Документ взят из кэша поисковой машины. Адрес оригинального документа : http://www.mrao.cam.ac.uk/~bn204/publications/2010/2010-08-General.pdf Дата изменения: Fri Aug 10 20:18:02 2012 Дата индексирования: Tue Oct 2 13:07:26 2012 Кодировка: Поисковые слова: http www.astronomy.ru forum index.php topic 4644.0.html

Oxygen sounding thermal profiler for ALMA
Bojan Nikolic & Emily Cur tis
Cavendish Laborator y, University of Cambridge

August 2010 OSF

Nikolic & Cur tis (University of Cambridge)

O2 sounder for ALMA

August 2010

1 / 26


Principle of operation

Outline

1

Principle of operation The Radiometrics oxygen sounder Outputs Role of temperature profiling in ALMA calibration Phase correction Amplitude calibration

2

3

4

Nikolic & Cur tis (University of Cambridge)

O2 sounder for ALMA

August 2010

2 / 26


Principle of operation

Atmospheric transmission at the ALMA site
1 PWV = 1 mm

Atmosperhic transmision

0.8

0.6

0.4

0.2

0 50 100 200 Frequency (GHz)
Nikolic & Cur tis (University of Cambridge) O2 sounder for ALMA August 2010 3 / 26

500

1000


Principle of operation

Atmospheric transmission at the ALMA site
1 PWV = 1 mm

Atmosperhic transmision

0.8

Band 8

Band 9 Band 10

0.6 Band 3 Band 4 Band 6

0.4

0.2 Band 1 50 Band 2 100 Band 5 200 Frequency (GHz)
Nikolic & Cur tis (University of Cambridge) O2 sounder for ALMA August 2010 3 / 26

0

Band 7 500 1000


Principle of operation

The three most impor tant components:
1

Water vapour :

2

Oxygen (O2 )

3

Ozone (O3 )

Nikolic & Cur tis (University of Cambridge)

O2 sounder for ALMA

August 2010

4 / 26


Principle of operation

The three most impor tant components: (1) Water
1

0.8

0.6 Tx 0.4 0.2 0 50 100 200 (GHz)
Nikolic & Cur tis (University of Cambridge) O2 sounder for ALMA August 2010 4 / 26

500

1000


Principle of operation

The three most impor tant components: (2) Oxygen
1

0.8

0.6 Tx 0.4 0.2 0 50 100 200 (GHz)
Nikolic & Cur tis (University of Cambridge) O2 sounder for ALMA August 2010 4 / 26

500

1000


Principle of operation

The three most impor tant components: (3) Ozone
1

0.8

0.6 Tx 0.4 0.2 0 50 100 200 (GHz)
Nikolic & Cur tis (University of Cambridge) O2 sounder for ALMA August 2010 4 / 26

500

1000


Principle of operation

Relationship between absorption and emission
1

0.8

0.6 Tx 0.4 0.2 0 50 100 200 (GHz)
Nikolic & Cur tis (University of Cambridge) O2 sounder for ALMA August 2010 5 / 26

500

1000


Principle of operation

Relationship between absorption and emission
300

250 Atmospheric brightness (Kelvin)

200

150

100

50

0 50 100 200 (GHz)
Nikolic & Cur tis (University of Cambridge) O2 sounder for ALMA August 2010 5 / 26

500

1000


Principle of operation

Effect of pressure on the oxygen absorption
1

Atmosperhic transmision

0.8

0.6

0.4 pressure pressure pressure pressure pressure 45 = = = = = 500 400 300 200 100 mBar mBar mBar mBar mBar 55 60 65 70

0.2

0 50 Frequency (GHz)
Nikolic & Cur tis (University of Cambridge) O2 sounder for ALMA August 2010 6 / 26


Principle of operation

Effect of pressure on the oxygen absorption
300 pressure pressure pressure pressure pressure = = = = = 500 400 300 200 100 mBar mBar mBar mBar mBar

250 Atmosperhic brightness

200

150

100

50

0 45 50 55 60 65 70 Frequency (GHz)
Nikolic & Cur tis (University of Cambridge) O2 sounder for ALMA August 2010 6 / 26


Principle of operation

Example: changing the tropospheric lapse rate
300 Lapse Lapse Lapse Lapse Lapse = = = = = 0 K/km -3 K/km -6 K/km -9 K/km -12 K/km

