Publications

A figure of merit for optimization of a complete Stokes polarimeter based on its measurement matrix is described from the standpoint of singular value decomposition and analysis of variance. It is applied to optimize a system featuring a rotatable retarder and fixed polarizer, and to study the effects of non-ideal retarder properties. A retardance of 132{degree} (approximately three-eighths wave) and retarder orientation angles of {+-}51.7{degree} and {+-}15.1{degree} are favorable when four measurements are used. An achromatic, form-birefringent retarder for the 3--5 {micro}m spectral region has been fabricated and characterized. The effects of non-idealities in the form-birefringent retarder are moderate, and performance superior to that of a quarter-wave plate is expected.

We present two figures of merit based on singular value decomposition, which can be used to assess the noise immunity of a complete Stokes polarimeter. These are used to optimize a polarimeter featuring a rotatable retarder and a fixed polarizer. A retardance of 132° (approximately three-eighths wave) and retarder orientation angles of ±51.7° and ±15.1° are found to be optimal when four measurements are used. Use of this retardance affords a factor-of-1.5 improvement in signal-to-noise ratio over systems employing a quarter-wave plate. A geometric means of visualizing the optimization process is discussed, and the advantages of the use of additional measurements are investigated. No advantage of using retarder orientation angles spaced uniformly through 360° is found over repeated measurements made at the four retarder orientation angles. © 2000 Optical Society of America .

Polarimetry is the method of recording the state of polarization of light. Imaging polarimetry extends this method to recording the spatially resolved state of polarization within a scene. Imaging-polarimetry data have the potential to improve the detection of manmade objects in natural backgrounds. We have constructed a midwave infrared complete imaging polarimeter consisting of a fixed wire-grid polarizer and rotating form-birefringent retarder. The retardance and the orientation angles of the retarder were optimized to minimize the sensitivity of the instrument to noise in the measurements. The optimal retardance was found to be 132{degree} rather than the typical 90{degree}. The complete imaging polarimeter utilized a liquid-nitrogen cooled PtSi camera. The fixed wire-grid polarizer was located at the cold stop inside the camera dewar. The complete imaging polarimeter was operated in the 4.42-5 {micro}m spectral range. A series of imaging experiments was performed using as targets a surface of water, an automobile, and an aircraft. Further analysis of the polarization measurements revealed that in all three cases the magnitude of circular polarization was comparable to the noise in the calculated Stokes-vector components.

The Air Force Research Laboratory`s Satellite Threat Warning and Attack Reporting (STW/AR) program will provide technologies for advanced threat warning and reporting of radio frequency (RF) and laser threats. The STW/AR program objectives are: (a) develop cost- effective technologies to detect, identify, locate, characterize, and report attacks or interference against U.S. and Allied satellites. (b) demonstrate innovative, light-weight, low-power, laser and RF sensors. The program focuses on the demonstration of RF and laser sensors. The RF sensor effort includes the investigation of interferometric antenna arrays, multi-arm spiral and butler matrix antennas, wideband receivers, adaptive processors, and improved processing algorithms. The laser sensor effort includes the investigation of alternative detectors, broadband grating and optical designs, active pixel sensing, and improved processing algorithms.

The Laser Sensor No. 1 (LS1) is a system designed and built by Sandia to detect and report laser illumination of an orbiting satellite. It was launched March 1994 as part of the U.S. Air Force Phillips Laboratory, Technology for Autonomous Operational Survivability (TAOS) satellite program. The engineering details of the system are described in this report. Operation characteristics and results have been reserved for inclusion in a classified Air Force report prepared by the TAOS Program Office of Phillips Laboratory.

A Multi-spectral Pushbroom Imaging Radiometer (MPIR) has been developed as a well-calibrated, imaging radiometer for studies of cloud properties from an unmanned aerospace vehicle platform. The instrument is designed to fly at altitudes up to 20 km and produce data from nine spectral detector modules. Each module has its own telescope optics, linear detector array, spectral filter, and necessary electronics. Cryogenic cooling for the long-wavelength infrared modules, as well as temperature regulation of the short- wavelength modules, is provided by a liquid nitrogen system designed to operate for multi-day missions. Pre- and post-flight calibration, combined with an on-board calibration chopper, provide an instrument with state-of-the-art radiometric measurement accuracies. Each module has a {+-}40{degree} across-track field-of-view and images a curved footprint onto its linear detector array. The long-wavelength array types have 256 detector elements while the short-wavelength arrays can have 512 elements. A modular design allows individual spectral bands to be changed to match the requirements for a particular mission.

A Multi Spectral Pushbroom Imaging Radiometer (MPIR) has been developed as are relatively inexpensive ({approximately}$IM/copy), well-calibrated,imaging radiometer for aircraft studies of cloud properties. The instrument is designed to fly on an Unmanned Aerospace Vehicle (UAV) platform at altitudes from the surface up to 20 km. MPIR is being developed to support the Unmanned Aerospace Vehicle portion of the Department of Energy`s Atmospheric Radiation Measurements program (ARM/UAV). Radiation-cloud interactions are the dominant uncertainty in the current General Circulation Models used for atmospheric climate studies. Reduction of this uncertainty is a top scientific priority of the US Global Change Research Program and the ARM program. While the DOE`s ARM program measures a num-ber of parameters from the ground-based Clouds and Radiation Testbed sites, it was recognized from the outset that other key parameters are best measured by sustained airborne data taking. These measurements are critical in our understanding of global change issues as well as for improved atmospheric and near space weather forecasting applications.

The Sandia Laser Tracker (LT) systems illuminate a cooperative target with a diverged Argon-ion laser beam and track the resulting bright target using a servo-controlled turning mirror. Raw data is digitally recorded in real time and analyzed later when more time is available. The recorded data consists of azimuth and elevation of the tracking mirror, tracking error signals, and range to the target. If the target is tracked perfectly, the error signals will always be zero. The data reduction for this simplified, zero-error condition can be accomplished with very few lines of code. To date, all data reduction for LTI has been done using this zero-error assumption. The more general data reduction problem using the tracking error signals is a much more involved calculation and is referred to as ``using the error foldback routine.`` Detailed theory and vector analysis behind the data reduction and error decoupling algorithms used in the LT systems are described. Errors and corrections to the original document uncovered in over ten years of use are also noted and corrected.