Instrument: | Submillimeterwave Limb Sounder (SLS) |
Principal Investigator: | Robert A. Stachnik |
Organization: | Mail Stop 183-701 Jet Propulsion Laboratory/California Institute of Technology 4800 Oak Grove Drive Pasadena, CA 91109 |
Measurement Description: The Submillimeterwave Limb Sounder (SLS) is a heterodyne radiometer measuring thermal emission spectra near 640 GHz (for detection of ClO, HCl, and O3) and 604 GHz. (for detection of HNO3 and N2O) designed for use on high altitude balloons and aircraft. The instrument consists of five subsystems:
The radiometer front-end is an uncooled second harmonic mixer using a waveguide mounted Schottky diode. The radiometer is operated double side band (DSB), i.e., spectral features occurring symmetrically above and below the effective local oscillator frequency (637.050 GHz) appear together in the IF output spectrum. The diode is pumped at a 318.525 GHz. This source is generated by a tripled 106.175 GHz phase-locked InP Gunn oscillator and wave guide coupled to the mixer block. The mixer produces an IF output spectrum of 10.5 to 13 GHz, which corresponds to signals at the mixer input at 647.5 GHz to 650.0 GHz (in the radiometer upper side band) and 626.5 GHz to 624.1 GHz ( in the lower side band). The design of the 604 GHz radiometer system is similar to 637 GHz system but operates at a lower IF frequency of 2 to 3 GHz.
Diagram of the SLS frequency down-conversion scheme. RF signals enter the signal flow path through mixer feeds at the left of the diagram. At the right side, the signal flow enters a set of UARS MLS-type filterbank spectrometers where bands are further spectrally resolved, power detected, and digitized.