Nghiên cứu biến đổi mực nước hồ và độ dày sông băng Tây Tạng bằng ICESat - Vu Hien Phan

Observing changes in lake level and glacial thickness on the Tibetan Plateau with the ICESat laser altimeter Vu Hien Phan Observing changes in lake level and glacial thickness on the Tibetan Plateau with the ICESat laser altimeter Proefschrift ter verkrijging van de graad van doctor aan de Technische Universiteit Delft, op gezag van de Rector Magnificus prof. Luyben, voorzitter van het College voor Promoties, in het openbaar te verdedigen op Maandag 26 January 2015 om 15:00 uur door Vu Hien PHAN Master of Engineering in Mapping, Remote Sensing and GIS Ho Chi Minh City University of Technology, Vietnam geboren te Sa Dec, Vietnam. -i- Dit proefschrift is goedgekeurd door de promotor: Prof. Menenti Copromotor: Dr.

Lindenbergh Samenstelling promotiecommissie: Rector Magnificus, voorzitter Prof. Menenti Technische Universiteit Delft, promotor Dr. Lindenbergh Technische Universiteit Delft, copromotor Prof. Scaloni Tongji University Prof.

Su Universiteit Twente Prof. van de Giesen Technische Universiteit Delft Dr. Kropacek Universität Tübingen Dr. Gourmelen The University of Edinburgh Prof.

Bastiaanssen Technische Universiteit Delft, reservelid Copyright 2015 by Vu Hien Phan. All rights reserved. No part of the material protected by this copyright notice may be reproduced or utilized in any form or by any means, electronic, mechanical, including photocopying, recording or by any information storage and retrieval system, without the prior permission of the author. ISBN 978-94-6186-426-0 Author email: v.nl or phanhienvu@gmail.com - ii - Preface Many people contributed to the successful completion of this thesis in different ways.

I wish to express my sincere gratitude to all of them. Firstly, I am extremely grateful to my co-promoter Dr. You were always there to help and support me whenever I ran into a problem. I think your support and commitment during my study made other PhDs jealous in our section.

In our weekly meetings, you always had excellent advice to give on my technical problems. I really appreciate your patience in correcting my English writing and the constructive feedback on how to write an effective article. Thank you for all your help and support to extend my knowledge and experiences in research. Secondly, I would like to thank Prof.

Massimo Menenti, for providing me with the opportunity to carry out my research and for your continuous support. With the extensive knowledge, you always gave me helpful ideas and provided me with clear and in-depth answers to my scientific and technical problems. Also, I would like to thank you for the constructive criticisms and relevant comments on the content of this dissertation. I want to thank the Vietnam Ministry of Education and Training and the CEOP- AEGIS project on the Hydrology and Climatology of the Tibetan Plateau, project no.

212921 of the European Commission FP7 program for funding this research. Furthermore, I wish to thank my friends at the OLRS section: Ali Mousivand, Hamid Reza Ghafarian Malamiri, and Seyed Enayat Hosseini Aria for sharing knowledge and experiences in studying and living in Delft and contributed to a nice and enjoyable life at TUDelft. I am thankful to Lidwien De Jong, for all the support to process a lot of documents in regularization enthusiastically. I am also very grateful to Vietnamese students and all other colleagues here at TU Delft.

I am indebted to my mother in law for having taken care of my daughter in Vietnam, to my lovely wife for being sympathetic and encouraging to me, and to my beautiful daughter for still recognizing and loving me. Last but not least, I wish to thank my lovely family and friends for their support and encouragement. - iii - Table of content Preface. iii Table of content.

The water balance of the Tibetan Plateau. ICESat laser altimetry. Organization of this thesis. EXPLOITED REMOTE SENSING DATA.

ICESat/GLAS data. GLAS data products. ICESat GLA14 land surface elevation data. Other remote sensing products.

