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.
This work describes the development of an improved vacuum compatible flat plate radiometric source used for characterizing and calibrating remote optical sensors, in situ, throughout their testing period. The original flat plate radiometric source was developed for use by the VIIRS instrument during the NPOESS Preparatory Project (NPP). Following this effort, the FPI has had significant upgrades in order to improve both the radiometric throughput and uniformity. Results of the VIIRS testing with the reconfigured FPI are reported and discussed.
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.
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 spacecraft's
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
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.
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 (STS's) 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.
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.