Empowering D&I Analysts to Maximize the Value of SAR

Defense and intelligence (D&I) analysts rely on high-resolution imagery with frequent revisit times to effectively monitor operational areas. While optical imagery is valuable, it faces limitations from cloud cover, smoke, and in some cases, infrequent revisit times. These challenges can hinder timely and accurate data collection and impact the decision-making process.

Synthetic Aperture Radar (SAR) sensors address these limitations by offering frequent, high-resolution data regardless of weather conditions or time of day. Unlike optical sensors, SAR can penetrate through clouds, smoke, and darkness, making it a robust tool for D&I applications. In addition, SAR’s ability to detect subtle changes on the Earth’s surface caused by human activity makes it indispensable for monitoring dynamic environments.

SAR Applications in D&I

SAR technology has proven invaluable for applications such as:

• Ship detection and tracking
• Border security
• Battlefield reconnaissance
• Improvised Explosive Device (IED) and mine placement (requires ultra-high-resolution data)
• Recent foot and vehicle traffic (requires ultra-high-resolution data)
• Land deformation from explosions and detonations
• Change detection

However, using SAR data for tactical purposes comes with challenges. Processing often consists of multiple workflows and steps, which can be time-consuming. Additionally, the side-looking nature of SAR sensors and the speckled appearance of SAR data makes visual interpretation less intuitive than optical imagery.

Streamline SAR Data Analysis with ENVI® SAR Essentials

ENVI SAR Essentials is designed to meet these challenges head-on, providing an intuitive user-friendly platform for analyzing SAR data. Built with the user experience in mind, ENVI SAR Essentials offers simple tools and workflows that enable users, regardless of their SAR expertise, to seamlessly extract actionable information from SAR data. It integrates with the display and analytical tools found in ENVI, and its workflows are designed to mirror those used for optical imagery, allowing users to focus on results rather than configuring parameters.

Basic Data Processing

The SAR Basic Data Processing workflow processes Single Look Complex (SLC) data to create multi-looked, filtered, and geocoded SAR images that are ready for visual analysis. Automatic filtering reduces the speckled noise that is inherent to SAR data.

Geocoded, multi-looked, filtered image of Rotterdam Port, Netherlands. Source: Capella Space Open Data Gallery.

Detecting Moving Targets

Most SAR platforms operate in multiple collection modes. Examples include stripmap, sliding stripmap, spotlight, and dwell. The SAR Color Sub-Aperture Generation tool in ENVI SAR Essentials renders moving objects as colored streaks, this enables users to distinguish man-made objects from their surrounding natural environment.

Color sub-aperture image of an airfield in Santiago, Chile. Source: https://registry.opendata.aws/umbra-open-data/.

For longer dwell times, the SAR Dynamic Sub-Aperture Generation tool creates dynamic aperture images that reveal the actual movement of objects, enhancing the detection of moving vehicles or aircraft.

Dynamic aperture animation showing moving vehicles or aircraft at a Russian airfield. Source: https://registry.opendata.aws/umbra-open-data/.

Finally, the SAR Velocity Estimation tool in ENVI SAR Essentials provides a quick and simple way to estimate the velocities and directions of moving objects.

Map of ship locations, movement direction, and velocities in November of 2023. Source: European Union, Copernicus Sentinel-1 imagery.

Detecting Change

ACD leverages the amplitude portion of backscattered radar signals to assess broad-scale changes to surface features. The SAR Amplitude Change Detection workflow in ENVI SAR Essentials creates an image where blue pixels indicate new features, while red pixels indicate features that are no longer present. This workflow is best used to monitor large-scale changes that occur across broad geographic regions.

ACD classification image showing new vessels (blue) and those that are no longer present (red) in the Strait of Gibraltar. Source Capella Space Open Data Gallery..

The SAR Amplitude Difference workflow in ENVI SAR Essentials similarly provides a method for simple change detection between two dates.

Amplitude difference image of a Turkish harbor. Source: Capella Space Open Data Gallery..

The SAR Coherent Change Detection workflow uses the phase information in backscattered SAR signals to detect subtle changes to features on the Earth’s surface. CCD can detect changes as small as a few millimeters, making it useful for monitoring illegal construction, enemy troop movement, border security, threat assessment, and more. CCD is especially useful in rocky and arid areas, since dry soils provide more accurate coherence measurements.

Coherence image of a village in Iran showing stable features (light grey) and highly coherent features (black) that have changed due to excavation. Source: Umbra SAR Open Data.

DSM Generation

The SAR DSM Generation workflow in ENVI SAR Essentials extracts a Digital Surface Model (DSM) from two SLC images. The DSM can be used to characterize local terrain, to assess the height of objects in an urban area, and to conduct viewshed analysis.

DSM created from two overlapping TerraSAR-X images. Source: Airbus Defence and Space.

SAR sensors provide insights and fill in the blanks left by other sensors. ENVI SAR Essentials empowers D&I analysts with simple yet powerful workflows to maximize the value of SAR data. With ENVI SAR Essentials, analysts can detect moving objects, monitor changing environments, characterize local terrain, and create other time-sensitive products, ultimately enhancing the effectiveness and precision of operations.