not have access to accurate maps.
Maps for public consumption were intentionally distorted by the government and lacked any details that might benefit an enemy should they fall into the wrong hands.

The Soviets mapped North America at different scales,

as seen in this 1959 small-scale map of the San Francisco Bay area.

Davies and Kent argue that the maps were a pre-digital Wikipedia, a repository of everything the Soviets knew about a given place.
Maps made by U.S. and British military and intelligence agencies during the Cold War tended to focus on specific areas of strategic interest.

This small-scale map printed in 1981 shows the area around Montreal.

Montreal is shown in greater detail on this large-scale Soviet map printed in 1986.

 The Soviets also mapped European cities, including Copenhagen,

shown here on a map printed in 1985.

Soviet maps contain plenty of strategic information too—like the width and condition of roads—but they also contain details that are unusual for military maps, such as the types of houses and businesses in a given area and whether the streets were lined with greenery.

This 1982 Soviet map of London took up four panels, stitched together in this composite image.

Exhaustive notes on transportation networks, power grids, and factories hint at the Soviets’ obsession with infrastructure.
Davies and Kent see the maps not so much as a guide to invasion, but as a helpful resource in the course of taking over the world.

 The Berlin Wall is outlined in magenta in this Soviet map printed in 1983.

“There’s an assumption that communism will prevail, and naturally the U.S.S.R. will be in charge,” Davies says.

Very little is known about how the Soviet military made these maps, but it appears they used whatever information they could get their hands on.
Some of it was relatively easy to come by.
In the U.S., for example, they would have had access to publicly-available topographic maps made by the U.S. Geological Survey (legend has it the Soviet embassy in Washington, D.C. routinely sent someone over to check for new maps).
To obtain more obscure information, they would have had to get creative.

A Soviet map of San Diego from 1980 (top) shows the buildings at the U.S. Naval Training Center and Marine Corps Recruiting Depot in more detail than does the USGS map published in 1979 (bottom).

In this map of San Diego, the added detail may have come from satellite imagery, which the Soviets had access to after the launch of their first spy satellite in 1962.

In other cases, detail may have come directly from sources on the ground.

According to one account, the Russians augmented their maps of Sweden with details obtained by diplomats working at the Soviet embassy, who had a tendency to picnic near sites of strategic interest and strike up friendly conversations with local construction workers.
One such conversation, on a beach near Stockholm in 1982, supposedly yielded information about Swedish defensive minefields—and led to the Soviet spy being deported after a Swedish counterintelligence agent lurking nearby overheard the conversation.

This red white and blue map of Zurich, Switzerland, printed in 1952, is an interesting departure from the typically more earthy Soviet cartographic color scheme.

Exactly how the Soviet maps came to be available in the West is a touchy subject.
They were never meant to leave the motherland, and they have never been formally declassified.
In 2012, a retired Russian colonel was convicted of espionage, stripped of his rank, and sentenced to 12 years in prison for smuggling maps out of the country.
In researching the book, Kent and Davies had hoped to speak with some of former military cartographers who worked on the maps, but they never found anyone willing to talk.

As the Soviet Union broke up in the late 1980s, the maps began appearing in the catalogs of international map dealers.
Telecommunications and oil companies were eager customers, buying up Soviet maps of central Asia, Africa, and other parts of the developing world for which no good alternatives existed.
Aid groups and scientists working in remote regions often used them too.

Map of Boston (1965)

For anyone who lived through the Cold War there may be something chilling about seeing a familiar landscape mapped through the eyes of the enemy, with familiar landmarks labeled in unfamiliar Cyrillic script.
Even so, the Soviet maps are strangely attractive and very well made, even by modern standards. “I continue to be in awe of the people who did this,” Davies says.

Links :

• National Geographic : Secret Japanese Military Maps Could Open a New Window on Asia's Past / See the Historic Maps Declassified by the CIA
• Soviet Maps by John Davies
• Architect of the Capital : Hyper Detailed Soviet Maps Of Washington (about errors in the Soviet maps)
• Canterbury University : Cartography and the Kutznetsov
• News : Secret Soviet maps among hundreds on display at British Library exhibition
• Android App (Atlogis Geoinformatics) : Soviet military maps Pro
• Medium : Mapmaking behind the Iron Curtain 
• Wired : The Soviet military's eerily detailed guide to San Diego
  
• GeoGarage blog : Inside the secret world of Russia's cold war mapmakers /
  The CIA is celebrating its cartography division’s 75th anniversary by sharing declassified maps / How maps became deadly innovations in WWI

Ophelia, strongest eastern Atlantic hurricane on record, roars toward Ireland

NOAA satellite picture

From Washington Post by Jason

On Saturday, Hurricane Ophelia accomplished the unthinkable, attaining Category 3 strength farther east than any storm in recorded history.
Racing north into colder waters, the storm has since weakened to Category 1, but it is set to hammer Ireland and the northern United Kingdom with damaging winds and torrential rain on Monday as a former hurricane.

