RESUMEN
Spatial heterodyne spectroscopy (SHS) has been successfully applied to measure variations in water vapor pressure in the lab. An imaging system is combined with a monolithic field-widened SHS to observe a white-light source through a 1 m length water vapor cell that is designed to produce predictable variations in the water vapor pressure. The performance of the spectrometer design is examined by comparing spectra simulated using a radiative transfer model to observed spectra at several cell pressures. The intended application of the instrument to vertically resolve the water vapor profile in the upper troposphere and lower stratosphere using limb-scattered radiation in a vibrational band of water (1363-1366 nm) is also introduced.
RESUMEN
In order to obtain information both of aurora and airglow in one image by the same detector, a PLCI based on liquid crystal plate LCP and super second-generation image intensifier SSGII is proposed in this research. The detection thresholds of the CCD for aurora and airglow are calculated. For the detectable illumination range of 10(4)-10(-2) lx, the corresponding electron count is 1.57×10(5) - 0.2 for every pixel of CCD. The structure and work principle of the PLCI are described. An LC is introduced in the front of CCD to decrease the intensities of aurora in overexposure areas by means of controlling transmittances pixel by pixel, while an image intensifier is set between the LC and CCD to increase the intensity of the weak airglow. The modulation transfer function MTF of this system is calculated as 0.391 at a Nyquist frequency of 15 lp/mm. The curve of transmittance with regard to gray level for the LC is obtained by calibration experiment. Based on the design principle, the prototype is made and used to take photos of objects under strong light greater than 2×10(5) lx. The clear details of [symbols: see text] presented in the image indicate that the PLCI can greatly improve the imaging quality. The theoretical calculations and experiment results prove that this device can extend the dynamic range and it provides a more effective method for upper atmospheric wind measurement.
RESUMEN
Polar cap mesospheric winds observed with a Fabry-Perot interferometer with a circle-to-line interferometer optical (FPI/CLIO) system have been compared with measurements from a field-widened Michelson interferometer optimized for E-region winds (ERWIN). Both instruments observed the Meinel OH emission emanating from the mesopause region (approximately 86 km) at Resolute Bay, Canada (74.9 degrees N, 94.9 degrees W). This is the first time, to our knowledge, that winds measured simultaneously from a ground-based Fabry-Perot interferometer and a ground-based Michelson interferometer have been compared at the same location. The FPI/CLIO and ERWIN instruments both have a capability for high temporal resolution (less than 10 min for a full scan in the four cardinal directions and the zenith). Statistical comparisons of hourly mean winds for both instruments by scatterplots show excellent agreement, indicating that the two optical techniques provide equivalent observations of mesopause winds. Small deviations in the measured wind can be ascribed to the different zenith angles used by the two instruments. The combined measurements illustrate the dominance of the 12-h wave in the mesopause winds at Resolute Bay, with additional evidence for strong gravity wave activity with much shorter periods (tens of minutes). Future operations of the two instruments will focus on observation of complementary emissions, providing a unique passive optical capability for the determination of neutral winds in the geomagnetic polar cap at various altitudes near the mesopause.
RESUMEN
A fully achromatic wide-angle interferometer that uses cat's-eye retroreflectors has been developed for optical Doppler imaging in the ultraviolet region. Here the solar flux is much weaker than in the visible, so the solar background control system ordinarily used in spacecraft optical instruments becomes unnecessary, which results in a much smaller instrument and a broader viewing geometry. The theory and the test results associated with the development of this instrument are described. Minimizing the aberrations involved in cat's-eye geometry resulted in optimum cat's-eye and interferometer designs. The results of tests conducted in the visible and the near-UV regions demonstrated experimentally that the field of view of the interferometer is 5 degrees and that the residual wave distortions are approximately 1/8 wave with visibilities sufficient for high-resolution Doppler imaging.
RESUMEN
The theory of and experimental results associated with field widening a Michelson interferometer in convergent light are described. The consequence of this configuration is a relatively compact optical system with improved system étendue and reduced system transmission loss. Although the convergence of light introduces significant wave aberration, adequate visibility of interference can still be obtained at a path difference sufficiently large for high-resolution Doppler imaging. Experimentally, a full-angle field of view of 9 degrees with a minimum visibility of 0.5 was achieved. The particular advantages of the new configuration in the application of two-dimensional interferometric Doppler imaging in the ultraviolet spectral region are also discussed.
RESUMEN
A solid Doppler Michelson interferometer, consisting of different refractive plates cemented in the two arms of the interferometer, can be designed to be field widened, achromatic, and thermally stable. If the mirror in one arm is allowed to step over one wavelength about a fixed optical path difference, then phase-stepping interferometry can be used to determine the phase of an input spectral line. This is the basis of an optical Doppler interferometer used to measure upper atmospheric winds from space: the wind imaging interferometer (WINDII) on the Upper Atmosphere Research Satellite, UARS, which was launched on 12 September 1991 and is still operating in orbit. The instrument employs a CCD imager to record a sequence of images at different phase steps from which images of optical emission rate, wind, and temperature are derived. The WINDII concept is reviewed, and its implementation is described. The performance in orbit is then reviewed, and a summary of some of the geophysical results is given. Finally, some suggestions for future applications of this concept are presented.
RESUMEN
A field-widened Michelson interferometer designed to measure upper atmospheric winds at three altitudes near the mesopause by using airglow emissions from O(1)S, OH, and O(2) is described. A very large path difference (11 cm) is used to suppress the fringes from the hot F-region emission of O(1)S and to facilitate accurate measurements. Field widening and thermal compensation are achieved over the large spectral range (557.7-866.0 nm) by the use of three types of glass in the interferometer's arms. The instrument was installed at Resolute Bay, Canada (74.3 N, 94.5 W), in November 1992 and has been operated remotely from Toronto for four winter seasons. Some examples of data are shown to illustrate ERWIN's performance.
