Tides, GPS and VDATUM...looking back...

Some people may look at VDATUM and see the demise of tides.  I think the transition from traditional tides to VDATUM is an interesting opportunity because they provide redundant methods of vertical height measurment on the water.  Each method informs the other, and neither is perfect.  Where VDATUM doesn't exist yet (Alaska), using GPS water level heights can aid in the creation of a traditional tidal zoning scheme or allow you to roll your own custom VDATUM.

Some of the projects JOA has been involved with relating to GPS tides/VDATUM.

2009
VDATUM evaluation using GPS heights from hydrographic survey vessels and Seabird SBE26 underwater tide gauges. Offshore of San Francisco, CA.
Unimak Pass, Aleutian Island in Alaska.  Supporting a hydrographic survey for nautical charting using GPS heights from hydrographic vessels to develop better tidal zoning in complex area where Pacific and Bering Sea meet.
VDATUM  evaluation using GPS buoy and radar tide gauge in Chesapeake Bay.

2008
Upper Cook Inlet, Alaska.  Supporting a hydrographic survey for nautical charting using GPS heights from hydrographic vessels,  Seabird SBE26 underwater tide gauges and traditional shore based tide gauges to develop better tidal zoning (10m tide range).  Developed ellipsoid/MLLW separation grid which was used to process soundings to final MLLW chart depth (roll your own VDATUM...).

2007
Akutan Pass, Aleutian Islands in Alaska. Supporting a hydrographic survey for nautical charting.  Started with a traditional tides approach, tide gauges at either end of pass, but couldn't develop adequate zoning using tide data from just a few points.  The Pacific to the south tends to have a much more regular semidiurnal tide, whereas the Bering Sea to the north has much less consistent tides which vary between semidiurnal and diurnal throughout the month.

Began extracting tide data from moving hydrographic survey vessels GPS measurements (corrected for pitch and roll) for the purpose understanding more about the tide over a geographic area, instead of one discrete point.  It was more of a descriptive tool at this point, since we really didn't have the tools to thoroughly correct and analyze the millions of points.  Crunched the data as best we could (in Excel and Access) and then painted a picture of the tide in ArcGIS and with post-it-notes on a large map.

2006
Mitrofania Island, Alaska.  Deployed JOA designed GPS buoy for 3 - 7 days at various locations throughout hydrographic survey area.  Testing concept of tides with GPS buoy.  Excellent tool to measure separation between MSL and geoid corrected ellipsoid surface, but deployment periods were too short to compute accurate datums.

2005
Shumagin Islands, Alaska.  Installed multiple tide gauges, tied their water level heights to the ellipsoid to create a MLLW/ellipsoid surface, so the survey vessels could process their soundings directly to MLLW from the ellipsoid, without tide corrections.