As Southern California battles relentless drought, an onslaught of winter rains have brought forth a new problem. The region experienced its wettest day on record as almost a foot of rain fell between January 8th and January 9th.
This sudden influx of water threatened Lake Cachuma to spill over for the first time since 2011. To exacerbate the situation, wooded areas closeby recently underwent a controlled burn and are now at a heightened risk of landslides.
For emergency responders, knowing which areas have the highest extent of flood damage can help organize and direct flood relief efforts.
Using synthetic aperture radar (SAR) data and a change detection analytic called Two-Color Multiview (TCMV), Ursa tracked the movement of water throughout the rain event as Lake Cachuma neared 100% capacity.
Electro-optical sensors cannot be reliably used to track weather events because of storm cloud coverage. SAR, on the other hand, can penetrate through these clouds and provide accurate measurements for flood mapping.
Using the unique properties of SAR and our in-house analytics, Ursa could track the movement of water throughout the rain event, viewing and measuring water surface area change in Lake Cachuma as it neared 100% capacity.
Ursa’s Two-Color Multiview (TCMV) analytic is a form of change detection, which shows decreases and increases in intensity and texture of objects. Red indicates a departure, while blue denotes an arrival.
TCMV can also be used to view standing water in agricultural fields as shown here in nearby Orcutt and Santa Maria, which are the site of ongoing relief efforts:
Visually, water has minimal returns in SAR and appears as black because of very low backscatter. This is because much of the incoming signal from a satellite gets redirected away from the sensor when reflecting off the water surface.
The high contrast in textures of land versus water allows differences in signal returns to be easily classified and measured.
January 1 – 13, 2023 – Santa Barbara
To visualize the difference between analytic types, here’s the SAR imagery alone:
Using differences in signal strength to measure water volume:
As monitoring of Santa Barbara County continues, SAR continues to have many useful applications, namely with measuring the physical movement of land.
Recently burned areas in Santa Barbara are at increased risk of landslides, presenting opportunities for Interferometric SAR (InSAR) analysis.
Using InSAR methodologies, we can measure the differences in wavelengths between two SAR images, allowing us to record land deformations as land moves closer or further away from the satellite with centimeter-scale accuracy.