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thesis.tex
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\documentclass[12pt,twoside]{book}
\usepackage[a4paper,width=150mm,top=25mm,bottom=20mm,headheight=14.5pt]{geometry}
\usepackage[natbib,style=apa,backend=biber,backref=true]{biblatex}
\bibliography{thesis.bib}
\usepackage{fancyhdr}
\pagestyle{fancy}
\usepackage{algorithm}% http://ctan.org/pkg/algorithm
\usepackage{algpseudocode}% http://ctan.org/pkg/algorithmicx
\usepackage{amsmath,amsfonts,amssymb}
\usepackage{caption}
\usepackage{subcaption}
\usepackage{CJKutf8}
\usepackage[T1]{fontenc}
\usepackage[acronym,symbols,nogroupskip,nonumberlist,toc]{glossaries-extra}
\usepackage{graphicx}
\graphicspath{ {figures/} }
% \DeclareGraphicsExtensions{.png,.pdf,.eps} % use during development
\DeclareGraphicsExtensions{.eps,.pdf,.png} % use for final production
\usepackage[bookmarks]{hyperref}
\usepackage[utf8]{inputenc}
\usepackage{lscape}
\usepackage{mathtools}
\usepackage{siunitx}
\usepackage{tabularx}
\usepackage{textcomp}
\usepackage{titlesec}
% SIrange using em-dash
\sisetup{range-phrase=--}
\sisetup{range-units=single}
% subsubsubsections paragraphs
\setcounter{secnumdepth}{3}
\titleformat{\paragraph}
{\normalfont\normalsize\bfseries}{\theparagraph}{1em}{}
\titlespacing*{\paragraph}
{0pt}{3.25ex plus 1ex minus .2ex}{1.5ex plus .2ex}
% glossary items
\makeglossaries[\acronymtype]
\glsxtrnewsymbol[description={hydropotential}]{phi}{\ensuremath{\phi}}
\glsxtrnewsymbol[description={time}]{t}{\ensuremath{t}}
\newacronym{ConvNets}{ConvNets}{Convolutional Neural Networks}
\newacronym{DBSCAN}{DBSCAN}{Density-based Spatial Clustering of Applications with Noise}
\newacronym{DEM}{DEM}{Digital Elevation Model}
\newacronym{ESRGAN}{ESRGAN}{Enhanced Super-Resolution Generative Adversarial Network}
\newacronym{ICESat-2}{ICESat-2}{
Ice, Cloud, and land Elevation Satellite 2. A near polar-orbit laser altimeter satellite that measures ice surface elevation.
}
\newacronym{IPCC}{IPCC}{Intergovernmental Panel on Climate Change}
\newacronym{ISSM}{ISSM}{Ice-sheet and Sea-level System Model}
\newacronym{LeakyReLU}{LeakyReLU}{Leaky Rectified Linear Unit}
\newacronym{REMA}{REMA}{
Reference Elevation Model of Antarctica. A high resolution, time-stamped Digital Surface Elevation Model of Antarctica created from stereophotogrammetry.
}
\newacronym{RES}{RES}{Radio-echo sounding}
\newacronym{SD}{SD}{Standard deviation}
\newacronym{SLE}{SLE}{Sea level equivalent}
%Not a Number (NaN)
\DeclareSIUnit\year{yr}
\title{
{The subglacial landscape and hydrology of Antarctica as mapped from space}\\
{\large Antarctic Research Centre, Victoria University of Wellington}\\
{\includegraphics[scale=0.5]{0_arc_logo.jpg}}
}
\author{Wei Ji Leong}
\date{\today}
\begin{document}
\input{titlepage}
\chapter*{Abstract}
To narrow uncertainties in the Antarctic ice sheet's contribution to sea level rise, we present a collection of novel machine learning and automated satellite remote sensing methods which use ice surface observations to infer the subglacial nature of Antarctica.
A super-resolution deep neural network called DeepBedMap was designed and trained to produce a high-resolution (\SI{250}{\metre}) bed elevation model of Antarctica called DeepBedMap\_DEM that preserves bed roughness details useful for catchment- to continent-scale ice sheet modelling.
