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38 st / September 2016 www.sea-technology.com be known. The Continuous Vertical Datum for Canadian Waters (CVDCW) project was conceived by CHS to devel- op hydrographic-quality ellipsoid to CD surfaces to support "through the ellipsoid" bathymetric reduction. This article will present an overview of the CVDCW proj- ect and its products, Hydrographic Vertical Separation Sur- faces (HyVSEPs). The CVDCW has developed HyVSEPs for a range of tidal target water levels. All are valuable resources for hydrogra- phy, coastal engineering, coastal planning, ecosystem man- agement, or any effort requiring knowledge of vertical or hori- zontal water level target or datum positioning. Building Surfaces from the Datum Up The vertical separation between the ellipsoid and the target datum is the sum of three components or layers: the geoid, which gives the separation between the reference ellipsoid and equipotential surface; the dynamic ocean S ince 1883, the Canadian Hydrographic Service (CHS) has studied the oceans to ensure safe navigation of Canada's waterways. Bathymetric surveys, and the nauti- cal charts and products they produce, play an important role in maritime transportation, ocean and freshwater mapping, identifying coastal hazards, and sovereignty— the four pillars of the CHS mandate. Over the past 130 years, hydrography has evolved from single-point measurements with weighted lines to the use of multibeam echosounders. With recent advances in Global Navigational Satellite Systems (GNSS) it is now possible to perform hydrographic survey reductions through the ellip- soid, simplifying hydrographic operations and leading to more rapidly available and improved bathymetric products. To accomplish this "through the ellipsoid" reduction pro- cess, the separation between chart datum (CD), the refer- ence for all charted depths and the reference ellipsoid must Continuous Vertical Datum Separations for Canadian Waters Creating Canada's First Hydrographic Vertical Separation Surfaces By Shannon Nudds • Catherine Robin • Phillip MacAulay Surveying to the ellipsoid. Bathymetry is measured relative to the reference ellipsoid and can be easily reduced to a value relative to chart datum if the separation between chart datum and the ellipsoid is known.