The Global Hawk unmanned aerial vehicle (UAV) recently acquired by NASA was flown for the first time in a hurricane field campaign in 2010, in the NASA Genesis and Rapid Intensification Processes (GRIP) experiment. One of the primary payloads was the High Altitude MMIC Sounding Radiometer (HAMSR) developed at the Jet Propulsion Laboratory. HAMSR is a cloud-penetrating microwave sounder that provides a picture of the state of the atmosphere, such as the thermodynamic environment around hurricanes and the convective structure in the inner core. We show results from GRIP, including analysis of observations of Hurricane Karl during 13 hours during a period of rapid intensification. We focus in particular on the evolution of the convective structure, as revealed by estimates of reflectivity derived from the HAMSR brightness temperatures using a new algorithm developed at JPL, applied to a sequence of 20 consecutive passes over the eye of Karl during the period of intensification.