GSW

Keynote Speakers

Keynote Speaker 1

Monday, 7th April 2025 | 10:30 – 11:00 AM | Sheikh Rashid Hall

Ms. Katie Baynes

Earth Science Data Officer in our Science Mission Directorate
NASA Headquarters

Keynote Speaker 2

Monday, 7th April 2025 | 11:00 – 11:30 AM | Sheikh Rashid Hall

Prof. Wolfgang Wagner

Professor for Remote Sensing
Vienna University of Technology

Title of Presentation

Monitoring Soil Moisture and Flooding in Arid Environments with Radar Satellite Constellations

Abstract

In arid regions, water is the primary limiting factor for all forms of life. The scarcity of water influences every aspect of life, from ecosystem health to agricultural production and human wellbeing. Even so, storms can occasionally bring intense rainfall that can lead to significant flooding in areas that have little capacity to handle large volumes of water. This sudden influx of water can cause rivers to overflow, erode the land surface, and overwhelm drainage systems. For these reasons, it is as important to monitor hydrological processes in arid environment as in more humid environments. In this contribution I will examine the capabilities of three European services to monitor soil moisture and flood extent in arid environments: The H SAF service of EUMETSAT uses C-band backscatter data acquired by the Advanced Scatterometer (ASCAT), which has been flown on board of a series of three Metop satellites, to provide coarse-resolution (15-25km) soil moisture data with sub-daily revisit times. The Copernicus Land Monitoring and Emergency Management services use C-band backscatter measurements acquired by the Sentinel-1 Synthetic Aperture Radar mission to provide flood maps at 20 m and soil moisture at 1km respectively. Although the ASCAT and Sentinel-1 backscatter measurements differ in terms of spatial and temporal resolution, they both measure the same physical property: the backscatter coefficient at two nearby C-band frequencies (5.255 GHz for ASCAT and 5.405 GHz for Sentinel-1). This frequency range is especially sensitive to water, whether within the soil or on its surface. Given that vegetation cover is typically low in arid environments, it might hence be expected that retrieving soil moisture and flood extent in these regions is relatively straightforward. Unfortunately, the opposite is true. The challenges are manifold. First, among all ice-free land surface areas, backscatter shows the greatest variation in arid environments. It can be very high over rough rock or stony surfaces, and extremely low over deep sand. Second, under dry conditions, C-band waves penetrate deep into the soil, making the measurements sensitive to subsurface scatterers. This results in a situation where (i) backscatter from deep sand is as low as for flood water, and (ii) backscatter does not have a unique relationship to soil moisture. Consequently, flood mapping and soil moisture retrieval are highly uncertain in many arid regions. After discussing how the three European services deal with this situation, I will explore potential approaches to enhance the radar-based soil moisture and flood data through the development of new algorithms, the incorporation of additional data, or a combination of both. Additionally, I will highlight how the pronounced backscatter signals in arid environments could offer valuable insights for creating new soil maps.