As an example, I propose to consider the trend of increasing the level of the Black Sea as a whole and the trend of the formation of level rise anomalies in two local zones in the north and anomalies in the east (attached slide). We all understand that water from the Sea of Azov can flow without obstacles into the Black Sea, and from the Black Sea into the Sea of Marmara. I have attached a slide showing data on sea level changes in the Bosphorus. Usually the level in the Black Sea is only 3 centimeters higher than the Sea of Marmara. The level of the Black Sea in 2005 was lower than in the Sea of Marmara.
Dear Boris,
Satellite sea level measurements could be calibrated by reference to the carefully defined (not measured) elevations of the nearest ground station. The primary system for use with satellite positioning is ETRS89 (European Terrestrial Reference System 1989). As the name suggests ETRS89 is for use over the whole of Europe and facilitates a standard coordinate system across the entire region that provides location and altitude of these ground stations. So, to get from/to ETRS89 and local mapping datums a coordinate transformation is required and a geoid model is required to transform heights. However, Precise Point Positioning (PPP) is now thought to provide decimetre to centimetre accurate positioning accuracy to satellite measurements without the need for a base receiver station.
So, to answer your question you need to know how the PPP system is calibrated with respect to a crustal geoid that is affected by tides, local sub-crustal uplifts and subsidences that change in the course of time.
Taking averages will not provide the cm. accuracy you are seeking.
Malcolm.
Dear Norman Malcolm McClure. You may be interested in my discussions on the geodynamics of Great Britain: A 1200x1200 km tectonic block centered in Great Britain rises and falls in 2 days. Is it possible? Changes on a global scale in autumn 2005, not related to climate change. What was that?
Dear Norman Malcolm McClure. You understand the problem very well. I found a drawing that illustrates the processes that need to be studied simultaneously and in parallel. If these processes are not taken into account, then there will be short-term errors, as shown in the Photograph of Odessa, where the tide height is 5 cm. But in this case, for three years, the measurement error is greater than the measured value.
Dear Borys
Since the early 19th century, following Darwin's voyage of the Beagle and Murchison's observations, it has been known that changes of Relative Sea Level (RSL) in historical time across oceans and saline seas are caused mainly by isostatic rise and fall of the continental crust. Thus eustatic sea level has remained essentially constant, unless affected by plate tectonic effects that are essentially trivial in the short term.
Later, those empirical conclusions were found to be incompatible with evidence of raised beaches formed in the late Quaternary. Geomorphologists then asserted alternative, largely unfounded ideas based on glacioisostasy and a hypothetical balance due to ice-sheet accumulation and melting in the northern hemisphere. Such conjectural processes were supposed to reduce and increase the global volume of sea water, and led to interpretations of significant changes in eustatic sea level — up to 130 metres in the past 25,000 years. This interpretation and numerous off-shoots that ignore simultaneous local movements of the continental crust have confounded geomorphologist's interpretations of the Quaternary for at least the past 50 years.
Malcolm
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