Temperature/Absorption Cross Integrals and the Validation
of Radiometric Temperatures for Space-Based Radiometers
1
1
2
3
Axel Murk , Arne Schröder , Mike Winser , Yichen Qian , and Richard Wylde
1
4
Institute of Applied Physics, University of Bern, Bern, Switzerland
2
Airbus Defence and Space, Portsmouth, United Kingdom
3
ANSYS UK Ltd Horsham, United Kingdom
4
Thomas Keating Ltd, Billingshurst, United Kingdom
MetOp-SG - The Second Generation of European Weather Satellites
Thermal Analysis of On-Board Calibration Target
I Meteorological satellites currently being developed by ESA (European Space
Agency) and EUMETSAT (European Organisation for the Exploitation of
Meteorological Satellites)
I Operational meteorology
. Climate monitoring
. Atmospheric chemistry
. Oceanography
I Two series of satellites
. MetOp-SG-A (first launch 2021)
. MetOp-SG-B (first launch 2022)
I 831 km altitude,
sun-synchronous orbit
I 10 different instruments cover a broad frequency spectrum, including radio
frequencies, mm-waves, the infrared, and visible spectrum.
I ANSYS Non-Linear Thermal (NLT) FEA Software running on 192 GB
Workstation modelling conducting and radiative environment
I Local radiative env. dominated by the slightly colder scanning mirror’s shroud
I MWS target needs to be well isolated from the CFRP mounting baseplate
given significant (8◦C) gradients across the mount
On-board Calibration Target for Microwave Sounder
Electromagnetic Analysis of Absorber Pyramids
I MicroWave Sounder (MWS)
. Prime: Airbus D&S UK
. Cross-track scanning radiometer
. Profiles of water vapour and
temperature
. Seven bands, 23 GHz – 230 GHz
I Design using periodic finite element method of ANSYS HFSS
I Rapid high frequency analysis based on ray tracing
FEM Unit Cell Model
Total Scattering of Different Pyramids
Floquet Port
CR110
CR114
-50
-70
PEC Boundary
i=1
Convergence Test of Quadrature Methods
I Pronounced temperature
gradients at pyramid tips
I Effective temperature far
below tip temperature
I Absorbed EM power
mostly at pyramid valley
for high frequencies
Reference Value
250
84.0
-1.36
82.0
-1.34
80.0
-1.32
78.0
-1.30
76.0
-1.28
Quadrature Method 1 74.0
Quadrature Method 2
72.0
1000
2000
3000
4000
Number of Mesh Elements × 1000
Initial Design, 1.5mm CR110, 1.5mm CR114
24 GHz
54 GHz
90 GHz
50
Tb @ 24 GHz: -1.3197 ◦C
Tb @ 54 GHz: -1.3185 ◦C
Tb @ 90 GHz: -1.3079 ◦C
z [mm]
40
30
20
10
5.0
10.0
15.0
20.0
Absorption Rate [W/m]
25.0
I Linear kernel layout with 1.5 mm meets RF but not temperature requirements
I Curved kernel layout with 1.0 mm meets RF and temperature requirements
-1.40
18.25mm
1.5mm
1.0mm
1.5mm
1.0mm
12.16mm
86.0
-1.38
www.iapmw.unibe.ch
200
A Curved Metallic Kernel Improves the Performance
88.0
0
100
150
Frequency [GHz]
0
0.0
Post Processing Meshes
Linear Kernel
Curved Kernel
-1.35
-1.30
-1.25
-1.20
Baseplate Temperature
-1.15
-1.10
Absorbed Power [µ W]
Effective Brightness Temperature [C◦]
-1.42
60
Effective Brightness Temperature
I Effective brightness temperature of the target is computed via
R
0
P
V abs(x, y, z, f ) · T (x, y, z) dV
Tb(f ) =
+ r(f )Tsurr
Pinc
I Analysis based on electromagnetic reciprocity
I Numerical cross integration of simulated temperature distribution T (x, y, z)
0
and simulated volume loss density Pabs
(x, y, z, f )
I Integral evaluation carried out on tetrahedral mesh using
Z
N
X
0
0
Pabs(x, y, z, f ) · T (x, y, z) dV ≈
Pabs(xi, yi, zi, f ) · T (xi, yi, zi) ∆Vi
-1.26
50
Fundamental Thermal and Electromagnetic Investigations
Estimation of Effective Brightness Temperature
-1.40
Goal: -40 dB
-40
-60
PEC Kernel
16mm
I Development of calibration load
. Thomas Keating: project
management, thermal simulations,
and manufacturing
. University of Bern: target design,
material characterization, and
validation
Straight Shape
Curved Kernel
Tapered Kernel
-30
Periodic Boundary
Conditions
Total Reflection [dB]
I Calibration load – temperature reference for radiometric measurements
. High emissivity e > 0.9999 (r <-40 dB )
. Low coherent backscatter S11 <-40 dB
. High temperature uniformity
. Pyramid design with metallic kernel
. Double layer absorber
1.0mm CR110, 1.0mm CR114, 1:3
-20
50
100
150
Frequency [GHz]
200
250
Conclusion and Outlook
22k Elements
160k Elements
I Numerical design meets MetOp-SG requirements
I Curved metallic kernels are proposed for an optimal balance of temperature
gradients and electromagnetic absorption
I Manufacturing of designed calibration targets under way
www.terahertz.co.uk
[email protected]