Satrec Initiative and ATSB have been developing a medium-sized aperture camera (MAC) for an earth observation payload on a small satellite. Developed as a push-broom type high-resolution camera, the camera has one panchromatic and four multispectral channels. The panchromatic channel has 2.5m, and multispectral channels have 5m of ground sampling distances at a nominal altitude of 685km. The 300mm-aperture Cassegrain telescope contains two aspheric mirrors and two spherical correction lenses. With a philosophy of building a simple and cost-effective camera, the mirrors incorporate no light-weighting, and the linear CCDs are mounted on a single PCB with no beam splitters. MAC is the main payload of RazakSAT to be launched in 2005. RazakSAT is a 180kg satellite including MAC, designed to provide high-resolution imagery of 20km swath width on a near equatorial orbit (NEqO). The mission objective is to demonstrate the capability of a high-resolution remote sensing satellite system on a near equatorial orbit. This paper describes the overview of the MAC and RarakSAT programmes, and presents the current development status of MAC focusing on key optical aspects of Qualification Model.
The Visible Infrared Imaging Radiometer Suite (VIIRS) sensor on the Joint Polar-orbiting Satellite System (JPSS)
mission has a solar diffuser as a reflective band calibrator. Due to UV solarization of the solar diffuser, the Solar
Diffuser Stability Monitor (SDSM) is on-board to track the reflectance change of the solar diffuser in visible to near IR
wavelengths. A 100 cm Sphere Integrating Source (SIS) has been used to configure and test the SDSM on the ground
since MODerate resolution Imaging Spectroradiometer (MODIS) programs. Recent upgrades of the radiance transfer
and BRDF measurement instruments in Raytheon have enabled more spectral data and faster measurement time with
comparable uncertainty to the previous methods. The SIS has a Radiance Monitor, which has been mainly used as a SIS
real-time health checker. It has been observed that the Radiance Monitor response is sufficiently linear and stable thus
the Radiance Monitor can be used as a calibrator for ground tests. This paper describes the upgraded SIS calibration
instruments, and the changes in the calibration philosophy of the SIS for the SDSM bands.
Recent trends in focal plane array (FPA) technology have led naturally to the development of very large format
remote sensors that require optically fast, wide field-of-view (FOV) imaging optics. Systems that cover broad
spectral ranges, such as multispectral imagers (MSI) and hyperspectral imagers (HSI), require reflective optics to
provide aberration and distortion control without the complication of wavelength dependent errors induced by
powered refractive elements. These large format systems require even wider fields-of-view than offered by the
conventional three-mirror anastigmat (TMA) and four-mirror anastigmat (4MA) designs. Recently, Raytheon has
demonstrated in hardware the first-ever aligned and tested five-mirror anastigmat (5MA) imager. The 5MA was
designed with an F/3.0 optical speed and a 36 degree cross-scan FOV for use with a large format imaging
spectrometer. The 5MA imager has useful features such as: (1) a real entrance pupil to support a full-aperture
calibrator or a small scan mirror, (2) an intermediate image for stray light control, and (3) a real exit pupil for
optimal cold-shielding in infrared applications. A computer-aided alignment method was used to align the 5MA
imager with a final target of balanced wavefront error (WFE) across the full 36 deg FOV. This paper discusses the
design and development of the first-ever 5MA imager and some potential air- and space-borne remote sensing
applications.
The Visible/Infrared Imager Radiometer Suite (VIIRS) is the next-generation imaging spectroradiometer for the future operational polar-orbiting environmental satellite system. A successful Flight Unit 1 has been delivered and integrated onto the NPP spacecraft. The flexible VIIRS architecture can be adapted and enhanced to respond to a wide range of requirements and to incorporate new technology as it becomes available. This paper reports on recent design studies to evaluate building a MW-VLWIR dispersive hyperspectral module with active cooling into the existing VIIRS architecture. Performance of a two-grating VIIRS hyperspectral module was studied across a broad trade space defined primarily by spatial sampling, spectral range, spectral sampling interval, along-track field of view and integration time. The hyperspectral module studied here provides contiguous coverage across 3.9 - 15.5 μm with a spectral sampling interval of 10 nm or better, thereby extending VIIRS spectral range to the shortwave side of the 15.5 μm CO2 band and encompassing the 6.7 μm H2O band. Spatial sampling occurs at VIIRS I-band (~0.4 km at nadir) spatial resolution with aggregation to M-band (~0.8 km) and larger pixel sizes to improve sensitivity. Radiometric sensitivity (NEdT) at a spatial resolution of ~4 km is ~0.1 K or better for a 250 K scene across a wavelength range of 4.5 μm to 15.5 μm. The large number of high spectral and spatial resolution FOVs in this instrument improves chances for retrievals of information on the physical state and composition of the atmosphere all the way to the surface in cloudy regions relative to current systems. Spectral aggregation of spatial resolution measurements to MODIS and VIIRS multispectral bands would continue legacy measurements with better sensitivity in nearly all bands. Additional work is needed to optimize spatial sampling, spectral range and spectral sampling approaches for the hyperspectral module and to further refine this powerful imager concept.
