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Data Aquisition
The data acquisition system can store up to 130 different channels
including analog data from the meteorological sensors and ARINC 429 data
from the avionics. Additional user data can also be stored on this system.
The standard data acquisition frequency is 10 Hz, data used for turbulence
investigations are sampled with 100Hz.
The quicklook onboard offers graphic and alphanumeric displays which
are configured according to the users specific needs.
Data processing can be done in the field, the final 1
second time series and quicklook plots of meteorological parameters are
available 3-4 hours after landing.
Aircraft Position, Velocity and Attitude
The Honeywell Laserref Innertial Reference System (IRS)
uses ring laser gyros and servo accelerometers to measure horizontal, vertical
and angular acceleration in the Cartesian aircraft reference system. The
IRS internal computer determines aircraft position, attitude and velocity
from the measured accelerations using advanced Kalmann filtering techniques
to reduce drift errors from signal integration.
The Flight Management Computer (FMC) uses IRS, GPS and other
navigation system to calculate a high precission blended position.
Output from the IRS and FMC is used in calculations of aircraft motion
and wind velocities.
Static Pressure
The Rosemount Model 1501 is a digital solid state sensor providing
low frequency high precision static pressure measurements. The principal
of operation is a mechanical vibrating element controlled by an integral
electronic oscillator to output a frequency proportional to the applied pressure.
Digitized data are output and recorded via ARINC 429 bus.
The Rosemount Model 1201F2 is an analog capacitive sensor providing
high frequency (100 Hz) static pressure measurements. The principal of
operation is the capacitive measurement of the deflection of a diaphragm
against a reference vacuum.
The static pressure port is part of the deiced Rosemount five hole
probe located at the tip of the nose boom.
The measured static pressure has to be corrected for the static pressure
error caused by the airflow disturbance of the aircraft . This error
was determined by extensive in-flight calibration using a trailing cone
reference measurement system.
All pressure sensors are housed in a temperature stabilized box to
minimize temperature drift errors of the sensors and electronics.
Dynamic Pressure
The Rosemount Model 1221F2 is an analog capacitive sensor providing
high frequency (100 Hz) differential pressure measurements. The principal
of operation is the capacitive measurement of the bi-directional deflection
of a diaphragm against a reference pressure port.
The dynamic pressure port is part of the deiced Rosemount five hole
probe located at the tip of the nose boom. As reference pressure port the
static pressure port of the five hole probe is used.
All pressure sensors are housed in a temperature stabilized box to
minimize temperature drift errors of the sensors and electronics.
Temperature
Two deiced Rosemount Total Air Temperature sensor housings BW102
are used for temperature measurement. As sensing elements a fast open wire
PT100 element and a slow encapsulated PT100 element are placed inside the
housings.
The principal of operation is the measurement of the temperature
dependent resistance of a platinum wire. To avoid errors by the airflow
disturbance of the aircraft the Total Air Temperature is measured. Total
Air Temperature is the maximum temperature attainable by air when brought
to rest adiabatically. The inability of achieving a 100% adiabatic compression
results in a recovery correction which has to be applied to the calculation
of the Static Air Temperature of the undisturbed air from the measured
temperature.
Since the sensing elements can get wet from hydrometeors it will
not give an accurate measurement in cloud or precipitation.
Flow Angle Sensor
A Rosemount 858 flow angle sensor is used to measure the 3-D airflow.
The principal of operation is sensing differential pressures across horizontally
and vertically aligned ports positioned on a hemispherical head. At zero
angle of attack/sideslip all ports sense equal pressures. As the aircraft
rotates to a positive angle of attack/sideslip a differential pressure
is sensed across the vetical/horizontal pressure port.
The deiced flow angle sensor (five hole probe) is mounted at the
tip of the nose boom.
The measurements of the flow angle sensor are used to calculate the
3-D wind vector.
Dew Point and Humidity
For water vapor measurements three different instruments are used:
a commercial aircraft dew point hygrometer (GE 1011B, General Eastern),
a slightly modified capacitive sensor (Humicap-H ,Vaisala) and
a Lyman-alpha absorption instrument (Buck Research, Boulder).
The General Eastern 1011B is a dew/frost point hygrometer developed
for aircraft application. A special reverse flow inlet is used for particle
separation. The principal of operation is the detection and control of a
thin layer of dew/frost on a mirror surface by optical methods and simultaneous
temperature measurement of the mirror surface. The mirror temperature is
controlled by a 2 stage peltier element.
Due to its slow time response and limited range the dew/frost point
hygrometer is mainly used for consistency check during takeoff and landing.
The Vaisala HMP230 is a capacitive humidity sensor. The principal
of operation is the measurement of the humidity dependent capacity of a
polymer coated capacitor.
The HMP230 shows excellent long term stability and good time response
in the lower troposphere. Time response degrades with decreasing temperatures.
The sensor is placed in a pressure tight flow channel together with
the Lyman-alpha instrument. A modified Rosemeount BW102 Total Air Temperature
housing is used as inlet. Since the HMP230 sensor measures relative humidity
an adiabatic compression correction has to be applied similar to the Total
Air Temperature sensor.
The Lyman-alpha absorption hygrometer is a fast (100 Hz) humidity
sensor. The principal of operation is the measurement of absorption of
water vapor molecules at 121 nm wavelength.
Due to its fast response time of a few milliseconds and wide sensitivity
range the data of the Lyman-alpha instrument are used whenever possible.
The absorption signal has to be corrected for O2 interference
and long term lamp intensity fluctuation. Therefore intensive laboratory
and in-flight calibration is performed.
The sensor is placed in a pressure tight flow channel together with
the Vaisala sensor. A modified Rosemeount BW102 Total Air Temperature housing
is used as inlet.
Radar Altimeter
The principal of operation is the ‘time of flight’
measurement of a series of RF pulses emitted by an antenna aboard the aircraft
being reflected off the ground. The radar altimeter is intentionally thought
as supporting system during landing and is limited in the height range
from 0-xxx m.
Remote Sensing (optional)
The Heitronics Model KT19.85 is used to remotely measure surface
or cloud top temperature in the range of –50 to 200 °C. The principal
of operation is the pyroelectric detection of infrared radiation emitted
by the earth referenced to an internal black body source. The spectral
range of the detector is 9.6 to 11.5 µm.
Radiation (optional)
Eppley Model Pyranometer
Measures global radiation (direct solar radiation and diffuse solar
radiation) using a wirewound plated thermopile. The PSP has a black sensor
protected by two precision ground, polished hemispheres. The wavelength
range is 0.285-2.8 µm. The direct solar radiation has to be attitude
corrected.
Eppley Model PIR Pyrgeometer
Measures global incoming or outgoing longwave terrestrial radiation using
a wirewound plated thermopile.
The wavelength range is 3.5-50 µm. The dome temperature and body
temperature are recorded and used to correct the measured raw ir radiation.
DLR Model PIR Pyrgeometer
Modified Eppley Pyrgeometer, measures global incoming or outgoing
longwave terrestrial radiation using a coated film thermopile. The wavelength
range is 3.5-50 µm. The dome temperature and body temperature are
recorded and used to correct the measured raw ir radiation.
Data Evaluation
RAMSES(Research Aircraft Meteorological Sensor data
Evaluation Software) is a universal data
processing software for the calculation and visualisation of meteorological
aircraft data. The software was developed at DLR Flight Facility and is
based on IDL (Research Systems Inc.), a platform independent interactive
programming language.
More
about RAMSES
Find some example files for download here.
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