The changes with altitude of the vertical electric field from seven VLF ground-based transmitters were measured during the ascent of the Extended Life Balloon-Borne Observatory (ELBBO) balloon test flight from Ft. Sumner, New Mexico. The altitude profiles of the VLF vertical electric field allowed us to determine the propagation modes based on the relative amplitude changes of the VLF signals with height. Three of the VLF transmitters had signals which crossed through the dawn terminator on their paths to the balloon's receiver. The observed height gains from these three stations show that at least two models of sunrise modal interference, those proposed by Crombie <1964> and by Kaiser <1968>, are occurring. For these three cases a time and altitude-varying height gain signal (the ratio E(z)/E(0) for altitude z above the surface z=0) was measured during the balloon's 70-min ascent to an altitude of 28.5 km. This method of balloon-measured VLF height gains allows a high level of discrimination between modes, which is shown to be a useful method for studying the phenomena of sunrise and sunset terminator effects on VLF modal interference. ¿ American Geophysical Union 1996