Development of four-dimensional imaging spectrometers (4D-IS)

The incentive for the 4D-IS concept was driven by the need to adequately resolve all four dimensions of data (2D spatial, spectral, and temporal) with a single, radiometrically calibrated sensor. Very fast changing phenomena are of interest; including missile exhaust plumes, missile intercept events, and lightning strikes, hypervelocity impacts, etc. Present sensor capabilities are limited to imaging sensors (producing spatial image), spectrometers (that produce a mean signature over an entire field of view with no spatial resolution), radiometers (producing in-band radiance over an entire FOV), or imaging spectrometers (or hyperspectral sensors, tunable filter type, pushbroom scanning, imaging Fourier Transform, Fabry-Perot, or CTHIS type) that produce a data cube containing spatial/spectral information but suffer from the fact that the cube acquisition process may take longer time than the temporal scale during which the event changes. The Computer Tomography Imaging Spectrometer (CTIS) is another sensor capable of 4D data collection. However, the inversion process for CTIS is computationally extensive and data processing time may be an issue in real-time applications. Hence, the 4D-IS concept with its ability to capture a full image cube at a single exposure and provide real time data processing offers a new and enhanced capability over present sensors. The 4D-IS uses a reformatter fiber optics to map a 2D image to a linear array that serves as an input slit to an imaging spectrometer. The paper describes three such instruments, a VNIR, a MWIR, and a dual band MW/LWIR. The paper describes the sensors' architecture, mapping, calibration procedures, and remapping the FPA plane into an image cube. Real-time remapping software is used to aid the operator in alignment of the sensor is described. Sample data are shown for rocket motor firings and other events.