We have fabricated a diamond-turned low-mass version of a toroidal mirror which is a key element for a spaceborne
visible-light heliospheric imager. This mirror's virtual image of roughly a hemisphere of sky is viewed by a conventional
photometric camera. The optical system views close to the edge of an external protective baffle and does not protrude
from the protected volume. The sky-brightness dynamic range and background-light rejection requires minimal wideangle
scattering from the mirror surface. We describe the manufacturing process for this mirror, and present preliminary
laboratory measurements of its wide-angle scattering characteristics.
White-light Thomson scattering observations from the Solar Mass Ejection Imager (SMEI) have recorded the
inner heliospheric response to many CMEs. Some of these are also observed from the LASCO
instrumentation and, most recently, the STEREO spacecraft. Here, we detail several CME events in SMEI
observations that have also been observed by the LASCO instrumentation and STEREO spacecrafts. We
show how SMEI is able to measure CME events from their first observations as close as 20° from the solar
disk until they fade away in the SMEI 180° field of view. We employ a 3D reconstruction technique that
provides perspective views as observed from Earth, from outward-flowing solar wind. This is accomplished
by iteratively fitting the parameters of a kinematic solar wind density model to the SMEI white-light
observations and, where possible, including interplanetary scintillation (IPS) velocity data. This 3D modeling
technique enables separating the true heliospheric response in SMEI from background noise, and
reconstructing the 3D heliospheric structure as a function of time. These reconstructions allow both
separation of CME structure from other nearby heliospheric features and a determination of CME mass.
Comparisons with LASCO and STEREO images for individual CMEs or portions of them allow a detailed
view of changes to the CME shape and mass as they propagate outward.
The Solar Mass Ejection Imager (SMEI) instrument consists of three CCD cameras
with individual fields of view of 60° × 3° degrees that combined sweep a 160° arc of sky. SMEI covers the entire sky in one spacecraft orbit of 102 minutes. Individual 4-s exposures from each orbit are assembled into full-sky maps. The primary objective in the SMEI data reduction is to isolate the Thomson-scattering signal across the sky from free electrons in the solar wind. One of the steps needed to achieve the required photometric precision is
the individual fitting and removal of stars brighter than 6th magnitude from the full-sky maps. The point-spread function of the SMEI optics has several unusual properties. It has a full width of about one degree, is asymmetric, and varies in width depending on where in the field of view the image is formed. Moreover, the orientation of the PSF on the sidereal sky rotates over 360 degree
over the course of a year. We describe the procedure used to fit and subtract individual stars from the SMEI full-sky maps. A by-product of this procedure are time series at the orbital time resolution for stars brighter than 6th magnitude. These results are used by Buffington et al. (2007) to calibrate the SMEI instrument against the LASCO C3 coronagraph.
Surface-brightness responses of the SOHO-LASCO C3 coronagraph and of the Solar Mass Ejection Imager (SMEI) are
compared, using measurements of a selection of bright stars that have been observed in both instruments. Seventeen
stars are selected that are brighter than 4.5 magnitudes, are not known variables, and do not have a neighboring bright
star. Comparing observations of these determines a scaling relationship between surface-brightness measurements from
one instrument to those from the other. We discuss units of surface brightness for the two instruments, and estimate a
residual uncertainty for the present scaling relationship.
KEYWORDS: Solar processes, 3D modeling, Solar radiation models, Tomography, Data modeling, Scintillation, Kinematics, Sun, Radar, 3D image reconstruction
The technique of interplanetary scintillation (IPS) can be used to probe interplanetary space between the Sun and Earth
most-commonly in terms of speed and also by using the scintillation-level (g-level) as a proxy for density. We combine
the large spatial-scale 3D tomographic techniques previously only applied to IPS data from the Solar Terrestrial Environment
Laboratory (STELab) array, Nagoya University in Japan, and the previously operational Cambridge IPS system in
England, with the finer-scale capabilities of the longer baselines between the systems of the Multi-Element Radio-Linked
Interferometer Network (MERLIN) in the UK, and the European Incoherent SCATter (EISCAT) radar and the EISCAT
Svalbard Radar (ESR) in northern Scandinavia. Using the UCSD 3D reconstruction technique, we present results of detailed
measurements of speed in the solar wind and also those of solar wind flow-directions, constrained by the large-scale
density tomography through the use of a kinematic model, as well as applying this tomographic technique for the first time
to the MERLIN, EISCAT, and ESR IPS solar wind speed observations in terms of velocity.
