Aerial and satellite images are valuable assets when it comes to securing borders, ensuring national security or even managing natural disasters. There’s now a range of new tools and functionality that make it easier to access greater levels of detail for these critical operations.
Recently, I wrote about Synthetic Aperture Radar (SAR) imagery — essentially an all-weather imaging capability — and its ability to identify the smallest details from 1,000 km away.
In this blog, I’m writing about Harris Geospatial’s new release of SARscape v 5.4 which can extract information from SAR imagery, enhancing the capabilities of Intelligence, Surveillance and Reconnaissance (ISR) teams.
SARscape 5.4 completely integrates with the ENVI development environment meaning that, like ENVI tasks, SARscape features can be used with Interactive Data Language (IDL).
From a business point of view, this means an enterprise-wide application of SARscape with employees not needing to run their own analysis. Instead they receive the required results with the push of a button anytime, anywhere and using any device of their choice.
With this latest release, SARscape capabilities have been significantly extended, allowing the technology to be applied to ISR operations.
Monitoring large areas with ScanSAR Interferometry
Because SAR satellites capture data with varying degrees of spatial resolutions and swath widths, it’s necessary to be able to adjust the area being viewed.
ScanSAR Interferometry allows for just that when monitoring the impact of natural disasters or to highlight topographical changes caused by human activity such as the digging of tunnels that span multiple high-resolution scenes.
The image above is a PALSAR-2 ScanSAR image of a 300 km-wide area around the epicentre of the 2015 earthquake in Nepal. The green and red areas show the displacement of terrain caused by the earthquake, allowing a precise determination of the epicentre and of the areas more affected by the event.
Being able to cover large regions helps emergency services and local governments better assess the damage and allocate the necessary resources.
Once the worst affected areas are precisely identified finer resolution sensors can be utilised for further analysis for an operational requirement to service the affected areas.
Change detection using publicly available SAR Imagery
Imagery from the European Space Agency’s Sentinel-1 (A and B) has provided free and regular satellite SAR imagery of most parts of the world and in turn has generated a proliferation of SAR image applications, making these images the key tools for detecting change in areas of interest 24/7 without any concern for cloud cover or the time of day.
It’s worth mentioning here that not all Sentinel-1 imagery is ready for analysis; captured data may be available for download but only in a raw format that needs to be focused to make it usable, and that’s where the latest version of SARscape comes to the rescue, providing processing tools to prepare software-ready data from raw scenes for subsequent analysis.
The good news is that SARscape can be designed to run automatically using the GSF/Esri Enterprise framework to monitor the change that takes place in an area affected by floods, for example, or the progress of the construction of an airstrip or naval base.
Leveraging SAR imagery for national security
SAR imagery also provides unique methods of detecting changes compared to optical imagery.
While we can see changes in the intensity of the backscatter (amplitude) between two or more images, we can also see changes that may not be immediately visible to an analyst. These changes — called coherent changes — are due to minor disturbances in the surface of the terrain and are usually the result of changes in signal phases between two or more images.
Difficult to spot using optical imagery, coherent changes can signal clandestine activity in that area.
Traditionally, coherent change detection methods are used to detect changes between two dates only; the latest version of SARscape extends this capability to perform multitemporal coherent change detection, colour coding them to provide a better understanding of the sequence of the events.
In the example below, change detected based on multitemporal coherence is illustrated using three SAR images acquired over Afghanistan. Each image shows coherent change as identified by comparing imagery on different dates, where the criss-cross of black lines indicates tracks that were seen on the later date while the rest of the white areas indicate no significant changes.
Combining these three scenes in a colour composite as shown in bottom left image shows the coherence in different colours -- colour coding the changes to understand the sequence of events taking place.
Multitemporal coherence workflow thus provides analysts with an ability to make sense of the chronology of events and draw conclusions based on it.
The change detection workflow now allows analysts to combine both amplitude and coherent changes to provide a whole new perspective in looking at the data.
SAR images acquired over an ISIS controlled area in Syria are used to illustrate this capability. The lines of light in the top left scene show trucks queuing for fuel just outside the city, which is identified by the bright clusters.
In the image on the top right, scattered light appears on the bottom left that was not present in the first scene, indicating that most trucks had left. The bottom right image shows changes in coherence between these dates.
The SARscape change detection workflow can then be combined to analyse and visualise change due to backscatter and phase where the red, green and blue areas show changes occurring at different times by bringing out the unique characteristics of the target.
Beyond land applications – analysing ocean traffic
SARscape is not limited to land applications; it can now be enhanced to automatically detect ships in the oceans.
In practical terms this can be useful in spotting and identifying illegal or unauthorised ships.
Large vessels with mandatory Automatic Identification System (AIS) transponder requirements are easy to track with the help of these signals (purple tracks in the image). The ships are detected in the SAR scene shown by SARscape, symbolised by yellow crosses.
A simple spatial overlay of the detected ships and the AIS vector shows the ships that may be of interest to the analysts (circled in red). While some ships may be deliberately withholding AIS signals, the analyst should be able to make an informed decision in either case.
One more functionality — right out of Hollywood — is visualising objects in colour. Objects moving in an azimuth direction are displayed as high-resolution blurry lines in SAR SLC images and would be detectable only by a trained eye. However, the new functionality allows non-experts to benefit from this technology as well.
The scene on the left shows an aircraft landing whereas the one on the right is a highway scene with moving cars. SARscape identifies the moving target more obviously by colourising it.
These are just some examples of how SAR technology is being applied to all-weather, 24/7 ISR operations.
The latest technology provided in SARscape assists emergency services and national security decision makers by extracting meaningful and actionable information that can be used to enhance ISR capabilities.
About the author
Dr Dipak Paudyal
Principal Consultant for Remote Sensing and Imagery