Modeling Study of the Field-Aligned, Ground-Based Imaging Technique

The field-aligned, ground-based imaging technique, in which a narrow-field imaging system is located approximately 17-23 degrees off the magnetic equator to observe equatorial ionospheric structure, has now been employed in two different longitude sectors. The images obtained using this technique provide detailed information on the development and dynamics of equatorial plasma bubbles associated with equatorial spread- F. The information provided by these imagers can be used to better specify the state of the ionosphere during the occurrence of equatorial plasma bubbles. However, there are several practical limitations and assumptions that are made in the analysis of these images, which we examine in detail in this study. These include the spatial resolution of the imaging system, the alignment of the imaging field-of-view with the magnetic field, and the assumed layer height of the emission being observed. We present results from a full three-dimensional simulation of the viewing geometry in which the 630.0-nm and 777.4-nm emissions are modeled using IRI2007 and NRLMSISE-2000. Field-aligned equatorial plasma bubbles with known parameters (scale size, location, and velocities) are imposed on the system. Images of the emissions are simulated by integrating through the models. We examine the effects of the assumed emission height layer on the derived spatial characteristics (scale size and location) and dynamics (velocities). We further examine the limitations imposed by the viewing geometry on resolving small-scale structure. This study highlights the strengths and practical limitations of the narrow-field viewing geometry in studying the properties of equatorial plasma bubbles.