ASHI: An All Sky Heliospheric Imager using Thomson-scattered Sunlight to Enable Near-Earth 3-D Plasma Reconstruction and Forecasts
Abstract
We have conceived, designed, and are now evaluating components for an All-Sky Heliospheric Imager (ASHI), suitable to fly on future NASA or DoD missions. ASHI's principal objective is the minute-by-minute and day-by-day acquisition of a precision photometric map of the inner heliosphere. The instrument's optical system is designed views a hemisphere of sky starting a few degrees from the Sun. Two such imagers on a single spacecraft, or a single imager whose spacecraft has a 180$^\circ$ rotation, can view nearly the whole sky. A key photometric specification for ASHI is 0.1% differential photometry in a one-degree sky bin at 90$^\circ$ elongation. This enables the three dimensional (3-D) reconstruction of heliospheric density starting from near the Sun and extending outward, with updates as heliospheric structures approach, and pass the spacecraft. Velocity can also be ascertained from the 2-D sequence of images, by following the motion of the background structures using correlation tracking techniques. Solar Mass Ejection Imager (SMEI) analyses using data from 2003 to 2011 have demonstrated the success of this technique to provide density reconstructions: applying this to ASHI data will yield an order-of-magnitude improvement in 3-D density reconstructions (better than 2 x 2 degrees in latitude and longitude, and a 2-hour time resolution near the spacecraft). Here we present the latest results of the ASHI laboratory evaluations, nighttime full-sky tests of the instrument data sets, and the instrument construction to date.
- Publication:
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43rd COSPAR Scientific Assembly. Held 28 January - 4 February
- Pub Date:
- January 2021
- Bibcode:
- 2021cosp...43E.745J