What is the purpose of the Tides function in Verify-QC?

VERIPOS Tides is a real-time tide estimation module within Verify-QC. The module uses the VERIPOS PPP high accuracy solution (e.g. Ultra or Apex) in conjunction with proprietary processing techniques to detect height variations relative to a vertical reference. Heights are typically determined to an accuracy of 10-20cm.

The VERIPOS Tides process provides two real-time tide observations relative to different vertical references.

The first method estimates the tide relative to a Geoid Model, either EGM96 or EGM08, which is a global approximation of MSS but only to the 2-3m level since it ignores the presence of Dynamic Ocean Topography. This observation, called Geoid Tide, is available instantaneously and is most suitable for short projects.

The second method first derives MSS using the VERIPOS Tide filter and then estimates the tide relative to this surface. This observation, called MSS Tide, is independent of uncertainties in the Geoid model. It does however require 39 hours of continuous Verify-QC operation and is therefore only suitable for longer-term offshore projects. The MSS Tide observation is more accurate since its vertical reference (MSS) is accurate at the cm level.

Recommendations on Using VERIPOS Tidal Estimates

An extensive range of tide and position related information is stored to file. This information allows users to incorporate relevant parameters into their real-time and/or post-process hydrographic data management activities and to do further calculations.

There are fundamental differences between real-time GPS-based tide estimation and a predicted tides model or a tide gauge. A predicted tides model will only calculate the predicted vertical movement of the sea surface caused by gravitation effects of mainly the sun and moon and ignore atmospheric and storm surge effects – hence a very smooth tidal curve is produced. A tide gauge can observe tide at a much higher frequency and correct for atmospheric pressure effects but may be effected by storm surge effects.

The VERIPOS Tides estimates provide the real-time total variation from a vertical reference (MSS for MSS Tide or EGM model for Geoid Tide). Fact is that the sea surface varies not only due to tidal effects but also due to additional effects like atmospheric effects (variations in pressure and wind) which in extreme cases will cause tidal surges.

The benefit of estimating a real-time total variation from a vertical reference is that a single vertical correction can be applied to marine survey depth information. In addition, VERIPOS Tides can be estimated with a high frequency, as low as once per minute, such that a very detailed sea surface variation pattern can be build up.