By Rud Istvan,
Nearly two years ago (January 2019) over a pleasant lunch, Charles urged me to examine whether the NASA satellite altimetry (satalt) measurements of sea level rise (SLR) were fit for purpose. I eventually provided a longish, somewhat technical guest post concluding they were NOT based on NASA’s newest ‘bird’, Jason-3, while also showing that NASA PR was provably obscuring that. Satalt simply does not correspond with the BEST SLR tide gauge measurements by a factor of about 1.5x. That is not rounding error; it is a big climate data problem.
Jason-3’s replacement, Sentinel-6a, has just completed ground testing and is scheduled to launch November 2020 from Vandenberg AFB. A bit of background. These satalts are necessarily in low earth orbit (LEO). That means they encounter slight atmospheric drag (from Earth’s thermosphere), so their orbit deteriorates, so they do not last long: an average of only 5 years operationally. Jason-3 launched in early 2016. This 4Q2020 launch will allow about 6 months of calibration overlap before Jason-3 must be decommissioned thanks to its orbital decay. Going to be close, because the Sentinel-6a launch was originally scheduled for 1Q2020. Conceptual image of Sentinel-6a below is courtesy of ESA. The ‘roof like’ projections are its solar cells. The downward projections are antennas aimed at Earth. And its odd house like configuration explains why thermospheric drag is such a big LEO orbit problem.
Sentinel-6 is actually two identical satellites, (a) and (b), both to be launched into the same LEO orbit as Jason-3 at 1336km mean original altitude. (b) will sit in inventory and launch in ~2025 to replace (a) for a total mission life to about 2030. Both were built in Europe by ESA, incorporating a couple of JPL.NASA developed instruments. Both will ride NASA launches.
NASA’s big press release yesterday on completion of Sentinel-6 operational ground testing says it will provide ‘centimeter’ precision: “measuring down to the centimeter for 90% of the world’s oceans.” Is that true? Dunno, and there is no way to tell yet because after several hours of researching, neither ESA nor NASA have evidently provided a detailed description of the accuracy and precision of their coming Sentinel-6 data products. But we know some relevant stuff…
It is true that Sentinel-6 contains new plus improved instruments. The five specifically named instruments for SLR by both NASA and ESA are:
- Poseidon-4, a new higher resolution synthetic aperture radar altimeter,
- AMR-C, a new ‘climate quality’ multi-frequency radiometer for humidity,
- GNSS-POD, a GPS guided POD (positional orbit detector),
- LRA, a laser retroflector array for POD,
- DORIS, a ‘Doppler orbitotography and Radio positioning integrated by satellite’ for POD—whatever that actually is and supposedly does.
This NASA/ESA technobabble requires both translation and then contextual positioning. Recall the three main Jason-3 accuracy/precision weaknesses from my previous technical Jason-3 post: orbital decay, humidity retarded radar altimetry, and ocean surface wave height.
The higher resolution synthetic aperture radar altimeter, at higher pulse rates, enables a rough estimation of wave heights, at least those above the 2 meter arbitrary average assumed by the Jason-3 signal processing. That helps some.
The multi-frequency radiometer (different frequencies for different altitudes) provides a better estimate of humidity retarding effects to the main altimeter.
The last three instruments collectively provide a more robust triangulation of the inevitable orbital decay over time.
So, it is conceptually possible that Sentinel-6 could achieve a statistically robust 1cm sea height resolution. But nowhere that I can today find is this ‘fact’ explained by published technical specs. There simply is nothing specific on line (yet?) about Sentinel-6 overall ‘data product’ accuracy and precision. Deliberate?
Two final thoughts
First, the best long record calibrated (to vertical land motion) tide gauge estimates of SLR are about 2.2mm/year, with NO acceleration, AND closure. So, even if the new Sentinel-6 1cm claims are true, they are still not fit for purpose by a factor of about 4x SLR mm/year. And this satalt only lasts ~5 years.
Second, if Sentinel-6 really is this good, then it should (inaccurately) find about 2.2mm of SLR per year, proving Jason-3 was a goof as its published tech spec showed. Personally, I think the chances of that data driven scientific outcome is near zero, because the Jason-3/Sentinel-6 calibration overlap period enables any necessary Sentinel-6 data processing algorithm ‘adjustments’. We already have such ‘adjustments’ shown many different ways for NOAA/NASA surface temperature UHI homogenization. (See essay ‘When Data Isn’t’ in ebook Blowing Smoke for multiple compelling examples.)
