Satellite sea level measurements have an error just as large as the trend they claim to measure. They hide this by using a different color scale in their error maps
I created this version of their error map by adjusting the color scales to be the same in both maps.
The only way a ten centimetre radar can measure to this accuracy is by comparing the signal phase on consecutive orbits. However, there is a world of difference between accuracy and resolution. Changes in cloud cover will affect the measurement, which is presumably why the least squares fit over many measurements is applied. But at the end of the day it is still little more than a Rohrschach test
Alternatively, the phase difference between a pair of carrier frequencies might be used, but when all is said and done, resolution is determined by swept bandwidth, which is typically about one tenth of the carrier.
Also, I seem to recall that sea clutter is notorious for producing signal spikes when the specular returns from wave crests are in phase. This is not a Gaussian noise process, as is implicitly assumed in a least squares fit.
If this were a Doppler measurement 1 mm/yr resolution would require an observation time of some 50 years. I marvel at the wizardry that can maintain phase coherence for that length of time.
As an amateur I’d like to ask some things.
Is it even a good and practical idea to try to measure milimeters from thousans of miles away?
With a device that is neither fixed in distance nor location and has to be adjusted regularly.
And considering that earth is said to be shaped more like a bowl than a ball.
Combined with the chaotic,changing structure
of water and its ability to mess up reflection. (and maybe even with some gravitational anomalies at work).
Isnt satellite data just an overexpensive and very problematic way to get results, that we can at sea level for less money with more accuracy?
Used cars salesman trick.
This 1000 dollar car is 200 mph fast.
The margin of error is 200 mph.
So the cars maximum speed is something between 0 -400 mph.
But for some unknown reasons the cars sold are always below 50mph
and usually so broken that they end up at 0 mph within 13 month.
You can’t measure anything within the tolerance of your device. Am I getting accuracy and tolerance mixed up? Your accuracy is +- some number. You can’t measure anything within that range, period, and furthermore anything of the same magnitude would have such a wide range of accuracy as to make its measurement iffy. My yard stick can measure to +- .1 inches. This thing is .5 inches long, means it is between .4 inches and .6 inches. The smaller the thing is the greater your % error might be.
Aside from the obvious nonsensical belief that a satellite 22,000 miles above the surface going some 18,000 miles per hour, in a non circular orbit, which is also influenced by both earth and moon tidal forces (thus disrupting it’s orbit and hence height above the surface) – and the other measuring accuracy and resolution factors, this rendering of sea level rise is utter bullsh*t and here is why:
Water, a liquid, will form a uniform mass distribution according to gravity and thus seek the lowest possible average surface level that the underlying solid surface allows. So you CANNOT have higher and lower average sea level regions or zones on the globe!!!! (temporary sea levels can vary due to waves, tides, temperature, and wind blown surges, but long term averages must be uniform)
So the idea you can have a map with +9 mm/yr zones between Australia and IndoChina but then -6 mm/yr on the west coast of North and South America is absolute fakery and full of manure! An average sea level must be uniform for all the connected bodies of water in the worlds oceans – period, end of discussion. The fact they paint these pretty pictures of differential sea levels of 10-15 mm per year in differing regions tells you this is not believable.
What it tells a real scientific method analysis of this data, is if you get higher and lower regions of the worlds oceans, your error is huge, and the method is unreliable.
Even GPS can only achieve a resolution of about 8 meters. Furthermore precision GPS used for navigating airliners can only place you within 0.3 Nautical Miles of the runway centerline using RNAV approach guidance. A Nautical Mile is 1850 meters, so 0.3 x 1850 = 555 meters. And that is using a minimum of 3 GPS satellites for your navigation!
https://www.faa.gov/air_traffic/publications/atpubs/aip_html/part2_enr_section_1.17.html
The point is, when your life is literally at stake in an airliner approaching an airport in the clouds, you can only trust satellite position and elevation data to within 555 meters, so you cannot ever trust it to a few mm. (the RNAV approach has a DA or Decision Altitude below which if the pilot does not see the runway, he/she must go around and try again – the RNAV guidance gets you close, but you must land visually) (this differs from an ILS Instrument Landing System approach which has transmitters on the end of the runway and at the touchdown point to give a precision of 1.2 to 7.6 meters depending on CAT I, II, or III ILS systems with lower DA than RNAV approaches) (only CAT III ILS runways can allow autoland capable aircraft to let the autopilot land the plane in zero visibility)
So any egghead telling you they can measure sea level to within a few mm is selling snake oil.
Lastly, if certain regions of the earth have higher than average sea level, this points to that region having a different gravitational force, so much more or less mass between that surface point and the geometric center of the earth. And if gravity is a variable, and you didn’t account for that in your resolution/accuracy rendering, your result is again garbage!
Everything that we are taught about liquids speaks against there being long term differences in sea level. Even heights of mountains are measured against sea level, so do mountains heights vary depending on which region of earth they are measured against? BUT even so, I am willing to believe it is possible for sea level to vary minimally from place to place, if someone can explain why to me. Earth isn’t perfectly round, so maybe there is a gravitation difference that would account for some variation. So water may weigh more at a different location on earth…..? But this would have to be an extremely tiny variation; one that only extremely sophisticated instruments could measure. To me, it makes much more sense that the land is moving up and down. This is something that is well documented and is a fundamental geological principle.
That is what I am questioning.
Is subsidence and uplift being factored in??
A 3cm radar might be expected to achieve an unambiguous range resolution of about 1 metre. Finer accuracy (not resolution) is achievable but only at the cost of ambiguity. This assumes the satellite position is known with absolute accuracy. What rubbish!
Nice summary.
When the valley 95ft below starts filling up with sea water THAN I will worry. Until than, New York and other coastal cities need to wear water wings okay?
Being facetious since i live at 985ft elevation in KY but the only ‘sinking’ city I know is Manhattan Island…a mud spit that is sinking cuz of BILLIONS of tons of concrete, steel, glass, asphalt, humans and other garbage (It’s NY so)!
When Florida as a whole disappears I will know that … Houston we have a problem. Say HI to Eddy the Minimum everybody cuz his cold ass is HERE and he ain’t leaving for DECADES!!!