Proceedings Article | 20 October 1999
KEYWORDS: Sensors, Spectral resolution, Spatial resolution, Imaging systems, Interferometers, Pollution, Fourier transforms, Hyperspectral imaging, Infrared radiation, Space telescopes
A unifying theme throughout the ESE science objectives is the identification of regions with large temporal and spatial gradients. Severe storm formation occurs in the boundary regions between airmasses with very different temperatures, pressures, water content, aerosol loading. Severe storm tracking and forecasting utilizes the discontinuities in observed fields and gradient fields to diagnose and forecast the formation, evolution, and motion of severe storms. In a similar fashion, heat islands, super-regional pollution, and rain shower formation are each the result of temporal and spatial gradients present in the atmosphere. Diagnosing and forecasting these events requires an ability to map atmospheric gradients and discontinuities in real-time on micro to meso-scales in the atmosphere (0.5 - 500 km). A new measurement concept, the Imaging Fourier Transform Spectrometer (IFTS) is capable of demonstrating a class of autonomous event identification, monitoring and tracking sensors. In order to provide this capability a sensor with the ability to combine high spatial resolution (0.5 - 1 km) imaging with high spectral resolution (0.25 cm - 1 across the mid infrared 3 -10 microns) in time intervals of a few seconds is required. An electronically programmable infrared camera that combines a large-format focal plane array with a Fourier transform spectrometer can deliver this capability. It also builds on currently fielded airborne demonstration systems and an instrument concept in development for the Next Generation Space Telescope (NGST). The IFTS concept is revolutionary in several aspects. It can produce 2 - 10 fold increase in spatial resolution, 2 fold increases in spectral resolution, and 30 fold increases in temporal resolution. In combination the measurement concept would require a 100 - 600 fold increase in telemetry bandwidth without a new approach to imaging. IFTS breaks this paradigm with a new approach to hyperspectral imaging. Severe storm forecasting requires gradient fields (i.e., first and second derivatives of atmospheric observations). Hence, this measurement concept for IFTS is enabled by four innovations: (1) directly observe the derivative fields, (2) Nyquist sample the image plane to enable full utilization of the telescope performance, (3) have multi-channel detection of gradient regions, and (4) provide an autonomous targeting and tracking system that identifies, subsets, and follows regions with significant discontinuities (i.e., regions where severe storms, toxic pollution, heat islands, or rain/thunderstorms will form).
