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www.sea-technology.com March 2015 / st 41 plitude was rather low during the test (less than 1-meter amplitude during the whole run), getting ac- curate heave from motion sensors was not an easy task. The swell spectrum containing signals in the range of 2 to 15 seconds, with almost equivalent amplitudes, was likely to cause important phase errors in most traditional real-time heave algorithms. The Ekinox delayed-heave algorithm was able to provide greatly improved performance by eliminating these phase errors, with a measurement delay of 450 seconds. The Ellipse's real-time heave is well beyond expecta- tions, with an average accuracy of 6 centimeters instead of a specifed average accuracy of 10 centimeters. The Ellipse is one of the very few miniature sensors to compute heave in addition to roll, pitch, heading and position. Furthermore, the Ellipse automatically adjusts heave measurement to the wave period, which greatly enhances accuracy. The Ekinox's real-time heave accuracy is much higher than its specifcations. It benefts from automatic adjustment to the wave frequency and integrates higher-grade acceler- ometers. Its accuracy is much higher than the miniature sen- sor and can compute heave over a large wave period. The Ekinox's real-time performance is illustrated with a print screen of the survey, extracted from QINSy software by CADDEN. The delayed-heave accu- racy is highly accurate, using a different algorithm than the one for real-time measurement. It makes use of past and future measurements to further en- hance heave output. The Ellipse is able to measure the overall swell signal, while the Ekinox real-time output provides lower phase errors thanks to a higher performance accelerom- eter. The delayed-heave output provides the best performance, with an output that preserves the shape of the actual heave signal without any phase error. Performing Beyond Specifcations CADDEN's main aim is to recommend the best hydro- graphic sensors corresponding to their customers' needs, which is why they carefully test them. CADDEN was sur- prised by the excellent performance of the SBG sensors and how simple they were to integrate. SBG Systems seeks to be prudent about their sensors' performance because the value of their clients' projects depends on the stated accuracy of the sensors. From the beginning, SBG says they have always been transparent with their customers to instill trust and build long-term relationships. Testing conducted with CADDEN proved that the Ellipse and Ekinox perform mostly above their specifed accuracy.