Airborne laser altimeter survey of Long Valley, California

Airborne laser altimetry has proved useful in recent years in examining volcanic landforms and glacial ice sheets. With the advent of accurate differential GPS aircraft tracking, we believe that airborne lasers will also prove useful in monitoring timevarying topographic uplift, with rates as low as several centimetres of vertical motion per year. The Long Valley, California, caldera provides an excellent testing ground for this new technology. The region has a history of extensive volcanism, and its central dome has recently been undergoing resurgent uplift of up to 4 cm per year. In September 1993 we conducted three aircraft topographic surveys over the caldera and resurgent dome, utilizing a NASA T39 jet aircraft outfitted with a nadir-profiling altimetric laser (ATLAS), two P-code GPS receivers, a Litton LTN92 inertial unit for attitude, and aerial cameras. In addition, we operated two base-station GPS receivers for post-flight differential navigation and conducted a kinematic automobile survey of roads crossing the dome.