VIIRS sensor for National Polar-orbiting Operational Environmental Satellite System (NPOESS) is one of the nation's
key civil space programs. The Flight Model 1 is planned to be launched in 2011. VIIRS is designed to measure the
radiometric data of Earth's atmosphere, ocean, and land surfaces from visible to infrared wavelengths, and precision pre-flight
radiometric calibration is required. A 100 cm Sphere Integrating Source (SIS(100)-1), which was used to calibrate
NASA's MODIS sensor, is used to calibrate VIIRS. Cary 14, a spectrophotometer used to calibrate reflectance and
transmittance of optical components since LANDSAT missions, is used to transfer the calibration of a NIST-traceable
standard lamp to SIS(100)-1 for different lamp levels from visible to short wave infrared wavelengths. In this paper, the
method and result of absolute radiometric calibration of SIS(100)-1 are discussed.
Medium-sized Aperture Camera (MAC) is the main payload for Earth observation satellite RazakSAT to be launched at the end of 2005. The flight model has been recently assembled and tested. The 300 mm diameter Cassegrain telescope optics and the focal plane assembly for a space camera have been aligned. Topics discussed in this paper include the lessons learned from the optics alignment and assembly of the telescope and the focal plane. A computer-aided alignment method was used for the alignment of the relatively wide field of view (+/-1 deg) telescope. RMS wavefront error measurement environment was found to be more critical than previously experienced, and the importance of the initial alignment is discussed. System modulation transfer function (MTF) was used as the figure-of-merit for the alignment of the focal plane assembly with linear CCD detectors. MTF was measured by a knife-edge scanning technique using a dedicated 450 mm diameter collimator with diffraction-limited performance.
Pre-flight performance has been characterized on the Medium-sized Aperture Camera (MAC) of the RazakSAT: capable of Earth observation at 2.5 m resolution and 20 km swath width. Topics discussed in this paper include measurements of system modulation transfer function (MTF) and pixel lines-of-sight (LOS); characterization of focal plane assembly (FPA) and signal processing electronics; end-to-end imaging. The MTF was obtained with knife-edge scanning technique, which is also used to align the FPA. For band-to-band registration, relative pixel LOS was measured using theodolite and effective focal length of the telescope was derived from the measurement. For the FPA and signal processing module, dark reference, pixel-to-pixel response variation and response linearity have been quantified. The end-to-end imaging tests were done to check the imaging function before the launch, by scanning a slide target at the focus of the collimator.
SAC is a compact camera for imaging in visible-NIR spectral ranges. SAC provides high-resolution images over the wide geometric and spectral ranges: 10 m GSD and 50 km swath-width in the spectral ranges of 520 ~ 890 nm. The missions incorporate various imaging operations: multi-spectral imaging; super swath-width imaging with cameras in parallel; along-track stereo imaging with slanted 2 cameras. In this paper, SAC is introduced with design and performance. Though developed for small satellites, presenting development status and test results will demonstrate the potential capability for worldwide remote sensing groups: short development period, cost-effectiveness, and high performance.
Medium-sized Aperture Camera (MAC) for earth observation on a small satellite is being developed by Satrec Initiative and ATSB. Designed as a cost-effective high-resolution camera, this push-broom type camera has 1 panchromatic and 4 multispectral channels using all-CCDs-in-one focal plane, and it does not split the channels by prisms. The panchromatic channel has 2.5m, and multispectral channels have 5m of ground sampling distance at a nominal altitude of 685km. The 300mm modified Ritchey-Chretien telescope contains two aspheric mirrors and two spherical correction lenses. MAC is the main payload of RazakSAT (formerly known as MACSAT) to be launched in 2005. RazakSAT is a 180kg (including MAC) small satellite, designed to provide high-resolution imagery of 20km swath width on a near equatorial orbit (NEqO). The mission objective is to demonstrate the capability of a high-resolution small remote sensing satellite system on a near equatorial orbit. This paper describes the status report on the development of the MAC Qualification Model and technical issues.
