A Vicarious Technique for Understanding and Diagnosing Hyperspectral Spatial Misregistration

Abstract

Pushbroom hyperspectral imaging (HSI) systems intrinsically measure our surroundings by leveraging 1D spatial imaging, where each pixel contains a unique spectrum of the observed materials. Spatial misregistration is an important property of HSI systems because it defines the spectral integrity of spatial pixels and requires characterization. The IEEE P4001 Standards Association committee has defined laboratory-based methods to test the ultimate limit of HSI systems but negates any impacts from mounting and flying the instruments on airborne platforms such as unmanned aerial vehicles (UAV’s) or drones. Our study was designed to demonstrate a novel vicarious technique using convex mirrors to bridge the gap between laboratory and field-based HSI performance testing with a focus on extracting hyperspectral spatial misregistration. A fast and simple extraction technique is proposed for estimating the sampled Point Spread Function’s width, along with keystone, as a function of wavelength for understanding the key contributors to hyperspectral spatial misregistration. With the ease of deploying convex mirrors, off-axis spatial misregistration is assessed and compared with on-axis behavior, where the best performance is often observed. In addition, convex mirrors provide an easy methodology to exploit ortho-rectification errors related to fixed pushbroom HSI systems, which we will show. The techniques discussed in this study are not limited to drone-based systems but can be easily applied to other airborne or satellite-based systems.

Small Target Radiometric Performance of Drone-Based Hyperspectral Imaging Systems

“…Excluding values at both ends of the wavelength range (i.e., close to 400 nm and 1000 nm), we see a significant trend of worsening measurement dispersion at the bluer wavelengths for point targets. We speculate that the reasoning for this is the interplay between orthorectification and the wavelength-dependent SPSF sharpness (Figure 17) [23]. Depending on how the point target is imaged, the orthorectification struggles with sharper targets compared to targets having a larger spatial extent.…”

“…Imaging point targets (i.e., SPARC) with remote sensing instruments has been in development since 2010 [8,9,15,16] with more recent engineering advances, by Labsphere Inc., to bring an automated calibration service to the satellite community [17][18][19][20][21]. Further advancements have been explored by the Rochester Institute of Technology on the application of point targets for drone-based HSI systems [22,23]. In this section, we will summarize the radiometric and spatial response of an imaging system to a point target.…”