Filtering altimetry data

[stef]

I'm interested in storm surges and I'm trying to understand how to use satellite altimetry. The ROMS 4DVar tutorial [1] mentions 'satellite SSH in the form of a gridded product from Aviso'. I'm wondering if one has to do any preprocessing (filtering?) on that data?

I read about how datasets like [2] provide SLA, ADT etc. for use in data assimilation by filtering out tides and 'high frequency' signals. In the documentation [3] it says:

[The] correction allows for the removal of high frequency variability induced by the atmospheric forcing and aliased by the altimetric measurements. The high frequency part is based on a barotropic model simulation forced by atmospheric pressure and winds (MOG2D; Carrère and Lyard 2003 [4]); the low frequency part is an inverse barometer response. A 20-day cutoff-period was chosen because it corresponds to the Nyquist period of T/P-Jason reference altimeters sampling and because the variability is mostly barotropic in this high frequency band. This correction is already included in the SLA ...

In Carrère and Lyard 2003 they use a FE mesh, ranging from 400 km in deep ocean to 20 km in coastal, shallow areas.


So do I understand correctly that e.g. the effect of seasonally varying wind stress is not filtered? For example (of storm surge modeling relevance), the FE model surely captures the effect of the monsoon in the Bay of Bengal, and hence reproduces a seasonal variation in sea level e.g. in the north-eastern Bay of Bengal. Is it true that the effect of this would be included in the altimetry product? I guess I don't understand what the low-pass filter with 20-days cutoff is applied to. The 'low frequency part' must be more than the inverse barometer effect. Shouldn't all low-frequency signals be in the altimetry product, regardless if wind stress or atmospheric pressure fluctuations?

I got the impression that the product [2] is geared toward global GCM's. I think NEMO uses this one (after browsing through other documentation on the global analysis/forecast distributed on the CMEMS site, e.g. [5]).

Are there any guides on preprocessing of altimetry data for regional/coastal models?

I have heard that altimetry is inaccurate on the continental shelves, but maybe the question should focus generally on the deep ocean.

Thanks for your help!


[1] https://www.myroms.org/wiki/4DVar_Tutorial_Introduction

[2] SEALEVEL_GLO_PHY_L4_REP_OBSERVATIONS_008_047

https://resources.marine.copernicus.eu/ ... NS_008_047

[3] http://marine.copernicus.eu/documents/P ... 32-062.pdf

[4] Carrère, Loren, and Florent Lyard. "Modeling the barotropic response of the global ocean to atmospheric wind and pressure forcing‐comparisons with observations." Geophysical Research Letters 30.6 (2003).

[5] https://resources.marine.copernicus.eu/ ... HY_001_024

[stef]

Ok today I searched for 'Dynamic Atmospheric Correction' and there are a lot of resources! Thanks.