The Van de Casteele diagrams consist of simultaneous sea level height measurements on the y-axis and tide gauge error on the x-axis (tide gauge sea level minus the GNSS-derived sea level).
Sea level height is presented along the y-axis of the diagram, and the tide gauge error, i.e., the difference in sea level height between the two sea level records, is presented along the x-axis of the diagram.
The tide gauge error for GPS L1 compared to wind speed, both for SNR analysis and phase delay analysis, is presented in Figure 8. Figure 8 Sensitivity of GNSS sea level results for wind speed.
The tide gauge error, i.e., the difference between the reference pressure tide gauge record and the GNSS-derived sea level, for GPS L1 versus wind speed.
The tide gauge error, i.e., the difference between the reference pressure tide gauge record and the GNSS-derived sea level, was then compared to the wind speed for identical epochs (wind speed measurements are available every 10 min).
The vertical black dashed line indicates a tide gauge error of zero.
The shapes of the four Van de Casteele diagrams, centered around zero tide gauge error, indicate that there are no systematic errors for the GNSS-derived sea level.
From Figure 7, it is again apparent that the phase delay sea level better resembles the tide gauge sea level, i.e., the tide gauge error is smaller, than the SNR sea level.
Gauge measurement errors result in underestimation of the actual process capability, consequently, the variance of gauge errors has to be assessed to better chart the relationship between the ACp and OCp.
In Figure 8, the tide gauge errors of the SNR solution are distributed around zero for wind speeds between 0.5 and 17.5 m/s, which were the lowest and highest wind speeds observed during the campaign, respectively.
