THE TRANSMISSION OF TERRESTRIAL VLF EMISSIONS THROUGH THE IONOSPHERE HAS A MEASURABLE AND OFTEN SIGNIFICANT EFFECT UPON BOTH ENERGETIC AND RELATIVISTIC ELECTRON POPULATIONS IN THE MAGNETOSPHERE. BOTH NATURAL (E.G. LIGHTNING TRANSIENTS) AND ARTIFICIAL (E.G. GROUND VLF TRANSMITTER RADIATION) SOURCES CONTRIBUTE SIGNIFICANTLY TO THESE VLF EMISSIONS. WHILE THE VLF PENETRATION PROCESS HAS BEEN MODELED AND THE WAVE AMPLITUDES MEASURED AT THE UPPER BOUNDS OF THE IONOSPHERE (600-800 KM ALTITUDE) THE ACTUAL ELECTRODYNAMICS OF THE ATTENUATION AND PROPAGATION PROCESS HAVE NOT BEEN MEASURED FROM THE EARTH-IONOSPHERIC WAVEGUIDE THROUGH THE IONOSPHERE AND ABOVE. WITH THIS DEFICIT IN THE OBSERVATIONAL DATABASE IN MIND WE PROPOSE TO FLY A FULLY 3D EM FIELD MEASUREMENT DC THROUGH VLF AND RELEVANT PLASMA AND NEUTRAL PARTICLE MEASUREMENTS AT MID-LATITUDES THROUGH THE RADIATION FIELDS OF AN EXISTING VLF TRANSMITTER (USN CALL SIGN NAA; 24.0 KHZ; CUTLER MAINE) AND NATURALLY-OCCURRING LIGHTNING IN ORDER TO EXPLORE THE FOLLOWING SCIENCE OBJECTIVES: 1 - WHAT IS THE VERTICAL AND HORIZONTAL PROFILE OF THE OBSERVED 3D ELECTRIC AND MAGNETIC RADIATED FIELDS OF THE VLF TRANSMITTER AND HOW IS THAT PROFILE RELATED TO THE OBSERVED PLASMA AND NEUTRAL DENSITIES? THE OBSERVED PLASMA AND NEUTRAL DENSITY PROFILES PROVIDE THE LOCAL DIELECTRIC TENSOR AND COLLISION FREQUENCIES; FROM THE VERTICAL E- AND B-FIELD PROFILES THE REFLECTION ABSORPTION AND TRANSMISSION PROCESSES AS A FUNCTION OF ALTITUDE CAN BE DETERMINED AND THUS APPLIED TO THE BROADER QUESTION OF TRANS-IONOSPHERIC ESCAPE OF TERRESTRIAL VLF RADIATION. 2 ARE THE EM WAVE PROPERTIES OF LIGHTNING RADIATED FIELDS QUALITATIVELY AND QUANTITATIVELY SIMILAR TO THOSE FROM THE STEADY-STATE NARROWBAND VLF TRANSMITTER PROPERTIES OR ARE THERE SIGNIFICANT DIFFERENCES IN APPARENT REFLECTION ABSORPTION AND TRANSMISSION THAT WOULD HAVE SIGNIFICANT IMPACTS ON THE LEAKAGE OF SUCH VLF SOURCES THROUGH THE IONOSPHERE? THE PROPOSED SOUNDING ROCKET CAMPAIGN WOULD CONSIST OF A SUMMER NIGHTTIME LAUNCH DURING QUIET MAGNETOSPHERIC CONDITIONS FROM WALLOPS FLIGHT FACILITY TO AN ALTITUDE OF 600-800 KM WITH A PAYLOAD CARRYING THE FOLLOWING INSTRUMENTATION: 2D E- AND 3D B-FIELD WAVEFORMS DC-1 KHZ; 3D ELF TO VLF WAVEFORMS 100 HZ TO 50 KHZ; 1D WIDEBAND E-FIELD MEASUREMENT OF PLASMA AND UPPER HYBRID LINES 100 KHZ TO 4 MHZ; AND LANGMUIR PROBE PLASMA DENSITY AND ION GAUGE NEUTRAL DENSITY MEASUREMENTS AT A SAMPLING RATE OF AT LEAST TENS OF HZ. THIS EFFORT WILL CONTRIBUTE TO THE NASA HELIOSPHERIC SCIENCE GOALS TO "EXPLORE THE PHYSICAL PROCESSES IN THE SPACE ENVIRONMENT FROM THE SUN TO THE EARTH ... " AND TO "ADVANCE OUR UNDERSTANDING OF THE CONNECTIONS THAT LINK THE SUN THE EARTH [AND] PLANETARY SPACE ENVIRONMENTS ... " BY MAKING DIRECT MEASUREMENTS OF THE ELECTRODYNAMICAL PROCESSES IN AND ACROSS THE IONOSPHERE THAT CONTRIBUTE TO THE ENERGIZATION SCATTERING AND LOSS OF ENERGETIC PARTICLES IN THE MAGNETOSPHERE.