This DeepBedMap\_DEM is compared with a smoother, medium-resolution (\SI{500}{\metre}) BedMachine topography in a basal inversion experiment over Pine Island Glacier, with results motivating more research into the interacting roles of subglacial hydrology which influences skin drag and high resolution bed topographies which influences form drag.
Active subglacial lakes in Antarctica were mapped using an unsupervised density-based classification method on ICESat-2 point cloud data from 2018-2020, yielding 194 active subglacial lakes, including 36 new lakes in the 86--88°S area not detected by the previous ICESat (2003-2009) mission.
This thesis showcases both the rich diversity in subglacial landscapes and the dynamic nature of subglacial hydrology in Antarctica, forming a foundation enabling the accurate modelling of overland ice flow in critical regions of the vulnerable West Antarctic Ice Sheet.
\section*{Plain language summary}
Antarctica has a lot of ice, but we're unsure how fast ice can slide into the sea and cause water to go up in beaches around the world.
So we teach computers to solve hard math problems that tell us how fast sea water might go up.
These computers are fed with lots of pictures taken from cameras up in the sky and space.
Ice sits on top of rock in Antarctica, and with practice, the computers get pretty good at telling us how high and bumpy the rock is.
The rock under the ice appears quite bumpy, and ice probably doesn't like sliding over bumpy rocks since it's rough.
Sometimes though, ice may not mind sliding over rough bits of rock if the rock moves along with it, or if water gets in between the rock and ice to makes things slippery, but we ask our smart computers to be sure.
There are also lasers from space shooting down at earth and bouncing back to tell us how ice in Antarctica is going up or down.
Once in a while, they tell us that ice in parts of Antarctica moved up or down a bit too fast.
Smart people think these are lakes hiding under the ice, filling up with water or draining, and we found many of these lakes over Antarctica, especially in an area called Whillans Ice Stream on the Siple Coast.
We hope that the computers can keep learning faster because there's a lot of pictures showing ice moving pretty fast, and it doesn't look like there's much time before a big chunk of ice might break away in Antarctica and flood beaches around the world.
\chapter*{Dedication}
To Penny, who led me, so profoundly, to be
\chapter*{Acknowledgements}
\begin{CJK*}{UTF8}{gbsn}
每一个成功男人的背后，都有一个伟大的女人。
Every step along this journey has not been without the support of a great community behind me.
My Chinese name is 梁伟吉，each character signifying a part of who I am, my duty in this world, and the enormous privillege that has allowed me to make it to this day.
Family 粱 (Leong) comes first.
My dearest partner Penny Qiu Yue 邱乐, you have went above and beyond what a normal long distance relationship entails, keeping me company daily through good times and bad, being patient, trusting and more than I could ever express in my supposedly native yet broken Malaysian/Bruneian Chinese.
Above all, thank you for sharing the most precious asset there is - 时间 - time - which for that, I am forever grateful.
To my younger sister Wei Qian 伟倩 and brother Wei Tong 伟桐，growing up with you two in Brunei has taught me the importance of sharing and looking after each other, so thank you for your understanding, for all the catch up calls, and simply for being.
For Dad and Mum，梁耀明 and 陈碹丝，it takes a million to raise one child, let alone three, and I have lost count of the number of side jobs you've had over the years, especially the struggles in recent times, both of you deserve a special thank you and a long holiday.
To my local family in Wellington, Jaclyn and David Chai, for the nourishment you have provided over the years in the form of yummy Malaysian style vegetarian food.
It is unbelievable how fast time flies, seeing your two kids ZH and Yi Ling grow tall and mature, you are all my second family and will always be remembered.
Greatness 伟 (Wei) of teachers is next.
To my great supervisor Huw Horgan (and his amazing partner Ruschle), I sometimes wonder how a person from the tropics without a trace of snow got into studying Antarctic ice, and obviously it was because of you, from that time in 2014 studying proglacial lakes at Mount Cook national park, to my 2015 Honours project on mapping potential subglacial estuaries in Antarctica, to this very PhD thesis 2017-2021.
A very big thank you for allowing me to do my work remotely using satellites, sending me randomly on exchanges to Alaska and Austria to realize how big the world truly is, for giving me the space to develop independently, while providing top notch Yoda-like advice that takes me weeks and months to figure out.
Thank you to all my Geography teachers and mentors over the years.
