Pushing back on Recent ‘Sea Level is Worse Now’ Claims: The Coordinate System That Ate the Coastline

Nice post Charles. It sent me tracking down references [thanks! 😉 ].
Speaking of sea level:
1) Satellites claim to measure sea level to the tenth of a mm yet the error in the measurement is in cm. How does that work? [the Abstract quoted below says “0.5m” accuracy!]
2) Since Earth’s gravity varies based on location then the resulting satellite orbits must vary as well.
How is this handled? [See #1 above]
3) All flooding is local. How does a global (mean) SLR measurement help assign risk?

And from a reference within the rabbit hole(s) you sent me down:
Remote Sensing [2020] https://www.mdpi.com/2072-4292/12/17/2827
From the Abstract: “The global LiDAR lowland DTM [digital terrain model] (GLL_DTM_v1) at 0.05-degree resolution (~5 × 5 km) is created from ICESat-2 data collected between 14 October 2018 and 13 May 2020. It is accurate within 0.5 m for 83.4% of land area below 10 m above mean sea level (+MSL), with a root-mean-square error (RMSE) value of 0.54 m, compared to three local area DTMs for three major lowland areas: the Everglades, the Netherlands, and the Mekong Delta. This accuracy is far higher than that of four existing global digital elevation models (GDEMs), which are derived from satellite radar data, namely, SRTM90, MERIT, CoastalDEM, and TanDEM-X, that we find to be accurate within 0.5 m for 21.1%, 12.9%, 18.3%, and 37.9% of land below 10 m +MSL, respectively, with corresponding RMSE values of 2.49 m, 1.88 m, 1.54 m, and 1.59 m. “