Envisat sea-level measurements, two versions

Satellites & sea-level measurement

(This material is mostly duplicated from https://sealevel.info/resources.html#satellite.)

Aviso's satellite altimetry sea level data, notes, and graph (and new version, old version, and criticism of their dramatic revisions to the ENVISAT data [alt] [2]).

Univ. of Colorado Sea Level Research Group, Aviso and NOAA all have groups working on sea-level measurement by satellite altimetry.

Even though the satellite measurements show no significant acceleration in sea-level rise, changes in how the satellite data is processed and adjusted have substantially increased the amount of sea-level rise which U. Colorado reports. There are many different factors [2] which can affect reported trends, but which are difficult to ascertain with certainty, and are subject to substantial and often mysterious corrections.

University of Colorado sea-level rise, rev 2 contrasted with rev 1.2

To see how malleable the satellite altimetry data is, consider this well-known paper, which sought to explain away an apparent declining trend in the rate of sea-level rise measured by satellite altimetry. They managed to massage the data until that embarrassing decline had almost entirely disappeared. (Does that remind you of anything?)

Here are two pairs of graphs from the paper, each with “before” and “after” versions, showing how they “corrected” the work of 5 (five!) different satellite altimetry analysis groups, to almost completely eliminate the decline, which all five groups had measured:

GMSL trends during the 1994-2002 and 2003-2011 periods (using satellite altimetry data from five processing groups) GMSL trends during the 1994-2002 and 2003-2011 periods (using satellite altimetry data from five processing groups)

This article & comments at WUWT have a good discussion of how adjustments have increased rate of sea-level rise reportedly “measured” by satellite altimetry. (h/t Steve Case [here & here])

Another example illustrating the malleability of the satellite altimetry data is a widely-hyped 2018 paper by U. Colorado's Dr. Steve Nerem et al, which claimed to have discovered “acceleration” in the satellite altimetry measurement record of sea-level — by reducing the rate of measured sea-level rise in 20 year-old Topex-Poseidon data, thereby making more recent measurements appear to have accelerated, by comparison.

From Frank Lansner and Jo Nova comes an enlightening but disturbing article about suspicious adjustments to sea-level measurement data from satellite altimetry.

Unfortunately, measurement of sea-level by satellite altimetry is fundamentally unreliable. Physicist Willie Soon explains the problems starting at 17:37 in this very informative hour-long lecture.

Willie Soon, Ph.D., July 13, 2013

To address some of these problems, in 2011 NASA proposed (and re-proposed in 2014 / 2015) a new satellite mission called the Geodetic Reference Antenna in SPace (GRASP). The proposal is discussed here, and its implications for measuring sea-level are discussed here. The Europeans are apparently considering a similar mission (E-GRASP).


More resources

DORIS (Doppler Orbitography and Radiopositioning Integrated by Satellite) is a Doppler satellite tracking system for determining satellite locations.

NOAA's National Geodetic Survey CORS program (Continuously Operating Reference Stations) provides satellite-based 3D positional data, measuring subsidence, uplift, and lateral movement of the Earth's surface at more than 1,900 locations. Here's a map showing the station locations: http://www.ngs.noaa.gov/CORS_Map/.

SONEL is a French organization; they have GPS station resources, vertical land motion (VLM) estimates, and tide-gauge data.

 

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