Influence of climate change has been a major thread on associated environment and the society at large leading to all categories of geohazard events in so many ways, approaches and perspectives. Amongst other threads, the intensity of hydrological cycle is leading to more and more extreme drought and precipitation events within and around the environment, society and eventually an increase in the frequency and extent of flood events as a result of water overflowing it banks (World, 2016; Cazenave & Gonéri, 2013; Benjamin et al., 2018; Bioresita & Puissant, 2021). As it is the most frequently occurring natural geohazard events, insights into their occurrence and dynamics will be of innermost importance for an effective disaster management as well as for the calibration and validation of flood prediction models, and the optimization of spatial planning (Landuyt, Coillie, Vogels, Dewelde, & Verhoest, 2021; Bovenga, 2020; Li et al., 2022). However, it won’t be out of place to appreciate the effort made in providing a systematic, synoptic and timely observation spaceborne remote sensing systems which have become the main source of data for large scale flood events.
As observed, optical sensors are hampered by cloud cover, which is often persistent during flood events (Artiola, Pepper, & Brusseau, 2004; Richards, Scheer, & William, 2011; Martinis et al., 2017; Matgen et al., 2020; Sadek et al., 2020; Bioresita & Puissant, 2021; Rajakumari et al., 2021), which make reliable measurement on the spatial occurrence of historical flood events obviously difficult (Cunha et al., 2011 and Rajakumari et al., 2021 and Bioresita & Puissant, 2021). Flooding is a global phenomenon, underlined by a range of source mechanisms, and widely considered as the most common natural hazard (Stefanidis and Stathis, 2013; Below and Wallemacq, 2018; Matgen et al., 2020; Rajakumari et al., 2021 and Sadek et al., 2020). Dartmouth Flood Observatory (DFO) made effort to collate and map inundation events as in Fig. 1.0, showing flood occurrence totaling 3,129 since 2000, Given the global nature of flooding, sufficient in-situ monitoring is considered geographically impracticable and likely to be expensive, whilst nominally providing point measurements that have questionable use for understanding the dynamics of such an event (Maheu et al., 2003; Alsdorf et al., 2007; Rajakumari et al., 2021 and Li et al., 2022). Hydrodynamic models were developed for most types of flooding with certain simulations which output flood extent, depth and velocity information (Teng et al., 2017; Rajakumari et al., 2021 and Li et al., 2022). It was made clear that, there are natural and epistemic uncertainties with the development of hydrodynamic models which hamper and reduce confidence in their outputs (Merz and Thieken, 2005; Rajakumari et al., 2021 and Li et al., 2022).
Figure 1.0. Centroid locations and impacted regions of floods event between 2000 and 2018 (n = 3129) recorded in DFO database
The records suggest there were over 390,000 fatalities from flooding during the period, with approximately 350 million people displaced (Clement, 2020). Urbanization and the replacement of natural land cover with impenetrable surfaces alter the storage and runoff properties by reducing infiltration and increasing surface runoff (Miller et al., 2014 and Clement, 2020). Both mechanisms result in water moving faster into the river network, either overland flow or via man-made culverts and sewer systems, which subsequently increases the peak flows whilst reducing the lag time (Huang et al., 2008; Braud et al., 2013 and Clement, 2020). Flood risk can be categorically made up of three components;
a. the probability and characteristics of the flood event,
b. the exposure of population and assets to the hazard, and
c. the extent on vulnerable community and its ability to cope with the impacts during and after the event (Jongman et al., 2012 and Clement, 2020).
This research is aim at investigating the dynamics of frequently occurring natural flood disaster around part of the Niger Delta basin of Nigeria base on the recently launched Sentinel-1 SAR satellite constellation for temporal feature extraction and extent assessment.
1.1 ESA Copernicus Programme and the Sentinels Mission
European Commission (EC) and the European Space Agency (ESA) started the Copernicus programme as a natural successor to the Global Monitoring for Environment and Security (GMES) programme in 2014 (Clement, 2020). Earth observation satellites provide efficient and suitable measurement for monitoring a wide variety of environmental variables. Remote sensing imagery has been used towards monitoring surface water extent (Huang et al., 2018 and Clement, 2020), soil moisture (Gao et al., 2017), wetlands (Muro et al., 2016) and snow cover (Snapir et al., 2019). Recently launch satellites actually increases the quantity and quality of available data, improving the potential of monitoring geohazard dynamic, environmental variables from space with the European Space Agency (ESA) Copernicus programme, including the Sentinel-1 SAR satellite constellation, which provides global imagery every 6–12 days at no cost to the end user (Clement, 2020; Matgen et al., 2020 and Sadek et al., 2020). Additionally, satellite data has been used for post-event damage assessments and has helped inform flood risk mitigation and adaptation strategies (Bovolo and Bruzzone, 2007; Rahman and Di, 2017; Matgen et al., 2020; Martinis et al., 2017 and Li et al., 2022).