Sippican, Inc. is introducing an advanced radioactivity-sensing radiosonde for balloon-borne atmospheric measurements. This instrument has been developed in cooperation with Canberra Industries, Inc., a world leader in radioactivity measuring equipment. Gamma and beta radioactivity levels are measured with two Canberra Geiger-Mueller detectors, specially adapted for the temperature and pressure conditions of atmospheric profiles. Canberra’s patented “Time-To-Count” technique is used to provide excellent linearity without saturation even in extremely high radiation fields. Sippican’s MKIIA radiosonde system measures GPS-derived wind and position, temperature, and humidity, and transmits these parameters with the radioactivity measurements to the ground station. Sippican’s WIN9000 ground system processes, displays and stores all parameters.