The role of GNSS Receiver in Marine Survey

The Global Navigation Satellite System (GNSS) can be referred to as the standard generic term for satellite navigation systems that provide autonomous geo-spatial positioning with global coverage. Since the late 1980s, GNSS has been used extensively by land surveyors primarily for geodetic control networks and for photo control. With technology advancement, the systems have become more compact, easier to use and with a full complement of satellites enabling 24-hour usage. This has led to a significant increment on the diversity of surveying applications. In today’s world the GNSS systems are readily available for many surveying and mapping tasks, including establishing control, setting out, real-time deformation monitoring, on-board camera positioning for aerial photography; fixing positions depending on the accuracy of the points to be fixed.

GNSS systems range from low-cost systems with a positional accuracy of tens of metres, to high-cost geodetic survey systems able to determine positions to the sub-centimetre level. For survey accuracies, it is essential that hardware and software specifically designed for survey applications are used; these should always be utilized in the manner for which they were designed.

But what exact role does GNSS receiver depicts in marine survey?

The Role of GNSS Receiver

Global Navigation Satellite System (GNSS) refers to a constellation of satellites providing signals from space that transmit positioning and timing data to GNSS receivers. The satellites transmit two carrier waves in the L-Band referred to as L1 and L2. The carrier waves transmit information from the satellite to the earth. The receivers then use this data to determine location.

Most GNSS receivers have two parts; antenna and processing unit. The antenna receives satellite signals while the processing unit uses the information received to compute the locations of the satellites and adjust for accurate positioning. To determine the position of the receiver it needs to collect information from a minimum of three satellites. The carrier waves transmit information from the satellite to the earth.

• Determining the depth and terrain of the seafloor

The Global Navigation Satellite Systems (GNSS) receiver records the precise location of an object or phenomenon on, above or below the earth’s surface using coordinates. In marine Survey, the GNSS-equipped sonobuoys and echo-sounders are used in underwater sonar systems for various tasks such as hydrographic, bathymetric surveys as well sea floor mapping. They are also used for submarine and underwater acoustic research; this is according to Mr. Felix Orina, MD Orbital Africa.

“The GNSS is often fitted with either sonobuoys or echo-sounders to record the coordinates in 3D reference frame i.e. X, Y and Z (where Z is the seafloor depth). With this data, it is possible to map the depth and terrain of the sea floor. Knowing the depth and terrain of the seafloor in areas around the ports and along the navigation channels in the sea is critical to safe marine navigation. The Maps and nautical charts of the ports and channels are often created using bathymetric sonar systems fitted with GNSS where the coordinates including depths are obtained and recorded using the GNSS receivers,” continues Mr. Orina.

• Determine the positions of surface shipping

According to Hollie Moran, Sales Manager of Modulus Technology Ltd, an AAE Technologies Group company, the use of global navigation satellite systems (GNSS) to determine the positions of surface shipping has long been the conventional method for monitoring and recording the location of marine traffic. Equipment installed high above the water surface will continually and accurately report its position, safely removed from the threat of submergence and harmful water damage. However, not all assets have sufficient elevation to allow for such installations, so the challenge exists of how to accurately log the positions of target platforms directly on, or even under the surface of the water while maintaining the operational integrity of the equipment used to log those positions.

“We find the role of GNSS receivers in marine survey very important, just as with regular surveying. There are lots of boats and ships out there, many GNSS receivers too. By putting receivers on every boat or ship, we are able to receive so much more information on the seabed. There’s so much unknown, GNSS receivers will help us make new discoveries,” says Jeroen Methorst, Marketing Executive at marXact.

• Determining real-time spatial positioning

Gaynor Deacon, Director at Amaza Survey Services (Pty) Ltd, is certain that, GNSS receivers are the essential heart of all survey operations and offer real-time spatial positioning, which can be enhanced using satellite based correction services, NTRIP RTK corrections and/or RTK corrections from shore-based base stations.

“Depending on the service you select, this can be as accurate as a few centimeters. We can advise on the optimal installation, system configuration and correction service based on your final deliverable and requirements,” she adds.

• Determining underwater (acoustic) positioning

Without GNSS receivers there is no modern marine survey possible. With the exception of underwater (acoustic) positioning and a few specialized cases all positioning is now done using GNSS receivers. For nearshore work augmented with RTK techniques using either a local base station or a networked solution whereas for offshore construction surveys PPP from one of the commercial providers is now a commonly used technique, says Johan Stam of Skilltrade.

“In marine survey, a such centimetric positioning is useful for bathymetric applications, dredging, marine construction and of course precise navigation in harbor infrastructures etc,” comments Romain Legros, Director General at Geoflex.

• High accuracy heading

René Boudreau, Sales Manager at Benchmark Canada, articulates that, GNSS receivers are used in the marine market by people needing high accuracy heading and positioning.

“These high end, and high accuracy receivers provide position, heading, heave, pitch, and roll. These receivers are ideal for anyone from a recreational user, to a professional marine surveyor looking to replace their gyrocompass without breaking the bank,” he affirms.

Words of knowledge

We are living in the era of GNSS, where everyone is now carrying a satellite receiver in their pocket and using them in their daily activities such as communicating, moving around, at work places, sports activities etc. Additionally, GNSS receivers are widely used in precision applications that require reliable positioning in the most demanding applications for a variety of industries including surveying, precision agriculture, marine navigation, machine control, aerial guidance and many more.