For some time now travelling this wide brown ancient continent with it’s weathered landscape and the odd coral reef far from the sea-
https://cooberpedytimes.com/2008/09/22/ancient-giant-underwater-reef-in-north-flinders/
or still in the sea-
https://iodp.org.au/ancient-mirror-image-of-great-barrier-reef-discovered-off-northern-australia/
you realize that all those other tide gauges still moving around in outer space or sinking into the sea or coming up with isostatic rebound or volcanic activity aren’t a patch on the ones firmly anchored to the globe nowadays at Fort Denison or Port Arthur and what they show is you’re off the planet and off with fairies doomsters.
Low earth orbits are not elliptical due to gravitational anomalies. Meanwhile, atmospheric drag varies with solar activity and local weather conditions. Can all these factors be charted and accounted for?
https://eos.org/research-spotlights/atmospheric-drag-alters-satellite-orbits
Verdeviewer — I don’t think anyone has used Keplerian(?) ellipses in satellite orbit work since the early 1960s. Instead, they use numerical integration. Take the satellite’s estimated position and estimate ALL the accelerations acting on the platform. Use the resulting velocity vector to move forward a tiny step in time. Calculate the accelerations at the new position. If they are pretty much the same, accept the new position and velocity. If they aren’t try a smaller step. It sounds kind of Rube Golbergish, but it works pretty well as verified by various satellite tracking technologies (radar,cameras,on-board position measuring devices, etc).
They’ve been at that for half a century and seem to have the bugs long since worked out.
The big problem is drag. It’s a continuous force acting backward on the satellite and it’s both variable and not very predictable.
“Take the satellite’s estimated position and estimate ALL the accelerations acting on the platform. Use the resulting velocity vector to move forward a tiny step in time. Calculate the accelerations at the new position. If they are pretty much the same, accept the new position and velocity. If they aren’t try a smaller step”
You neglected to define what you mean by “pretty much the same”. There are a host of devils therein.
Your algorithm might possibly work short term for a circular Earth orbit if you have a very accurate map of gravity versus the satellite’s instantaneous altitude and geocentric position. In all cases, it doesn’t work over the long term. The fundamental problem is inability to determine ALL the accelerations to infinite accuracy.
I believe that you have oversimplified the means of orbital determination via special perturbation methods.
Gordon — No, actually, I didn’t oversimplify it much. It’s really what is done. How can it possibly work? Well, after you figure in gravity from an oblate Earth, the Sun, the Moon, and a guess at atmospheric drag, you’re pretty close. Maybe you throw in a few more accelerations. Maybe you don’t. Doesn’t make much difference. Yes, you’d be quite a bit off on the satellite position after a few months or years. But you would be anyway because you don’t really know exactly what the drag is. To get around that, you have a ground station point a large antenna at the satellite every once in while and send out some radar pulses. That gets you a mediocre estimate of azimuth and elevation and a very good estimate of range. You process that/those (you likely have several sets of tracking data) through some complex software, and get a corrected set of orbital elements.
You may do something a bit more elaborate if knowing the orbital elements exactly is really important. But if you just want to point satellite instruments at the Earth and know where you are observing to within a few tens of meters or maybe a few tens of kilometers, that’s adequate. In the case of Topex-Poseidon, you are surely going to use their on-board position estimates in preference to your ground based tracking anyway. You just need position estimates good enough to schedule ground stations and aim their uplink/downlink antennae.
At least, that’s how it used to work in the 1960s-1980s. I doubt it’s changed much.
Rud:
How do they take into account the movement of the Pacific Plate in Southern California – it moves north every year (by more than a few mm)?
Rud, I don’t know if you’ve seen this https://www.nodc.noaa.gov/media/pdf/jason2/j3_user_handbook.pdf
It’s the 3rd gen JASON handbook. I rarely agree with these folks, but I do admire their sort of transparency. If can call valuable info buried in a generous coating of increasingly obtuse and not very transparent jargon , kant, and acronyms, transparency. I used to be willing to argue about this wonderful stuff at the drop of a hat, but have come conclude that those that choose to ignore it are saving themselves extra time to do something useful like playing with the grandkids or golf. Ask yourself this question what difference would it make to you
personally if our recorded elevation for the ocean’s surface was off by 10 feet, as long as the ocean stayed where its always been?
To put it bluntly, they try to measure the height of an irregular surface with mm precision from a distance of about 1300km using a 10cm ruler & guess the fractions. The satellites are calibrated using other satellites, ground gauges, computer models and the drifting of the old data. The ground gauges also use the satellites to calibrate movements and computer models are based on the other corrected/adjusted data. So now we have verification using partial circular proofs and guesswork dressed up as “now the corrected data are more accurate because we trust the other data uncertainties as being accurate”. Or, if we take more measurements we can turn garbage into gold. Easy to loose track of previous adjustments & why. If the sensor/raw data doesn’t agree with their assumptions they adjust the process to produce a rough slope that intersects previous data with smoothing. They can amplify a natural +7.5mm/decade into +30mm and amplify the panic. So now they can more accurately measure their garbage data and insure they can prove their assumptions when using enough adjustments.