GLIMS / CAREERI glacier mask. MODIS land-water mask. HydroSHEDS hydrographic data. Landsat TM images.

ASSESSING GLACIAL THICKNESS CHANGES AT THE TIBETAN PLATEAU USING ICESAT LASER ALTIMETRY. Estimating surface slope and roughness from SRTM DEM. Determining a sampled glacial area. Identifying a glacial elevation difference.

Different settings with respect to slope and roughness. Obtaining mean glacial elevation differences. Estimating a temporal glacial thickness change trend. Overall glacial thickness changes: Tibetan Plateau and its basins.

Impact of orientation on glacial thickness change. Exploring terrain surface criteria. State of the GLIMS glacier mask. Glacial thickness changes for sub-regions.

Representativeness of an observed glacial area. ESTIMATING ANNUAL LAKE LEVEL TRENDS ON THE TIBETAN PLATEAU. Annual lake level trends all over the Tibetan Plateau. Case studies: comparing GLAS results to LEGOS data.

Disadvantages of the supporting image data: the 250 m MODIS land-water mask and Landsat data. Anomalies in the candidate ICESat lake elevations. Determining the threshold value in the RANSAC algorithm. Link to physical processes.

ASSESSING SEASONAL LAKE LEVEL VARIATIONS USING ICESAT LASER ALTIMETRY 69 5. Estimating lake level trends per season. Obtaining seasonal lake level variations. Annual trends based on lake levels from fixed seasons.

Lake level changes during the monsoon and the dry season. IDENTIFYING GEOMETRIC LINKS BETWEEN GLACIERS AND LAKES ON THE TIBETAN PLATEAU. Determining the catchment of a Tibetan lake. Identifying connections between glaciers and lakes.

Calculating the area of a lake catchment. Computing the total area of glaciers draining into a lake. Defining the geometric dependency of a lake on glacial runoff. Lakes with glacial runoff at the Tibetan Plateau.

The hydrological interpretation of geometric dependency on glacial runoff. Details on computing the geometric dependency of lakes on glacial runoff. 129 Table A: Rates of glacial thickness changes on the Tibetan Plateau between 2003 and 2009. 135 Table B1: Rates of individual lake level changes between 2003 and 2009 on the Tibetan Plateau.

135 Table B2: The list of additional Tibetan observed lakes when the threshold value increases. 145 Table C: Lakes dominated by glaciers on the Tibetan Plateau. 145 - viii - Abbreviations ASCII American Standard Code for Information Interchange CAREERI Cold and Arid Regions Environmental and Engineering Research Institute DEM Digital Elevation Model EMG96 Earth Gravitational Model 1996 EMG2008 Earth Gravitational Model 2008 FWHM Full Width at Half Maximum pulse GLAS Geoscience Laser Altimeter System GLIMS Global Land Ice Measurements from Space GRACE Gravity Recovery And Climate Experiment HDF Hierarchical Data Format HydroSHEDS Hydrological data and maps based on SHuttle Elevation Derivatives at multiple Scales ICESat Ice, Cloud, and Land Elevation Satellite MODIS Moderate Resolution Imaging Spectroradiometer NASA National Aeronautics and Space Administration NSIDC National Snow and Ice Data Centre SRTM Shuttle Radar Topography Mission TOPEX/Poseidon Topography Experiment/Poseidon UTC Universal Coordinated Time WGS84 World Geodetic System 1984 - ix - Summary Observing changes in lake level and glacial thickness on the Tibetan Plateau with the ICESat laser altimeter The Tibetan Plateau is a vast, elevated plateau in Central Asia. It occupies an area of ~2.5 million km2 and has an average elevation of over 4,500 m.

The Tibetan Plateau is not only the highest and largest plateau of the world, but also contains a large amount of glaciers. In addition, there are thousands of lakes in this region. Most of them supply fresh water for people, livestock and agriculture while some are salt water lakes. The Tibetan Plateau is also the origin of Asia’s big rivers such as Brahmaputra, Ganges, Indus, Mekong, Salween, Yellow River, and Yangtze.

