MARSCHALS is the airborne simulator of a proposed future satellite instrument to measure millimetre-wave limb emission from O3, H2O, 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.
The Millimetre-wave Acquisitions for Stratosphere-Troposphere Exchange Research (MASTER) instrument is intended to sound the gaseous composition of the upper troposphere and lower stratosphere (UTLS) in a future ESA space mission. A significant and inherent advantage of operation at millimetre and sub-millimetre wavelengths in comparison to limb-sounders operating at infra-red and shorter wavelengths is low sensitivity to cirrus clouds. MASTER will employ relatively small vertical and horizontal spacings between limb views, in order to over-sample the atmosphere in the orbit plane. By viewing each air mass from different directions, and including this information in the retrieval, horizontal as well as vertical structure of atmospheric fields may be captured. In order to examine this tomographic limb-sounding approach for MASTER, a state-of-the-art 2-D radiative transfer model and retrieval model have been developed and used in simulation experiments. A linear analysis has been performed to establish achievable horizontal and vertical retrieval resolution for target species and to identify additional parameters to include in the state vector in order to reduce error sensitivities. A realistic mid-latitude scenario and appropriate instrument and model errors have been considered. By accurately modelling radiative transfer in two dimensions within the orbit plane, and using multiple limb-sequences simultaneously in a 2-D retrieval, a horizontal resolution better than 200 km can be achieved, together with ~2 km vertical resolution for retrievals of water vapour, ozone and other trace gases in the UTLS.
We present a design concept for a new state-of-the-art balloon borne atmospheric monitor that will allow enhanced limb sounding of the Earth's atmosphere within the submillimeter and far-infrared wavelength spectral range: TELIS, TErahertz and submm LImb Sounder. The instrument is being developed by a consortium of major European institutes that includes the Space Research Organization of the Netherlands (SRON), the Rutherford Appleton Laboratory (RAL) will utilize state-of-the-art superconducting heterodyne technology and is designed to be a compact, lightweight instrument cpaable of providing broad spectral coverage, high spectral resolution and long flight duration (~24 hours duration during a single flight campaign). The combination of high sensitivity and extensive flight duration will allow evaluation of the diurnal variation of key atmospheric constitutenets sucyh as OH, HO2, ClO, BrO togehter will onger lived constituents such as O3, HCL and N2O. Furthermore, TELIS will share a common balloon platform to that of the MIPAS-B Fourier Transform Spectrometer, developed by the Institute of Meteorology and Climate research of the over an extended spectral range. The combination of the TELIS and MIPAS instruments will provide atmospheric scientists with a very powerful observational tool. TELIS will serve as a testbed for new cryogenic heterodyne detection techniques, and as such it will act as a prelude to future spaceborne instruments planned by the European Space Agency (ESA).
MARSCHALS (Millimeter-wave Airborne Receivers for Spectroscopic CHaracterization in Atmospheric Limb Sounding) is being developed with funding from the European Space Agency as a simulator of MASTER (Millimeter-wave Acquisitions for Stratosphere Troposphere Exchange Research), a limb sounding instrument in a proposed future ESA Earth Explorer Core Mission. The principal and most innovative objective of MARSCHALS is to simulate MASTER's capability for sounding O3, H2O and CO at high vertical resolution in the upper troposphere (UT) using millimeter wave receivers at 300, 325, and 345 GHz. Spectra are recorded in these bands with 200 MHz resolution. As such, MARSCHALs is the first limb-sounder to be explicitly designed and built for the purpose of sounding the composition of the UT, in addition to the Lower Stratosphere (LS) where HNO3, N2O and additional trace gases will also be measured. A particular attribute of millimeter-wave measurements is their comparative insensitivity to ice clouds. However, to assess the impact on the measurements of cirrus in the UT, MARSCHALs has a near-IR digital video camera aligned in azimuth with the 235 mm limb-scanning antenna. In addition to UT and LS aircraft measurements, MARSCHALs is capable of making mid-stratospheric measurements from a balloon platform when fitted with a 400 mm antenna. Provision has been made to add further receiver channels and a high resolution spectrometer.
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