Description of the Mozaic System
The
measurement uses the aircraft’s power supply and is driven by a
computer which controls the instruments. It receives the aircraft
parameters and stores the data every 4 seconds on removable high
capacity disks. The system works automatically, without involving the
flight crew. It automatically detects the differents phases of the
flight (to control instruments and data recording) and provides
maintenance informations (fault lamp, error messages) on the ground.
The airline’s routine maintenance consists only in the replacement of
data disk and water vapour sensor during each "A check" of the
aircraft after 500 hours of flight. 1° Ozone measurements LA/CNRS (Toulouse) The ozone analyzer is a dual beam UV absorption instrument (Thermo-Electron, Model 49-103). Much care is taken to control the quality of the measurements. A Teflon KNF Neuberger pump is used for pulling air through the analyzer, from the external pressure of 150-250 mbar at cruise altitude. In these conditions, the characteristics of ozone measurements by MOZAIC are the following: detection limit 2 ppbv, overall precision ± [2 ppbv + 2%]. This corresponds to an upper limit of the error on the measurements, and studies of MOZAIC data have in fact shown better characteristics. 2° CO measurements LA/CNRS (Toulouse) The MOZAIC CO analyser is the improvement of a commercial Model 48CTL from Thermo Environmental Instruments, with major modifications to improve the instrument specifications :
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3° Water vapour measurements FZJ (Jülich) For water vapor, a special airborne humidity sensing device (AD-FS2), developed by Aerodata (Braunschweig, Germany) and based on the humidity and temperature transmitter HMP 230 of Vaisala (Helsinki, Finland), is used for measuring relative humidity and temperature of the atmosphere. The sensing element itself is a combination of a capacitive relative humidity sensor (Humicap-H, Vaisala) and a Pt100-temperature sensor which have been installed in an appropriate housing (Model 102-BX, Rosemount, United States), mounted near the ozone inlet pitot tube. Before installation in the A340, and after every 500 hours of flight operation, each water vapour sensing unit is calibrated in the environmental simulation chamber in FZJ/Jülich. The calibrations have shown that the sensor is reliable for measurements of relative humidity from the surface up to the upper troposphere. 4° NOy measurements FZJ (Jülich) A small, fully automatic instrument for the measurement of total odd-nitrogen (NOy) was developed at FZJ and was installed in 2001 aboard an A-340 long-range aircraft of the Deutsche Lufthansa. The NOy -instrument is installed in the avionic bay below the cockpit next to the special flange which carries the air inlets for the MOZAIC instruments. An avionic oxygen cylinder is mounted under the instrument. 5° Rack installation and instruments LA/CNRS The MOZAIC instrumentation has been developed for automatic measurements during in-service flights of the aircraft. It consists of a specially designed rack, installed in the right side of the avionic compartment (below the cockpit), and of a probe plate located on the fuselage seven metres back from the nose of the aircraft. |
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Mozaic II system | Mozaic III system |
Schema of the Mozaic III system
The
plate holds the pitot tube (ozone) and Rosemount housing (humidity,
temperature) such that the inlets (seven and ten cm height above the
plate) are well outside the aircraft boundary layer (3 cm thick there,
as calculated by Aerospatiale engineers).
6° The inlet system LA/CNRS The ozone inlet and the Rosemount housing installed on a removal plate, located on the left side of the fuselage in the noze of the aircraft are installed on a removal plate, located on the left side of the fuselage in the noze of the aircraft. |
 The ozone inlet and the Rosemount housing |
The
procedure of sampling the external air for ozone measurement only after
takeoff and before landing is used to prevent contamination of the
input line by deposition of organic compounds and dust while the
aircraft is on the ground and subject to local pollution. |
Operation
The system uses the aircraft
power supply and is computer controlled, with an auto-start mode.
Through software held on the storage disk, an electronic interface
controls the auxiliary devices (pumps, Teflon electrovalves, mass
flowmeters, error detection system, water vapor, and temperature
electronic transmitter units). Measurements are taken every 4 s,
starting after takeoff and continuing up to landing. Data (O3, H2O,
T, and status of control parameters) and aircraft parameters from
the Air Data Computer (time, latitude, longitude, altitude, pressure,
aircraft speed, wind direction, and velocity) are stored and
compressed on 128 Mbytes PCMCIA cards. The system operates entirely
automatically, without involving the flight crew. The data disk and
water vapor sensor are replaced on a (roughly) monthly basis, at every
"A Check", about every 500 flight hours. In addition, there is a
check of the unit’s operation (fault lamp, error messages) made by
the airline’s maintenance staff during routine stopovers.