# Applications of Satellite Radar Imagery for Hazard Monitoring: Insights from Australia
## 1 Introduction  
Hazards may be defined as any \"process, phenomenon or human activity that may cause loss of life, injury or other health impacts, property damage, social and economic disruption or environmental degradation\" [1]. Hazard identification, assessment, and monitoring is a keystone of disaster risk reduction activities, and space-based Earth Observation (EO) data, including from Synthetic Aperture Radar (SAR), are well-documented to be valuable tools for monitoring, mapping, and characterizing natural and man-made hazards. Globally, Australia is one of the largest users (by volume and variety) of EO data derived from satellites [2], with EO contributing to national hazard monitoring and response [3] and over 100 state and federal government programs. As such, Australia isplaying a leading role in global efforts for the provision of operational standardised EO datasets (i.e., Analysis Ready Data), including through Open Data Cube initiatives such as Digital Earth Australia (DEA: [4]); [[http://www.ga.gov.au/dea](http://www.ga.gov.au/dea)]([http://www.ga.gov.au/dea](http://www.ga.gov.au/dea)); accessed on 16 March 2021). Despite this well-established and extensive use of EO data across multiple sectors, Australian uptake of data from SAR satellites (for hazard monitoring or other purposes) is limited. Therefore, despite the advantages of using these data for hazard assessment (described throughout this study), less is known about how these data apply in the Australian context and how they could aid in national hazard identification and monitoring. Major factors contributing to the limited uptake of SAR include: the limited spatial and temporal coverage of open-access datasets, which, for Australia, historically offered few consistent (20 images or more e.g., [5]) time-series (see Figure 1 for the example of the European Space Agency's ENVISAT ASAR, which operated between 2004-2011--refer to Table S2 in the Supplementary Material for further sensor specifications); the cost of commercial datasets; the well-established and successful use of optical/multi-spectral EO data under Australian conditions (e.g., 25 years of archived Landsat imagery used to map continental-scale variations of surface water: [6]); and a subsequent lack of proven SAR applications or expertise, hindering support in industry and government (e.g., [7]). Significantly, the European Space Agency SAR satellite constellation, Sentinel-1, has now consistently imaged the whole Australian continent since 2016 (Figure 1), presenting the first opportunity to implement SAR as a systematic hazard-monitoring tool on a national scale. Simultaneously Australia's federal scientific research agency (Commonwealth  
Figure 1: Expansion in the availability of open-access Synthetic Aperture Radar (SAR) imagery over Australia. Demonstrated by a comparison between (**A,B**) the past European Space Agency sensor ENVISAT ASAR (2004-2011) and (**C,D**) the current European Space Agency constellation Sentinel-1 (2014–present), with the number of scenes calculated as of July 2018. Sensor specifications can be found in Table S2, Supplementary Material. Science and Industrial Research Organisation-CSIRO) has also secured fractional ownership over tasking of the UK-owned and operated SAR satellite NovaSAR-1 [8], marking Australia's first-ever civilian EO capability [9]. In response to these step-changes in data availability and the ongoing need to improve hazard monitoring, here we review past usage of SAR for hazard assessment in the context of Australia and use a suite of new case studies to scope the potential of these data to enhance national hazard-monitoring efforts. In Section 2, we begin by providing a brief overview of SAR for hazard monitoring in the context of the applications described in this paper (supported by further resources for non-specialist readers in Table S1 and information about SAR sensors in Table S2, Supplementary Material).