Update on the Stratospheric Water Inventory: Tomography of ConvectiveHydration (SWITCH) project.

Resolution of many outstanding science questions in the Upper Troposphere and Lower Stratosphere (UT/LS) demands atmospheric composition observations with the near-global coverage attained by past and current passive limb sounders but with greater spatial resolution than currently achievable from space. We describe a new spaceborne active microwave occultation sounder system under development, making two-dimensional tomographic atmospheric composition observations with unprecedented spatial resolution (~500m vertical, 10km along track). The measurement approach employs multiple small (e.g., 6U-"CubeSat"-class) transmitters orbiting in the same plane and flight direction as a separate receiver instrument. The transmitters emit continuous distinct tones, and the receiver observes all transmitters simultaneously and continuously, in an occultation viewing geometry. The vertical resolution of the measurements is set, to first order, by the along-orbit spacing of the transmitters, with the horizontal resolution set by signal to noise and radiative transfer considerations. We review the underlying receiver and transmitter technologies being developed, along with our work to test the measurement system in a balloon-to-balloon configuration. Specific science targets for such a measurement system include the contribution of overshooting convection to the budget of stratospheric water vapor. This talk will review the goals and status of the NASA Instrument Incubator project to develop the SWITCH technology.