1. Polarization Properties of the John A. Galt 26-m Radio Telescope
A Workshop Celebrating the Career of John A. Galt
Polarization Properties of the John A. Galt 26-m Radio Telescope
Xuan Du
Sep 23, 2014

2. Challenges in Astronomical Polarimetry
The Polarized Sky
Instrumental Polarization
The polarized emission from the Galactic plane
T.L.Landecker et al, A&A, 2010, 520, A80

3. Simulate a Randomly Polarized source
CST
Model the Feed Pattern
GRASP
Surface Roughness
Model the Reflector
Mesh Leakage
Simulate a Randomly Polarized source
Ng et al, 2005, Radio Science, 40, 5014

4. Simulate a Randomly Polarized source
CST
Model the Feed Pattern
GRASP
Surface Roughness
Model the Reflector
Mesh Leakage
Simulate a Randomly Polarized source
Ng et al, 2005, Radio Science, 40, 5014

5. Total Intensity Patterns

6. Total Intensity Patterns
T.L.Landecker et al, Radio Sci 1991, 363

7. Total Intensity Patterns

8. Polarization Patterns

9. Intensity Patterns Radial Average
Aperture Efficiency & Beam Efficiency
Beam Efficiency
Strut scatter cones
Spillover Lobes
Aperture Efficiency

10. Ground Radiation (1400 MHz)
0.4 k
4.2 k
Add arrows showing the fluctuation
𝑇 𝑔𝑟𝑜𝑢𝑛𝑑 = 1 Ω 𝑓 𝜃,𝜙 𝑇 𝐺 𝜃,𝜙 𝑑𝜔
0.6 k
𝑇 𝐺 𝜃,𝜙 = 300 [K] (80°<𝜃<180°)

11. Atmospheric Emission (1400MHz)
0.015k
3.5 k
𝑇 𝑎𝑡𝑚 = 1 Ω 𝑓 𝜃,𝜙 𝑇 𝜃,𝜙 𝑑𝜔
0.004k
𝑇 𝐴 𝜃,𝜙 = 2⋅sec(z) [K] (0°≤𝜃<80°)
Gibbins, C.J. 1986, Radio Science, 21, 949

12. Ground temperature Profile
Measurements
Computation is not perfect
Strut Modeling
Ground Modeling
Ground temperature Profile

13. Footer Text
4/22/2019

14. Conclusions GRASP can successfully predict polarization profile.
Strut scattering and spillover contribute to the instrumental polarization.
Aperture efficiency was calculated for GMIMS calibration.
The ground contribution to the instrumental polarization is predicted.