Physical Sciences Inc. (PSI) is developing a longwave infrared (LWIR) compressive sensing hyperspectral imager (CS HSI) based on a single pixel architecture for standoff vapor phase plume detection. The sensor employs novel use of a high throughput stationary interferometer and a digital micromirror device (DMD) converted for LWIR operation in place of the traditional cooled LWIR focal plane array. The CS HSI represents a substantial cost reduction over the state of the art in LWIR HSI instruments. Radiometric improvements for using the DMD in the LWIR spectral range have been identified and implemented. In addition, CS measurement and sparsity bases specifically tailored to the CS HSI instrument and chemical plume imaging have been developed and validated using LWIR hyperspectral image streams of chemical plumes. These bases enable comparable statistics to detection based on uncompressed data.In this paper, we present a system model predicting the overall performance of the CS HSI system. Results from a breadboard build and test validating the system model are reported. In addition, the measurement and sparsity basis work demonstrating the plume detection on compressed hyperspectral images is presented.Key Words: Compressive sensing, hyperspectral imager, sparsity basis, single pixel camera
TECHNOLOGY OVERVIEW
Capability OverviewStandoff chemical vapor detection in the longwave infrared (LWIR) spectral range is currently dominated by high-priced interferometric systems, including the single pixel Joint Services Lightweight Standoff Chemical Agent Detector (JSLSCAD) and the Bruker Rapid as well as the imaging Telops HyperCam and Adaptive Infrared Imaging Spectroradiometer (AIRIS). The JSLSCAD employs an FTIR modulator and scanning mirrors to obtain a spatially coarse data cube acquired over 360° in azimuth and -10 to +50° in elevation. AIRIS employs a tunable Fabry-Perot filter and a LWIR FPA to acquire the data cube. Similar technologies are present in the HyperCam. The fundamental limitation of these systems with regard to wider deployment is the multiple $100k price. Secondary limitations include large size, interferometric moving parts, slow acquisition speed, and large data bandwidth. All of these factors can be mitigated with a low-cost hyperspectral sensor based on compressive sensing (CS) in a single pixel architecture.Efforts to apply CS in the LWIR spectral region include those by Fernandez et al [1] who explored the feasibility of a coded aperture LWIR HSI system. This approach employs an FPA to simultaneously capture spectral and spatial data in a single frame and boasts improved throughput relative to traditional grating based systems. However, the use of a LWIR FPA will limit cost reduction of this particular solution. An attempt has been made to integrate a tunable (Fabry-Perot) filter with a CS solution in the LWIR [2] with limited success in terms of performance, primarily owing to diffraction by the digital micromirror device (DMD) employed as a spatial light modulator (SLM). PSI in cooperation ...