On Analysis of Dual Spacecraft Stereoscopic Observations to Determine the ThreeDimensional Morphology and Plasma Properties of Solar Coronal Flux Tubes
Abstract
By using two spacecraft equipped with multibandpass Xray telescopes, it is possible to obtain direct 3dimensional morphology of coronal structures which is essential for understanding the energetics and dynamics of the solar atmosphere. Xray observations taken only in orbit about the Earth are inadequate to fully resolve the 3dimensional nature of the solar corona. These Earthorbit observations produce 2dimensional images and an appropriate model must be included to derive the 3dimensional structures from the lineofsight information. Stereoscopic observations from space will remove this limitation and are needed if we are to improve our knowledge of the 3dimensional morphology of the corona. Several important points regarding a stereoscopic mission are investigated and illustrated using model coronal flux tubes and imagerendering techniques. Synthesized images are formed by integrating the emission from volume elements along the lineofsight path through a 3dimensional volume in which a set of model flux tubes are located. The flux tubes are defined by (1) a plasma model defining the emissivity for a specific density, temperature, and pressure distribution, and (2) a magnetic field model from which a set of field lines are selected to define the geometry of the flux tubes. The field lines are used to define the fluxtube volume by assuming an initial base radius and conservation of flux. An effective instrumental spectralresponse function is folded into the integration. Analysis of pairs of these synthesized images with various angular perspectives are used to investigate the effect of angular separation on mission objectives. The resulting images and analysis provide guidelines for developing a stereoscopic mission. Our study produced four important results, namely: (1) An angular separation of ~30 degrees maximizes the scientific return by direct triangulation analysis because of the tradeoff between increased lineofsight resolution of position and decreased recognition of individual loop structures arising from the overlapping of multiple loops with increasing angular separation. (2) The analysis benefits from the use of timedifferential images to select flux tubes from the collection of numerous overlapping systems by selecting only recently heated or cooled flux tubes. (3) An analysis needs to be developed for algebraic reconstruction techniques applying a priori information, specific to the solar coronal structures, i.e., fluxtube continuity, maximum emission strength, nonnegative emission, previous history, and maximum gradients of emission. (4) An analysis strategy combining triangulation, modeling techniques, and algebraic restoration is necessary to derive a complete understanding of the 3dimensional morphology of the magnetic field. In the same way that helioseismology is classical viewing of the Sun with a tailored set of analysis tools for probing the interior of the Sun, heliostereoscopy is classical viewing of the Xray emitting corona and requires a tailored set of analysis tools to deduce the true 3dimensional structure of the corona.
 Publication:

Solar Physics
 Pub Date:
 November 1998
 DOI:
 10.1023/A:1005018925963
 Bibcode:
 1998SoPh..183...45G