AMSOS - Airborne Microwave Stratospheric Observing System

Airborne Microwave Stratospheric Observing System (AMSOS)

Instrumental details

AMSOS is a passive microwave radiometer operating at 183GHz for water vapor respectively at 175GHz for ozone measurements. The signal is downconverted by a local oscillator at 179.6GHz to an intermidate frequency (IF) of 3.7GHz. Sideband supression is realized by a Martin-Pupplett Interferometer (MPI). The IF is splitten up and downconverted again to the input frequencies of the several attached spectrometers.

Calibration is done by two loads hot and cold. The first is at ambient temperature, the latter cooled down to boiling temperature of liquid nitrogen.

Table: AMSOS instrumental details
Observation frequencies: 183.3GHz±0.5GHz (H2O) and 175.9GHz±0.5GHz (O3)
Intermediate frequency: 3.7GHz
Sideband supression: Martin-Puplett Interferometer with possibility to switch on the fly from upper (183GHz) to lower (176GHz) sideband.
Quasioptics:
  • Corrugated horn (radiometer output HPBW=1deg)
  • Parabolic mirror
  • Martin-Puplett-Interferometer (sideband filter)
  • λ/4-Isolator at 183GHz (baseline suppression)
  • Elliptic mirror
  • Microwave transparent aircraft window
Spectrometers:
Calibration technique: Hotload (ambient) - Coldload (LN2) calibration.
Receiver noise temperature: 2800K SSB
Frontend and backend inside the Learjet
Fig: Racks inside the aircraft.
Learjet Arena Arctica, Kiruna (SWE)
Fig: Learjet Arena Arctica in Kiruna.