Ritchey-Chretien type or Cassegrain type has been widely used for earth-observing space camera. As most earth-observing cameras are required to scan the wide area in a single path, they generally have a wider field of view, compared to the ground-based telescope. However, the alignment of Cassegrain or RC telescope with a wide-field of view is not easy. One reason is that it has a central hole in the primary mirror so that it is difficult to find an optical axis. Another reason is that it can introduce much off-axis aberration such as coma and astigmatism, when it is aligned at on-axis with zero-coma condition. In this paper, we calculate the alignment accuracy using a conventional method for a RC type telescope of which diameter is 300 mm and field of view is 2.08 degrees. We suggest that the most effective alignment method for wide field of view system is a computer-aided alignment. With this method, it was found that the variation of rms wavefront error of the telescope over the entire field of view was less than 10 %.
In this work, multi-physics simulation software (CA/MEMS) and design-optimization software (DS/MEMS) tailored for MEMS devices are introduced. The CA/MEMS, which is a simulation engine for DS/MEMS, is a 3-D multi-physics analysis code utilizing various numerical methods such as FEM, BEM and FVM to efficiently model MEMS application problems. The current CA/MEMS includes analysis- modules for structural, thermal, electric, electromagnetic and fluidic fields and is capable of the analyses of various coupled- field problems for MEMS applications. DS/MEMS is design optimization engine for MEMS devices. With integrating CA/MEMS and pre/post processor into CAD environment, DS/MEMS is organized to work in parametric CAD platform. DS/MEMS consists of optimal design module and robust design module. The optimal design module provides users three methods nonlinear programming, Taguchi parameter design and the response surface method. The robust design module, which is specially developed for MEMS application, can be used to minimize the perturbation of performances of MEMS devices under uncertainties of MEMS devices, such as process tolerance and the change of operating environments. To verify the efficiency and accuracy of CA/MEMS and the practical usefulness of DS/MEMS, we have been comparing the simulated results of CA/MEMS with those of other commercial codes and experimental data of manufactured MEMS devices, and investigating the performances of the optimized designs through DS/MEMS.
This paper describes progress on the development of a new process for producing precision surfaces for the optics industry, and potentially for other sectors including silicon wafer fabrication and lapping and polishing of precision mechanical surfaces. The paper marks an important milestone in the development program, with the completion of the construction of the first fully-productionized machine and the first results from the commissioning process.
We report on the development of a novel industrial process, embodied in a new robotic polishing machine, for automatically grinding an polishing aspheric optics. The machine is targeted at meeting the growing demand for inexpensive axially symmetric but aspherical lenses and mirrors for industry and science, non-axisymmetric and conformal optics of many kinds, the planarization of silicon wafers and associated devices, and for controlling form and texture in other artifacts including prosthetic joints. We describe both the physics and the implementation of the process. It is based on an innovative pressurized tool of variable effective size, spun to give high removal rate. The tool traverse and orientation are orchestrated in a unique (and patented) way to avoid completely the characteristic fast peripheral-velocity and center-zero left by conventional spinning tools. The pressurized tooling supports loose abrasive grinding and polishing, plus a new bound-abrasive grinding process, providing for a wide range of work from coarse profiling to fine polishing and figuring. Finally we discuss the critical control, data handling and software challenges in the implementation of the process, contrast the approach with alternative technologies, and present preliminary results of polishing trials.
Computer controlled polishing of large optics has required complex and expensive tooling, which is impractical at the smaller scale. This paper describes the simulation of a simple aspheric polishing regime using a large active lap, and its embodiment in a new generalized aspheric polishing machine for instrumentation optics.
This paper outlines recent progress in a novel active fabrication technique for severely aspheric optics. The underlying technology has been initially developed at the Optical Science Laboratory (OSL), at University College London, and has been incorporated in the OSL full-size active lap, used for polishing large astronomical optics. Optical Generics Limited (OGL) and OSL are currently collaborating to further develop the technology. A prototype OGLP-400 computer controlled polishing machine has been developed which exploits the technology for use with smaller aspheric optics up to 600mm diameter. The recent experimental results on both machines are presented, and their implications discussed.
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