That’s why uncertainty in measurements add in quadrature, i.e., they get bigger. Too many statisticians and not enough machinist precision tool makers.
As NASA and NOAA have proven time and time again, if their data don’t match the bogus CAGW narrative, the data are tortured until they confess to the results they’re looking for; i.e. 4mm+/year and accelerating, regardless of reality..
It’s amazing what shysters and Leftist hacks (I’m being redundant) will do for $100’s of trillions in wasteful CAGW spending to keep the hoax alive….
The alarmista and others sometimes think the Earth’s surface is stationary, (like climate was before CO2)
IT ISN’T
It would only take a small, probably unmeasurable, bulging at the bottom of, say, the Pacific Ocean to account for all sea level rise.
We know so little about what is happening down there.
It’s worth reminding ourselves that the coast is the only place where supposed sea level rise matters. The only place where it even exists as an issue. The millimetre level of the surface of the middle of an ocean is, well, the best definition I can think of of a purely academic problem in the cosmically irrelevant sense.
By now, for it to be believable and remotely relevant, it needs to be something we can see. It’s not. And probably never will be. More ghosts and gaslighting.
“It’s worth reminding ourselves that the coast is the only place where supposed sea level rise matters.” Really?
Global SLR (and that includes SLR in mid-ocean areas) is important to understanding how melting of land-supported ice and increases in overall ocean temperatures (causing sea water thermal expansion) correlate—or not—to understanding and modeling climate change. It is a key metric that is used to check on the overall validity of Earth’s hydrological cycle.
As but one example, an overall increase in global sea-level will mean that the total area of the Earth permanently covered by oceans will increase, which in turns means that more water can evaporate from the oceans into the atmosphere (all other things being equal), thereby resulting in a slight increase in atmospheric humidity and perhaps additional rainfall on the planet. Atmospheric water vapor content (aka humidity) is the predominant “greenhouse gas” factor among forcing functions for those attempting to understand/model climate change. Cloud coverage (extent of condensed-but-not-precipitated atmospheric humidity) is also an extremely important variable governing climate.
The study and research of climate change “matters”to a great many people—scientists, bureaucrats, politicians, WUWT readers, real estate agents, and “common folk”—most of whom do not live in costal areas.
And, as I previously posted (it ‘s worth reminding ourselves): There is the simple fact that costal tide gauges DO NOT measure global sea level change. Never have, never will.
Errrr . . . make that “coastal”, not “costal”.
Has there been a paper that gives the sea level change for a change in air temperature? As in the seas acting like a liquid thermometer?
If not, why not?
Geoff S
Geoff
I remember once, as a kid, swimming in the reservoir Lake Shasta in Northern California. The air temperature was in the 90s, and the surface of the water was a rather pleasant low-70s. I dove under the surface and at about 5 feet or thereabouts, it was frigid! Probably in the 50s, which would be close to the average annual temperature for that elevation and latitude.
Now the point of that is, thermosteric expansion would only take place above the thermocline. To calculate the ‘thermometer-like’ response of a water body would require knowing the depth of any thermocline present, and if not, a temperature profile to the bottom. Unlike an actual thermometer, the entire water column is not exposed to the same air temperature and is not uniform. One needs far more detail than is usually available unless you are the captain of the Red October.
“thermosteric expansion would only take place above the thermocline.”
Not necessarily. The deep water comes down from the surface though the thermohaline circulation. If it becomes warmer the total volume of the ocean will increase. Of course this is a very slow process since the turnover time is about 1,000-2,000 years. The deep water coming back up in upwelling areas now went down during the MWP, so it is actually possible that the deep ocean is net cooling now.
https://science.sciencemag.org/content/363/6422/70
tty
The point being, is that only water that is warming will contribute to thermosteric volume increase. Not all oceanic water is experiencing recent warming!
“In the ocean, the thermocline divides the upper mixed layer from the calm deep water below.
Depending largely on season, latitude, and turbulent mixing by wind, thermoclines may be a semi-permanent feature of the body of water in which they occur, or they may form temporarily in response to phenomena such as the radiative heating/cooling of surface water during the day/night. Factors that affect the depth and thickness of a thermocline include seasonal weather variations, latitude, and local environmental conditions, such as tides and currents.” — source: https://en.wikipedia.org/wiki/Thermocline
So, it is incorrect to consider the thermocline as an insulating layer. Where and when it exists, it basically marks the depth(s) at which fairly large convective heat transfer in upper surface waters basically ceases and where the depths below it have relatively little convective heat transfer.
However, heat transfer by thermal CONDUCTION in seawater still occurs above, below and across the thermocline.
