SONDRAD

SondRad is a two radiometer system that is designed for usage in sounding rockets. The first flight of SondRad will be in the summer 2011 on the PHOCUS experiment (Particles, Hydrogen and Oxygen Chemistry in the Upper Summer Mesosphere), designed to explore the circumstances under which noctilucent (night shining) clouds appear.

The radiometers cover the water absorption lines at 183 and 557 GHz with 100 kHz resolution. The 183 GHz channel is a horizontal looking radiometer which is placed in the side module together with the rest of the SondRad system, while the 557 GHz radiometer is forward looking and placed in the top module. Since the rocket will rotate with about 5 Hz, the horizontal looking receiver will be sampled at 300 Hz while the forward looking receiver will be sampled at 10 Hz.

SondRad has been developed in a collaboration between Omnisys and the Group for Advanced Receiver Development (GARD) at Chalmers University of Technology. GARD has been responsible for the optics and the calibration system and Omnisys has been responsible for the two front ends, the back end, power and control, and for the overall design and implementation.

Both the radiometer channels employ subharmonic Schottky mixers and FFT spectrometer back ends. Active multiplier chains up to 85 and 91 GHz have been developed by Omnisys. The active multiplier chains pump the mixer at 183 GHz directly and use a power amplifier and x3 varistor multiplier to pump the 557 GHz mixer.

The calibration of the 183 GHz channel employs a CW pilot signal spaced 40 MHz apart from the 183 GHz water line and for the 557 GHz channel the IF-chain is calibrated by injecting noise through a directional coupler, inserted between the mixer and the LNA.