Upload
others
View
4
Download
0
Embed Size (px)
Citation preview
The Effects of the Atmosphere on
Radio Astronomy Observations
Dana S. Balser
The Effects of the Atmosphere on the Radio Signal
Atmospheric Refraction
Green (1985)
Maddalena & Johnson (2006)
R = 𝐸𝑜 − 𝐸𝑡
𝑛𝑜𝐶𝑜𝑠 𝐸𝑜 = 𝐶𝑜𝑠(𝐸𝑡)
𝑅 ~ (𝑛𝑜 −1) 𝐶𝑜𝑡(𝐸𝑜)
𝑅 = 𝑟𝑜𝑛𝑜𝑆𝑖𝑛(𝑧𝑜) 𝑑𝑛
𝑛(𝑟2𝑛2 − 𝑟𝑜2𝑛𝑜
2𝑆𝑖𝑛2(𝑧𝑜))1/2
𝑛𝑜
1
Plane Parallel
Spherical
Anomalous Refraction (Seeing)
𝑚50 = 𝑓
100 𝐺𝐻𝑧
𝐷
50 𝑚
5/6
= 0.4 at 10 GHz for Arecibo
= 1.8 at 100 GHz for the GBT
= 3.0 at 300 GHz for the LMT
𝐼𝑚𝑝𝑜𝑟𝑡𝑎𝑛𝑡 𝑤ℎ𝑒𝑛 𝑚50 > 1
Olmi (2002)
Atmospheric Absortion
𝑇𝐴 ∝ 𝑒−𝜏
Condon (2007)
Atmospheric Emission (Noise)
𝑇𝑠𝑦𝑠 = 𝑇𝑜 + 𝑇𝑏
~ 𝑇𝑟𝑐𝑣𝑟+ 6𝐾
𝑇𝑏= 𝑇𝑘(1 − 𝑒−𝜏)
𝑇𝑜 ~ 𝑇𝑟𝑐𝑣𝑟 + 𝑇𝑠𝑟𝑐 + 𝑇𝑔𝑟𝑑 + 𝑇𝑐𝑚𝑏
Condon (2007)
Balser (2004)
Syste
m T
em
pera
ture
Elevation
Atmospheric Stability
Mason & Perera (2011) Balser (2011)
9 GHz 90 GHz
Sta
bili
ty
Fra
ction
IR Irradiance Tsys (90GHz)
good poor
Weather Forecasts
Vertical Profiles from
GOES and Balloon
Soundings (NOAA)
Maddalena: www.gb.nrao.edu/
~rmaddale/Weather
→ 𝑇𝑠𝑦𝑠 𝑓 , 𝜏(𝑓)
The Effects of the Atmosphere on the Telescope
Repeatable Errors:
Gravity
Static Corrections
Non-repeatable Errors:
Thermal (slow)
Wind (fast)
Dynamic Corrections
Telescope Adjustments
Focus
Surface
Pointing
Telescope Performance
20.0 10% :Pointing2
s
2/95.0 :Focus sa
yg
4/37.0 :Surface s
Thermal Effects: pointing, focus, surface shape
GHz 30at 3 mm 30
GHz 3 at /3 mm 03
Time
Axia
l F
ocus
Telescope Pointing and Focus: thermal model
Constantikes (2007)
Telescope Surface: OOF Holography
𝑟𝑚𝑠 = 330𝜇𝑚
𝑟𝑚𝑠 = 220𝜇𝑚
Nikolic et al. (2007)
Wind Effects: pointing
1''
12
2
11
68
2)(
sec16.0)(
Law sHooke'
smsat
windwind
arcsm
swind
Condon (2003)
Quadrant Detector
Flag bad data
Correct maps from arrays
Real-time corrections
Map Corrections
Ries et al. (2009)
Before After
Fini