Water is a relatively good conductor of heat . . . at STP, it conducts heat about 20 times better than air. The thermal conductivity of seawater is about 0.6 W/m/K at 25 °C and a salinity of 35 g/kg, although it is only very weakly dependent on absolute salinity.
The relatively large thermal conductivity of seawater, albeit much less than the heat transfer ability associated with convection, is the reason that NOAA can state:
“Below 3,300 feet to a depth of about 13,100 feet, water temperature remains constant. At depths below 13,100 feet, the temperature ranges from near freezing to just above the freezing point of water as depth increases.” (Ref: https://oceanservice.noaa.gov/facts/thermocline.html )
So – the short answer is – you can’t measure sea level rise from space.
“‘Centimeter’ precision”? As in Texas accuracy?
And they are claiming to achieve millimeter SLR measurements using an instrument with plus/minus centimeter accuracy?
Sounds like they’re going to get SLR measurements that are plus/minus .75 of an inch…
Proving, again, that claims to SLR measurement accuracy to the millimeter are all smoke, unicorns and delusions.
Consider this. SWEPOS Class A geodetic stations have multiple GPS antennas solidly anchored in carefully selected crack-free precambrian bedrock of the Baltic Shield. They use GPS, GLONASS and Galileo in parallel. Their antennas are individually calibrated, and the antennas and other equipment is continuosly maintained and upgraded and the measurements are monitored in real time.
They claim an uncertainty of 0.6 mm/yr in measurements of vertical movement for the bedrock they are anchored to.
Satellites measure a constantly moving uneven surface approximately 1300 km away. They can never be calibrated, maintained or upgraded once launched. They move in an orbit that can by necessity never be nearly as exactly measured as a static position on ground.
They claim an uncertainty of 0.4 mm/yr in vertical movement for the uneven surface 1300 km away.
Which is more credible?
When reading any discussion related to the MSL, I’m always reminded of a simple calculation: during the most recent glaciation event, ca. 12,000-18,000 yrs ago, the MSL was 120 m below the current value. 120,000 / 12,000 = 10 mm/yr *on average* or, in the worst case, 120,000 / 18,000 = 6.7 mm/yr. Again, on average.
Why the panic?
TG
1. Panic? What panic?
2. 10,000 years ago, Mankind population was between 5 and 10 million. They were humble hunters and collectors. No towns, no infrastructures, no trade, no industry.
And what do you see today, TG?
J.-P. D.
J.-P.D.
I see a lot of panicky and alarmist papers and articles about the supposedly exceptionally fast MSL increase which, according to a simple calculation, is several times smaller than a very long-term average.
I can understand the feeling of those whose grandparents built beach houses on stilts, but they never had a chance in the first place–and who now want *us* to pay their flood insurance premiums. That is what I see.
tty
I have of course read the comment
https://wattsupwiththat.com/2020/09/07/sentinel-6-and-sea-level-rise/#comment-3078896
you wrote two days ago. I apologize for not having replied earlier, and btw for having been a bit too ‘indignerad’ about your repeated hints on your favorite gauge.
But… your reply to my comment
– tells that ‘ Kungsholmsfort is rising at 1.6 +-0.8 mm/yr, and is showing NO relative sea level change’.
But… what exactly do you mean with that?
I have generated a year ago lots of single station data with VLM correction, many of them based on GPS data, e.g.
– Kungsholmsfort:
KUNGSHOLMSFORT;15.58930300;56.10520000;KUN0;2004;12;31;108;70
– Furuögrund:
FURUOGRUND;21.23079100;64.91574600;SKE0;1992;06;15;9530;203
and may many others.
And I repeat: this was for Kungs the result:
https://drive.google.com/file/d/1cZB1vNyIZD23EsWzDBetTUO2-moYx8xU/view
Moreover, in your reply, you don’t manage to escape out of your second favorite, namely the Bothnian Gulf.
What about looking at this, tty?
https://drive.google.com/file/d/12ulz1gkkkAD4S5Y_sHIufqLeuXZm0HmO/view
You see a comparison (here of course without VLM correction) of
– Furuögrund
– 6 gauges at the end of the Gulf (the latter one together with Ratan, Pietarsaari, Raahe, Skagsudde and Kaskinen)
– 36 gauges in Sweden, including thoese above
– a lot of PMSL gauges in the whole Northern Europe
– all these together with all available gauges at the Northern Atlantic coast down to Florida.
Maybe you think a bit about that?
Btw, it’s amazing to see how such a simple tool like a running mean generator can extract similarities out of time series we otherwise never would be able to detect.
Look how all the bumps in the downward consecutive means decrease step by step, until they vanish.
Simply beautiful.
J.-P. D.
–