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40 st / March 2015 www.sea-technology.com much higher than the stated specifca- tions, and heading accuracy was com- pletely within specifcations. This new series integrates very-low-noise gyro- scopes and algorithms inherited from the higher-grade Ekinox Series, which greatly enhances Ellipse's attitude performance. In addition, the use of an RTK GNSS re- ceiver also slightly improves the sensor's performance. With pitch and roll accuracy better than 0.1° RMS, the Ellipse series is three to fve times more accurate than most of its com- petitors. The Ekinox-D showed very good results in roll and pitch during testing, higher than the specifed accuracy. Those re- sults, in the range of 0.03° real time, are consistent with our testing on a hexapod in June 2013 and with several undis- closed customer test results. The heading accuracy in the Oc- tober 2014 testing is within the specifcations of the sensor, given that the baseline on this setup was 2.4 meters. Higher heading accuracy can be achieved with a longer baseline between the 2 antennas (0.05° with a 3-meter baseline). Heave Performance Results As a reference, we used a tide-compensated RTK altitude output from the Ekinox-D. Although the average heave am- The model tested was the Ellipse-E, an inertial navigation system that can be connected to an external GPS. The GPS used was the Hemisphere (Scottsdale, Arizona) VS330 GNSS with two antennas. The Hemisphere receiver provided RTK accuracy and true heading. The use of a dual-antenna GPS receiver, fused with the inertial sensor, provides an accurate and robust heading source, even in the case of short GPS outages. The VS330 is connected to the Ellipse-E through a serial interface using the standard NMEA protocol. Both systems are synchronized using the PPS output of the GPS linked to the Ellipse synchronization input. This allows the Ellipse to enhance its clock accuracy and to time stamp all outputted data to UTC time. The Ekinox Series is a survey-grade line of compact inertial sensors that integrates a data logger and a Web in- terface for easy confguration. The line is composed in the same way as the El- lipse Series. The tested model was the Ekinox-D, the inertial navigation sys- tem integrating a dual-frequency GNSS receiver with two antennas. Test Conditions The test was performed on October 28 and 29, 2014 in Pornic, France. CADDEN used their own 9-meter survey vessel, equipped with an R2Sonic (Austin, Texas) SONIC 2024 multibeam echosounder. CADDEN used QPS (Zeist, Netherlands) QINSy software for both real-time acquisition and data processing. The test performed a typical survey path. Each leg of the survey path was about 550 meters long. A warm-up period and sensor calibration was performed during the frst minutes before running the survey. Attitude Performance Results Attitude performance was compared to a very high ac- curacy fber-optic gyro compass, whose performance was much better than the tested MEMS sensors in terms of roll and pitch angles. However, the heading accuracy is com- parable, so the measured heading performance should be considered more as a consistency check than as an absolute accuracy measurement. The Ellipse's average roll and pitch accuracy during testing was actually (Top) The Ellipse-E model, a miniature INS that can be connected to an exter- nal GPS. (Middle) The Ekinox-D survey- grade INS with an integrated dual- antenna bifrequency GNSS receiver. (Bottom) This graph shows typical Ek- inox (blue lines) and Ellipse (red lines) instantaneous errors when compared to the reference in terms of roll, pitch and yaw angles. Given that both sensors pro- vide excellent performance, this graph shows how stable the Ekinox outputs are compared to the Ellipse ones.