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1. An Optical and SAR Based Fusion Approach for Mapping Surface Water Dynamics over Mainland China

Author

Daniel Druce, Xiaoye Tong, Xia Lei, Tao Guo, Cecile M.M. Kittel, Kenneth Grogan, and Christian Tottrup

Subjects
surface water mapping, SAR and optical data fusion, logistic regression, water resource management, sustainable development, Science
Abstract

Earth Observation (EO) data is a critical information source for mapping and monitoring water resources over large inaccessible regions where hydrological in-situ networks are sparse. In this paper, we present a simple yet robust method for fusing optical and Synthetic Aperture Radar (SAR) data for mapping surface water dynamics over mainland China. This method uses a multivariate logistic regression model to estimate monthly surface water extent over a four-year period (2017 to 2020) from the combined usages of Sentinel-1, Sentinel-2 and Landsat-8 imagery. Multi-seasonal high-resolution images from the Chinese Gaofen satellites are used as a reference for an independent validation showing a high degree of agreement (overall accuracy 94%) across a diversity of climatic and physiographic regions demonstrating potential scalability beyond China. Through inter-comparison with similar global scale products, this paper further shows how this new mapping technique provides improved spatio-temporal characterization of inland water bodies, and for better capturing smaller water bodies (< 0.81 ha in size). The relevance of the results is discussed, and we find this new enhanced monitoring approach has the potential to advance the use of Earth observation for water resource management, planning and reporting.

Published
2021
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2. Altimetry for the Future: Building on 25 Years of Progress

