IMAGE/HENA: ENA Observation of a substorm onset P. C. Brandt, D. G. Mitchell, E. C. Roelof We present ENA images from above the north pole of a substorm onset on the 24 September, 2000. ENA emission appears at 1532 UT around L=6 at local midnight while Pi2 pulsations are observed at local midnight at approximately 1538 UT. The ENA emission is not visible above 40 keV due to the fall off of the charge exchange cross section with energy. However, there is no ENA emission below 16 keV for this event, which then is a representation of a decrease in the low energy end of the ion spectrum. We will relate the ion distribution derived from the ENA images to in-situ ion data. The ENA images implies that the onset for this event starts on, at least, L=6. The decrease of the hydrogen geocorona with altitude makes any ENA emissions from high altitudes weak and difficult to detect. We will try to put an upper limit on the onset region. _______________ Submitted to the Spring 2001 AGU Meeting, Boston, Massachusetts