The Solar Mass Ejection Imager (SMEI) was launched on 6 January 2003, and shortly thereafter raised to a nearly circular orbit at 840 km. Three SMEI CCD cameras on the zenith-nadir oriented CORIOLIS spacecraft cover most of the sky beyond about 20°. from the Sun, each 102-minute orbit. Data from this instrument provide precision visible-light photometric sky maps. Once starlight and other constant or slowly varying backgrounds are subtracted, the residue is mostly sunlight that has been Thomson-scattered from heliospheric electrons. These maps enable 3-dimensional tomographic reconstruction of heliospheric density and velocity. This analysis requires 0.1% photometry and background-light reduction below one S10 (the brightness equivalent of a 10th magnitude star per square degree). Thus 10-15 of surface-brightness reduction is required relative to the solar disk. The SMEI labyrinthine baffle provides roughly 10-10 of this reduction; the subsequent optics system provides the remainder. We analyze data obtained over two years in space, and evaluate the full system's stray-light rejection performance.
We present a volume rendering system developed for the real time visualization and manipulation of 3D heliospheric volumetric solar wind density and velocity data obtained from the Solar Mass Ejection Imager (SMEI) and interplanetary scintillation (IPS) velocities over the same time period. Our system exploits the capabilities of the VolumePro 1000 board from TeraRecon, Inc., a low-cost 64-bit PCI board capable of rendering up to a 512-cubed array of volume data in real time at up to 30 frames per second on a standard PC. Many volume-rendering operations have been implemented with this system such as stereo/perspective views, animations of time-sequences, and determination of coronal mass ejection (CME) volumes and masses. In these visualizations we highlight one time period where a halo CMEs was observed by SMEI to engulf Earth on October 29, 2003. We demonstrate how this system is used to measure the distribution of structure and provide 3D mass for individual CME features, including the ejecta associated with the large prominence viewed moving to the south of Earth following the late October CME. Comparisons with the IPS velocity volumetric data give pixel by pixel and total kinetic energies for these events.
The Solar Mass Ejection Imager (SMEI) records a photometric white-light response of the interplanetary medium from Earth orbit over most of the sky. We present the techniques required to process the SMEI data in near real time from the raw CCD images to their final assembly into photometrically accurate maps of the sky brightness of Thomson scattered sunlight. Steps in the SMEI data processing include: integration of new data into the SMEI data base; conditioning to remove from the raw CCD images an electronic offset (pedestal) and a temperature-dependent dark current pattern; placement ("indexing") of the CCD images onto a high-resolution sidereal grid using known spacecraft pointing information. During the indexing the bulk of high-energy-particle hits (cosmic rays), space debris inside the field of view, and pixels with a sudden state change ("flipper pixels") are identified.
Once the high-resolution grid is produced, it is reformatted to a lower-resolution set of sidereal maps of sky brightness. From these we remove bright stars, background stars, and a zodiacal cloud model (their brightnesses are retained as additional data products). The final maps can be represented in any convenient sky coordinate system, e.g., Sun-centered Hammer-Aitoff or "fisheye" projections.
Time series at selected sidereal locations are extracted and processed further to remove aurorae, variable stars and other unwanted signals. These time series of the heliospheric Thomson scattering brightness (with a long-term base removed) are used in 3D tomographic reconstructions.
White-light Thomson scattering observations from the Solar Mass Ejection Imager (SMEI) have recorded the inner heliospheric response to many CMEs. Here we detail how we determine the extent of several CME events in SMEI observations (including those of 28 May 28 and 28 October, 2003). We show how we are able to measure these events from their first observations as close as 20° from the solar disk until they fade away in the SMEI 180° field of view. We employ a 3D reconstruction technique that provides perspective views from outward-flowing solar wind as observed at Earth. This is accomplished by iteratively fitting the parameters of a kinematic solar wind density model to the SMEI white light observations and to Solar-Terrestrial Environment Laboratory (STELab), interplanetary scintillation (IPS) velocity data. This 3D modeling technique enables separating the true heliospheric response in SMEI from background noise, and reconstructing the 3D heliospheric structure as a function of time. These reconstructions allow both separation of the 28 October CME from other nearby heliospheric structure and a determination of its mass. Comparisons with LASCO for individual CMEs or portions of them allow a detailed view of changes to the CME shape and mass as they propagate outward.
