Do any anons here have experience with oceanography or the harmonic analysis and prediction of tides? I am recently starting to get into this data and have been diving into Special Publication 98 by Schureman. My background is in physics and the mathematics involved are easy enough, although I don't think I have enough statistics knowledge to manually apply the harmonic analysis method of least squares to a year's worth of water level measurements.
I have a more general question. Often when I am examining tide level data and water level data from NOAA (almost always, in fact), the data seems out of phase. I know that tide predictions and water level won't match due to local bathymetry and weather effects among other reasons, but they don't even follow the same pattern. This is true for NOAA's tide predictions compared NOAA's measured water level as well as their tide predictions compared to predicted water levels.
The predicted water levels follow the same pattern as measured water levels except in extreme outlier cases. What is going on here? I would, at least, expect water level predictions to follow tide predictions (water level increasing when the tide is predicted to increase and vice versa), but that isn't the case. Take pic related as an example. Predicted and measured water levels in Washington DC on Christmas vs tidal predictions for the same day. Does anyone know what else goes into the equations for predicting water levels besides the 37 tidal harmonic constituents?
Lastly, a more detailed question. I understand certain harmonic constants like the amplitude and phase must be determined from a minimum year's worth of analysis data and a harmonic alanysis method of least squares, but how are the nodal factors and greenwhich equilibrium constants computed. They depend only on epoch/Julian year, but I'm not sure in what way they are actually determined.
I have a more general question. Often when I am examining tide level data and water level data from NOAA (almost always, in fact), the data seems out of phase. I know that tide predictions and water level won't match due to local bathymetry and weather effects among other reasons, but they don't even follow the same pattern. This is true for NOAA's tide predictions compared NOAA's measured water level as well as their tide predictions compared to predicted water levels.
The predicted water levels follow the same pattern as measured water levels except in extreme outlier cases. What is going on here? I would, at least, expect water level predictions to follow tide predictions (water level increasing when the tide is predicted to increase and vice versa), but that isn't the case. Take pic related as an example. Predicted and measured water levels in Washington DC on Christmas vs tidal predictions for the same day. Does anyone know what else goes into the equations for predicting water levels besides the 37 tidal harmonic constituents?
Lastly, a more detailed question. I understand certain harmonic constants like the amplitude and phase must be determined from a minimum year's worth of analysis data and a harmonic alanysis method of least squares, but how are the nodal factors and greenwhich equilibrium constants computed. They depend only on epoch/Julian year, but I'm not sure in what way they are actually determined.
