Synthetic Aperture Radar

Background

The use of optical imagery from aircraft such as Colorado’s Multi-Mission Aircraft (MMA) or Unmanned Aerial Vehicles to monitor and map wildfires is becoming more common and important in wildland fire response. However, optical sensors are passive and rely on sunlight reflecting from the earth’s surface. This can be blocked by clouds or smoke, and are ineffective when there is insufficient ambient light. Infrared (IR) imagery detected by these systems can see through smoke, but not through clouds. Synthetic Aperture Radar is an active sensing technology. Instead of relying on reflected light or emitted IR, Synthetic Aperture Radar, uses its antenna to transmit a radio signal to the terrain and then interprets the signal reflected by the terrain to create an image. Synthetic Aperture Radar imagery requires a different way of thinking in that the signal is based on surface characteristics like structure and moisture. Optical imaging is similar to taking a picture of the Earth, whereas Synthetic Aperture Radar imaging is more similar to measuring the topography of the Earth.
Synthetic Aperture Radar’s signal is capable of penetrating clouds and smoke, as well as imaging during day or night. Whether as a standalone sensor or used in conjunction with EO/IR sensors, the analysis of Synthetic Aperture Radar products may greatly increase firefighter capabilities and assist in wildfire containment.

Pine Gulch Fire - Synthetic Aperture Fire Investigation.

During the Pine Gulch Synthetic Aperture Radar project, the CoE evaluated the use of an airborne synthetic aperture radar (SAR) to detect post-wildfire changes in vegetation, changes to the surface resulting from erosion and depositional responses of the burned watershed in the Big Salt Wash area. Burn area boundary detection was also evaluated. This effort was undertaken to look at how a SAR might be used in support of wildland fire monitoring and for other applications such as detecting subsidence and landslides, flood events, forest health and degradation among others. Changes between flights were detected using Coherence Change Detection (CCD) imagery.

The IMSAR NSP-7 SAR was evaluated to determine the ability of SAR to detect post-fire erosion, soil movement and well-detect burn boundaries following a high intensity wildfire in northwest Colorado. Flights were conducted in the Big Salt Wash area within the Pine Gulch Fire burn scar. The Pine Gulch Fire was a wildfire that burned in Mesa County and Garfield County, Colorado. The fire was started by a lightning strike and first reported on July 31, 2020 and quickly grew and eventually burned 139,000 acres (InciWeb 2021).

Read the CoE "Use of Synthetic Aperture Radar for Wildfire Monitoring" for more information on this investigation and future plans.