Finally: JPL intends to get a GRASP on accurate sea level and ice measurements

A climate science bombshell: New proposal from NASA JPL admits to “spurious” errors in current satellite based sea level and ice altimetry, calls for new space platform to fix the problem.

People send me stuff. Today it is a PowerPoint presentation from NASA JPL that touts the new GRASP (Geodetic Reference Antenna in Space) satellite project. I’d say it is more than a bit of a bombshell because the whole purpose of this new mission is to “fix” other mission data that apparently never had a stable enough reference for the measurements being made. This promises to rewrite what we know about sea level rise and acceleration, ice extent and ice volume loss measured from space.

What is most interesting, is the admissions of the current state of space based sea level altimetry in the science goals page of the presentation:

The difference between tide gauge data and space based data is over 100% in the left graph, 1.5 mm/yr versus 3.2mm/yr. Of course those who claim that sea level rise is accelerating accept this data without question, but obviously one of the two data sets (or possibly both) is not representative of reality, and JPL’s GRASP team aims to fix this problem they have identified:

TRF errors readily manifest as spurious sea level rise accelerations

That’s a bucket of cold water reality into the face of the current view of sea level rise. It puts this well-known and often cited graph on Sea Level Rise from the University of Colorado (and the rate of 3.1 mm/yr) into question:

What’s  a TRF error? That stands for Terrestrial Reference Frame, which is basically saying that errors in determining the benchmark are messing up the survey. In land based geodesy terms, say if somebody messed with the USGS benchmark elevation data from Mt. Diablo California on a regular basis, and the elevation of that benchmark kept changing in the data set, then all measurements referencing that benchmark would be off as well.

In the case of radio altimetry from space, such measurements are extremely dependent on errors related to how radio signals are propagated through the ionosphere. Things like Faraday rotation, refraction, and other propagation issues can skew the signal during transit, and if not properly corrected for, especially over the long-term, it can introduce a spurious signal in all sorts of data derived from it. In fact, the mission summary shows that it will affect satellite derived data for sea level, ice loss, and ice volume in GRACE gravity measurements:

In a nutshell, JPL is saying we don’t have an accurate reference point, and therefore the data from these previous missions likely has TRF uncertainties embedded:

The TRF underlies all Measurement of the Earth

Without that stable Terrestrial Reference Frame that puts the precision of the baseline measurements well below the noise in the data, all we have are broader uncertain measurements. That’s why the plan is to provide ground based points of reference, something our current satellite systems don’t have:

To help understand the items in the side panels:

GNSS = Global Navigation Satellite System – more here

SLR = Satellite Laser Ranging  – more here

DORIS = Doppler Orbitography and Radiopositioning Integrated by Satellite – more here

VLBI = Very Long Baseline Interferometry – more here

Taken together, these systems will improve the accuracy of the TRF, and thus the data. It’s rather amazing that the baseline accuracy didn’t come first, because this now puts all these other space based measurement systems into uncertainty until their TRF issues are resolved, and that’s an inconvenient truth. We’ll never look at satellite based sea level data or GRACE ice volume data in quite the same way again until this is resolved.

PowerPoint here: Poland 2012 – P09 Bar-Sever PR51 (PDF)

More info: http://ccar.colorado.edu/~nerem/EV-2_GRASP-final.pdf

UPDATE: Here’s an estimate of impacts:

Source: http://www.gps.gov/governance/advisory/meetings/2011-06/bar-sever.pdf