How to Choose the Best Inertial Solution for your Application and Accuracy Needs

All kinds of surveying, and more generally, oceanography and hydrography, need an inertial sensor. These solutions range from MRU to high-end INS/GNSS, and their selection shouldn’t be taken lightly. It is crucial to select the right sensor depending on the type of application and its needs. So How to Choose the Best Inertial Solution ?

This is the reason why we put our different products lines to the test during a 3-day survey with a multibeam echosounder in 3 areas of the port of Hamburg (Germany): Hamburg’s docks, under bridges, and in the city’s river channels.

Being able to attest our solutions’ performance in various environments and at several levels of accuracy was key to being able to recommend which INS to use depending on the application and conditions.

Let’s together discover more about How to Choose the Best Inertial Solution.

 

Small Marine Integrations and Surveying in Very Shallow Waters

Hydrography doesn’t involve only surveying on large vessels but also includes AUV, USV, or even buoys. Considering the size of such applications, a miniature and robust inertial sensor can prove to be ideal. SBG-Systems developed the most innovative answer for your requirement : How to Choose the Best Inertial Solution ?

 

SBG Systems’ miniature Ellipse product line ranges from AHRS to dual-antenna RTK GNSS/INS in small IP68 enclosures.

Robustness being crucial in marine applications, all SBG Systems’ MRU and INS benefit from an individual high-end calibration procedure from -40 to 85°C.

We rigorously screen inertial sensors, ensuring only those meeting specifications deliver consistent measurements for professionals’ missions.

Ellipse sensors deliver a 5-cm accurate real-time heave that automatically adjusts to the wave period and provides unmatched performance in attitude (0.05°) and heading (0.2°).

In addition to buoys, small USV, and AUV solutions for navigation or surveying, these inertial sensors can also compensate and stabilize a single beam or side scan echosounder.

However, they can only offer optimal performance in open-sky surveys in very shallow waters (< 10 meters) in near-shore areas with low motion, offering a cost-effective package for these types of surveys. Indeed, the Ellipse’s RTK Heave directly provides a precise altitude, which is well-suited for near-shore surveying.

 

 

 

Open-Sky and Shallow Surveys

The bathymetric and inertial data collected during the survey show that all sensors deliver highly accurate motion, heading, and position in an open-sky and shallow water survey.

While the Ellipse is not recommended for high-accuracy MBES surveys, the Ekinox, or Navsight Ekinox, is the best-fit solution and can provide an attractive package in real-time for open-sky and shallow surveys in coastal areas.

The Ekinox Inertial Navigation Systems come in either all-in-one industrial-grade sensors ranging from MRU to high-end RTK INS/GNSS or as part of the Marine solution.

Both provide the same performance and accuracy: 0.02° Roll/Pitch (RTK), 0.05° GNSS Heading, and centimeter-level position.

As all-in-one compact sensors, they can be integrated into equipment where space is critical, such as USV for hydrographic surveys.

Designed to ease hydrographers’ tasks, the Navsight Marine Solution comes as a Motion Reference Unit (MRU), providing roll, pitch, and heave, or as a complete Navigation Solution embedding a tri-frequency GNSS receiver or using an external GNSS receiver.

The Ekinox IMU is connected to the processing unit. This very practical set-up allows the IMU to be located close to the echo-sounder while the processing unit is in the cabin and connected to the operator’s computer.

 

An Inertial Solution for Each type of GNSS Outages

GNSS outages can happen in various environments, including when navigating under bridges or surveying river channels and ports facilities.

They represent a challenge for all hydrographic surveys and highlight the necessity of an inertial navigation system coupled with GNSS, which fuses inertial and GNSS data for a continuous higher accuracy trajectory.

Survey results under the bridges show that the inertial sensor maintains accuracy with enhanced RTK, attitude, heading, and heave data. Heading appears to be much more stable with the Navsight Apogee, as it embeds higher performance gyroscopes.

This solution also provides more precise inertial and position data, making it the right choice for this application.

SBG Systems’ Qinertia software resolves GNSS outages by post-processing survey data, ensuring accurate results through advanced PPK technology.

The combination of both Apogee and Qinertia allows a reliable and extremely accurate solution in long GNSS outages.

 

Strong GNSS multipath effects in river channels cause frequent small outages, more challenging than long GNSS outages.

Multipath effects disrupt GNSS dual heading and position computation, increasing errors, making Loosely coupled inertial solutions unreliable in such conditions.

 

Complementarity with a PPK Post-processing Software

This environment demands high-end INS/GNSS for stable roll/pitch data, with tight coupled post-processing to filter multi-path effects.

PPK computation enhances heading and motion, and tight coupling significantly improves position.

Highly performant, the Navsight Apogee solution (0.008° Roll/Pitch, 0.015° GNSS Heading, and centimeter-level Position) provides, along with Qinertia PPK software, the optimum package in such conditions. It also enables high-accuracy surveys in deep water, even offshore.

While the Ekinox and Apogee motion and navigation solutions are MEMS-based, the Navsight Horizon integrates a closed-loop FOG IMU that allows robust and consistent performance in the most demanding environments like highly dense areas or low dynamic surveys.

We post-processed this system data for surveying tests in Hamburg, ensuring the highest performance as a reference system.

Furthermore, SBG Systems sensors are compatible with all Hydrographic software that accept ASCII, NMEA, and TSS protocols. Other software have developed drivers that fit with SBG’s binary protocol, facilitating the sensor’s integration.

Did you get the answer to the dilemma : How to Choose the Best Inertial Solution ?

 

Real-time or Post-Processing?

In these different surveys, post-processing has proved to improve survey results in the harshest conditions.

In challenging GNSS environments, post-processing software ensures optimal performance, unlike open-sky surveys that rely on real-time data for accuracy.

Forward and backward computation and cutting-edge PPK algorithms help achieve the highest level of accuracy. Robust against the multi-path effect, tight coupling is essential in such conditions.

Qinertia simplifies post-processing for hydrographers, offering an intuitive tool designed to ease surveyors’ tasks and streamline workflows effectively.

Efficient, fast, and straightforward, this full-featured GNSS only and INS/GNSS post-processing software gives access to offline RTK corrections from more than 8,000 base stations located in 164 countries. It supports third-party IMUs and all GNSS receivers and includes a VBS (Virtual Base Station) feature and PPP computing.

This cost-effective solution allows surveys even in harsh conditions and allows installation parameter corrections afterward to save the day!

Marine Technology Reporter featured the complete article in its August edition.