KEYWORDS: Solar processes, Tomography, Solar radiation models, 3D modeling, Reconstruction algorithms, Thomson scattering, Remote sensing, Scintillation, Kinematics, Sun
Over the past years we have developed a tomographic technique for using heliospheric remote sensing observations (i.e. interplanetary scintillation and Thomson scattering data) for the reconstruction of the three-dimensional solar wind density and velocity in the inner heliosphere. We describe the basic algorithm on which our technique is based. To highlight the details of the reconstruction algorithm we specifically emphasize the implementation of corotating tomography using IPS g-level and IPS velocity observations as proxies for the solar wind density and velocity, respectively. We provide some insight into the modifications required to expand the technique into a fully time-dependent tomography, and to use Thomson scattering brightness (instead of g-level) as a proxy for the solar wind density.
KEYWORDS: Solar processes, Visualization, Volume rendering, Data modeling, RGB color model, Computing systems, Light sources and illumination, Solar radiation models, Sun, Image segmentation
We demonstrate a software application designed for the display and interactive manipulation of 3D heliospheric volume data, such as solar wind density, velocity and magnetic field. The Volume Explorer software exploits the capabilities of the Volume Pro 1000 (from TeraRecon, Inc.), a low-cost 64-bit PCI board capable of rendering a 512-cubed array of volume data in real time at up to 30 frames per second on a standard PC. The application allows stereo and perspective views, and animations of time-sequences. We show examples of three-dimensional heliospheric volume data derived from tomographic reconstructions based on heliospheric remote sensing observations of the heliospheric density and velocity structure. Currently these reconstructions are based on archival IPS and Thomson scattering data. In the near future we expect to add reconstructions based on the all-sky observations from the recently launched Solar Mass Ejection Imager.
The Air Force/NASA Solar Mass Ejection Imager (SMEI) launched January 6, 2003 is now recording whole sky data on each 100-minute orbit. Precise photometric sky maps of the heliosphere around Earth are expected from these data. The SMEI instrument extends the heritage of the HELIOS spacecraft photometer systems that have recorded CMEs and other heliospheric structures from close to the Sun into the anti-solar hemisphere. SMEI rotates once per orbit and views the sky away from Earth using CCD camera technology. To optimize the information derived from this and similar instruments, a tomographic technique has been developed for analyzing remote sensing observations of the heliosphere as observed in Thomson scattering. The technique provides 3-dimensional reconstructions of heliospheric density. The tomography program has been refined to analyze time-dependent phenomena such as evolving corotating heliospheric structures and more discrete events such as coronal mass ejections (CMEs), and this improved analysis is being applied to the SMEI data.
KEYWORDS: Magnetism, Solar radiation models, Data modeling, Solar processes, Tomography, 3D modeling, Space operations, Kinematics, Curium, In situ metrology
Our tomographic techniques developed over the last few years are based on kinematic models of the solar wind. This allows us to determine the large-scale three-dimensional extents of solar wind structures using interplanetary scintillation (IPS) observations and Thomson scattering brightness data in order to forecast their arrival at Earth in real time. We are specifically interested in a technique that can be combined with observations presently available from IPS velocity data and with observations which will become available from the Solar Mass Ejection Imager. In this paper, we introduce magnetic field projections from solar surface magnetogram data using the Stanford Current-Sheet Source Surface model at the source surface of our model and extrapolate the magnetic field out to and beyond Earth. The results are compared with in situ data. Real time projections of these data are available on our web site at:
http://cassfos02.ucsd.edu/solar/forecast/index_v_n.html and http://cassfos02.ucsd.edu/solar/forecast/index_br_bt.html
The spaceborne Solar Mass Ejection Imager (SMEI) is scheduled for launch into near-earth orbit (>800 km) in early 2003. Three SMEI CCD cameras on the zenith-oriented CORIOLIS spacecraft cover most of the sky each 100-minute orbit. Data from this instrument will provide precision visible-light photometric maps. Once starlight and other constant or slowly varying backgrounds are subtracted, the residue is mostly sunlight that has Thomson-scattered from heliospheric electrons. These maps will enable 3-dimensional tomographic reconstruction of heliospheric density and velocity. The SMEI design provides three cameras, one of which views to within 18 degrees of the solar disk with a field of view 60° long by 3° wide. Placed end-to-end, three fields of view then cover a nearly 180° long strip that sweeps out the sky over each orbit. The 3-dimensional tomographic analysis requires 0.1% photometry and background-light reduction below one S10 (the brightness equivalent of a 10th magnitude star per square degree). Thus 10-15 of surface-brightness reduction is required relative to the solar disk. The SMEI labyrinthine baffle provides roughly 10-10 of this reduction; the subsequent optics provides the remainder. We describe the baffle design and present laboratory measurements of prototypes that confirm performance at this level.
