Ball Aerospace has field tested an Engineering Design Unit (EDU) of a Low Light Imager (LLI) instrument capable of
high dynamic range imaging in the Visible to Near Infrared (VNIR) wavelength range. The instrument design is wellsuited
to imaging scenes at low illumination levels or with radiance levels spanning a high dynamic range, including
night scenes with clouds or anthropogenic light sources, and scenes that span the earth's terminator. A novel operating
mode autonomously sets gains individually for each pixel and continuously updates the settings. Utilizing this scheme,
the LLI EDU achieves a measured dynamic range > 10<sup>7</sup> in each image pixel of a scene. The upper and lower ends of the
LLI dynamic range enable imaging of scenes illuminated by full sunlight or by a quarter moon only, as well as
terminator scenes that span the two. The modular instrument configuration facilitates designs with different total Fields
of View, including a three-module design with a cross-track FOV of 113 degrees. Testing and validation performed on
the EDU include stray light testing, calibration and acquisition of ground images from an airborne platform.
Radiometric test results demonstrate compliance with all radiometric requirements for the day/night imager for the
National Polar Orbiting Environmental Spacecraft and Sensor (NPOESS) program.
Ball Aerospace & Technologies Corp. (BATC) has added a powerful capability to its existing imaging spectrometer
alignment and test facilities: Scanning Fabry-Perot source filters. These interferometers provide a means for efficient
instrument testing with full characterization from the ultra-violet (UV) to longwave infrared (LWIR). Spectral Response
Functions (SRF) and geometric distortions are accurately determined with a common approach. The techniques were
demonstrated with a two band cryogenic LWIR spectrometer and with the mid-wave infrared (MWIR) Spaceborne
InfraRed Atmospheric Sounder for Geosynchronous Earth Orbit (SIRAS-G) laboratory demonstration imaging
spectrometer. The spectrometer testing and performance is presented.
The spatial response of a FPA is an important attribute of image quality. A novel test station for determining detector MTF has been developed and used on LWIR FPAs. The test station focuses an illuminated pinhole aperture onto a FPA, creating a sub-pixel spot. Total system MTF is determined by scanning the spot across the FPA. Optics MTF is measured by moving the imaged spot through focus and applying phase retrieval methods. The Optics MTF is then removed from the measured total MTF to produce the detector MTF. The technique has been applied to large area LWIR FPAs.
BATC is developing the Spaceborne Atmospheric Infrared Sounder for Geosynchronous Earth Orbit (SIRAS-G) under NASA's 2002 Instrument Incubator Program. SIRAS-G represents a new approach to infrared imaging spectrometry suitable for Earth observation from geosynchronous orbit. SIRAS-G is an instrument concept with lower mass and power requirements than contemporary instruments that offers enhanced capabilities for measuring atmospheric temperature, water vapor, and trace gas column abundances in a compact package. In addition, the SIRAS-G concept is adaptable to airborne, low-Earth orbit and geosynchronous deployment. SIRAS-G employs a wide field-of-view hyperspectral infrared optical system that splits the incoming radiation to four separate grating spectrometer channels. Combined with large 2-D focal planes, this system provides simultaneous spectral and high-resolution spatial imaging designed to measure infrared radiation in 2048 spectral channels with a nominal spectral resolution (l/Dl) of between 700 and 1400. Design parameters and the associated basic design trades for a SIRAS-G laboratory demonstration instrument are presented in this paper. Results of completed instrument design analyses along with instrument performance predictions are included. Using these performance predictions, we offer a comparison of current technology with SIRAS-G's capabilities for measuring atmospheric temperature, water vapor profiles, and trace gas column abundances.