Validation of Recent Altimeter Missions at Non-Dedicated Tide Gauge Stations in the Southeastern North Sea

Round 1

Reviewer 1 Report

This paper “ Validation of recent altimeter missions at non-dedicated tide gauge stations in the Southeastern North Sea” by Esselborn et al. presents some results using coastal tidal gauge stations to validate the satellite altimetry measurements around the Southeastern North Sea. While the tide gauge observations can be an crucial in situ  validation for satellite sea level measurements in open waters, using coastal tide gauge  is difficult due to the accuracy of the altimeter measurements near the coastal area. And often the global bias was evaluated instead of regional mean SSH bias from different altimetry missions.  So this study is significant in using coastal tidal gauges to investigate the regional bias of the SSH measurements from different altimetry mission. The validation method is novel through comparing different mean SSH model to select the best one and applying an empirical tidal model for position corrections. The logic is sound. And the results support the analysis. The figures are clearly generated.  I recommended this paper published at Remote Sensing with minor editions.

 

Minor Comments:
1.) Line 71, please explain how the virtual stations are determined.

2.) Line 111, please explain what’s 20/40HZ mean. As I recalled, these are the satellite SSH sampling rate.

3.) Line 121, full name of Bfg abbreviation.

4.) Line 214, M2 with 1 m amplitude can give rise to the position difference of up to 4cm. How about other tidal constituents, such as S1 etc? Are the amplitudes too small to be considered here?

5.) Line 270, please rephrase this sentence.

6.) Figure 7, the large RMSD for several stations such as Dwa,Cux,Zehn, Witt, Sylt all are close to the coastal line. Can you explain why the uncertainty increases? Some references regarding the GDR tropospheric correction, and the microwave radiometric measurement (at ~23.8GHZ) might be helpful. The land/ocean has clear differences at this water vapor channel.

7.) Figure 6. The time series after box-car smoothing has some up and downs. Can you explain more about these? Are these caused by the uncertainty in the mean seal level model or instrument jitters/anomalies? Can this tidal gauge validation detect the abrupt changes/instrument malfunctions/algorithm adjustments for satellite altimetry measurements?  A few more discussion on this would elaborate more the significance of the study.

 

Author Response

Please see the attachment

Author Response File: Author Response.pdf

Reviewer 2 Report

In the manuscript, the authors describe the results of their analysis of the possibility of determining the sea level in the German Bight (North Sea). They show that taking into account the existing measurement infrastructure and the modified methodology of measurement data processing, the credibility and precision of the findings as to the dynamics of sea level changes can be improved. I suppose that the methodology shown in the manuscript may be inspiring to researchers studying the change of sea level in other regions of the sea.

It is worth making minor technical adjustments. For example:

L115, critereon -> criterion

L208, 5 min -> 5 min

Space needed after L215

there is too much space after L 246

the letters in figure 5 are too small compared to the other figures.

Author Response

Please see the attachment

Author Response File: Author Response.pdf