Focal Plane Arrays (FPA) consisting of multiple Sensor Chip Assemblies (SCA) in a precision aligned mosaic are being increasingly used in optical instruments requiring large format detectors. The Joint Milli-Arcsecond Pathfinder Survey Mission (JMAPS) requires very precise positional alignment and stability of its 2 x 2 SCA mosaic at operational temperatures to meet its precision sky mapping mission requirements. Key performance requirements include: detector active area co-planarity, in-plane alignment, and thermal stability. This paper presents an overview of the JMAPS Focal Plane Array Assembly, its alignment and thermal-mechanical stability requirements, and associated test-validated performance in a cryogenic vacuum environment.
The Multiple Kill Vehicle (MKV) system, which is being developed by the US Missile Defense Agency (MDA), is a
midcourse payload that includes a carrier vehicle and a number of small kill vehicles. During the mission, the carrier
vehicle dispenses the kill vehicles to address a complex threat environment and directs each kill vehicle toward the
intercept point for its assigned threat object. As part of the long range carrier vehicle sensor development strategy, MDA
and project leaders have developed a pathfinder sensor and are in the process of developing two subsequent
demonstration sensors to provide proof of concept and to demonstrate technology. To increase the probability of
successful development of the sensor system, detailed calibration measurements have been included as part of the sensor
development. A detailed sensor calibration can provide a thorough understanding of sensor operation and performance,
verifying that the sensor can meet the mission requirements. This approach to instrument knowledge will help ensure the
program success and reduce cost and schedule risks. The Space Dynamics Laboratory at Utah State University (SDL)
completed a calibration test campaign for the pathfinder sensor in April 2008. Similar calibration efforts are planned in
2009 for the two demonstration sensors. This paper provides an overview of calibration benefits, requirements,
approach, facility, measurements, and preliminary results of the pathfinder calibration.
Space Dynamics Laboratory (SDL) recently designed, built, and delivered the Solar Occultation for Ice Experiment (SOFIE) instrument as the primary sensor in the NASA Aeronomy of Ice in the Mesosphere (AIM) instrument suite. AIM's mission is to study polar mesospheric clouds (PMCs). SOFIE will make measurements in 16 separate spectral bands, arranged in eight pairs between 0.29 and 5.3 μm. Each band pair will provide differential absorption limb-path transmission profiles for an atmospheric component of interest, by observing the sun through the limb of the atmsophere during solar occulation as AIM orbits Earth. A pointing mirror and imaging sun sensor coaligned with the detectors are used to track the sun during occulation events and maintain stable alignment of the sun on the detectors. This paper outlines the mission requirements and goals, gives an overview of the instrument design, fabrication, testing and calibration results, and discusses lessons learned in the process.
Space Dynamics Laboratory (SDL), in partnership with GATS, Inc., designed, built, and calibrated an instrument to conduct the Solar Occultation for Ice Experiment (SOFIE). SOFIE is the primary infrared sensor in the NASA Aeronomy of Ice in the Mesosphere (AIM) instrument suite. AIM's mission is to study polar mesospheric clouds (PMCs). SOFIE will make measurements in 16 separate spectral bands, arranged in 8 pairs between 0.29 and 5.3 μm. Each band pair will provide differential absorption limb-path transmission profiles for an atmospheric component of interest, by observing the sun through the limb of the atmosphere during solar occultation as AIM orbits Earth. A fast steering mirror and imaging sun sensor coaligned with the detectors will track the sun during occultation events and maintain stable alignment of the Sun on the detectors. This paper outlines the instrument specifications and resulting design. The success of the design process followed at SDL is illustrated by comparison of instrument model calculations to calibration results, and lessons learned during the SOFIE program are discussed. Relative spectral response predictions based on component measurements are compared to end-to-end spectral response measurements. Field-of-view measurements are compared to design expectations, and radiometric predictions are compared to results from blackbody and solar measurements. Measurements of SOFIE detector response non-linearity are presented, and compared to expectations based on simple detector models.