In particular, to my secondary school teacher Veronica Chan at Chung Hwa Middle School, for your great style of Geography teaching with funny stories and sketches, it was weird that you didn't recommend me taking Geography in high school, but here I am now.
% To my high school teacher
To my university lecturer Mairéad de Róiste, for putting me on this journey into Geographic Information Systems (GIS), setting good examples on how to tutor the next generation of students, and also for drilling in Cartogrphic best practices.
To Karl Baker at e-Spatial, for passing on your guru level of stacking and mosaicking aerial imagery, arranging map layers to perfection, and for being a role model on how to be a respectable GIS professional.
Luck 吉 (Ji) is the last but not least.
I feel really fortunate to be able to stand on the shoulders of giants, and would like to acknowledge at least some of the many people I've met along this journey.
\paragraph{Open source}
To Leonardo Uieda, DongDong Tian 田冬冬, Liam Toney and the rest of the PyGMT team, and also to Paul Wessel for his enduring work on the Generic Mapping Tools (GMT) package over many decades, it is a pleasure to have such a great tool for producing beautiful maps.
To all the folks maintaining the Python and Pangeo ecosystem of geospatial packages, from Xarray to RAPIDS AI and every imaginable library in between, thank you for all the new features and bug fixes, keep up the good work!
\paragraph{Europe}
To Poonam Vishwas, KaiKai Xue 薛凯, Yawen Tan 谭雅文, and all the friends I met in the 2019 Erasmus+ exchange at ZGIS, University of Salzburg, Austria, it was an awesome experience having so many like-minded people researching GIS together in Europe, an experience I will always treasure.
To Dr. Hermann Klug, thank you for warmly inviting me to Salzburg and sorting out all manners of logistics in German, and to Dr. Dirk Tiede for introducing me to Object Based Image Analysis and providing a conceptual framework for understanding the place of Convolutional Neural Networks in the wider field of supervised classification in GIS.
\paragraph{United States}
To Anushilan Acharya, Indraneel Kasmalkar, Whyjay Zheng, and all my friends in the 2018 McCarthy International Summer School in Glaciology, it was a great pleasure meeting you all, and I look forward to seeing some of you again at some point!
To Dr. Regine Hock, thank you for inviting me to Alaska and giving me a once in a lifetime experience of stepping on a big glacier, and to Dr. Kelly Brunt for some great lessons on the ICESat-2 laser altimetry satellite!
To the International Glaciological Society (IGS), thank you for the generous early career travel grant and the chance to present a talk at the 2019 IGS Five Decades of Radioglaciology Symposium at Stanford University.
\paragraph{New Zealand}
To Arran Whiteford, Alanna Alevropoulos-Borrill, Francesca Baldacchino, my CO522 office mates at the Antarctic Research Centre, for all the yarns about ice and other topics, I couldn't have asked for a nicer group of friendly folks to do my PhD with!
To Dao Polsiri and Michelle Dow, thank you for sorting out all sorts of paperwork from flight ticket changes to funding for trivial things, and also to Aleksandr Beliaev, for troubleshooting issues with the UNIX servers and putting up with my overuse of storage, RAM, GPU resources and all.
Finally to anyone that I left out, you are not unnoticed, this sentence is for you, and I hope you enjoy reading this thesis just as much as I do.
\end{CJK*}
\tableofcontents
\listoffigures
\listoftables
% \printnoidxglossary[type=symbols,sort=use,style=long,title={List of Symbols}]
\glsaddall
\setglossarystyle{altlist}
\printglossary[type=\acronymtype]
\chapter{Introduction}
\input{chapters/01_introduction}
\chapter{DeepBedMap: a deep neural network for resolving the bed topography of Antarctica}
\label{ch:2}
\chaptermark{DeepBedMap}
\input{chapters/02_chapter}
\chapter{The role of subglacial topography on Antarctic ice flow}
\label{ch:3}
\chaptermark{Basal inversion}
\input{chapters/03_chapter}
\chapter{Automated classification of active subglacial lakes in Antarctica from ICESat-2/ATLAS laser altimetry (2018--2020)}
\label{ch:4}
\chaptermark{ICESat-2 subglacial lakes}
\input{chapters/04_chapter}
\chapter{Conclusion}
\input{chapters/05_conclusion}
\appendix
\input{chapters/06_appendix}
\printbibliography
\end{document}