Yan Betremieux

SPINR: two-dimensional spectral imaging through tomographic reconstruction

We describe a novel technique that enables us to conduct 2-D imaging spectroscopy with a 1-D imaging spectrometer. A typical imaging spectrometer obtains a series of 1-D monochromatic images that contain the entire field of view, but the spatial information in the dispersion direction is lost. By rotating the instrument (hence, rotating the field of view), we compile a series of time-dependent profiles. We use a numerical tomographic reconstruction method to recover the second spatial dimension and thereby obtain 2-D monochromatic images of the field of view. This technique is more sensitive and, hence, collects a full 2-D image more quickly than a conventional push-broom scan. We present the results of numerical simulations and discuss the prospects of this method for magnetospheric imaging applications.

HST observation of the atmospheric composition of Jupiter’s equatorial region: evidence for tropospheric C2H2☆

Abstract This paper presents the first detailed analysis of acetylene absorption features observed longward of 190.0 nm in a jovian spectrum by the Faint Object Spectrograph on board the Hubble Space Telescope. The presence of two features located near 207.0 nm can only be explained by a substantial abundance of acetylene in the upper troposphere. Using a Rayleigh–Raman radiative transfer model, it was determined that the acetylene vertical profile is characterized by a decrease in the mole fraction with increasing pressure in the upper stratosphere, a minimum around 14 to 29 mbar, followed by an increase to about 1.5 × 10 −7 in the upper troposphere. Longward of 220 nm, the relatively high contrast of Raman features to the continuum precludes the existence of an optically significant amount of clouds from 150 to 500 mbar unless they are highly reflective. Instead, the reflectivity at these long wavelengths is determined by stratospheric, not tropospheric, scatterers and absorbers. Analysis of the data also suggests that ammonia is extremely undersaturated at pressures below 700 mbar. However, no firm conclusions can be reached because of the uncertainties surrounding its cross section longward of 217.0 nm, which are due to vibrationally excited states.

Ultraviolet-imaging spectroscopy of dust in the interstellar medium

This paper describes a system for performing high resolution spectroscopy with 2D spatial imaging. We motivate the discussion by describing the application of our system to the astronomical study of dust in the interstellar medium. Our methodology can be implemented on a wide variety of optical systems from a wide variety of platforms. Several such configurations are discussed.

Spectrograph for photometric imaging with numeric reconstruction (SPINR) simulations

Our spectrograph for photometric imaging with numeric reconstruction uses a novel technique to produce 2D spectral images using a 1D imaging spectrometer. By varying the dispersion direction with respect to the center of the field-of-view, we produce a series of images with the intensity of each pixel equal to the integrated intensity of the field-of-view along the dispersion direction. Reconstruction of the 2D spectral image from this series of profiles can be accomplished with a variety of numerical methods. We present results obtained using the maximum entropy algorithm on lab tests, which include expected instrument noise, and compare this method to analytical backprojection methods. Finally, in each of these tests, we present improvements in speed over previous results through code optimization, which improves the viability of using the maximum entropy algorithm for spectroscopic imaging.

SPINR: high-resolution two-dimensional spectral imaging

We describe a novel technique which enables us to conduct two-dimensional imaging spectroscopy using a one-dimensional imaging spectrometer. A typical imaging spectrometer obtains a series of one-dimensional monochromatic images containing the entire field of view, but the spatial information in the dispersion direction is lost. By rotating the instrument (hence rotating the field of view) we compile a series of time dependent profiles. We use a numerical tomographic reconstruction method to recover the second spatial dimension and thereby obtain two-dimensional monochromatic images of the field of view. This technique is more sensitive and hence collects a full two-dimensional image more quickly than a conventional push-broom scan. We present the results of numerical simulations and discuss the prospects of this method for magnetospheric imaging applications.