Interferometric ISAR Jonathan Owen University of Kansas Owen

Interferometric ISAR Jonathan Owen University of Kansas Owen - SAR Project 2 1

MTI or ISAR? Owen - SAR Project 2 2

Like looking in a mirror MTI ISAR Owen - SAR Project 2

Algebraic! MTI ISAR Owen - SAR Project 2

“Cost effective” hardware Q: Wait a minute, what even was the point of making the distinction between MTI and ISAR? A: (A bold claim) MTI is the poor man’s ISAR system! Think about all of the processing involved with (I)SAR processing… depending on which method is used to correct for range-cell migration, we must sinc interpolate at least a bagillion times! – Okay, maybe slightly less than a bagillion. Not every system needs the capability to image, nor wants to perform heavy duty computations! An MTI system may use considerably less bandwidth to make range-walking less significant (due to coarser slant range resolutions), or simply due to that system not needing an imaging capability. Just tell me where it is !!! Owen - SAR Project 2

Strip(map) my funding and spot(light) a better option Q: Are you crazy? You really expect a drone to just fly through your scene without fidgeting in the wind or maneuvering? Those things are made of recycled plastic. A: I simply listed the stripmap (I)SAR mode as an analogy to MTI. Absolutely, stripmap mode will almost never be ideal for ISAR (unless maybe tracking a lot of targets, but then individual target motions must be compensated on receive… sounds painful). Not to mention the issues with resolution. Drones are very small!!! (< 1 meter). To obtain the needed along-track resolution, the drone would have to fly across the scene predictably for 10’s of meters (if stripmap). To obtain the needed cross-track resolution, at least 1 GHz of spectral bandwidth is necessary. Owen - SAR Project 2

Oh, and it gets harder. MTI ISAR Owen - SAR Project 2

GO BACK, DELETE MTI ISAR Lasers! Owen - SAR Project 2

A moving notion… • Two options for drone ISAR 1. Stare broadly at a wide swath; accurately motion compensate for each individual detected target moving through the beam. 2. Spotlight/Sweep ISAR via fine array beamforming to search the environment Owen - SAR Project 2

A moving notion… • Two options for drone ISAR 1. Stare broadly at a wide swath; accurately motion compensate for each individual detected target moving through the beam. Will be much easier when there are only a few targets (or just one). Me after realizing how to limit the scope of this project Owen - SAR Project 2

Hope you don’t get motion sickness ISAR focusing can be very difficult if targets are maneuvering significantly This diagram represents a severe oversimplification Target maneuvers add depth to images and make them easier to characterize, assuming the receive signal can be focused Owen - SAR Project 2 11

Use the (brute) force Why did the ISAR system need coffee? Because it was having trouble focusing Owen - SAR Project 2 12

Oh, and good luck seeing the target. Owen - SAR Project 2 13

Q: Wasn’t this project supposed to be a study about interferometric ISAR? Owen - SAR Project 2 14

What’s in it for me? • Interferometric ISAR provides two significant benefits (assuming focused images are created at both baselines) 1. 3 -D “cloud” images are extractable from ISAR images. The baseline provides a slightly different glance angle to provide additional feature extraction via phase unwrapping / comparison assuming resolution is sufficiently fine. Wide bandwidth and B Owen - SAR Project 2

What’s in it for me? • Interferometric ISAR provides two significant benefits (assuming focused images are created at both baselines) 2. Coordinates of the target can be estimated via a joint “stereo co-registration (homework 6) + phase comparison (homework 5)” estimate. • Co-registration yields approximate coordinates based on absolute time delays of the focused ISAR maps. The co-registration is used to reduce spatial ambiguities. • Phase comparison can further pinpoint a more precise drone coordinate B Owen - SAR Project 2

What’s in it for me? • Interferometric ISAR provides two significant benefits (assuming focused images are created at both baselines) 2. Coordinates of the target can be estimated via a joint “stereo co-registration (homework 6) + phase comparison (homework 5)” estimate. • May wish to stack a few baselines in different dimensions (vertical) for reduction of co-registration error. • This method is useful if resolutions under consideration are coarser such that phase unwrapping can’t be used (nothing to unwrap relative to) B B Owen - SAR Project 2