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Soil Moisture Map Construction by Sequential Data Assimilation Using an Extended Kalman Filter

  • Author / Creator
    Agyeman, Bernard

  • In response to rapid population growth and increased population densities, changes must occur in agriculture to meet the higher food demand. With a limited potential to increase arable cropland, irrigation has become an increasingly important tool to ensure sufficient global food supply. Increased levels of irrigation put more pressure on freshwater supply. Currently, the water-use efficiency in irrigation is estimated to be between 50\% to 60\% due to poor irrigation practices. A critical step towards mitigating the freshwater supply crisis is to increase the water-use efficiency in irrigation through precision irrigation. One important step towards precision irrigation is to close the irrigation decision loop to form a closed-loop irrigation system. To implement closed-loop irrigation, moisture sensing techniques must be employed to provide the required soil moisture information for feedback control.
    In the context of obtaining soil moisture measurements, microwave remote sensing can be useful and has demonstrated the capability of inferring the near-surface soil moisture quantitatively. Microwave sensors mounted on center pivot irrigation systems provide a feasible approach to measure soil moisture content. These sensors measure the moisture content as the center pivot rotates and provide the moisture information in the form of water content maps at the end of the pivot’s rotation cycle. There however exist three main challenges with this approach which reduce the usability of the soil water content maps in the implementation of closed-loop irrigation. Firstly, it takes between two to three days for a center pivot to complete one rotation cycle which means that it also takes between two to three days to obtain a single water content map from the microwave sensors. This significant time delay in the soil moisture measurements means that continuous feedback and control cannot be effectively implemented. Secondly, the current approach lacks a predictive capability in the sense that the sensors cannot provide soil moisture information when the center pivot is stationary. Lastly, the current approach does not provide moisture information in the root zone, knowledge of which is required for closed-loop irrigation. This work seeks to find solutions to the aforementioned challenges and consequently propose a water content map construction procedure that is suitable for the implementation of closed-loop irrigation. Firstly, we propose an agro-hydrological modeling framework, specifically the cylindrical coordinates version of the Richards equation, which can naturally model a field equipped with a center pivot irrigation system. The measurements obtained from the microwave sensors are then integrated with the field model and a state estimator, the Extended Kalman filter, to form an information fusion system that will provide frequent estimates and predictions of soil moisture in the form of moisture content maps. The proposed information fusion system is first investigated with simulated microwave sensor measurements where its performance is analyzed based on extensive simulations. The information fusion system is then applied to a real case study where soil moisture measurements from passive microwave sensors are considered. We demonstrate the effectiveness of the proposed solution in effectively dealing with the challenges. Three performance evaluation criteria are used to validate the soil moisture estimates and predictions provided by the proposed information fusion system.

  • Subjects / Keywords
  • Graduation date
    Fall 2020
  • Type of Item
    Thesis
  • Degree
    Master of Science
  • DOI
    https://doi.org/10.7939/r3-zmde-1881
  • License
    Permission is hereby granted to the University of Alberta Libraries to reproduce single copies of this thesis and to lend or sell such copies for private, scholarly or scientific research purposes only. Where the thesis is converted to, or otherwise made available in digital form, the University of Alberta will advise potential users of the thesis of these terms. The author reserves all other publication and other rights in association with the copyright in the thesis and, except as herein before provided, neither the thesis nor any substantial portion thereof may be printed or otherwise reproduced in any material form whatsoever without the author's prior written permission.