For a sample of 96,951 galaxies from the Sloan Digital Sky Survey Data Release 3, we study the distribution of apparent axis ratios as a function of r-band absolute magnitude and surface brightness profile type. We use the parameter ''fracDeV'' to quantify the profile type (fracDeV ¼ 1 for a pure de Vaucouleurs profile; fracDeV ¼ 0 for a pure exponential profile). When the apparent axis ratio q am is estimated from the moments of the light distribution, the roundest galaxies are very bright (M r $ À23) de Vaucouleurs galaxies and the flattest are modestly bright (M r $ À18) exponential galaxies. When the axis ratio q 25 is estimated from the axis ratio of the 25 mag arcsec À2 isophote, we find that de Vaucouleurs galaxies, at this low surface brightness, are flatter than exponential galaxies of the same absolute magnitude. For a given surface brightness profile type, very bright galaxies are rounder, on average, than fainter galaxies. We deconvolve the distributions of apparent axis ratios to find the distribution of the intrinsic short-to-long axis ratio , making the assumption of constant triaxiality T. For all profile types and luminosities, the distribution of axis ratios is inconsistent with a population of oblate spheroids, but is usually consistent with a population of prolate spheroids. Bright galaxies with a de Vaucouleurs profile (M r À21:84, fracDeV > 0:9) have a distribution of q am that is consistent with triaxiality in the range 0:4 P T P 0:8, with mean axis ratio 0:66 P hi P 0:69. The fainter de Vaucouleurs galaxies are best fit with prolate spheroids (T ¼ 1) with mean axis ratio hi % 0:51.
Abstract. Iterative retrievals of trace gases, such as carbonyl sulfide (OCS), from satellites can be exceedingly slow. The algorithm may even fail to keep pace with data acquisition such that analysis is limited to local events of special interest and short time spans. With this in mind, a linear retrieval scheme was developed to estimate total column amounts of OCS at a rate roughly 10 4 times faster than a typical iterative retrieval. This scheme incorporates two concepts not utilized in previously published linear estimates. First, all physical parameters affecting the signal are included in the state vector and accounted for jointly, rather than treated as effective noise. Second, the initialization point is determined from an ensemble of atmospheres based on comparing the model spectra to the observations, thus improving the linearity of the problem. All of the 2014 data from the Infrared Atmospheric Sounding Interferometer (IASI), instruments A and B, were analysed and showed spatial features of OCS total columns, including depletions over tropical rainforests, seasonal enhancements over the oceans, and distinct OCS features over land. Error due to assuming linearity was found to be on the order of 11 % globally for OCS. However, systematic errors from effects such as varying surface emissivity and extinction due to aerosols have yet to be robustly characterized. Comparisons to surface volume mixing ratio in situ samples taken by NOAA show seasonal correlations greater than 0.7 for five out of seven sites across the globe. Furthermore, this linear scheme was applied to OCS, but may also be used as a rapid estimator of any detectable trace gas using IASI or similar nadir-viewing instruments.
Atmospheric oxygen absorption bands in observed spectra of boost phase missiles can be used to accurately estimate range from sensor to target. One method is to compare observed values of band averaged absorption to radiative transfer models. This is most effective using bands where there is a single absorbing species. This work compares spectral attenuation of two oxygen absorption bands in the near-infrared (NIR) and visible (Vis) spectrum, centered at 762 nm and 690 nm, to passively determine range. Spectra were observed from a static test of a full-scale solid rocket motor at a 900 m range. The NIR O 2 band provided range estimates accurate to within 3 %, while the Vis O 2 band had a range error of 15 %. A Falcon 9 rocket launch at an initial range of 13 km was also tracked and observed for 90 seconds after ignition. The NIR O 2 band provided in-flight range estimates accurate to within 2 % error for the first 30 seconds of tracked observation. The Vis O 2 band also provided accurate range estimates with an error of approximately 4 %. Rocket plumes are expected to be significantly brighter at longer wavelengths, but absorption in the NIR band is nearly ten times stronger than the Vis band, causing saturation at shorter path lengths. An atmospheric band is considered saturated when all the in-band frequencies emitted from the rocket plume are absorbed before reaching the sensor.
The SuperNova/Acceleration Probe (SNAP) mission will require a two-meter class telescope delivering diffraction limited images spanning a one degree field in the visible and near infrared wavelength regime. This requirement, equivalent to nearly one billion pixel resolution, places stringent demands on its optical system in terms of field flatness, image quality, and freedom from chromatic aberration. We discuss the advantages of annular-field three-mirror anastigmat (TMA) telescopes for applications such as SNAP, and describe the features of the specific optical configuration that we have baselined for the SNAP mission. We discuss the mechanical design and choice of materials for the telescope. Then we present detailed ray traces and diffraction calculations for our baseline optical design. We briefly discuss stray light and tolerance issues, and present a preliminary wavefront error budget for the SNAP Telescope. We conclude by describing some of tasks to be carried out during the upcoming SNAP research and development phase.
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