Planetary-scale surface water detection from space

This thesis studies automated methods of surface water detection from satellite imagery. Multiple existing methods are explored, discussed, and some new algorithms are introduced to allowvery accurate detection of surface water and surfacewater changes. Themethods range in applicability from the local level to global, and from detecting high-frequency changes to low-frequency changes. Their trade-offs regarding the accuracy and applicability of the surface water detection methods are also discussed.Several applications are presented to test the introduced methods. One of the studies focuses on a long-term global surface water change detection over the past 30 years at 30m resolution. The other application looks at the generation of a permanent surface water mask for Murray-Darling River Basin in Australia. Additionally, an in-depth validation for a small reservoir in California, USA is presented, to demonstrate performance of the new methods.The algorithms discussed in the thesis were applied and tested to process both passive optical multispectral and active Synthetic Aperture Radar (SAR) satellite data. Combining data fromall freely available satellite sensors requires harmonizations of the satellite data, but also, significant computing resources. In this thesis, Google Earth Engine parallel processing platformwas used to performmost of the experiments.We will see, thatwhen studying surface water dynamics, the best results can be achieved by combining discriminative and generative methods of surface water detection. This way, the surface water can also be detected from satellite images where surface water is only partially visible.In the thesis, top-of-atmosphere reflectance images are used to detect surface water. The atmospheric correction is not required when dynamic local thresholding methods are used to detect surface water.Water Resource

Functional coverages

A new Application Programming Interface (API) is presented which simplifies working with geospatial coverages as well as many other data structures of a multi-dimensional nature. The main idea extends the Common Data Model (CDM) developed at the University Corporation for Atmospheric Research (UCAR). The proposed function object model uses the mathematical definition of a vector-valued function. A geospatial coverage will be expressed as a vector-valued function whose dependent variables (the vector components) are fully defined by its independent variables (the coordinates). Our goal is to provide an API using a terminology and an object model that is both appealing to computer scientists and numerical modelers and is flexible enough to enable defining data structures for a wide range of applications. Examples of such data structures can be: wind velocity as a continuous variable defined along the channels in a river network. Precipitation data defined as a time-dependent variable on a set of sub-catchments of a drainage basin, preserving association with sub-catchment features. The new object model provides a basis for both continuous and discrete coverages including non-geospatial data structures such as time series. Different storage models for variables are implemented, based on the Network Common Data Format (NetCDF), the Geospatial Data Abstraction Library (GDAL) and memory. The API is available as set of open source libraries developed in C# consisting of a multi-dimensional arrays library; a scientific data structures library defining variables, functions, units of measure; a geospatial extensions library built on top of GeoAPI.NET and NetTopologySuite, defining specialized coverages: network coverage, feature coverage, regular grid coverage, and unstructured grid coverage.Hydraulic EngineeringCivil Engineering and Geoscience

Benefits of the use of natural user interfaces in water simulations

The use of natural user interfaces instead of conventional ones has become a reality with the emergence of 3D motion sensing technologies. However, some problems are still unsolved (for example, no haptic or tactile feedback); so this technology requires careful evaluation before the users can benefit from it. We argue, that the best benefits can be achieved when these natural user interface technologies are combined with classical computer interaction devices such as mouse and keyboard. In our demonstration, we will show how the LEAP Motion controller can be applied in environmental modeling when combined with the shallow water flow model engine D-Flow Flexible Mesh and a 3D scientific visualization library. We will analyze where the new approach provides benefits compared to the classical computer input devices such as mouse and keyboard. We will also demonstrate a number of visualization and interaction techniques used during manipulation of model input data (bathymetry, roughness, etc.) or during exploration of the results of a running morel.Hydraulic EngineeringCivil Engineering and Geoscience

Quality assessment of OpenStreetMap water mask using LANDSAT 8 imagery and Google Earth Engine

