<p>The Michelson Interferometer for Global High-Resolution Thermospheric Imaging (MIGHTI) instrument on NASA’s Ionospheric Connection Explorer’s mission will measure neutral winds in the Earth’s thermosphere. We investigate how thermal changes to the instrument’s optical bench affect the relative position of the image recorded by the camera. The thermal shift is measured by fitting the image of a series of reference notches and determining their current position on the camera with subpixel precision. Analyzing ground-based calibration data, we find that the image position is not affected within the uncertainty of the analysis for the applied thermal changes. We also address the question of the analysis uncertainty with signal-to-noise ratio.</p>
We describe the design and ground-based performance of the two-color calibration lamp for the Michelson Interferometer for Global High-Resolution Thermospheric Imaging (MIGHTI) instrument on the NASA Ionospheric Connection (ICON) satellite. The calibration lamp assembly contains radio frequency excited krypton and neon lamps, which generate emission lines at 557 and 630 nm, respectively, and which are used to monitor thermal drifts in the two MIGHTI Doppler asymmetric spatial heterodyne interferometers. The lamps are coupled to two mixed optical fiber bundles that deliver the calibration signals to the two MIGHTI optical units. The assembly starts reliably, consumes <8 W, and has passed environmental testing for the ICON satellite. The total mass of the lamp assembly is 1.8 kg. Special features of the assembly and its implementation are described along with results of life tests.
Highly sensitive trace gas measurements in planetary atmospheres can yield information about a planet’s atmosphere and surface. One prominent example is methane in the Martian atmosphere, which could originate biogenically and provides answers to one of the most intriguing questions in planetary science: “Does life currently exist on Mars?” Recently, in situ measurements by the Mars Science Laboratory (MSL) have resulted in an upper limit of 1300 parts per trillion by volume (pptv), whereas previous measurements using terrestrial telescopes and an instrument orbiting Mars reported significantly higher values of 10,000 pptv or more. These results are not necessarily contradictory, due to the possibility of spatial and temporal variability of the trace gas concentration. Thus, more measurements will be required to gain clarity. The concept of a miniaturized Mars methane monitor, a high spectral resolution, midinfrared spectrometer observing the sun through the Mars atmosphere from either the Mars surface, a Mars balloon or plane, or a Mars orbiting satellite is presented. The instrument would measure atmospheric methane and water vapor volume mixing ratios with equal or higher precision than the tunable laser spectrometer on MSL. The spectrometer concept uses the spatial heterodyne spectroscopy technique, which has previously been used for ground- and space-based observations of the Earth’s atmosphere.
A Doppler Asymmetric Spatial Heterodyne (DASH) interferometer is a device that is suited to making line-of-sight
measurements of thermospheric wind speeds from either ground- or space-based platforms. However, DASH
interferometer characteristics are sensitive to temperature changes. These instrument changes can be tracked
with calibration sources and subsequently corrected during data analysis. Even though these thermal effects
can be corrected, a quantitative understanding of the physics driving them is important for future instrument
designs. A previous study of the thermal behavior of a monolithic DASH system [Harlander et al, Opt. Express,
2010] measured a thermal response that was not consistent with a simplified model. It was suggested that this
discrepancy was a result of the rotation of various optical components caused by the thermoelastic distortion of
the monolithic interferometer elements which were cemented together yet had different coefficients of thermal
expansion. This distortion effect was not included in the simplified model. In this study we assemble an
interferometer with separate optical components which are allowed to expand independently with changes in
temperature and therefore eliminates any distortion due to stresses induced by different coefficients of thermal
expansion. Thus, by measuring the thermally induced change to the interference pattern generated by this
interferometer, we may characterize the thermal behavior of the system and verify whether all the relevant
physics is included in the simplified model. We find that the thermal drift measured by the experimental
interferometer closely matches that predicted by the model. This important result will help in the material
selection and overall design of future monolithic interferometers.