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