Coronal and Heliospheric Science Opportunities with the SECCHI Heliospheric Imager

The Heliospheric Imager (HI) is part of the SECCHI suite of instruments on-board the two STEREO spacecrafts. The two HI instruments will provide stereographic image pairs of solar coronal plasma and coronal mass ejections (CME) over a wide field of view (85 degrees), with an inner field limit of approximately 13 solar radii. These observations compliment the 15 solar radii field of view of the solar corona obtained by the other SECCHI instruments to provide unbroken coverage of the solar corona and heliosphere from the Sun to the Earth. The as-built characteristics of the HI will be presented along with the current data reduction and analysis approach. The constraints that HI observations place on models of CME propagation in the interplanetary medium will be discussed.