James Q. Peterson

Component level prediction versus system level measurement of SABER relative spectral response

A 10-channel infrared (1.25-17.24 µm wavelength) radiometer known as SABER (Sounding of the Atmosphere using Broadband Emission Radiometry) is one of four experiments that will fly on the TIMED (Thermosphere, Ionosphere, Mesosphere, Energetics, and Dynamics) mission that was successfully launched on 7 December 2001. Theoretical models of the relative spectral response (RSR) for each SABER channel were developed during the design and build of the instrument. The RSR calculations were then refined using a component level technique where theoretical predictions of filter transmittance were replaced with measurements from filter witness samples. During SABER ground calibration, full system measurements of RSR were performed using a Michelson step-scan interferometer to present an interferometrically modulated infrared source to the instrument with the resultant interferogram recorded by the instrument detectors. Fourier transform of this interferogram and correction of the resulting spectrum for the spectral output of the interferometer and the transmittance of any intervening optics provide a measurement of the system level RSR. We compare the full system level measurements with the theoretical and component level RSR predictions for both in-band and out-of-band spectral regions. Our results show that the system level method for determining RSR provides the clearest picture of the instruments spectral properties.

Polarimetric imaging using a continuously spinning polarizer element

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.

Imaging polarimetry capabilities and measurement uncertainties in remote sensing applications

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.

Hyperspectral imaging polarimeter in the infrared

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.

SOFIE instrument overview

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. AIMs 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.

SOFIE Instrument Model and Performance Comparison

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. AIMs 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.

Measurement results from flight measurements with the hyperspectral imaging polarimeter

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.

Calibration of the Hyperspectral Imaging Polarimeter

Abstract not available.

Estimated performance of the Wide-field Infrared Explorer (WIRE) instrument

The Wide-Field IR Explorer (WIRE) is a small spaceborne cryogenic IR telescope being readied for launch in September 1998. Part of NASAs 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.

Four-wavelength lidar for in-situ speciation of aerosols

The system and mechanical design of a four-wavelength lidar system is described. The system is designed to be maximally adaptive to deployment scenario in terms of both size/weight/power and detection application. The wavelengths included in the system are 266 nm, 355 nm, 1064 nm, and 1574 nm – all generated from Nd:YAG based pump laser sources. The system is designed to have a useful range from 400 meters to 5,000 meters, depending on the wavelength and atmospheric conditions.