# You can call me Doctor now.

Glorious bearded philosopher-king is clearly more appropriate, but Doctor will do.

After six years of chasing a crazy goal and burrowing down far too many rabbit holes in search of answers to engineering problems, I got a letter from the Dean of graduate research back in late October. My PhD is done!

So what exactly did I do? The ten minute recap is this:

1. I assessed the utility of a class of empirical models for estimating snow depth on sea ice using altimetry (snow height). The models were derived from as many in situ (as in holes drilled in the ice) measurements as I could find, and I discovered that they are great in a broad sense (say hundreds of metres), but don’t quite get the picture right at high resolutions (as in metres). This is expected, and suspected – but nobody actually did the work to say how. So this was published (and of course, is imperfect – there is much more to say on the matter).

2. For a LiDAR altimetry platform I spent a lot of time tracking down noise sources, and ended up implementing a method to estimate the 3D uncertainty of every single point. This was hard! I also got quite good at staring at GPS post-processing output, and became quite insanely jealous anytime anyone showed me results from fixed-wing aircraft.

3. Now having in hand some ideas about estimating snow depth and uncertainties, I used another empirical model to estimate sea ice thickness using snow depths estimated from sea ice elevation (see 1), and propagating uncertainty from LiDAR points through to get an idea of uncertainty in my thickness estimates (see 2). Because of spatial magic I did with a robotic total station on SIPEX-II (see the blog title pic – that’s me with my friendly Leica Viva), I could also coregister some under-ice observations of sea ice draft and use them to come up with parameters to use in the sea-ice thickness from altimetry model at the scale of a single ice floe. For completeness, I did the same with a very high resolution (10cm) model I made from 3D photogrammetry on the same site. I then used this ‘validated’ parameter set to estimate sea-ice thickness for some larger regions.

Overall, the project changed direction three our four times, reshaping as we learned more – and really taking shape after some new methods for sea ice observations were applied in 2012.

What I discovered was that it is actually pretty feasible to do sea ice thickness mapping from a ship-deployed aircraft in the pack ice zone. This is important – because it means regions usually very difficult to access from a land-based runway can be examined.

I also showed that observations of sea ice so far may be underestimating sea ice thickness in certain ice regimes – and also likely to be overestimating sea ice thickness in others. This has pretty important implications for modelling the fresh water flux and other stuff (habitat availability) on the southern ocean – so more work is already underway to try and gather more data. Encouragingly, I showed that drill holes are actually quite accurate – and showed how some new approaches to the practice of in situ sampling might markedly increase the power of these observations.

The possibilities of a robotic total station and a mad keen field sampling nutter on an ice floe – endless! (we did some awesome work with a hacky sack and the total station, hopefully coming to light soon).

…and like all PhD theses, the last part is a vast introspection on where the soft underbelly of the project lies, and what could/should be done better next time.

Needless to say, I’m really relieved to be done. I go wear a floppy hat and collect my bit of paper next month.

What next? Subject the ice thickness work to peer review! Aiming for publication in 2017.