KEYWORDS: Tomography, Photometry, Solar radiation models, Space operations, Sun, Data modeling, Imaging systems, Solar processes, 3D modeling, Coronagraphy
Precise photometric images of the heliosphere are expected from the Air Force/NASA Solar Mass Ejection Imager (SMEI) now scheduled for launch in February 2003, and the all-sky cameras proposed for other NASA missions. To optimize the information available from these instruments, we are developing tomographic techniques for analyzing remote sensing observations of heliospheric density as observed in Thomson scattering (e.g. using the Helios photometer data) for eventual use with SMEI. We have refined the tomography program to enable us to analyze time-dependent phenomena, such as the evolution of corotating heliospheric structures and more discrete events such as coronal mass ejections. Both types of phenomena are discerned in our data, and are reconstructed in three dimensions. We use our tomography technique to study the interaction of these phenomena as they move outward from the Sun for several events that have been studied by multiple spacecraft in situ observations and other techniques.
Tomographic techniques developed at UCSD over the last few years incorporate a kinematic model of the solar wind to determine and forecast the large-scale three-dimensional extents of velocity and density using interplanetary scintillation (IPS) observations or Thomson scattering brightness data. In this paper, we introduce magnetic field calculations from the Stanford Current-Sheet Source Surface (CSSS) model into our kinematic model. The CSSS model is used to extrapolate the photospheric magnetic field to a source surface at 15 solar radii (Rs). The UCSD kinematic model convects magnetic field from 15 Rs out to and beyond Earth. We compare the results with in situ data near Earth. The spatial relationship between the heliospheric current sheet and coronal mass ejections (CMEs) is shown in remote views of the inner heliosphere
Emerging techniques allow instruments to view very large sky areas, a hemisphere or more, in visible light. In space, such wide-angle coverage enables observation of heliospheric features form close to the Sun to well beyond Earth. Observations from deep-space missions such as Solar Probe, Stereo, and Solar Polar Sail, coupled with observations near Earth, permit 3D reconstruction of solar mass ejections and co-rotating structures, discovery and study of new comets and asteroids, and detailed measurements of brightness variations in the zodiacal cloud. Typical heliospheric features have 1 percent or less of ambient brightness, so visible-light cameras must deliver < 0.1 percent photometry and be well protected from stray background light. When more than a hemisphere of viewing area is free of bright background-light sources, we have shown that corral-like structures with several vane-like walls reduces background light illuminating to wide-angle optical system by up to ten orders of magnitude. The optical system itself typically provides another five orders of surface-brightness reduction. With CCDs as the light-detection device, images of point-like sources must cover typically 100 pixels to average down sub-pixel response gradients and provide the above 0.1 percent photometry. With present-day CCDs this requires images of order 1 degree in angular size. Tolerating such large images in turn enables wide-angle sky coverage using simple reflecting and refracting optical systems such as convex spherical reflectors, toroids and thick lenses. We show that combining these with light- reducing corrals yields practical, light-weight instruments suitable for inclusion on deep-space probes.