RESUMEN
A linear InGaAs array was used in an interference filter spectral imager to monitor the twilight decay of the O(2) Infrared Atmospheric (0-1) band in the twilight airglow. The interference filter was centered at 1.582 µm and had a bandwidth (full width at half-maximum) of 1.0 nm. The imaging lens was a simple doublet, and a Fresnel lens was used for smearing any possible sky inhomogeneities. Spectra measured over Toronto in October 1994 show that the sensitivity and spectral discrimination against the contaminating OH spectrum are potentially sufficient to infer meaningful rotational temperatures. The improvements that would result from an area InGaAs array are discussed.
RESUMEN
The Wind Imaging Interferometer is a field-widened Michelson interferometer onboard the Upper Atmosphere Research Satellite. The characterization of the instrument required a pixel-by-pixel evaluation of the instrument performance. Some of the configurations, techniques, and results of the characterization are summarized. Throughput was excellent and equivalent to a total system quantum efficiency of ~10%. Localized spatial noise in response has been attributed to scattering from residual surface effects on the CCD. Instrument visibility factors greater than 90% were measured with distinct distribution patterns over the field of view that were different for the night and day apertures. The instrument phase for zero wind was determined with laboratory airglow sources.
RESUMEN
An imaging Fabry-Perot spectrometer specifically designed for ground-based studies of thermospheric photochemistry in twilight has been built, tested, and successfully applied to the measurement of the atomic-oxygen O I 844.6-nm emission. It employs a narrow-band interference filter in series with a stabilized étalon with fixed-plate separation and a 512 × 512 pixel bare CCD, and it achieves a bandpass of 0.02 nm. A least-squares data-reduction technique is shown to be effective in extracting the target feature from the surrounding background continuum. Data from one evening show slant column emission rates of 600 to 130 R.
RESUMEN
The design and construction of a set of four high reflectance metal-dielectric thin film multilayers which produce phase changes on reflection that differ by 90 degrees in the 0.55-0.77-microm spectral range are described. This provides the basis for a new type of optical Doppler Michelson imaging interferometer for use in upper atmospheric studies in which achromatic phase shifts are produced without mirror motions.
RESUMEN
The inversion of satellite photometry data to produce a 2-D distribution of volume emission rate of optical emissions in the upper atmosphere does not provide a unique solution, but this problem may be alleviated by the application of the minimum cross-entropy (MCE) principle. This principle provides a rational criterion of choice for the selection of that distribution of volume emission rate which is maximally noninformative a subject to the constraints imposed by the data (namely, the integrated column brightness measurements). A practical and effective iterative algorithm is developed to compute the MCE reconstruction of volume emission rates. This algorithm is then applied to both synthetic and real satellite photometer data to demonstrate the effectiveness of the proposed inversion scheme.
RESUMEN
A wide-angle Michelson Doppler imaging interferometer (WAMDII) is described that is intended to measure upper atmospheric winds and temperatures from naturally occurring visible region emissions, using Spacelab as a platform. It is an achromatic field-widened instrument, with good thermal stability, that employs four quarterwave phase-stepped images to generate full images of velocity, temperature, and emission rate. For an apparent emission rate of 5 kR and binning into 85 x 105 pixels, the required exposure time is 1 sec. The concept and underlying principles are described, along with some fabrication details for the prototype instrument. The results of laboratory tests and field measurements using auroral emissions are described and discussed.
RESUMEN
The effect of multiple reflections from a semireflecting surface such as an interference filter located in front of or behind a wide-angle Michelson interferometer (WAMI) is examined. By considering the instrument as a complex operator on the incident electric field, theoretical results are obtained which describe a large variety of configurations. Experimental results are presented which are consistent with these results. It is concluded that since the presence of these reflections changes the form of the observed fringes and affects measurements of the phase and visibility of the fringes, care must be taken to avoid such reflections in designing WAMIs.
RESUMEN
A Michelson interferometer of fixed-path difference, capable of scanning over only one fringe, has been shown to be useful for the measurement of Doppler shifts from isolated emission lines. It is straightforward to field widen this type of configuration, but if different wavelengths are to be selected, the field widening must be achromatic. Further, for Doppler shift measurement, one requires a path difference that is highly stable with respect to temperature. The generalized requirements for meeting all these conditions are set out and a configuration that satisfies them is described. Sample characteristics are given for a number of different systems.
RESUMEN
An interference filter photometer on the ISIS-1l spacecraft generates global maps of the atomic oxygen emission at 6300 angstroms from the ionosphere. The most prominent feature observed is a band of permanent red aurora on the dayside of the earth, centered on magnetic noon at about 78 degrees magnetic (invariant) latitude, brighter than the quiet-time nightside aurora.
RESUMEN
One of the new features of the ISIS-II spacecraft, fourth in the Alouette/ISIS series, is the inclusion of two optical instruments. The scanning auroral photometer is described by Anger et al. in a companion paper [Appl. Opt. 12, 1753 (1973)]. The red line photometer described here is similar in concept; it is designed to map the global distribution of the 01 6300-A emission with a spatial resolution of about 100 km, a measurement accuracy of 10%, and a detection threshold of 10 R. The objective is to delineate the various processes leading to the excitation of O((1)D) in the airglow and aurora by observing the global variation and by comparison with data from other instruments on board the same spacecraft. The device is now operating successfully in orbit, and detailed orbital performance characteristics will appear in a later publication.