Author

Saleh Abdalla, Abdolnabi Abdeh Kolahchi, Susheel Adusumilli, Suchandra Aich Bhowmick, Eva Alou-Font, Laiba Amarouche, Ole Baltazar Andersen, Helena Antich, Lotfi Aouf, Brian Arbic, Thomas Armitage, Sabine Arnault, Camila Artana, Giuseppe Aulicino, Nadia Ayoub, Sergei Badulin, Steven Baker, Chris Banks, Lifeng Bao, Silvia Barbetta, Barbara Barcelo-Llull, Francois Barlier, Sujit Basu, Peter Bauer-Gottwein, Matthias Becker, Brian Beckley, Nicole Bellefond, Tatyana Belonenko, Mounir Benkiran, Touati Benkouider, Ralf Bennartz, Jerome Benveniste, Nicolas Bercher, Muriel Berge-Nguyen, Joao Bettencourt, Fabien Blarel, Alejandro Blazquez, Denis Blumstein, Pascal Bonnefond, Franck Borde, Jerome Bouffard, Francois Boy, Jean-Paul Boy, Cedric Brachet, Pierre Brasseur, Alexander Braun, Luca Brocca, David Brockley, Laurent Brodeau, Shannon Brown, Sean Bruinsma, Anna Bulczak, Sammie Buzzard, Madeleine Cahill, Stephane Calmant, Michel Calzas, Stefania Camici, Mathilde Cancet, Hugues Capdeville, Claudia Cristina Carabajal, Loren Carrere, Anny Cazenave, Eric P. Chassignet, Prakash Chauhan, Selma Cherchali, Teresa Chereskin, Cecile Cheymol, Daniele Ciani, Paolo Cipollini, Francesca Cirillo, Emmanuel Cosme, Steve Coss, Yuri Cotroneo, David Cotton, Alexandre Couhert, Sophie Coutin-Faye, Jean-Francois Cretaux, Frederic Cyr, Francesco d’Ovidio, Jose Darrozes, Cedric David, Nadim Dayoub, Danielle De Staerke, Xiaoli Deng, Shailen Desai, Jean-Damien Desjonqueres, Denise Dettmering, Alessandro Di Bella, Lara Dıaz-Barroso, Gerald Dibarboure, Habib Boubacar Dieng, Salvatore Dinardo, Henryk Dobslaw, Guillaume Dodet, Andrea Doglioli, Alessio Domeneghetti, David Donahue, Shenfu Dong, Craig Donlon, Joel Dorandeu, Christine Drezen, Mark Drinkwater, Yves Du Penhoat, Brian Dushaw, Alejandro Egido, Svetlana Erofeeva, Philippe Escudier, Saskia Esselborn, Pierre Exertier, Ronan Fablet, Cedric Falco, Sinead Louise Farrell, Yannice Faugere, Pierre Femenias, Luciana Fenoglio, Joana Fernandes, Juan Gabriel Fernandez, Pascale Ferrage, Ramiro Ferrari, Lionel Fichen, Paolo Filippucci, Stylianos Flampouris, Sara Fleury, Marco Fornari, Rene Forsberg, Frederic Frappart, Marie-laure Frery, Pablo Garcia, Albert Garcia-Mondejar, Julia Gaudelli, Augusto Getirana, Lucile Gaultier, Ferran Gibert, Artur Gil, Lin Gilbert, Sarah Gille, Luisella Giulicchi, Jesus Gomez-Enri, Laura Gomez-Navarro, Christine Gommenginger, Lionel Gourdeau, David Griffin, Andreas Groh, Alexandre Guerin, Raul Guerrero, Thierry Guinle, Praveen Gupta, Benjamin D. Gutknecht, Mathieu Hamon, Guoqi Han, Daniele Hauser, Veit Helm, Stefan Hendricks, Fabrice Hernandez, Anna Hogg, Martin Horwath, Martina Idzanovic, Peter Janssen, Eric Jeansou, Yongjun Jia, Yuanyuan Jia, Liguang Jiang, Johnny A. Johannessen, Masafumi Kamachi, Svetlana Karimova, Kathryn Kelly, Sung Yong Kim, Robert King, Cecile M.M. Kittel, Patrice Klein, Anna Klos, Per Knudsen, Rolf Koenig, Andrey Kostianoy, Alexei Kouraev, Raj Kumar, Sylvie Labroue, Loreley Selene Lago, Juliette Lambin, Lea Lasson, Olivier Laurain, Remi Laxenaire, Clara Lazaro, Sophie Le Gac, Julien Le Sommer, Pierre-Yves Le Traon, Sergey Lebedev, Fabien Leger, Benoit Legresy, Frank Lemoine, Luc Lenain, Eric Leuliette, Marina Levy, John Lillibridge, Jianqiang Liu, William Llovel, Florent Lyard, Claire Macintosh, Eduard Makhoul Varona, Cécile Manfredi, Frédéric Marin, Evan Mason, Christian Massari, Constantin Mavrocordatos, Nikolai Maximenko, Malcolm McMillan, Thierry Medina, Angelique Melet, Marco Meloni, Stelios Mertikas, Sammy Metref, Benoit Meyssignac, Jean-François Minster, Thomas Moreau, Daniel Moreira, Yves Morel, Rosemary Morrow, John Moyard, Sandrine Mulet, Marc Naeije, Robert Steven Nerem, Hans Ngodock, Karina Nielsen, Jan Even Øie Nilsen, Fernando Niño, Carolina Nogueira Loddo, Camille Noûs, Estelle Obligis, Inès Otosaka, Michiel Otten, Berguzar Oztunali Ozbahceci, Roshin P. Raj, Rodrigo Paiva, Guillermina Paniagua, Fernando Paolo, Adrien Paris, Ananda Pascual, Marcello Passaro, Stephan Paul, Tamlin Pavelsky, Christopher Pearson, Thierry Penduff, Fukai Peng, Felix Perosanz, Nicolas Picot, Fanny Piras, Valerio Poggiali, Étienne Poirier, Sonia Ponce de León, Sergey Prants, Catherine Prigent, Christine Provost, M-Isabelle Pujol, Bo Qiu, Yves Quilfen, Ali Rami, R. Keith Raney, Matthias Raynal, Elisabeth Remy, Frédérique Rémy, Marco Restano, Annie Richardson, Donald Richardson, Robert Ricker, Martina Ricko, Eero Rinne, Stine Kildegaard Rose, Vinca Rosmorduc, Sergei Rudenko, Simón Ruiz, Barbara J. Ryan, Corinne Salaün, Antonio Sanchez-Roman, Louise Sandberg Sørensen, David Sandwell, Martin Saraceno, Michele Scagliola, Philippe Schaeffer, Martin G. Scharffenberg, Remko Scharroo, Andreas Schiller, Raphael Schneider, Christian Schwatke, Andrea Scozzari, Enrico Ser-giacomi, Frederique Seyler, Rashmi Shah, Rashmi Sharma, Andrew Shaw, Andrew Shepherd, Jay Shriver, C.K. Shum, Wim Simons, Sebatian B. Simonsen, Thomas Slater, Walter Smith, Saulo Soares, Mikhail Sokolovskiy, Laurent Soudarin, Ciprian Spatar, Sabrina Speich, Margaret Srinivasan, Meric Srokosz, Emil Stanev, Joanna Staneva, Nathalie Steunou, Julienne Stroeve, Bob Su, Yohanes Budi Sulistioadi, Debadatta Swain, Annick Sylvestre-baron, Nicolas Taburet, Rémi Tailleux, Katsumi Takayama, Byron Tapley, Angelica Tarpanelli, Gilles Tavernier, Laurent Testut, Praveen K. Thakur, Pierre Thibaut, LuAnne Thompson, Joaquín Tintoré, Céline Tison, Cédric Tourain, Jean Tournadre, Bill Townsend, Ngan Tran, Sébastien Trilles, Michel Tsamados, Kuo-Hsin Tseng, Clément Ubelmann, Bernd Uebbing, Oscar Vergara, Jacques Verron, Telmo Vieira, Stefano Vignudelli, Nadya Vinogradova Shiffer, Pieter Visser, Frederic Vivier, Denis Volkov, Karina von Schuckmann, Valerii Vuglinskii, Pierrik Vuilleumier, Blake Walter, Jida Wang, Chao Wang, Christopher Watson, John Wilkin, Josh Willis, Hilary Wilson, Philip Woodworth, Kehan Yang, Fangfang Yao, Raymond Zaharia, Elena Zakharova, Edward D. Zaron, Yongsheng Zhang, Zhongxiang Zhao, Vadim Zinchenko, and Victor Zlotnicki

