Rising sea levels are going to mess with the internet

Thu Jul 26 19:44:53 UTC 2018

I agree with this.  I suppose you could take tons of measurements and average them out to be pretty accurate but I am not sure how you would account for tidal gravitational effects which vary all the time.  Seems like the precision claimed would be really hard to pull off without knowing exactly the gravitational effect at that location at exactly the same time.  I am also wondering how many points on the ocean you would have to take this measurement and how often to get that level of precision.  Given the altitude of the satellites the percentage of error here is super small, not even OTDR units can get that kind of precision on a measurement.

You would also have to align the satellite measurements with the pre-satellite measurement which could not have possibly have the same level of precision.  A statistics person would have to tell me if that methodology is even valid.  The level charts go back to the 1880s and I can't imagine a global network of measurement for that time.  I'm also pretty sure they were not taking measurements in mm in the United States so there is that conversion error to deal with not to mention the lack of international measurement standards.

Steven Naslund
Chicago IL

>Chris,
>
>I understand how radar altimetry works. I would like to understand how
>they achieve the claimed precision. 3.2mm is one heck of a precise
>measurement from a flying platform hundreds of kilometers away,
>particularly when that requires the platform itself to be located with
>even higher precision against some reference points deemed stable for
>the purpose of making the measurement.
>
>