Engineering topics

Reginald, Nelson

Publications and source records attributed to Reginald, Nelson.

5 records

NASA NTRS2019

Measuring Electron Temperature Using a Linear Polarizer Versus a Polarization Camera

Polarized K-coronal brightness (pB) of the solar corona can be measured by taking four successive coronal brightness images through a linear polarizer, by turning it through four successive angles in intervals of 45∘ and using a standard formula to measure pB from the total coronal brightness (TB) that contains both the polarized K- and the unpolarized F-coronal brightness. The question is: will the time-dependent, highly dynamic corona illuminate each pixel with the same brightness during the time it takes to take the four successive images? To mitigate this problem we now have the polarization camera, in which, each super-pixel is made up of four sub-pixels, and built in to these four sub-pixels is a polarization mask that contains four linear polarizers orientated at four angles 45∘ apart. This allows the measurement of pB to be made in a single exposure. Here, the question is: will the variations of the coronal brightness in the four adjacent sub-pixels in a super-pixel be sufficiently negligible to assume that they observe the same part of the corona? This article looks for answers to these two questions by conducting two synthetic experiments to measure the electron temperature in the plane of the sky on a spherically asymmetric model (SAM) corona by first using a linear polarizer, and then replacing it with a polarization camera and use statistical analyses to determine how well the measured temperature matched the true temperature for the two cases.

Reginald, Nelson↗

NASA NTRS2019

Dependence of DOLP on Coronal Electron Temperature, Speed, and Structure

The degree of linear polarization (DOLP) is an important measure of the fraction of the total K-coronal brightness due to Thomson scattering of photospheric brightness off the coronal electrons that is linearly polarized. However, the corona is also brightened by the F-coronal brightness due to scattering of photospheric brightness off everything else in the corona except the electrons, which remains totally unpolarized at least up to a coronal height of 5 R. As a result, to measure the DOLP, the F- and K-coronal brightness need to be separated by taking three consecutive images by turning a linear polarizer through three well-defined angles or with a single image using a polarization camera. In this regard, the theoretically computed DOLP would be a helpful tool to compare with the experimentally measured DOLP on the real corona in order to estimate how well the F-coronal brightness is removed from the total coronal brightness to isolate the K-coronal brightness. This is important because the K-coronal brightness ratios at (410.3 nm/390.0 nm) and (423.3 nm/398.7 nm) can be used to generate maps of electron temperature and speed, respectively, and the individual K-coronal brightness at all four wavelengths can be used independently to generate maps of the electron density in the corona. In this article, for a spherically symmetric model (SSM) corona with assumed temperatures of 1.0 MK and 2.0 MK and radial flow speeds of 0.0 km/s and 250.0 km/ s for the coronal electrons, we have computed the wavelength-dependent DOLP from 370.0 nm to 470.0 nm in intervals of 1.0 nm, and for a spherically asymmetric model (SAM) corona containing a simulation of the Bastille Day coronal mass ejection, streamers, and quiet areas, we have generated maps of DOLP at the four wavelengths 390.0, 398.7, 410.3, and 423.3 nm. Finally, we have used these theoretically computed models of DOLP to compare with the experimentally measured DOLP.

Reginald, Nelson↗

NASA NTRS2018

Spherical Occulter Coronagraph Cubesat

The present invention relates to a space-based instrument which provides continuous coronal electron temperature and velocity images, for a predetermined period of time, thereby improving the understanding of coronal evolution and how the solar wind and Coronal Mass Ejection transients evolve from the low solar atmosphere through the heliosphere for an entire solar rotation. Specifically, the present invention relates to using a 6U spherical occulter coronagraph CubeSat, and a relative navigational system (RNS) that controls the position of the spacecraft relative to the occulting sphere. The present invention innovatively deploys a free-flying spherical occulter, and after deployment, the actively controlled CubeSat will provide an inertial formation flying with the spherical occulter and Sun.

Davila, Joseph M.↗

NASA NTRS2008

Measuring the Electron Temperature in the Corona

We report on an experiment to demonstrate the feasibility of a new method to obtain the electron temperature and flow speed in the solar corona by observing the visible Kcoronal spectrum during the total solar eclipse on 29 March 2006 in Libya. Results show that this new method is indeed feasible, giving electron temperatures and speeds of 1.10 $\pm$ 0.05 MK, 103.0 $\pm$ 92.0 $kmsA{-l}$; 0.98 $\pm$ 0.12 MK, 0.0 + 10.0 $kmsA{-1)s; 0.70 $\pm$ 0.08 MK, 0.0 + 10.0 $kmsA{-l)$ at l.l{\it R)$ {\odot}$ in the solar north, east and west, respectively, and 0.93 $\pm$ 0.12 MK, 0.0 + 10.0 $kmsA{-l}$ at 1.2{\it R}$ {\odot}$ in the solar east. This new technique could be easily used from a space-based platform in a coronagraph to produce two dimensional maps of the electron temperature and bulk flow speed at the base of the solar wind useful for the study of heliospheric structure and space weather.

Davila, Joseph↗

NASA NTRS2003

COR1 Engineering Test Unit Measurements at the Mauna Loa Solar Observatory, September 2003

The COR1 Engineering Test Unit (ETU), which had been previously tested at the NCAR/HAO and NRL test facilities, was modified into an instrument capable of observing the Sun. It was then taken to the Mauna Loa Solar Observatory to observe the corona. The changes made to observe the Sun were as follows: 1. The plate scale was changed to accommodate the smaller Apogee camera. This change had already been made for the NRL tests. 2. The previous Oriel polarizer was replaced with a commercial Polarcor polarizer from Newport to be more flight-like. However, because of cost and availability considerations, this polarizer was smaller than those which will be used for flight. 3. A structure was placed around the back section of the instrument, to protect it from stray light. 4. A pointing spar borrowed from HAO was used to track the Sun. A few days into the test, it became evident that some artifacts were appearing in the data, and these artifacts were changing as the polarizer was rotated. It was decided to test two other polarizers, the Oriel polarizer which had been used in the previous tests at HAO and NRL, and a Nikon polarizer which was borrowed from a camera belonging to one of the observatory staff members. These three polarizers had much different qualities are shown.

Thompson, William↗