To derive the polarization characteristics of a remotely sensed object, a time-sequential polarimeter must create multiple polarization response states during the course of each measurement set. A common method of creating these states is to rotate a polarizer element to a discrete location and hold that position while the detectors integrate and are sampled. The polarizer element is then rotated to the next position and the process is repeated. This time-sequential, advance-and-hold technique is widely used and easily understood because of its simplicity. However, it is not well suited for remote sensing applications where time delays caused by the advance-and-hold mechanism can limit measurement speed and reduce measurement accuracy. This paper introduces a continuously spinning polarizer (CSP) technique that eliminates the time delays and associated problems of an advance-and-hold polarimeter. A performance model for a linear Stokes polarimeter containing a CSP is derived, and a demonstration of the CSP technique based on the performance of the hyper-spectral imaging polarimeter (HIP) is presented.
The Space Dynamics Laboratory at Utah State University has built and flown an airborne infrared Hyperspectral Imaging Polarimeter (HIP) as a proof-of-principle sensor for a satellite-based polarimeter. This paper briefly reviews the instrument design that was presented in previous SPIE papers1,2, details the changes and improvements made between the 1998 and 1999 measurements, and presents measurement data from the flights.
Measurement data from a series of flights in 1998 indicated the need for wider-band measurements than could be made with our ferroelectric liquid crystal polarimeter design. For this reason, the existing sensor was modified to use a rotating wire-grid polarization filter. The reasons for this choice, equipment design, and measurement equations will be given. A short description of the 1999 flights aboard FISTA3 (Flying Infrared Signatures Technology Aircraft), an Air Force KC-135 based at Edwards Air Force Base will be given, as well as a small sample of the four-dimensional data set will be presented.
The Space Dynamics Laboratory at Utah State University (SDL/USU) has built and flown an airborne hyperspectral imaging polarimeter (HIP)1,2 as a proof-of-principle sensor for a satellite-based polarimeter. This paper discusses measurement limitations and uncertainties associated with imaging polarimetric measurements in remote sensing applications, using experience and lessons learned from the HIP program and the design study for the proposed satellite demonstration sensor.
The Space Dynamics Laboratory at Utah State University is building an infrared Hyperspectral Imaging Polarimeter (HIP). Designed for high spatial and spectral resolution polarimetry of backscattered sunlight from cloud tops in the 2.7 micrometer water band, it will fly aboard the Flying Infrared Signatures Technology Aircraft (FISTA), an Air Force KC-135. It is a proof-of-concept sensor, combining hyperspectral pushbroom imaging with high speed, solid state polarimetry, using as many off-the-shelf components as possible, and utilizing an optical breadboard design for rapid prototyping. It is based around a 256 X 320 window selectable InSb camera, a solid-state Ferro-electric Liquid Crystal (FLC) polarimeter, and a transmissive diffraction grating.
The Wide-Field Infrared Explorer (WIRE) is a small cryogenic spaceborne infrared telescope being readied for launch in September 1998 as the fifth of NASA's Small Explorers. WIRE utilizes two 128 X 128 Si:As Focal Plane Arrays (FPAs) produced by Boeing North American with a 30 cm diameter Ritchey Cretien diamond turned mirror system. This mission takes advantage of recent advances in infrared array detector technology to provide a large sensitivity gain over previously flown missions. Two broad pass bands are defined for a deep pointed survey to search for protogalaxies and to study the evolution of starburst galaxies. The Space Dynamics Laboratory at Utah State University (SDL/USU) used the multifunction infrared calibrator and other special purpose cryogenic equipment to perform a ground characterization of the WIRE instrument. The focus was verified cold with two independent measurements. Both in-band and out-of-band Relative Spectral Response measurements were made; some sensitivity to temperature, bias voltage, and location on the long wavelength focal plane array were found. Dark current and dark noise measurements are also reported.
The Wide-Field IR Explorer (WIRE) is a small spaceborne cryogenic IR telescope being readied for launch in September 1998. Part of NASA's Small Explorer program, WIRE will carry out a deep pointed survey in broad 24 and 12 micron passbands designed primarily to study the evolution of starburst galaxies and to search for protogalaxies. The strategy for the WIRE survey and its stare-and-dither technique for building up long exposure times are described. An overview of the WIRE instrument is presented, with emphasis on the results of ground characterization and expected on-orbit performance of the WIRE optics and the Si:As focal plane arrays. The result of the ground characterization demonstrate that WIRE will meet or exceed the requirements for its science objectives. A brief overview is given of the primary and additional science that will be enabled by WIRE.