MARSCHALS: airborne simulator of a future space instrument to observe millimeter-wave limb emission from the upper troposphere and lower stratosphere

Abstract

ABSTRACT MARSCHALS is the airborne simulator of a proposed future satellite instrument to measure millimetre-wave limb emission from O 3 , H 2 O, CO and other trace gases in the upper troposphere and lower stratosphere. To achieve comparatively high vertical resolution and pointing stability, MARSCHALS scans the atmospheric limb in 1km vertical steps using a 235mm diameter antenna controlled by a dedicated inertial measurement unit. A quasi-optical network directs radiation from the antenna or an ambient (~300K) or cold (~90K) calibration target into three front-end receivers and suppresses each unwanted side-band by >30dB using multi-layer frequency selective surfaces. Each receiver comprises a waveguide mixer pumped subharmonically by a phase-locked LO and a wideband IF preamplifier. The IF outputs are directed to channeliser spectrometers of 200MHz resolution which instantaneously and contiguously cover 12GHz wide (RF) frequency bands centred near 300, 325 and 345GHz. To identify clouds, images of near-IR sunlight scattered into the limb direction are recorded concurrently by an 850nm wavelength camera. MARSCHALS has been built under ESA contract by a consortium led by Rutherford Appleton Laboratory in the UK, and had its first flights on the Russian Geophysica (M55) aircraft during 2005, culminating in a deployment during the SCOUT-O3 campaign based in Darwin, Australia. This paper describes the MARSCHALS instrument and an initial assessment of its performance, determined on ground and during flight. Keywords: MARSCHALS, limb sounding, millimetre wave, millimeter wave, Geophysica, airborne, MASTER