Currently, the GNSS receivers are providing a very high-performance timing and synchronisation solutions. However, improving accuracy remains a continuous challenge for manufacturers, thus precise calibration of the antenna position is used to improve timing accuracy. Moreover, receiver configuration and algorithms are implemented as well to reduce time-pulse jitter and give room to smoother and more accurate timing solutions from GNSS, even in single frequency.

Let’s now learn more on what the GNSS experts have to say in regards to marine GNSS Receivers.

Johan Stam: GNSS seems to be a simple technique. Everybody is now using it in a smart phone or car. However, as simple as it seems, getting the best accuracy out of a GNSS requires a deep knowledge of possible errors and how to counteract them. One of the greatest pitfalls with accurate GNSS is not having the geodesy behind it correct. Many surveyors are unaware of the small differences that accumulate due to shifting continents and the positioning errors in GNSS associated from them. Secondary the lack of accurate height models makes the vertical component of GNSS inaccurate in many places. A good understanding of how GNSS works combined with the geodetics are a must have for anybody entering marine surveying.

Gaynor Deacon: We work in a challenging environment with sea salt covering everything and waves pummeling us and the equipment, so go for proven recommended systems which will handle the environments we work in. Consider purchasing the best system you can afford to get the most reliable, consistent and repeatable surveys. Try to have as many connectivity options as possible e.g. Bluetooth / wireless / serial / ethernet. This gives you redundancy when you are stuck in the field and support or replacement gear is days away. Likewise, with corrections, consider RTK base station with radio repeaters and satellite corrections as back-up, as this gives you more flexibility if you move further away from your base on a stretch of river, lose sight of it due to vegetation or the battery dies and you still have hours to work.

Felix Orina: Different Marine GNSS receivers yield different performances in different environments, and the choice that one makes before purchasing the GNSS should depend largely on various factors including the name of manufacturer, target application, sea depth in marine environment, receiver features and its capabilities, durability, power consumption, cost and most importantly performance and accuracy. The buyer also needs to do some research on the use and absorption of a given brand of GNSS receiver in the market i.e. how many organizations or individuals are using the same GNSS receiver. The feedback from such organizations is crucial in enabling a buyer to make an informed decision on the best cost-effective brand and model of the GNSS receiver to purchase.

Romain Legros: Source for pure and agnostic GNSS augmentation services operators delivering its corrections data streams in an interoperable format (RTCM3 SSR) that provides integrators with the possibility to fully develop their own applications. For solution integrators evolving in marine domain, one should source for a GNSS precise and robust technological brick to serve their applications.

Hollie Moran: Utilise GNSS systems that can be used on the water surface and can survive submersion of several thousand metres water depth, that would make them the perfect partner for your observation class or deep-water work class ROV’s and subsea ploughs. Also ensure the GNSS system when used in conjunction with subsea acoustic positioning systems such as the Applied Acoustics’ USBL, real-time monitoring of vehicles in the undersea or surface environments becomes possible and enables surface tracking/recovery and lost asset relocation. And when installed on a subsea vehicle such as an AUV, accurate positional information can be transmitted to any location on the globe once the vehicle has broken the water surface, a crucial component in remote asset monitoring.

Jeroen Methorst: Look into what sets GNSS receivers apart. We believe a receiver should be easy to learn and use. Universal as well, ready to be connected to and work with independent software and cloud solutions. Not just the software of the same brand the receiver is from, but to all sorts, so you choose what works best for you.

René Boudreau: Always do your research. Just because you recognize the product, does not mean it is the right one for you. Make sure you ask questions, and explain what you plan to do with the equipment. Oftentimes, when a customer explains their application, it is easier to find a better solution for them than the one they had in mind. It is important to have an open dialogue with your supplier in order to ensure that you get the right equipment, and don’t buy something you regret.

Conclusion

The benefits of global navigation satellite system have already been demonstrated with the availability of the core GNSS which are the America’s (GPS), Russia’s (GLONASS), European Union’s (GALILEO) and China’s (BeiDou) which is now fully functional serving global demand as of June this year. There are two other regional systems, Japan’s (QZSS) and India’s (IRNSS or NavIC). With the global GNSS, applications are continuously being developed, covering a large range of sectors, not only in transport and communication but also in other markets such as Marine Survey, land survey, agriculture, scientific research, tourism and others.

The GNSS services are rapidly penetrating all segments of marine surveys and are becoming a vital tool for marine surveyors. The role played by the GNSS in combination with the receiver systems is set to grow considerably, and is expected to reveal new sources of business in the years ahead.

According to a recent market report by the European GNSS Agency (GSA), global GNSS downstream market revenue from both devices and services will grow from €150 bln in 2019 to €325 bln in 2029, and in 2029, revenue from GNSS added value services will amount to €166 bln, accounting for 51% of total global GNSS revenue.

The report further states that, growth on the GNSS market will be stimulated by global macro trends such as digitalization, big data, the sharing economy and artificial intelligence, all of which use GNSS for position, navigation and timing. In combination with other technologies, GNSS will also contribute to tackling the climate change challenge by supporting environmentally friendly transport solutions, sustainable agriculture and meteorological monitoring.