Sequential analysis of stray light through a system in the past has only incorporated stray light from a point source scattering off optical surfaces due to contamination and roughness. Any analysis requiring more fidelity required the power of non-sequential ray trace software, which is limited in both speed and sampling. The software presented in this paper expands upon the previously discussed sequential analysis by adding more functionality and detail to the analysis. This includes scatter contributions from an ideal mechanical baffle located at the entrance to the system and the stray light resulting from extended sources, such as an illuminated Earth or Moon. An example case study is presented to demonstrate the correlation to a matching non-sequential analysis of the system.
Individual focal plane size, yield, and quality continue to improve, as does the technology required to combine these into
large tiled formats. As a result, next-generation pushbroom imagers are replacing traditional scanning technologies in
remote sensing applications.
Pushbroom architecture has inherently better radiometric sensitivity and significantly reduced payload mass, power, and
volume than previous generation scanning technologies. However, the architecture creates challenges achieving the
required radiometric accuracy performance. Achieving good radiometric accuracy, including image spectral and spatial
uniformity, requires creative optical design, high quality focal planes and filters, careful consideration of on-board
calibration sources, and state-of-the-art ground test facilities.
Ball Aerospace built the Landsat Data Continuity Mission (LDCM) next-generation Operational Landsat Imager (OLI)
payload. Scheduled to launch in 2013, OLI provides imagery consistent with the historical Landsat spectral, spatial,
radiometric, and geometric data record and completes the generational technology upgrade from the Enhanced Thematic
Mapper (ETM+) whiskbroom technology to modern pushbroom technology afforded by advanced focal planes.
We explain how Ball’s capabilities allowed producing the innovative next-generational OLI pushbroom filter radiometer
that meets challenging radiometric accuracy or calibration requirements. OLI will improve the multi-decadal land
surface observation dataset dating back to the 1972 launch of ERTS-1 or Landsat 1.
Non-sequential ray tracing for stray light analyses have demonstrated value, but are over-constrained when high
sampling and speed are both needed. In cases where real geometry and mechanical surface properties are critical, such
analyses are certainly required. But the goal of these analyses is often to attempt to approach the performance that would
be achieved if only the optics contributed scatter and only through the sequential optical path. In other words, optical
element scatter is the limiting case for system performance. An analysis technique is therefore presented that enables
approximate but rapid sequential stray light estimates through deterministic modeling. Results of correlation to nonsequential
analyses demonstrate the large range of applicability of this approach. Examples of parametric studies show
the value of rapid paraxial estimates for understanding system performance sensitivities.
The telescope for the Operational Land Imager (OLI) completed alignment in July, 2009. Environmental testing was
completed in September, 2009. This paper presents the as-designed and as-built performance of the telescope and
demonstrates compliance to the OLI requirements. Performance parameters to be discussed include: Effective Focal
Length, Modulation Transfer Function, Throughput, Polarization and Pointing.
We present the latest optical design concepts for the Joint Dark Energy Mission (JDEM). This mission will tightly
constrain the cosmological parameters describing the accelerating expansion of the universe. The current candidate
designs are based on extensive examination of the interplay of requirements for the leading techniques being considered
for space borne observation: Baryon Acoustic Oscillation (BAO), Type Ia Supernovae (SN), and gravitational Weak
Lensing (WL). All techniques require very large fields of view across the visible/near infrared spectrum; BAO uniquely
requires a moderate dispersion wide field spectroscopy capability. Weak lensing requires very good stability and
knowledge of the point spread function in order to enable detection of local variations in galaxy ellipticities caused by
the intervening dark matter. SN imaging spectroscopy should be done to high photometric signal to noise in order to
make best use of these 'standard candles.' We have studied medium class and smaller, "Probe" class implementations
enabling from one to three of these techniques. We describe two concepts that were submitted to the 2010 Astrophysics
Decadal review as well as current concepts.
The Joint Dark Energy Mission (JDEM)1,2 is a proposed dark energy space mission that will measure the
expansion history of the universe and the growth of its large scale structure. It is intended to provide tight
constraints on the equation of state of the universe and test the validity of general relativity. Three
complementary observational analyses will be employed: Baryon Acoustic Oscillations, Type 1a Supernovae
and Gravitational Weak Lensing. An observatory designed for efficient accommodation of these techniques
combines wide-field, diffraction-limited observations, ultra-stable point spread function, and spectroscopy.
In this paper we discuss optical configurations capable of simultaneous wide-field imaging and spectroscopy,
using either afocal or focal telescope configurations. Spectroscopy may be performed by an integral field unit
(IFU), grism or prism spectrometer. We present a flowdown of weak lensing image stability requirements
(the most demanding technique optically) to telescope thermo-mechanical stability limits, based on variations
in the optical transfer function of combinations of Zernike modes, and the sensitivity of these mode
combinations to thermo-mechanical drift of the telescope. We apply our formalism to a representative threemirror
anastigmat telescope and find quantitative relations between the second moments of the image and the
required stability of the telescope over a typical weak lensing observation.
The K-Correlation or ABC model for surface power spectral density (PSD) and BRDF has been around for years.
Eugene Church and John Stover, in particular, have published descriptions of its use in describing smooth surfaces. The
model has, however, remained underused in the optical analysis community partially due to the lack of a clear summary
tailored toward that application. This paper provides the K-Correlation PSD normalized to σ(λ) and BRDF normalized
to TIS(σ,λ) in a format intended to be used by stray light analysts. It is hoped that this paper will promote use of the
model by analysts and its incorporation as a standard tool into stray light modeling software.