Subjects
Space Sciences (General), Geosciences (General)
Abstract

In 2018 we celebrated 25 years of development of radar altimetry, and the progress achieved by this methodology in the fields of global and coastal oceanography, hydrology, geodesy and cryospheric sciences. Many symbolic major events have celebrated these developments, e.g., in Venice, Italy, the 15th (2006) and 20th (2012) years of progress and more recently, in 2018, in Ponta Delgada, Portugal, 25 Years of Progress in Radar Altimetry. On this latter occasion it was decided to collect contributions of scientists, engineers and managers involved in the worldwide altimetry community to depict the state of altimetry and propose recommendations for the altimetry of the future. This paper summarizes contributions and recommendations that were collected and provides guidance for future mission design, research activities, and sustainable operational radar altimetry data exploitation. Recommendations provided are fundamental for optimizing further scientific and operational advances of oceanographic observations by altimetry, including requirements for spatial and temporal resolution of altimetric measurements, their accuracy and continuity. There are also new challenges and new openings mentioned in the paper that are particularly crucial for observations at higher latitudes, for coastal oceanography, for cryospheric studies and for hydrology. The paper starts with a general introduction followed by a section on Earth System Science including Ocean Dynamics, Sea Level, the Coastal Ocean, Hydrology, the Cryosphere and Polar Oceans and the ‘‘Green” Ocean, extending the frontier from biogeochemistry to marine ecology. Applications are described in a subsequent section, which covers Operational Oceanography, Weather, Hurricane Wave and Wind Forecasting, Climate projection. Instruments’ development and satellite missions’ evolutions are described in a fourth section. A fifth section covers the key observations that altimeters provide and their potential complements, from other Earth observation measurements to in situ data. Section 6 identifies the data and methods and provides some accuracy and resolution requirements for the wet tropospheric correction, the orbit and other geodetic requirements, the Mean Sea Surface, Geoid and Mean Dynamic Topography, Calibration and Validation, data accuracy, data access and handling (including the DUACS system). Section 7 brings a transversal view on scales, integration, artificial intelligence, and capacity building (education and training). Section 8 reviews the programmatic issues followed by a conclusion.

