LASER-ACOUSTIC SYSTEM FOR VERTICAL PROFILING BURIED AND SURFACE ICE

INNOVATIVE DYNAMICS PLANS TO INVESTIGATE SOLID-STATE LASERS TO BE INCORPORATED IN A LASER-ACOUSTIC SYSTEM FOR REMOTE SENSING APPLICATIONS IN THE ARCTIC ENVIRONMENT. THIS SYSTEMCONSISTS OF A PULSED LASER TRANSMITTER AND AN ACOUSTIC RECEIVER, BOTH OPERATED IN THE AIR. THE LASER BEAM IS FOCUSED TO A SMALL SPOT ON THE SURFACE OF THE GROUND. STRONG ABSORPTION OF THE LASER ENERGY AT THE SURFACE LIMITS PENETRATION OF THE BEAM TO A FEW WAVELENGTHS. INSTANT EVAPORATION OF SURFACE MOLECULES TAKES PLACE IF THE PEAK POWER DENSITY OF THE LASER SPOT ON THE SURFACE IS SUFFICIENTLY INTENSE. THE SUPERHEATED STEAM SUBSEQUENTLY EXPLODES, CREATING AN ACOUSTIC FIELD WHICH PROPAGATES THROUGH THE MEDIUM AND IS REFLECTED AT THE MEDIA INTERFACE. AN ACOUSTIC RECEIVER DETECTS THE REFLECTED SOUND FROM THE INTERFACE. PRECISE TIMING OF THESE SIGNALS MAKES IT POSSIBLE TO ACCURATELY MEASURE THE THICKNESS OF THE GIVEN MEDIUM. THE REFLECTIONS WOULD ALSO REVEAL CHARACTERISTICS OF THE MEDIUM. INITIAL ICE FIELD MEASUREMENTS PROVED THE FEASIBILITY OF THIS CONCEPT FOR MEASURING 1 METER THICK ICE USING A CO2 LASER OPERATING IN THE INFRARED PORTION OF THE SPECTRUM (10.6 UM). THE EMPHASIS OF THE PROPOSED PROGRAM ISTO DETERMINE THE FEASIBILITY OF USING A ND:YAG LASER OPERATING IN THE NEAR INFRARED REGION (1.06 UM) TO GENERATE ACOUSTIC PULSES IN VARIOUS MEDIA INCLUDING WATER, ICE, SNOW,AND SOIL. THE RESULTS OF THESE EXPERIMENTS WILL YIELD IMPORTANT INFORMATION AS TO THE POTENTIAL UTILITY OF AIRBORNE LASER REMOTE SENSING FOR RAPID AND WIDE SCALE MEASUREMENT OF SPATIAL AND TEMPORAL VARIATIONS IN SNOW, ICE,AND FROZEN CONDITIONS.