A KID Camera for Long-Range Imaging Through Optical Obscurants
Abstract
Passive mm-wave imaging offers the possibility of target detection and classification through optical obscurants such as fog. In particular, the relatively short wavelengths compared to traditional RADAR allow for better ground sampling distances (GSDs), while the atmospheric transmission is still sufficiently good to allow for detection ranges of several km. The ability to collect images passively in the mm-wave regime is also advantageous. Recently, new detector technologies, and in particular superconducting kinetic inductance detectors (KIDs), have allowed for the construction of large-format focal planes with thousands of mm-wave detectors.With support from the ONR, our team has developed a 4,000-KID 150 GHz passive imager in combination with an Alt/Az telescope with a 1.5 m primary mirror. We demonstrated this imager at the Point Loma Naval Base in October 2022, reliably detecting small boats and rock islands at a range of a 2#3 km through fog with an optical visibility of #100 m. The telescope provides a GSD of a couple meters at that range, sufficient for target identification in some cases.This successful demonstration of the capabilities of our imager establishes passive mm-wave imaging with KIDs as a viable technology for imaging through optical obscurants. In fact, this success at PointLoma was achieved despite some non-idealities in our system related to stray light and excess noise. Based in large part from the #lessons learned# during this demo, we have identified a range of modifications necessary to improve the performance and usability ofthe existing imager concept and a viable path to upgrade the performance of the imager with a new multichroic KID focal plane. We also propose a new technology that would allow for improved GSDs and electronic steering of the imager.In particular, we propose to improve the performance and usability of the existing imager by: 1) mitigating the stray light that currently degrades the GSD and introduces excess noise via new baffling and a cryogenic aperture stop and 2) Develop a new highly configurable graphical user interface (GUI) for the imager, along with 3) algorithms to partially deconvolve the imager point spread function to improve the GSD.We also propose to combine a range of technologies our team has developed, including hierarchical phased antenna arrays for broadband optical coupling and AlMn KIDs for operation at longer millimeter wavelengths, to produce a 20,000-KID focal planesimultaneously sensitive to 90, 150, 220, and 270 GHz. The lower frequency bands maximize target detection range, while the higher frequency bands providebetter GSD, and established image processing techniques allow the four bands to be optimally combined for both acquisition and identification of targets. Finally, we also propose to develop a distributed aperture system that can be coupled to the KID array to provide an order of magnitude improvement in GSD compared to the existing telescope.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Jan 13, 2025
- Source ID
- N000142512109
Entities
People
- Jack Sayers
Organizations
- California Institute of Technology
- Office of Naval Research
- United States Navy