Published
2021
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3. Flow regime changes in the Lancang River, revealed by integrated modeling with multiple Earth observation datasets

Author

Xingxing Zhang, Liguang Jiang, Zhaofei Liu, Cecile M.M. Kittel, Zhijun Yao, Daniel Druce, Rui Wang, Christian Tøttrup, Jun Liu, Hou Jiang, and Peter Bauer-Gottwein

Subjects
Environmental Engineering, Environmental Chemistry, Pollution, Waste Management and Disposal
Abstract

The flow regime change of rivers, especially transboundary rivers, affected by reservoir regulations is evident worldwide and has received much attention. Investigating dam-induced flow regime alterations is essential for understanding potential adverse downstream effects and facilitating dialogue around coordinated water use in transboundary basins, such as the Lancang River Basin (LRB). This study explored the value of combining several types of satellite Earth observation (EO) datasets that monitor different water balance components to constrain the parameter space of lumped conceptual hydrological models. Thus, we aimed to reconstruct the natural flow regimes upstream and downstream of the cascade reservoirs. Specifically, reservoir water storage changes were first estimated using satellite imagery and altimetry datasets. Then, storage changes were combined with hydrological model simulations of reservoir inflow to estimate the regulated flow regime downstream. Our results showed that integrated hydrological modeling combined with EO datasets exhibited better overall performance. Continuous warming and drying of the LRB resulted in a decrease in discharge of approximately 47 %. By comparing the simulated natural and regulated flow regimes, we revealed the pivotal role of the Xiaowan and Nuozhadu reservoirs in regulating natural flows. The wet season shortens (approximately 45 days), the flood peak flattens, and the low flow in the dry season has primarily increases. The two reservoirs attenuated 50 % of the flood peaks in the wet seasons and mitigated droughts by releasing up to 100 % of the natural flows in the dry seasons at the China-Laos border. Overall, these results enhance the understanding of upper reservoir operation, and the approaches can be applied to studies of dammed basins under climate change scenarios when knowledge of the upstream area is limited.

Published
2023

4. Spatio-temporally varying Strickler coefficient: A calibration approach applied to a Danish river using in-situ water surface elevation and UAS altimetry

Author

Jun Liu, Liguang Jiang, Filippo Bandini, Cecile M.M. Kittel, Nicola Balbarini, Nisha G. Hansted, Henrik Grosen, and Peter Bauer-Gottwein

Subjects
Hydrodynamic modeling, Steady-state solver, Global optimization, UAS altimetry, Roughness coefficient, Water Science and Technology
Abstract

Hydraulic roughness (e.g., expressed in terms of Manning's or Strickler’s coefficient) is an essential input to numerical hydrodynamic models. One way to estimate roughness parameters is by hydraulic inversion, using observed water surface elevation (WSE) collected from gauging stations, satellite platforms, or Unmanned Aerial System (UAS) -based altimeters. Specifically, UAS altimetry provides close to instantaneous observations of longitudinal profiles and seasonal variations of WSE for various river types, which are helpful for calibrating roughness parameters. However, it is computationally expensive to run high-resolution hydrodynamic models thousands to millions of times as required for the global optimization of distributed parameter sets (e.g., spatio-temporally varying river roughness). This study presents an efficient calibration approach for hydrodynamic models using a simplified steady-state hydraulic solver, UAS altimetry datasets, and in-situ observations. The calibration approach minimized the weighted sum of a misfit term, spatial smoothness penalty, and an a-priori sinusoidal temporal variation constraint. The approach was first demonstrated for several synthetic calibration experiments, and the results indicated that the global search algorithm accurately recovered the variations of Strickler coefficient (Κs) for short river reaches in temporal (due to the seasonal growth cycle of the aquatic vegetation) and spatial (e.g., due to spatially variable vegetation density) scales. Subsequently, the calibration approach was demonstrated for a real WSE dataset collected at a Danish test site (Vejle Å). In this river friction is dominated by submerged vegetation growing in the stream and shows strong seasonal and longitudinal variations due to the plant growth cycle and variable vegetation density and species composition. Results indicated that spatio-temporal variation of Κs was required to fit in-situ observations and UAS altimetry accurately. This study illustrates how UAS altimetry and hydrodynamic modeling can be combined to achieve an improved understanding and better parameterization of small and medium-sized rivers, where river channel conveyance is controlled by vegetation growth and other spatio-temporally variable factors.

Published
2022

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