Browsing by Author "Courrier, Hans T."

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An on Orbit Determination of Point Spread Functions for the Interface Region Imaging Spectrograph.
(2018-09) Kankelborg, Charles C.; Courrier, Hans T.; De Pontieu, Bart; Wülser, Jean-Pierre
Decades of research into the Bacteria and Archaea living in geothermal spring ecosystems have yielded great insight into the diversity of life and organismal adaptations to extreme environmental conditions. Surprisingly, while microbial eukaryotes (protists) are also ubiquitous in many environments, their diversity across geothermal springs has mostly been ignored. We used high-throughput sequencing to illuminate the diversity and structure of microbial eukaryotic communities found in 160 geothermal springs with broad ranges in temperature and pH across the Taupō Volcanic Zone in New Zealand. Protistan communities were moderately predictable in composition and varied most strongly across gradients in pH and temperature. Moreover, this variation mirrored patterns observed for bacterial and archaeal communities across the same spring samples, highlighting that there are similar ecological constraints across the tree of life. While extreme pH values were associated with declining protist diversity, high temperature springs harbored substantial amounts of protist diversity. Although protists are often overlooked in geothermal springs and other extreme environments, our results indicate that such environments can host distinct and diverse protistan communities.
Using local correlation tracking to recover solar spectral information from a slitless spectrograph
(2018-01) Courrier, Hans T.; Kankelborg, Charles C.
The Multi-Order Solar EUV Spectrograph (MOSES) is a sounding rocket instrument that utilizes a concave spherical diffraction rating to form simultaneous images in the diffraction orders m=0, +1, and -1. MOSES is designed to capture high-resolution cotemporal spectral and spatial information of solar features over a large two-dimensional field of view. Our goal is to estimate the Doppler shift as a function of position for every MOSES exposure. Since the instrument is designed to operate without an entrance slit, this requires disentangling overlapping spectral and spatial information in the m=Â±1 images. Dispersion in these images leads to a field-dependent displacement that is proportional to Doppler shift. We identify these Doppler shift-induced displacements for the single bright emission line in the instrument passband by comparing images from each spectral order. We demonstrate the use of local correlation tracking as a means to quantify these differences between a pair of cotemporal image orders. The resulting vector displacement field is interpreted as a measurement of the Doppler shift. Since three image orders are available, we generate three Doppler maps from each exposure. These may be compared to produce an error estimate.
Using local correlation tracking to recover solar spectral information from a slitless spectrograph
(2015-10) Courrier, Hans T.; Kankelborg, Charles
The Multi-Order Solar EUV Spectrograph (MOSES) is a sounding rocket instrument that utilizes a concave spherical diffraction grating to form simultaneous solar images in the diffraction orders m = 0, +1, and −1. The large 2D field of view allows a single exposure to capture spatial and spectral information for large, complex solar features in their entirety. Most of the solar emission within the instrument passband comes from a single bright emission line. The m = 0 image is simply an intensity as a function of position, integrated over the passband of the instrument. Dispersion in the images at m = ±1 leads to a field-dependent displacement that is proportional to Doppler shift. Our goal is to estimate the Doppler shift as a function of position for every exposure. However, the interpretation of the data is not straightforward. Imaging an extended object such as the Sun without an entrance slit results in the overlapping of spectral and spatial information in the two dispersed images. We demonstrate the use of local correlation tracking as a means to quantify the differences between the m = 0 image and either one of the dispersed images. The result is a vector displacement field that may be interpreted as a measurement of the Doppler shift. Since two dispersed images are available, we can generate two independent Doppler maps from the same exposure. We compare these to produce an error estimate.