Robert R. Bousquet

A hyperspectral image projector for hyperspectral imagers

We have developed and demonstrated a Hyperspectral Image Projector (HIP) intended for system-level validation testing of hyperspectral imagers, including the instrument and any associated spectral unmixing algorithms. HIP, based on the same digital micromirror arrays used in commercial digital light processing (DLP*) displays, is capable of projecting any combination of many different arbitrarily programmable basis spectra into each image pixel at up to video frame rates. We use a scheme whereby one micromirror array is used to produce light having the spectra of endmembers (i.e. vegetation, water, minerals, etc.), and a second micromirror array, optically in series with the first, projects any combination of these arbitrarily-programmable spectra into the pixels of a 1024 x 768 element spatial image, thereby producing temporally-integrated images having spectrally mixed pixels. HIP goes beyond conventional DLP projectors in that each spatial pixel can have an arbitrary spectrum, not just arbitrary color. As such, the resulting spectral and spatial content of the projected image can simulate realistic scenes that a hyperspectral imager will measure during its use. Also, the spectral radiance of the projected scenes can be measured with a calibrated spectroradiometer, such that the spectral radiance projected into each pixel of the hyperspectral imager can be accurately known. Use of such projected scenes in a controlled laboratory setting would alleviate expensive field testing of instruments, allow better separation of environmental effects from instrument effects, and enable system-level performance testing and validation of hyperspectral imagers as used with analysis algorithms. For example, known mixtures of relevant endmember spectra could be projected into arbitrary spatial pixels in a hyperspectral imager, enabling tests of how well a full system, consisting of the instrument + calibration + analysis algorithm, performs in unmixing (i.e. de-convolving) the spectra in all pixels. We discuss here the performance of a visible prototype HIP. The technology is readily extendable to the ultraviolet and infrared spectral ranges, and the scenes can be static or dynamic.

New NIST reference goniospectrometer

Coatings can be classified by either their appearance, such as glitter, or by their function, such as corrosion protection. However, pigments are currently being manufactured with new and unique appearance attributes that can not be characterized by traditional methods. These coatings may exhibit differences in their perceived color with changes in the illumination or viewing angle, or both. Properties such as these have become rudimentary in the production of currency, cosmetics, and retroreflective materials. The primary impetus of goniospectrometry at NIST is to develop accurate measurement protocols for reproduction and quality control of appearance attributes, such as color matching, by determining the minimum set of illumination and viewing geometries needed to accurately characterize the perceived color. Here, we present a new goniospectrometer developed at NIST that allows the measurement of the complete bi-directional reflectance distribution function (BRDF) for colored surfaces with the objective of differentiating between the scattering mechanisms in the coating. The illumination is provided by a monochromator with a spectral resolution of 0.05 nm between 360 nm and 780 nm. The sample can be moved about 3 different axes, allowing illumination and viewing for any direction within the hemisphere about the sample, including grazing angles, with accuracy better than 0.01° for each axis. This equipment will become the future provider of standard BRDF measurements at NIST, for the characterization of complex surfaces like gonioapparent coatings or retroflective surfaces.

Hyperspectral image projector for advanced sensor characterization

In this work, we describe radiometric platforms able to produce realistic spectral distributions and spatial scenes for the development of application-specific metrics to quantify the performance of sensors and systems. Using these platforms, sensor and system performance may be quantified in terms of the accuracy of measurements of standardized sets of complex source distributions. The same platforms can also serve as a basis for algorithm testing and instrument comparison. The platforms consist of spectrally tunable light sources (STSs) coupled with spatially programmable projection systems. The resultant hyperspectral image projectors (HIP) can generate complex spectral distributions with high spectral fidelity; that is, scenes with realistic spectral content. Using the same fundamental technology, platforms can be developed for the ultraviolet, visible, and infrared regions. These radiometric platforms will facilitate advanced sensor characterization testing, enabling a pre-flight validation of the pre-flight calibration.

