TY - JOUR
T1 - Mapping the Structure of the Corona Using Fourier Backprojection Tomography
AU - Morgan, Huw
AU - Habbal, Shadia Rifai
AU - Lugaz, Noé
PY - 2009/1/1
Y1 - 2009/1/1
N2 - Estimating the structure, or density distribution, of the solar corona
from a set of two-dimensional white-light images made by coronagraphs is
a critical challenge in coronal physics. This work describes new
data-analysis procedures which are used to create global maps of the
coronal structure at heights where the corona becomes approximately
radial (>= 3 R sun). The technique, which is named
Qualitative Solar Rotational Tomography (QSRT), uses total brightness
white light observations, processed with a suitable background
subtraction and a Normalizing Radial Graded Filter (NRGF). These
observations are made with high frequency by the Large Angle and
Spectrometric Coronagraph Experiment (LASCO) C2 coronagraph, which
allows a standard Fourier-transform-based tomographical reconstruction.
In this paper, we first test the technique using a model corona. QSRT is
then applied to a set of observations made during Carrington Rotation
(CR) 2000-2001 (2003 March 16 to 2003 March 31). Since the maps are
constructed from data which are normalized using the NRGF process, QSRT
cannot give electron density directly. Nevertheless, the tests using the
model corona demonstrate the technique's ability to give a good
qualitative reconstruction of the coronal structure at high latitude,
with decreasing but acceptable accuracy at the equator. These tests also
demonstrate QSRT's insensitivity to noise. For the LASCO C2
observations, good agreement is found between synthetic images
calculated from the reconstructed corona and the original observations,
and good agreement is found between the distribution of density in a
QSRT reconstruction and that found using a global MHD model. Despite
their lack of quantitative information on absolute electron density, the
resulting maps (which are constructed directly from high-resolution
coronal data observed at the appropriate height), contain useful
information on the distribution of density in the corona.
AB - Estimating the structure, or density distribution, of the solar corona
from a set of two-dimensional white-light images made by coronagraphs is
a critical challenge in coronal physics. This work describes new
data-analysis procedures which are used to create global maps of the
coronal structure at heights where the corona becomes approximately
radial (>= 3 R sun). The technique, which is named
Qualitative Solar Rotational Tomography (QSRT), uses total brightness
white light observations, processed with a suitable background
subtraction and a Normalizing Radial Graded Filter (NRGF). These
observations are made with high frequency by the Large Angle and
Spectrometric Coronagraph Experiment (LASCO) C2 coronagraph, which
allows a standard Fourier-transform-based tomographical reconstruction.
In this paper, we first test the technique using a model corona. QSRT is
then applied to a set of observations made during Carrington Rotation
(CR) 2000-2001 (2003 March 16 to 2003 March 31). Since the maps are
constructed from data which are normalized using the NRGF process, QSRT
cannot give electron density directly. Nevertheless, the tests using the
model corona demonstrate the technique's ability to give a good
qualitative reconstruction of the coronal structure at high latitude,
with decreasing but acceptable accuracy at the equator. These tests also
demonstrate QSRT's insensitivity to noise. For the LASCO C2
observations, good agreement is found between synthetic images
calculated from the reconstructed corona and the original observations,
and good agreement is found between the distribution of density in a
QSRT reconstruction and that found using a global MHD model. Despite
their lack of quantitative information on absolute electron density, the
resulting maps (which are constructed directly from high-resolution
coronal data observed at the appropriate height), contain useful
information on the distribution of density in the corona.
UR - http://hdl.handle.net/2160/9125
U2 - 10.1088/0004-637X/690/2/1119
DO - 10.1088/0004-637X/690/2/1119
M3 - Article
SN - 0004-637X
VL - 690
SP - 1119
EP - 1129
JO - Astrophysical Journal
JF - Astrophysical Journal
IS - 2
ER -