The Receiver Assembly Unit (RAU) for IASI
The three Receiver Assembly Units (RAU) for IASI was designed
and manufactured by KDA. The first flight model was launched in
2006 onboard METOP-A. The second and third flight unit are due
for launch in 2012 (METOP-B) and 2016 (METOP-C) respectively.
The IASI instrument is a Fourier Transform interferometer that
measures the spectrum of infrared light. The interferogram is
obtained by scanning one of two interferometer mirrors and
recording the resulting interference signal. The light from the
reference laser (LAS) is injected into the interferometer and
detected with the RAU. The signal detected by the RAU, which is
governed by the position of the scanning mirror, is used for
controlling the sampling of the interferogram. The spectrum of the
incoming light is determined via a Fourier transformation of the
interferogram.
Incoming
infrared light
Fixed
Mirror
Mirror
Scanning
Mirror
LAS
light
RAU Flight Models
Features
RAU Optical Unit
• Nominal and Redundant lens/detector
systems
• Large aperture of 8.5 mm to accommodate
misalignment of input beam
• Large area detectors for ease of alignment
and long-term stability
• Dielectric coated optics
• Designed for storage qualification
temperature -25°C to +45°C and operation
5°C to +35°C.
RAU Electronics Unit:
• Filters and common mode noise suppression
for low noise
• Settable pulse delay
• Full redundancy at PCB level
• Bias for detectors
• RS422 compatible line transmitters
• Temperature sensor
Beam
splitter
Michelson
Interferometer,
functional diagram
R
A
U
L
A
S
C
B
S
The IASI instrument performs high accuracy measurements in the 3.7 - 15.5 µm spectral range. The application
is weather forecasting and the instrument collects data for EUMETSAT. The following data is collected:
•
Temperature measurements with accuracy of 1K for 1 km
•
Humidity measurements with accuracy of 10 %
•
Atmospheric chemistry measurements to gases like ozone, methane or carbon monoxide.
Kongsberg Defence & Aerospace AS
E-mail: [email protected]
Telephone: +47 32 28 82 00
WORLD CLASS – through people, technology and dedication
The RAU is divided into two units
•
RAU Optical unit (RAO) containing beam splitters, lenses and InGaAs photodetectors
•
RAU Electronics unit (RAE) containing preamplifiers, detection electronics (amplitude and signal
crossing) and temperature sensors
•© Kongsberg Defence & Aerospace AS –
The prime function of the RAU is to detect the reference laser light, after its propagation through the
interferometer, and output pulses at the zero crossings of this signal. Inside the RAU, the input beam
is separated into two parts by a beam splitter and sent to photodetectors (one for the nominal, one
for the redundant unit) which generate fringe signals. These signals are further processed by the
electronics. The electronics outputs digital zero crossing pulses and an analogue amplitude signal.
IASI RAU Technical data
DESIGN
Detector Type
Beam splitter
Focusing lens
InGaAs photodiode
Non-Polarising beam splitter
Dielectric Fused Silica
MASS
600 g
ENVIRONMENT
Temperature
Vibration
+5 ºC to +35 ºC (operating level)
30 – 150 Hz, 35 g (qualification level)
20 – 2000 Hz, 16 gRMS (qualification level)
PERFORMANCE
Input Wavelength
Input frequency
Input Optical Power
Beam Diameter
1537.7 +/- 10 nm
134 kHz 21 kHz (interferogram)
Between 0.1mW and 0.4 mW
Between 3mm and 6mm
OUTPUT
Format
Time Delay
Delay stability
Zero crossing pulses and amplitude signal
Nominally 3.4µs, settable with 0.2 µs accuracy
<4ns@173Hz for calibration period (80s)
POWER CONSUMPTION
1.5 W
LIFETIME
5 years operation
WORLD CLASS – through people, technology and dedication