After a long snooze (21 years), Greenland researchers have embarked on analyzing all the ice-penetrating radar data beyond just ice thickness bedrock topography and ice thickness. There is a tremendous amount of information about post-Eemian rates of snow accumulation and past, present and future ice sheet dynamics in the isochron radar horizons if only those could be digitized and interpreted.
Easier said than done give 394,000,000 km of tracks from 1993-2012. However the Cresis group has been able to determine all the regions containing at least 25 not too badly deformed isochronous reflectors: over half the flight path data points had them at 1000-3000 m depth plus more in cold older ice.
Isochronous information in a Greenland ice sheet radio echo sounding data set
Louise C. Sime et al Geophysical Research Letters DOI: 10.1002/2013GL057928 (paywall)
http://tinyurl.com/o9dlw25 (free supplemental)
In the slow slide show below, the first one summarizes the data set. Subsequent image pairs show the outcome of automatic image analysis from 2010-12 fights. Here green indicates no suitable reflectors, blue so-so regions of too few horizons, red regions of too much slope variability, and black the bedrock profile.
I sure hope they retained something better than these clumsy dot texture overlays -- masking should have been done in gimp with a translucency layer because the next step will be automatic tracking of individual horizons on what's left, probably digitizing them with some level of human supplementation in fiducial transects.
In Antarctica, they have a long-established numbering system for radar horizons. I have not seen this for Greenland but now that calendar dates are established and correlated across the five main cores, a sensible way to number radar horizons would be by isochron date b2k because that allows new horizons detected at future higher resolution to be intercalated without upsetting numbering.
In the case the reflector layer arose from a global deposition event of volcanic ash and sulfate on the ice sheet surface, its date will transfer to Antarctica as well. Although many radar striations don't correspond to anything in the ice core annual layer read-outs, they still allow transfer of those dates to remote regions of the Greenland ice sheet that will never have drilled cores, hence the need for a detailed post-Eemian timeline.
The cores were drilled along the plateau ridge in the first place because the layers are thick (rarely melt) and flat (deformation stress ~ downhill slope ~ 0). Thus a composite flight track connecting up the drill sites is the top priority in establishing an island-wide horizon numbering system.
Lots of these have been flown over the years; no one has compared them for consistency and optimal resolution (though technology improved over the years). It may be certain radar configurations have better resolution say at Holocene depth and others were more tuned to reaching bedrock or determining basal melt status.
Once the primary summit line profile has been established, secondary tracks crossing it can extend horizon dates to the ice sheet margins in favorable cases. It's very clear to me that simple pattern matching can extend many horizon sets past basal topography bumps and bottom freezeup deformations -- the horizons do not really need to be continuous if there is sufficient quality flanking disruptions.Tertiary tracks -- those intersecting secondaries -- then extend the dates to tracks parallel to the primaries and to dense track sets along the coasts.
This still does not result in volumetric filling since the radar sectioning is only on the order of 100 m wide. However it does allow for isochron hypersurface construction by interpolation of the surface/bedrock DEMs. ImageJ is all set up to do this -- horizons correspond to electrophoresis gel lanes of molecular biology -- as well as display them interactively.
These hypersurfaces will have exceedingly efficient analytic descriptions as second order polynomials in two variables which is convenient for re-gridding. Because the Greenland surface DEM is well approximated by a cylinder with north-south axis, we are going to see a lot of downstream cylindrical harmonics (Bessel functions) in the analysis of ice sheet dynamic flow. Separation of variables very much levels the playing field in modeling as main-frame numerical methods won't be needed -- anyone can play.
Give it 10 seconds, then click if it doesn't animate:
