125 research outputs found
Benchmarking water productivity in agriculture and the scope for improvement - remote sensing modelling from field to global scale
No full textAgriculture is the largest consumer and water. In the context of an increasing population and less water available for the agricultural sector, the water productivity needs to be sustained or increased to secure food security. This study provides benchmark values for water productivity for the major crops globally. Data were obtained from a literature review of measured water productivity values from field experiments, whereas remote sensing and modelling were used to assess the water productivity of wheat on a regional and on a global scale. The SEBAL model was applied to obtain spatially distributed values of water productivity in eight irrigated wheat systems globally. The analysis showed that the scope for improvement is significant in several of these systems in China, Pakistan and India. A new model, WATPRO, was developed that was applied on a global scale to benchmark water productivity of wheat at the beginning of the millennium.WatermanagementCivil Engineering and Geoscience
Understanding water resources conditions in data scarce river basins using intelligent pixel information, Case: Transboundary Indus Basin
No full textWater ManagementCivil Engineering and Geoscience
Estimating Water Balance Components of Lakes and Reservoirs Using Various Open Access Satellite Databases
No full textThere are millions of lakes and ten thousands of reservoirs in the world. The number of reservoirs is still increasing through the construction of large dams to meet the growing demand for water resources, hydroelectricity and economic development. Accurate information on the water balance components of lakes and reservoirs is deemed necessary for managing demand (i.e. of the various water user communities) and supply (gauged and ungauged inflow from surrounding catchments). Information on storage and availability of fresh water is a national security issue in many countries. In-situ hydrological measurements of reservoirs are usually not publically available. Satellite measurements and the application of specific interpretation algorithms are alternative sources of information which are publicly accessible and can help communities to better utilize scarce water resources. Ultimately, a rich, readily available and accessible data source will lead to better management decisions, with various benefits and services for all stakeholders. This thesis explores the use of satellite measurements to estimate the various key water balance components of lakes and reservoirs, ultimately leading to predictions of releases from reservoirs. Various open-access satellite databases have been explored. This thesis places emphasis on the following aspects: (i) improving existing satellite products linked to lakes and reservoirs; (ii) integrating and customizing various satellite products; (iii) evaluating and comparing alternative satellite products and (iv) developing remote sensing algorithms for the generation of new products for lakes and reservoirs. A summary of some existing open-access databases pertaining to water balance components of lakes and reservoirs is presented in the Appendix of this thesis. A pre-requisite for estimating the inflow to lakes and reservoirs from the surrounding catchments is to have access to accurate precipitation data at high spatial resolution and for the mountains where gauges are often absent. A new integrated downscaling-calibration procedure is described in Chapter 2. It is based on an integration of the TRMM (Tropical Rainfall Measuring Mission) 3B43 precipitation product (at 0.25° resolution) and NDVI (Normalized Difference Vegetation Index) from SPOT-Vegetation satellite data. This procedure creates an improved product of monthly pixel-based precipitation data at 1 km resolution. Only limited rain gauge datasets are required for calibration. This new procedure has been successfully tested in two different basins: Lake Tana Basin in Ethiopia with a humid climate and the Caspian Sea Region in Iran with a semi-arid climate. Chapter 3 describes the quantification of time series of water level, lake surface area and lake water volume from open-access databases based on satellite measurements. The four currently available satellite altimetry databases providing lake levels are firstly evaluated for three different lakes: Lake Mead (U.S.A), Lake Tana (Ethiopia) and Lake IJssel (The Netherlands). The four databases are: (i) Global Reservoir and Lake Monitoring (GRLM), (ii) River Lake Hydrology (RLH), (iii) Hydroweb and (iv) ICESat-GLAS level 2 Global Land Surface Altimetry data (ICESat-GLAS). Time series of lake surface areas were determined from Landsat TM/ETM images using the Modified Normalized Difference Water Index (MNDWI) method. A new method has been developed to estimate lake water volume, using purely satellite data, by combining satellite altimetry databases and Landsat TM/ETM images. The new method makes it possible to estimate the volume of water above the historical minimum level identified from satellite altimetry databases. The validation shows that all estimated water volumes agreed well with in-situ water volume measurements derived from bathymetric surveys for both Lake Mead and Lake Tana, with R2>0.95 and RMSE ranging between 4.6 and 13.1% of corresponding mean values of in-situ measurements. Similar successful application of the proposed method has also been shown for Lake Nasser (Egypt-Sudan) and Roseires Reservoir (Sudan). Evaporation is a major component of the water and energy balance of lakes and reservoirs. The heat storage changes (Qt) term is in turn an essential part of the energy balance of lakes. Qt should be quantified and incorporated into surface energy balance combination models (including the Penman equation) to estimate lake evaporation. Qt is often ignored in both scientific literature and practical engineering type studies mainly due to the lack of routine data of vertical water temperature profiles. In Chapter 4, a first experimental dataset of heat storage changes in 22 lakes has been created from selected international publications. A hysteresis model (Qt=a*Rn+b+c*dRn/dt) was developed that fits the 22 independently gathered bi-weekly and monthly datasets satisfactory when the three coefficients (a, b and c) were determined using local measured flux data. Predictive models for the three coefficients using net radiation (Rn) and water surface temperature (T0) time series have been developed. The simple Slob’s equation that computes Rn from shortwave solar radiation (Rs) was evaluated and showed to perform well for lakes. Since Rs and T0 can be accurately estimated from various operational satellite measurements, the proposed procedure can be applied to estimate Qt for various lakes and reservoirs for which no local measurements are available. The performance of evaporation models, using as input Qt estimated by the developed hysteresis model, is described in Chapter 5. Three energy balance-based evaporation models were evaluated: the De Bruin-Keijman (DK), Penman, and Duan-Bastiaanssen (DB) models. The DB model is a non-published energy balance residual model based on an Ohm-type parameterization of sensible heat flux H with standard empirical coefficients for surface roughness, and the difference of surface water temperature and air temperature. A thorough analysis was conducted on the performance of three different evaporation models for five different lakes with different geographical conditions. Using an estimate of Qt, based on the theories outlined in Chapter 4, all three model’s evaporation estimates agreed well with measurements, and considerably better than cases with Qt excluded. The DK model with its minimum data requirements generally performed best for the five lakes. For two lakes, the new DB model ranked second, followed by the classical Penman model. Therefore, the widely used Penman model should be evaluated more critically, as it appears not always to be the most accurate method. One integrated case study on Lake Tana was conducted by combining the methods proposed in the individual chapters. Chapter 6 quantifies the water balance components of the poorly gauged Lake Tana in a wet year 2006. The specific question is whether the outflow from Lake Tana can be estimated accurately from the residual of the lake water balance. The lake inflow was estimated as the total runoff from the surrounding catchments. The runoff was approximated as the residual of the land-based catchment water balance. The estimated runoff and lake outflow were satisfactory at annual time scales but not at monthly time steps. The discrepancy of the estimated runoff into the lake at monthly time scale can be ascribed to the poor quantification of underground storage changes (changes in soil moisture and groundwater storages). The GLDAS (Global Land Data Assimilation System) open-access database was used for soil moisture storage. Given the coarse resolution of GLDAS and a similar limitation of the current GRACE satellite gravity mission (Gravity Recovery and Climate Experiment), it is preferred to apply a local rainfall-runoff model that takes into account soil moisture and groundwater storage changes at monthly and shorter time scales. Hence, the daily, weekly and monthly water balance of lakes and reservoirs requires the involvement of a hydrological model, and cannot be solved solely on the basis of earth observation data. The estimates of precipitation, evaporation from land and water surface, and the changes of open water storage are however crucial for describing the hydrological system behavior adequately, including the outflow from reservoirs and the determination of deep percolation losses. In summary, the following aspects of lakes and reservoirs have been investigated: (1) improving existing satellite products; An integrated procedure to generate local rainfall at high spatial resolution and with improved accuracy has been developed. (2) integrating and customizing various satellite products; Water volume above a reference level in lakes and reservoirs can now be calculated by integrating levels and surface areas from satellite products. (3) evaluating and comparing alternative satellite products; Different products on water levels, solar radiation, surface temperature and net radiation were tested. (4) developing remote sensing algorithms for the generation of new products; A new procedure for estimating heat storage changes Qt from operational satellite products was developed which is essential for calculating open water evaporation.Water ManagementCivil Engineering and Geoscience
Land and water use classification by means of spectral index based time series analysis
No full textCurrently available land and water use maps don’t meet the needs of hydrologists and water managers in many cases, particularly in developing countries. Existing maps often lack the resolution and detail required by hydrological models, and those that do meet requirements are limited in spatial coverage. The research presented in this report attempts detailed land and water use classification in the Netherlands and California using time series analysis of spectral indices generated from reflectance data of the European Space Agency’s PROVBA-V. The satellite combines high temporal resolution (2-3 day revisit time) with moderate spatial resolution (100 m pixels) which is especially attractive for coverage at the scale of river basins. The Harmonic Analysis of Time Series (HANTS) algorithm was used to perform Fourier transformation of the selected spectral indices resulting in frequency domain harmonic component maps and gap-free, cloud-corrected reconstructed time series images. Two approaches for classification were attempted: unsupervised classification of the harmonic component maps after undergoing principle component analysis and supervised classification of time series index curves using a root-mean-square (RMSE) error minimization approach. Neither approach was able to reproduce the ground truth maps used in either location with an accuracy much higher than 50%. Both approaches were also outperformed by traditional unsupervised classification using reflectance data from 3 cloud-free images acquired during different seasons. Thus, the hypothesis that time series with very high frequency would be a suitable source for the determination of water and land use classes in river basins appeared false for the approaches used in this report. The results found that accuracy of classification using time series data was limited by low variation of time series index curves between classes and high variation within classes. While the high temporal resolution data used in this research may be useful in vegetation monitoring of one particular agro-ecosystem, the limitations posed by time series curve variability suggest that applications in land and water use classification of river basins with a heterogeneous land use is limited and perhaps a higher spectral resolution would prove more useful. The results also found that accuracy was also lowered by strong seasonality in the Netherlands and that classification performed better in larger contiguous areas less affected by the mixed-pixel effect. In some instances the RMSE classifier output seemed to exhibit correlation to vegetative and water features in richer detail than the ground truth map it was compared to. Thus, recommendations for alternate ground truth sources were suggested. Overall, the method showed some promise but will likely need to be fine-tuned for better performance and may be better suited for detailed differentiation of hydrological behavior within a certain land use classes, rather than as a first-pass classifier. It may be worth investigating if this technique can be used to improve the performance of existing classification techniques, perhaps by contextual application within a decision tree classifier. Notably, the mapping of vegetation cover, soil moisture and development intensity by spectral indices could help to classify the heterogeneous landscape of a river basin into certain land use classes with similar hydrological characteristics.WatermanagementCivil Engineering and Geoscience
The Ruijsenaars Function Transform
No full textAnalysisApplied mathematicsElectrical Engineering, Mathematics and Computer Scienc
Comparative Analysis Among Near-Operational Evapotranspiration Products for the Nile Basin Based on Earth Observations
No full textFollowing the success of open access rainfall products based on earth observation data, similar global products are now under development for actual evapotranspiration. In this research, seven prototype evapotranspiration products based on MODIS and geostationary satellites were compared for the Nile basin. They include the special MOD16 version of the Nile basin, SEBS, SSEBSop, ALEXI, GLEAM, LSA-SAF and CMRSET. Most datasets are not yet released, and are in their testing phase before being disseminated to a wide audience. These remotely sensed ET products are fundamentally different in their parameterizations, ranging from reference ET based fractions products to two-layer turbulent transfer schemes for sensible and latent heat. Furthermore the used spectral radiances vary widely from near-infrared and shortwave infrared reflectance to thermal infrared and microwaves emissions. This study covers the time span 2005 -2010 for the Nile basin. The independent validation datasets are based on flux towers and augmented with water balances of catchments and subbasins of the Nile system. Significant differences between the different evapotranspiration products are observed both on subbasin and field scale. A comparison based on land-use class shows that for some land-use classes the estimation of the varies products correspond whereas for other land-use classes the differences between the products is substantial. The different input data and different parameterization of the ET products, together with the large observed differences in ET values for certain land-classes and areas, calls for an ensemble product. A set of ET products based on different level of physics and spectral data is the necessary basis for creating an ensemble ET product. The validation reveals that using an ensemble product instead of a single remote sensing evapotranspiration product yields more reliable and consistent results when compared on a subbasin and basin level. Three ensemble products have been proposed and evaluated in this study: A mean product, an ensemble product based on land-class selection and an ensemble product based on outlier statistics. The ensemble mean product based on land-use class selection is a logical solution because it recognizes that not all ET products have an equally good performance for various land surface conditions. Although all proposed ensemble products show better results when compared to subbasin water-balances, more research is needed to further formulate the best ensemble ET product.Water ResourcesWater ManagementCivil Engineering and Geoscience
Jacobi polynomen en representaties van SU(2)
No full textIn deze scriptie beginnen we met het opbouwen van wat algemene Lie-theorie. Om dat te doen leggen we eerst uit wat variëteiten zijn. Ook zullen we enkele eigenschappen van matrix Lie groepen en Lie algebra's bestuderen. Daarna definiëren we Jacobi polynomen door middel van hypergeometrische reeksen. Ook zullen we een aantal eigenschappen van Jacobi polynomen, op een analytische manier, afleiden. In hoofdstuk 4 introduceren we representatietheorie. We zullen laten zien hoe Jacobi polynomen terug zijn te vinden in de representaties van SU(2). Ook bekijken we wat het verband is tussen SU(2) en Schurs orthogonaliteitsrelaties. Vervolgens bekijken we hoe representatietheorie van SU(2) binnen de Lie-theorie past en zullen daarmee enkele eigenschappen voor Jacobi polynomen afleiden.Industrial and Applied MathematicsApplied mathematicsElectrical Engineering, Mathematics and Computer Scienc
Finding the Optimum Unsaturated Zone Storage Change Estimation Method to Improve Water Accounting in Vietnam
No full textCivil Engineering and GeosciencesWater Managemen
De Hankeltransformatie via de Cherednik algebra: The Hankel transform via the Cherednik algebra
No full textIn deze Bachelorscriptie bestuderen we een integraaltransformatie welke een generalisatie is van de Fouriertransformatie, deze integraaltransformatie wordt de Hankeltransformatie genoemd. Allereerst bestuderen we de symmetrische variant waarna we overstappen op de niet-symmetrische Hankeltransformatie. We gaan de niet-symmetrische Hankeltransformatie beschrijven aan de hand van een algebra met behulp van representatietheorie wat ons in staat stelt om een Hankeltransformatie te definiëren op een eindig-dimensionale ruimte.Electrical Engineering, Mathematics and Computer ScienceDelft Institute of Applied Mathematic
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