Improved thermal-vacuum compatible flat plate radiometric source for system-level testing of optical sensors

In this work, development of a fiber-optically coupled, vacuum-compatible, flat plate radiometric source applicable to the characterization and calibration of remote sensing optical sensors in situ in a thermal vacuum chamber is described. The original flat plate radiometric source configuration’s performance was presented at the 2009 Berlin SPIE. Following the original effort, design upgrades were incorporated in order to improve radiometric throughput and uniformity. Results of thermal and radiometric performance, with incorporated upgrades, of a flat plate illumination source in a temperature-controlled vacuum chamber operating at liquid nitrogen temperature are presented. Applications, including use with monochromatic tunable laser sources for the end-to-end system-level testing of large aperture sensors, are briefly discussed.

Single-Person Spacecraft: Progress toward Flight Testing

Someday, astronauts will have safe, any-time access to space without the risk of the “bends” or need of an airlock. With recent progress in the development of the Single-Person Spacecraft (SPS), “someday” could be very soon. This will be a welcomed improvement for servicing the aging International Space Station (ISS), satellites, telescopes, habitats, the deep space Gateway, and Mars mission vehicles. Today, it takes a long time for suited astronauts to get to the work site but with SPS there is no lengthy pre-breathe, depressurizing an airlock, or hand-over-hand translation. Instead, astronauts fly directly to the site spending more time on the job rather than in preparation or translating back and forth. Furthermore, the SPS is designed for crew autonomy providing an information-rich cockpit with displays and controls to assist with infrequent and unplanned tasks. This new capability is moving closer to reality and the purpose of this paper is to describe the recent engineering accomplishments leading to flight testing.

Improved thermal-vacuum compatible flat plate radiometric source for system-level testing of remote optical sensors

In this work, we describe an improved thermal-vacuum compatible flat plate radiometric source which has been developed and utilized for the characterization and calibration of remote optical sensors. This source is unique in that it can be used in situ, in both ambient and thermal-vacuum environments, allowing it to follow the sensor throughout its testing cycle. The performance of the original flat plate radiometric source was presented at the 2009 SPIE1. Following the original efforts, design upgrades were incorporated into the source to improve both radiometric throughput and uniformity. The pre-thermal-vacuum (pre-TVAC) testing results of a spacecraft-level optical sensor with the improved flat plate illumination source, both in ambient and vacuum environments, are presented. We also briefly discuss potential FPI configuration changes in order to improve its radiometric performance. Keywords: Calibration, radiometry, remote sensing, source.

Optical coating performance for heat reflectors of JWST-ISIM electronic component

The James Webb Space Telescope (JWST) consists of an infrared-optimized Optical Telescope Element (OTE) that is cooled down to 40 degrees Kelvin. A second adjacent component to the OTE is the Integrated Science Instrument Module, or ISIM. This module includes the electronic compartment, which provides the mounting surfaces and ambient thermally controlled environment for the instrument control electronics. Dissipating the 200 watts generated from the ISIM structure away from the OTE is of paramount importance so that the spacecrafts own heat does not interfere with the infrared light detected from distant cosmic sources. This technical challenge is overcome by a thermal subsystem unit that provides passive cooling to the ISIM control electronics. The proposed design of this thermal radiator consists of a lightweight structure made out of composite materials and low-emittance metal coatings. In this paper, we will present characterizations of the coating emittance, bidirectional reflectance, and mechanical structure design that will affect the performance of this passive cooling reflector.

Laser based cleaning methods for optics and electronics

Contamination is a primary concern in the optics and electronics industry since it can lead to both reduced performance and premature failures. This work is concerned with evaluating the performance of laser based cleaning methods for removal of contaminants (dielectrics, metals) from the surface of optics. In general, the art of cleaning contaminants from surfaces is a balance between the energy used to remove the contaminant while minimizing the amount that is applied to the substrate. In this work we present our work with a dry, non-contact method of cleaning that is ideal for, but not limited to, delicate surfaces where traditional contact cleaning methods are not possible. The photo-absorption technique being explored utilizes the absorbed laser light in the surface to thermo-mechanically remove the particle from the substrate. In this work, the process of photo-absorption method will be discussed and the challenges associated with this cleaning method will be presented.