There has been a general awareness for several years that the IEST-STD-CC1246 standard particle distribution with a slope of -0.926 does not reasonably represent the contamination on optics that have not been recently cleaned. As a result, the CL (Cleanliness Level) nomenclature actually counters effective communication and modeling of particulate contamination scatter. An analysis method and communication standard centered on Percent Areal Coverage (PAC) and particle distribution slope is presented that improves the ability of Contamination Engineering and Stray Light Engineering to tackle ever more difficult instrument stray light requirements in the most cost-effective manner. Modeling the expected particle distributions for multiple contamination species improves accuracy and reduces costly overdesign.
The standard use of the parameter σ for the rms surface roughness of optics has obscured the fact that the effective
surface roughness is a function of both the measurement wavelength and bandwidth. A more appropriate method for the
flowdown of surface specifications from stray light requirements is presented. Acceptance test methods for validating
surface properties of optics using a Zygo NewView Profilometer are also discussed.
Interferometric testing of large-sized optics in a thermal vacuum environment poses challenges not normally found in an optical metrology lab. Unless the test equipment is thermal-vacuum compatible, it must be installed in an ambient environment with the test item viewed through a window in the thermal-vacuum chamber. Limitations in chamber port size preclude normal-incidence viewing of the full aperture of large-sized optical elements. This necessitates the use of a mechanical translation of the test item to acquire multiple overlying interferograms. The interferograms are then concatenated in order to produce a full-aperture surface map of the test item. This is then used to confirm surface deformation of the entire test mirror. This paper will discuss the challenges, solutions, and results of a series of thermalvacuum tests performed on a large-scale (>40cm) silicon carbide mirror at ambient temperatures.
The Ozone Mapping and Profiler Suite (OMPS) for the United States National Polar-orbiting Operational Environmental Satellite System (NPOESS) consists of a two sensor suite and Level 1 and 2 data
processing algorithms to produce calibrated radiance data and ozone total column and profile values. We describe the profiling system design that matches the limb-observing space sensor performance to
measurement requirements of the retrieval algorithm and uses algorithm techniques to achieve the data quality needed for limb-scatter-based ozone profiling.
The Ozone Mapping and Profiler Suite (OMPS) is being developed for the United States National Polar-orbiting Operational Environmental Satellite System (NPOESS). We describe the optical design and predict the performance of the OMPS earth limb-imaging spectrometer. Limb-scattered solar radiation is measured at selected ultraviolet (UV), visible, and near infrared (NIR) wavelengths to determine ozone profile concentrations for the altitude range of 8 to 60 km. The sensor consists of a telescope with three separate crosstrack fields of view of the limb, a prism spectrometer covering 290 to 1050 nm, and a solar-diffuser calibration mechanism. The sensor provides 3 km vertical resolution profiles of atmospheric radiance with channel spectral resolutions (full-width at half-maximum, FWHM) ranging from 2.7 nm in the UV to 35 nm in the NIR and handles the demanding spectral and spatial dynamic range of the limb-scattered solar radiation with the required sensitivity for ozone retrievals.
The Ozone Mapping and Profiler Suite (OMPS) is being developed for the United States National Polar-orbiting Operational Environmental Satellite System (NPOESS). We describe the optical design and predict the performance of the OMPS nadir-looking imaging spectrometer. Backscattered solar ultraviolet radiation is dispersed and measured to determine the ozone total column amounts and profile concentrations. The sensor consists of a wide field (110 degree) telescope, with a solar-diffuser calibration mechanism, and two spectrometers: an imager covering 300 to 380 nm with a 50 km nadir footprint for mapping total column ozone across a 2800 km swath, and a 250 to 310 nm spectrometer with a single 250 km footprint to provide ozone profile data with SBUV/2 heritage. Both spectrometers provide 1 nm resolution (full-width at half-maximum, FWHM) spectra and handle the demanding dynamic range of the backscattered solar radiation with the required sensitivity for ozone retrievals.
The 1992 work by Paul Spyak and William Wolfe correlating particulate contamination scatter with the predictions of Mie scatter theory has been extended and applied to the analysis of optical systems. Spyak & Wolfe's BRDF results, as applied to Mil-Spec 1246B particle distribution have been often misunderstood and misapplied. This paper provides the application of MIE theory to the modeling of scatter from particulate contaminated optics based on the Mil-Spec 1246B particle distribution and particle distributions more commonly seen in cleanroom fallout.
The Composite Infrared Spectrometer (CIRS) is an instrument currently under development at NASA Goddard Space Flight Center for the Cassini mission to Saturn. The CIRS optical design heritage extends back to the Infrared Interferometer Spectrometer (IRIS) which flew on Voyager. CIRS is the next logical step in the exploration of the atmosphere of Saturn and Titan. It will obtain more complete sets of data with broader spectral coverage, higher spectral and spatial resolution, and greater sensitivity. The CIRS optical design consists of four subassemblies: (1) a 50.8 cm diameter Cassegrain telescope, (2) a Mid-Infrared (MIR) Michelson interferometer, (3) a Far-Infrared (FIR) polarizing interferometer, and (4) a Reference interferometer (RI).
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