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3.2 Interpreting MTI & Other Radar Data Products
Radar data used to form SAR images can be processed into other products, including MTI, CCD and ISAR. With some basic understanding, these products are easy to interpret and enable users to more quickly and effectively advance their missions.
MTI modes provide detections and tracks that indicate the location, direction, and speed of moving targets. Using advanced processing, MTI modes can detect slow-moving targets by extracting data from the surrounding clutter. These indicators enable a user to monitor the activity of several targets over a large area. MTI can be used on land or sea, for a wide range of target sizes including vehicles, dismounts (people), large vessels, and even small targets like fishing boats, RHIBs, and rafts.
- Yellow dots: Detected targets moving away from the sensor
- Faded magenta dots: Detected targets moving toward the sensor
- Magenta lines: Estimated tracks of specific targets based on detections
- Magenta arrowheads: Direction of travel of tracked targets
In the screenshot below from a GMTI data collection, several targets have been detected during a circular scan of an area of interest.
Lisa 3D Software Display of GMTI Processing
IMSAR’s MTI modes send out energy in pulses or “chirps” at specifically timed intervals and process the returns to measure the Doppler shift of moving targets. The radar’s processing manipulates the returns to distinguish moving targets from non-moving background clutter. The system then uses complex processing technology to track moving targets and provide the user valuable data about the tracks, including the following information:
- Relative size of targets
- Speed of targets
- Heading and bearing of targets
The screenshot below shows detections and tracks from a maritime data collection. The colored markings follow the same interpretation key as for GMTI processing described above.
Lisa 3D Software Display of MMTI Processing from an Open-Water Data Collection
CCD and MCD
Coherent and magnitude change detection images are the result of an automated comparison of SAR images over the same area, but collected at different times. MCD highlights magnitude changes, such as vehicles that have entered or left the scene, and CCD highlights subtle changes, such as vehicle tracks or footprints. CCD products display changes in gray against a white background. MCD products display new objects in the scene as blue and objects that have left the scene in red. These designations are easy to remember with the monikers red-fled and blue-new.
IMSAR data processing combines CCD and MCD processes into one image, which is collectively referred to as CCD. Analysis tools can be used to view CCD with MCD disabled. CCD is primarily useful to identify disturbances over land, but can be useful in littoral and maritime environments, though it is generally less effective due to the continual movement of water.
In the CCD product below, the blue, red, and gray markings show the changes that have occurred between the first and second SAR collection passes. The tire tracks along the road and the dismount footprints to and from the road are immediately evident in the imagery. The red and blue pixels represent the position of a vehicle that has moved from its position in the first pass (red) to a new position in the second pass (blue). The image gives several clues that allow an analyst to interpret what occurred between the two collection passes:
- Single gray tracks: Dismount walking path
- Large gray spot: Ground disturbance
- Red spot: Fled vehicle location
- Blue spot: New vehicle location
- Double gray tracks: Vehicle tracks
Analysis: A person walked away from a vehicle, dug a hole in the ground, returned to the vehicle, drove the vehicle down a road, left the vehicle, and walked away from the road.
CCD/MCD Products Reveal Activity That Occurred Between Surveillance Events
MCC: Multiple Coherent Change (MCC) is an enhanced change detection product that is formed from three SAR passes of a target. A comparison is made of two CCD images from the three radar passes. This product helps analysts quickly distinguish changes that are common to an area like moving bushes, water, or regular activity from unusual or suspicious activity. MCC images also include the red and blue highlighting present in MCD products to indicate magnitude change detection.
In the data products below, a SAR image collected on the first and second passes of the radar shows three vehicles lined up off of a dirt roadway, in parallel near a line of foliage and a stream. In the image collected on a third pass, one of the vehicles is missing. The CCD/MCD image reveals several changes that took place between the passes: a red/fled marking where the vehicle was and several dark gray markings where surfaces were disturbed. The MCC product minimizes the markings from the common activity of the moving foliage and water and highlights the new tracks made by the fled vehicle.
Weather Effects: Weather events can cause subtle changes that are detectable by CCD. For example, rainstorms may cause the ground to become less coherent. However, collecting data before and after rainstorms may be useful if analysts are looking for data related to flooding. Water reflects energy away from the radar. That means flooded areas will return less energy and will be shown as red in the CCD image. Once the water has receded, the dry ground will return more energy to the sensor, and those regions will be shown as blue.
CCD/MCD and Water/Flooding: Red Represents Flooded Areas; Blue Represents Receded Areas
Pattern-of-Life Analysis: A pattern-of-life analysis of an area is critical for mission success and will further help the analyst determine what normal activity is in a certain area. Analysts use CCD data to determine the patterns of life or traffic patterns at specific locations. Well-used trails, roads, and fields will show more change than places with irregular traffic.
CCD Data Shows Patterns of Life: Areas of heavy use appear darker and more defined, such as roads and paths.
Subtle changes in an area can be difficult to detect from human observation or optical images alone. Because radar sees roughness, it can detect disturbances in surfaces, such as minute changes caused by tire tracks and footprints in the dirt, which might be unobservable by the human eye. In maritime environments SAR systems are capable of processing coherent change detection along beaches and shorelines to find ingress and egress points to the water. NOTE: CCD does not work over water because the surface of the water is in a state of constant change.
ISAR data of both a cargo (container) ship and a tugboat, shown as a Range-Doppler Map (RDM) and an ISAR image
Automated processing of radar data into products reduces the manual processing load of image analysts. To interpret the resulting products, analysts need some basic understanding of the representations displayed on the product. With a little additional training and some understanding of their mission management software, analysts will be equipped to make effective and timely decisions in various CONOP situations.
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Updated Sept. 22nd, 2021