Overview
The MARSCHALS project is an ESA supported project devoted to the development and the study of the performance of the homonymous instrument that was designed as an airborne-based simulator of the future satellite-based MASTER instrument.
MARSCHALS (Millimetre-wave Airborne Receivers for Spectroscopic CHaracterisation in Atmospheric Limb Sounding) is an heterodyne instrument that measures the atmospheric thermal emission in the millimetre and sub-millimetre region with a limb sounding technique. It differs from the MASTER (Millimetre-wave Acquisition for Stratosphere-Troposphere Exchange Research) space project, because it operates from within the atmosphere on an air-borne platform.
MARSCHALS has been developed by an European consortium led by RAL (Rutherford and Appleton Laboratories) under an ESA (European Space Agency) contract and has flown on board of the M-55 Russian aircraft (Geophysica) up to an altitude of 21 km. Incoming radiation is distributed into a number of discrete spectral bands, each of which is down converted and amplified. Spectrometers measure the spectral power density across each band. For reasons of cost, the design of MARSCHALS does not permit instantaneous coverage of all five MASTER bands and only three bands (MASTER bands B, C and D) are time multiplexed.
The main instrument requirements of the MASTER and the main MARSCHALS instrument characteristics are summarised respectively in Table 1 and 2.
| Table 1– MASTER instrument requirements | ||||||
| Primary Targets | Height Domain | Band
| Spectral Coverage(GHz) | Spectral resolution (MHz) | NEBT /accuracy (K) | Vertical HPBW(^) (km) |
| O3, N2O, O2 (pointing) | UTLS | B | 294.0-305.5 | 50 | 1.2/1.0 | 2.3 |
| H2O | UTLS | C | 316.5-325.5 | 50 | 1.3/1.0 | 2.3 |
| CO, HNO3 | UTLS | D | 342.25-348.75 | 50 | 0.5/1.0 | 2.3 |
| ClO, O3, N2O, BrO | LS | E | 497.0-506.0 | 50 | 0.6/1.0 | 1.6 |
| HCl | LS | F | 624.0-626.5 | 50 | 2.0/1.0 | 1.6 |
| (*)UTLS – Upper Troposphere – Lower Stratosphere (°) Noise Equivalent Brightness Temperature (^) Half Power Beam Width | ||||||
| Table 2 – The MARSCHALS instrument | |
| Instrument Type | Total Power Single Sideband Radiometer |
| RF bands | Band B 294 – 305.5 GHz Band C 316.5 – 325.5 GHz Band D 342.2 – 348.8 GHz |
| Instantaneous bandwidth | 12 GHz |
| Spectral Resolution | 200 MHz (with provision for addition of high resolution 2MHz spectrometer with 4-12 GHz bandwidth) |
| NET (250ms) | <1.5K |
| NET (10 scans) | < 0.6K (MASTER specification) |
| Side-band Rejection | > 22dB (characterised to better than 30dB) |
| Beam Pointing | <<0.0025 deg. rms pointing knowledge during scan, bias excepted |
| Scan range | Tangent heights from –2 km to platform altitude (21 km on aircraft) in 1 km steps with +20 deg. “space view” |
| Mass | 330 kg |
| Dimensions | 1.55 x 0.76 x 0.56m |
The major objective of MARSCHALS is to test the measurement capabilities of MASTER (Millimetre-wave Acquisition for Stratosphere-Troposphere Exchange Research) instrument with real observations from a stratospheric platform in order to verify the extent of millimetre-wave advantages and to validate the spectro-radiometric requirements of MASTER. As a matter of fact, theoretical simulations indicate that MASTER, a millimetre-wave heterodyne spectrometer, is the only instrument that can satisfactory meet the challenging requirements for UTLS (Upper Troposphere / Lower Stratosphere) studies considered in the planned ACECHEM (Atmospheric Composition Explorer for CHEMistry and climate) ESA Earth Explorer Mission, but the full measurement capabilities of MASTER have not yet been demonstrated with real instruments.
Species that are expected to be detected in the bands of MARSCHALS are: H2O, O3, HNO3, N2O, CO and O2. Since the concentration of molecular oxygen in the atmosphere is well known, the measurement of this species can be used for pointing and temperature determination. Other species could be present with weak signals.
MARSCHALS is supported by a co-aligned optical cloud monitor (OCM) that images in the near-infrared (835-875 nm) the same scene observed by the millimetre instrument. The vertical resolution of the OCM is about 100 m and is intended to characterise the cloud discontinuities.
The activities related to the deployment, campaign preparation, data acquisition and data analysis (up to the level of geo-located calibrated radiances and instrument characterisation) of the MARSCHALS instrument are the subject of the MALSAC 2002 ( Microwave Atmospheric Limb Sounding Airborne Campaign) Study. It is carried out by an European consortium led by RAL (Rutherford and Appleton Laboratories) under an ESA (European Space Agency) contract.
Level 1 was devoted to the development and the testing of the acquisition capabilities; Level 2a was devoted to the first handling of the acquired data. These activities, related to the deployment, campaign preparation, data acquisition and data analysis (up to the level of geo-located calibrated radiances and instrument characterisation) of the MARSCHALS instrument was the subject of some ESA financed study.
The Level 2b analysis of the MARSCHALS measurements, is the subject of a second study with the following objectives:
1. to develop algorithms and codes for simulation and retrieval of MARSCHALS data,
2. to consolidate and validate these codes and perform an error analysis on theoretical basis,
3. to analyse and validate all data taken from potential campaigns during the study,
4. to exploit scientifically the MARSCHALS data obtained in this set of campaigns.
This web site is devoted to this second study.