Glacial melt water supplies large inflow for the rivers during the summer monsoon and is a primary water source in the dry season. It means that the Tibetan Plateau keeps the water resources under control for Southeast Asia, the most densely populated region on Earth. However, recent research reported that the glaciers have been retreating significantly in the last decades. That is expected to affect the water storage of this region.

Therefore, understanding hydrologic processes and quantifying the water storage of the Tibetan Plateau is essential. In general, the water storage of the Tibetan Plateau is determined by precipitation, surface runoff, evaporation and infiltration. Due to the vastness, high relief and the complicated climate, only a limited number of hydrometeorologic gauge measurements are available in this region. Thus it is difficult to quantify this water storage.

However, the net annual water storage of a lake or river basin, considered as a simple water balance model, is one component of the total water storage of the Tibetan Plateau. Changes in water storage of open water bodies can be assessed by analyzing changes in their water levels. Moreover, one of the variables directly affecting water levels of lakes and rivers on the Tibetan Plateau is glacial melt water. Therefore, monitoring changes in glacial thickness and water level is a potential useful contribution to the understanding of the hydrologic processes and the water balance of the Tibetan Plateau.

In January 2003, the ICESat satellite was launched for measuring ice sheet mass balance, cloud and aerosol heights, as well as land topography and vegetation structure. The available ICESat/GLAS-derived land surface elevations have a vertical accuracy at the decimeter level over flat terrain and a horizontal accuracy in the order of meters. Each GLAS waveform was the result of the interaction of the emitted Gaussian pulse with the terrain surface within a ~70 m diameter footprint, much smaller than for example radar footprints. In addition, ICESat only obtained measurements along track with an along track distance between - xi - Summary consecutive footprints of 170 m.

This small footprint makes the ICESat/GLAS laser altimeter more advantageous in monitoring changes in lake level and glacial thickness on the Tibetan Plateau than other remote sensing techniques. The changes in lake level and glacial thickness can be converted to water volumes that can be used as input of water balance models. These contribute to improve the understanding of changes in the water storage of the Tibetan Plateau. That is why observing changes in lake level and glacial thickness on the Tibetan Plateau with the ICESat laser altimeter is reasonable.

The research consists of three main parts: i) monitoring lake level changes, ii) monitoring glacial thickness changes and iii) assessing relationships between changes in lake level and glacial thickness. Monitoring changes in lake levels: the ICESat GLA14 land surface elevation data in combination with the MODIS land-water mask was used to obtain water level variations of Tibetan lakes. The GLA14 elevations representing lake surface elevations were basically selected by using the lake outlines, derived from the MODIS land-water mask. For each ICESat sampled lake, anomalies in observed surface elevations due to e.

clouds, saturation or surface characteristics, were removed using the RANSAC algorithm. Then the mean elevations corresponding to the ICESat acquisition times were determined. They were representative for lake levels during the observed period. Subsequently, a temporal lake level trend was estimated by linear regression.

The results indicated that water level variations of 154 lakes spread all over the Tibetan Plateau between 2003 and 2009 could be obtained. Moreover, most of the lakes with a serious downwards trend are in the southern Tibetan Plateau and along the Himalaya mountain range and, vice versa, most of the lakes with a positive water level trend are in the inner Tibetan Plateau. In addition, GLA14 elevations were grouped into three seasonal datasets following to the ICESat acquisition schedule: late dry season, wet season, and early dry season. Yearly trends were estimated using lake levels in the same season and different years.

The results indicated that seasonal influences were more obvious in the South of the Tibetan Plateau than those in the Northwest. The seasonal influence on lake level gradually decreased from the Southeast to the Northwest of the Tibetan Plateau. These results correspond to trends in precipitation, temperature and humidity as documented in recent research on climate change at the Tibetan Plateau.