Water ManagementCivil Engineering and Geoscience

Detectability of variation in river flood from satellite images

Floods are major natural disasters that have considerable consequences worldwide. As the frequency and magnitude of flooding are expected to be affected by ongoing climate change, understanding their past changes is important for developing adequate adaptation measures. However, the limited spatiotemporal coverage of flood gauges hinders detection of changes in flooding, particularly in poorly gauged regions. Here, we propose a method using surface water data of river floodplain inundation as a proxy of the magnitude and frequency of flooding. Surface water data − Aqua Monitor which represented the probability linear trend changes in land and water surface area based on 30-m Landsat images between 1984–2000 and 2000–2013 was used in this study. The changes in water surface area over the floodplain obtained from Aqua Monitor showed high correspondence with historical trends observed or simulated annual maximum daily discharge, indicating the potential to detect changes in frequency and magnitude of flood from satellite data. In regions where changes could be measured with sufficient satellite images, 29% showed an increase in water surface area in the flood plain, 41% showed a decrease, and 30% showed small or no changes.Water Resource

A 30 m Resolution Surface Water Mask Including Estimation of Positional and Thematic Differences Using Landsat 8, SRTM and OpenStreetMap: A Case Study in the Murray-Darling Basin, Australia

Accurate maps of surface water are essential for many environmental applications. Surface water maps can be generated by combining measurements from multiple sources. Precise estimation of surface water using satellite imagery remains a challenging task due to the sensor limitations, complex land cover, topography, and atmospheric conditions. As a complementary dataset, in the case of hilly landscapes, a drainage network can be extracted from high-resolution digital elevation models. Additionally, Volunteered Geographic Information (VGI) initiatives, such as OpenStreetMap, can also be used to produce high-resolution surface water masks. In this study, we derive a high-resolution water mask using Landsat 8 imagery and OpenStreetMap as well as (potential) a drainage network using 30 m SRTM. Our approach to derive a surface water mask from Landsat 8 imagery comprises the use of a lower 15% percentile of Landsat 8 Top of Atmosphere (TOA) reflectance from 2013 to 2015. We introduce a new non-parametric unsupervised method based on the Canny edge filter and Otsu thresholding to detect water in flat areas. For hilly areas, the method is extended with an additional supervised classification step used to refine the water mask. We applied the method across the Murray-Darling basin, Australia. Differences between our new Landsat-based water mask and the OpenStreetMap water mask regarding positional differences along the rivers and overall coverage were analyzed. Our results show that about 50% of the OpenStreetMap linear water features can be confirmed using the water mask extracted from Landsat 8 imagery and the drainage network derived from SRTM. We also show that the observed distances between river features derived from OpenStreetMap and Landsat 8 are mostly smaller than 60 m. The differences between the new water mask and SRTM-based linear features and hilly areas are slightly larger (110 m). The overall agreement between OpenStreetMap and Landsat 8 water masks is about 30%.Water ResourcesComp Graphics & Visualisatio

eWaterCycle: A global operational hydrological forecasting model

Water ManagementCivil Engineering and Geoscience

The State of the World’s Beaches

Coastal zones constitute one of the most heavily populated and developed land zones in the world. Despite the utility and economic benefits that coasts provide, there is no reliable global-scale assessment of historical shoreline change trends. Here, via the use of freely available optical satellite images captured since 1984, in conjunction with sophisticated image interrogation and analysis methods, we present a global-scale assessment of the occurrence of sandy beaches and rates of shoreline change therein. Applying pixel-based supervised classification, we found that 31% of the world’s ice-free shoreline are sandy. The application of an automated shoreline detection method to the sandy shorelines thus identified resulted in a global dataset of shoreline change rates for the 33 year period 1984–2016. Analysis of the satellite derived shoreline data indicates that 24% of the world’s sandy beaches are eroding at rates exceeding 0.5 m/yr, while 28% are accreting and 48% are stable. The majority of the sandy shorelines in marine protected areas are eroding, raising cause for serious concern.Coastal EngineeringWater Resource

Global operational hydrological forecasts through eWaterCycle

Water ManagementCivil Engineering and Geoscience

Next Generation Hydro Software

An overview paper, describes motivation and main deliverables of the Next Generation Hydro Software (NGHS) project. Important technological innovations include development of the new computational core Delft3D Flexible Mesh, as well as the open modelling environment Delta Shell.Water ManagementCivil Engineering and Geoscience