Synthetic Aperture Radar

built at MIT Lincoln Laboratory RISE

Authors: Wilson Harper, Rony Korab, Soledad Quainoo, and Chloe Zabounidis

What is Synthetic Aperture Radar?

  • Collects data by taking multiple snapshots of an area/surroundings to recreate a model
  • Unlike other radar modes, SAR can be used for detailed 2-D modeling
The radar

SAR Modes

  • SAR Spotlight (Frame)
  • SAR Strip Map (Scan)

Crossrange & Downrange

  • Range: Distance from the radar to the target
  • Crossrange: Field perpendicular to the range

How our SAR works

  • Takes a specific number of data captures
  • Data appears as radar pulse compression returns
  • Combines data by back projection, like “smear and add”

Smear and Add

The final result

Setup

Measurements are taken every inch
The radar is moved along the tape measure every time a tone is heard

Experiments: Finding the Limits of SAR

Settings

  • Mode: MTI
  • Voltage Gain: 20
  • Bandwidth: 300 MHz
  • SAR Step Size: 60

Experiment 1: Shadowing

Question: Will a large object prevent our radar from detecting a smaller object placed directly behind it?

Hypothesis: A large plastic trash can will block the detection of Wilson because the trash can reflects most of the waves back to the radar.

The field where we ran the experiment
Empty field (control); just Wilson (control); Wilson & trash can

Experiment 2: Movement

Question: How does a moving object’s speed affect its appearance on a SAR image?

Hypothesis: The faster a target moves, the weaker it will appear on a SAR image.

Our testing location
The perspective of the radar and the produced data

Results:

Results with fast movement (left) and slow movement (right)
The results layered with Google Earth data

Experiment 3: Aerial Data

Question: Can we replicate aerial SAR data using our handheld radar?

Hypothesis: We will be able to capture useable aerial SAR data using our radar.

Procedure:

The location we scanned without reflector and with reflector
Aerial SAR data collection results without reflector and with reflector

Conclusion

  • We demonstrated the ability of using SAR as a high-resolution 2D imaging method that overcomes traditional radar limitations. Using our small radar, we were able to create a larger synthetic aperture that captured much more detail.
  • Strip Map and Spotlight Modes: We focused primarily on the Strip Map mode, using it to create maps that could be confirmed with visual inspection and satellite imagery.
  • We determined that shadowing and blocking properties vary depending on an object’s density or metallic properties. It was possible to obscure objects behind more reflective objects, although our SAR had some ability to “see around” objects.
  • Fast movement blurs the resulting image, creating smears and less useful data. Slower—or no—motion results in better clarity.
  • Aerial data was best collected at an angle. Scanning from 45 degrees down from horizontal created data that had a better contrast between foreground objects and the environment compared to scanning top-down. It also reduced shadowing compared to collecting data from a horizontal viewpoint.

Acknowledgements

A special thanks to:

and the MIT Lincoln Laboratory.