Sponsors: National Science Foundation
Students: Courtney Di Vittorio
Description:
Hydrologic models of wetlands enable hydrologists and water resources managers to appreciate the environmental and societal roles of wetlands and manage them in ways that preserve their integrity and sustain their valuable services. However, wetland model reliability and accuracy are often unsatisfactory due to the complexity of the underlying processes and the lack of adequate in-situ data. In this research, we demonstrate how MODIS satellite imagery can be used to characterize wetland flooding over time and to support the development of more reliable wetland models. We apply this method to the Sudd, a seasonal wetland in South Sudan that is part of the Nile River Basin.
The database consists of 16 years of 8-day composite ground surface reflectance data with a 500-m spatial resolution. After masking poor quality pixels, monthly distributions of wetness and vegetation indices were extracted. Based on literature and personal accounts describing the Sudd as well as Google Earth imagery, a set of ground truth locations were identified for nine land classes. Using the ground truth locations, a novel classification procedure was developed that uses the empirical monthly distributions of each individual pixel. This procedure allows pixels to be classified as mixed pixels (or mixels) if their distributions share properties with two different classes. Once the full area of interest was classified, each pixel was evaluated on a monthly scale to determine if, when, and how long it was flooded using a procedure that incorporates spatial information and monthly precipitation data. The result is a set of monthly inundation maps for the full period of interest (2000–2015). An independent set of ground truth locations were selected to validate the land cover classification procedure, which demonstrated a high level of accuracy. The derived monthly inundation series agrees well with existing literature, limited ground observations, and estimated water fluxes into the wetland. This information is currently being used to develop a wetland model as part of a comprehensive modeling system for the Nile River Basin. This novel procedure is general and has many advantages over those in existing research for applications in data scare areas.
Publications:
C. A. Di Vittorio & A. P. Georgakakos. Land cover classification and wetland inundation mapping using MODIS. Remote Sensing of Environment 204, 1-17 (2018). https://doi.org/10.1016/j.rse.2017.11.001
Acknowledgements:
We are grateful to the Ministries of Water and Irrigation in Uganda, Sudan, and Egypt for the provision of in-situ river flow and other hydrologic data. Moreover, we are grateful to Dr. Georg Petersen for sharing his ground measurements on the Sudd Wetland. This research was supported in part by the National Science Foundation Graduate Research Fellowship Program under Grant No. DGE-1650044. Any opinions, findings, and conclusions or recommendations expressed in this article are those of the authors and do not necessarily reflect the views of the National Science Foundation or other organizations.