 Wind wave height (until 13-14 meters forecasting) on Ventusky
see also CEFAS WaveNet interactive map
or Irish weather buoy network (IMOS) for live observations

The Irish Times reported that the storm could be the strongest to hit Ireland in 50 years.
The Daily Mail reported that the UK Met Office had compared the storm to Hurricane Katia, the tail end of which struck the region in 2011.

(National Hurricane Center)

The storm, about 700 miles south-southwest of Ireland’s southern tip and packing 90 mph winds, is jetting to the northeast at 38 mph.
As it heads north, it is forecast to weaken further and morph into what’s known as a post-tropical storm by Sunday night.

It is passing over progressively colder water, which is stripping the storm of its tropical characteristics.
However, even as these cold waters cause the eye of the hurricane and its inner core to collapse, its field of damaging winds will expand and cover more territory — even if it doesn’t pack quite the same punch near its center.

Percent likelihood of at least tropical storm-force winds over Ireland and the United Kingdom. (National Hurricane Center)

Maximum sustained winds of at least 70 mph are projected by the time Ophelia reaches Ireland, and the National Hurricane Center forecast shows almost the entirety of Ireland guaranteed to witness tropical-storm force winds of over 39 mph.
Hurricane force gusts of up to 80 mph are possible.

“This will be a significant weather event for Ireland with potentially high impacts — structural damage and flooding (particularly coastal) — and people are advised to take extreme care,” the Irish Meteorological Service said.
It issued a “red warning,” its highest-level storm alert for the southern and coastal areas.

GFS model projects wind gusts near 80 mph over southwest Ireland early Monday. (WeatherBell.com)

The UK Met Office issued an “amber wind warning” for northern Ireland, the second-highest alert, where it is predicting wind gusts up to 70-80 mph, and released the following statement:

A spell of very windy weather is expected on Monday in association with ex-Ophelia. Longer journey times and cancellations are likely, as road, rail, air and ferry services may be affected as well as some bridge closures.
There is a good chance that power cuts may occur, with the potential to affect other services, such as mobile phone coverage.
Flying debris is likely, such as tiles blown from roofs, as well as large waves around coastal districts with beach material being thrown onto coastal roads, sea fronts and properties.
This leads to the potential for injuries and danger to life.

Parts of southern and central Scotland and northern England also may face a hazardous combination of tropical storm-force winds and heavy rain.
Because the storm is moving so fast, its powerful blow will be brief, the worst lasting six to 12 hours in most locations.
It will leave the British Isles by Tuesday morning.

On Sunday, ahead of the storm, strong southerly winds were drawing abnormally warm conditions into the British Isles, with high temperatures up to 77 degrees (25 Celsius) forecast.
The Daily Mail reported that “swarms of deadly jellyfish” (actually, Portuguese man o’ war) had washed ashore on southern beaches.

Ophelia’s place in history

Ophelia near peak intensity Saturday. (NOAA)

When Ophelia became a major — Category 3 (or higher) — hurricane Saturday, it marked the sixth such storm to form in the Atlantic this year, tied with 1933, 1961, 1964 and 2004 for the most through Oct. 14, according to Phil Klotzbach, tropical weather researcher at Colorado State University.

 A singular trajectory

The storm is most remarkable, however, for where it reached such strength — becoming the first storm to reach Category 3 strength so far east.

This figure really says it all. #Ophelia is a huge outlier from the typical envelope of major hurricane tracks in the Atlantic

— Sam Lillo (@splillo) October 14, 2017

Much-above-normal water temperatures and light upper-level winds helped the storm reach such unusual intensity so far north and east in the Atlantic Ocean.

 Sea surface temperature difference from normal over Atlantic waters which Ophelia traversed. (NOAA)

While having a major hurricane so far east in the Atlantic Ocean is rare, it is not particularly unusual for former tropical weather systems to slam into Ireland and the United Kingdom.
As we wrote Friday, this happens about once every several years, on average, conservatively.

Links :

• WashingtonPost : Ophelia may slam Ireland, Britain as an ex-hurricane, but this isn’t as rare as you might think
• NYTimes : Ireland and Britain Brace for Unusual European Hurricane  / 10 Hurricanes in 10 Weeks: With Ophelia, a 124-Year-Old Record is Matched
• CNN : Hurricane Ophelia heading to Ireland, then Scotland
• Mashable : 'Red' alert in Ireland as ex-hurricane Ophelia roars ashore with destructive winds 
• Weather Underground : Ophelia Hits Category 3; Destructive Winds On Tap for Ireland
• Irish Times : Why is Hurricane Ophelia so powerful and why is it heading for Ireland? 

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