The Solar Polar Sail Mission uses solar-sail propulsion to place a spacecraft in a circular orbit 0.48 Au from the Sun with an inclination of 90 degrees. The spacecraft's orbit around the Sun is in 3:1 resonance with Earth phased such that the Earth-Sun-spacecraft angle range from 30 degrees to 150 degrees. The polar view will further our understanding of: (1) the global structure and evolution of the corona, (2) the initiation, evolution, and propagation of coronal mass ejections; (3) the acceleration of the solar wind; (4) the interactions of rotation, magnetic fields, and convection within the Sun; (5) the acceleration and propagation of energetic particles; and (6) the rate of angular momentum loss by the Sun. Candidate imaging instruments are a coronagraph, an all-sky imager for following mass ejections and interaction regions from the Sun to 1 AU, and a disk imager. A lightweight package of fields and particle instruments is included. A mission using a 158 m square sail with an effective areal density of 6 g/m2 would cost approximately $LR 250-300M for all mission phases, including the launch vehicle. This mission depends on the successful development and demonstration of solar-sail propulsion.
All-sky cameras for viewing the heliosphere in white light are included in the design of several future spacecraft missions. The first of these to ge put in Earth-orbit will be the solar mass ejection imager, a joint project of the US Air FOrce, NASA, and the University of Birmingham, UK. Other missions, including an all-sky imager in their current design, are STEREO, Solar Probe and Solar Probe Sail. The white-light signal includes Thomson-scattered light from heliospheric electrons, which can be used to study the structure and evolution of large-scale heliospheric features. These studies are the principal reason for putting all-sky cameras in Earth-orbit or deep space. We discuss a tomographic technique, which uses the 2D information in the all-sky images provided by these cameras to reconstruct the heliospheric density structure in 3D. We present preliminary results of this tomographic technique applied to Thomson scattering data from the photometers onboard the two HELIOS spacecraft.
Dennis Socker, S. Antiochos, Guenter Brueckner, John Cook, Kenneth Dere, Russell Howard, Judith Karpen, James Klimchuk, Clarence Korendyke, Donald Michels, J. Daniel Moses, Dianne Prinz, N. Sheely, Shi Wu, Andrew Buffington, Bernard Jackson, Barry Labonte, Philippe Lamy, H. Rosenbauer, Rainer Schwenn, L. Burlaga, Joseph Davila, John Davis, Barry Goldstein, Henry Harris, Paulett Liewer, Marcia Neugebauer, E. Hildner, Victor Pizzo, Norman Moulton, J. Linker, Z. Mikic
A STEREO mission concept requiring only a single new spacecraft has been proposed. The mission would place the new spacecraft in a heliocentric orbit and well off the Sun- Earth line, where it can simultaneously view both the solar source of heliospheric disturbances and their propagation through the heliosphere all the way to the earth. Joint observations, utilizing the new spacecraft and existing solar spacecraft in earth orbit or L1 orbit would provide a stereographic data set. The new and unique aspect of this mission lies in the vantage point of the new spacecraft, which is far enough from Sun-Earth line to allow an entirely new way of studying the structure of the solar corona, the heliosphere and solar-terrestrial interactions. The mission science objectives have been selected to take maximum advantage of this new vantage point. They fall into two classes: those possible with the new spacecraft alone and those possible with joint measurements using the new and existing spacecraft. The instrument complement on the new spacecraft supporting the mission science objectives includes a soft x-ray imager, a coronagraph and a sun-earth imager. Telemetry rate appears to be the main performance determinant. The spacecraft could be launched with the new Med-Lite system.
The Solar Mass Ejection Imager (SMEI) experiment is designed to detect and measure transient plasma features in the heliosphere, including coronal mass ejections, shock waves, and structures such as streamers which corotate with the Sun. SMEI will provide measurements of the propagation of solar plasma clouds and high-speed streams which can be used to forecast their arrival at Earth from one to three days in advance. The white light photometers on the HELIOS spacecraft demonstrated that visible sunlight scattered from the free electrons of solar ejecta can be sensed in interplanetary space with an electronic camera baffled to remove stray background light. SMEI promises a hundred-fold improvement over the HELIOS data, making possible quantitative studies of mass ejections. SMEI measurements will help predict the rate of energy transfer into the Earth's magnetospheric system. By combining SMEI data with solar, interplanetary and terrestrial data from other space and ground-based instruments, it will be possible to establish quantitative relationships between solar drivers and terrestrial effects. SMEI consists of three cameras, each imaging a 60 degree(s) X 3 degree(s) field of view for a total image size of 180 degree(s) X 3 degree(s). As the satellite orbits the earth, repeated images are used to build up a view of the entire heliosphere.
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