250 Atmosperhic brightness

200

150

100

50

0 45 50 55 60 65 70 Frequency (GHz)
Nikolic & Cur tis (University of Cambridge) O2 sounder for ALMA August 2010 7 / 26


Principle of operation

Example: changing the tropospheric lapse rate
300 Lapse Lapse Lapse Lapse Lapse = = = = = 0 K/km -3 K/km -6 K/km -9 K/km -12 K/km

250 Atmosperhic brightness

200

150

100

50

0 45 50 55 60 65 70 Frequency (GHz)
Nikolic & Cur tis (University of Cambridge) O2 sounder for ALMA August 2010 7 / 26


The Radiometrics oxygen sounder

Outline

1

Principle of operation The Radiometrics oxygen sounder Outputs Role of temperature profiling in ALMA calibration Phase correction Amplitude calibration

2

3

4

Nikolic & Cur tis (University of Cambridge)

O2 sounder for ALMA

August 2010

8 / 26


The Radiometrics oxygen sounder

Radiometrics oxygen sounder

Nikolic & Cur tis (University of Cambridge)

O2 sounder for ALMA

August 2010

9 / 26


The Radiometrics oxygen sounder

Radiometrics oxygen sounder: concept
The Sky

LNA Filter LO Chain Calibration load 50to60 GHz LO Signal

Detection, Sampling & Readout

Noise Diode

Readout via RS422

"Agile" Freq. Synth

Nikolic & Cur tis (University of Cambridge)

O2 sounder for ALMA

August 2010

10 / 26


The Radiometrics oxygen sounder

Calibration

Calibration is critically impor tant! Changes in the gain of the receiver (like in all radio receivers, this dominates normally-distributed noise) Other effects ­ receiver zero point, radome window transparency, non-linearity, etc.
1 2 3

Noise diode injection of known signal (100+ times/second) Observing the internal ambient load (once every 10 seconds) Observing the external liquid nitrogen calibration load (once every 6 months)

Nikolic & Cur tis (University of Cambridge)

O2 sounder for ALMA

August 2010

11 / 26


The Radiometrics oxygen sounder

Inver ting the measurements to obtain temperature profile

Want Have Temperature as function of height Sky brightness measurements at above ground 14 frequencies
1 2

Not a one-to-one problem Need to include information about what temperature profiles are plausible Radiometrics software is based on a neural-network approach Linear approximation methods have also been used

3 4

Nikolic & Cur tis (University of Cambridge)

O2 sounder for ALMA

August 2010

12 / 26


The Radiometrics oxygen sounder

The sounder within ALMA
AOS Radiometrics RS422 Sounder Perle IOLAN TCP/IP over Ethernet

Linux Control Local files ALMA SOAP Interface SW

Nikolic & Cur tis (University of Cambridge)

O2 sounder for ALMA

August 2010

13 / 26


Outputs

Outline

1

Principle of operation The Radiometrics oxygen sounder Outputs Role of temperature profiling in ALMA calibration Phase correction Amplitude calibration

2

3

4

Nikolic & Cur tis (University of Cambridge)

O2 sounder for ALMA

August 2010

14 / 26


Outputs

Brightness of the sky as function of time

At radio frequencies
300 250 200

In the infrared
320 300 280 260 Tir (K) 240 220 200 180

Tsky (K)

150 100 50 18

19

20

21 22 GMT Time (hours)

23

24

160 18

19

20

21 22 GMT Time (hours)

23

24

Nikolic & Cur tis (University of Cambridge)

O2 sounder for ALMA

August 2010

15 / 26


Outputs

Temperature profile of the atmosphere
10 8 Height above AOS (km) 6 4 2 0 180 200 220 240 260 280 300 320 Temperature (K)
Nikolic & Cur tis (University of Cambridge) O2 sounder for ALMA August 2010 16 / 26


Outputs

Temperature profile of the atmosphere
10 8 6 4 2 0 18

20100817

336 318 300

Height (km)

282 264 246 228 210 19 20 21 22 GMT Time (hours) 23 24 192

Nikolic & Cur tis (University of Cambridge)

O2 sounder for ALMA

Temperature (K)
August 2010

16 / 26


Outputs

What happens to the outputs?

1

Real-time plotting
Plots of retrieved profile & infrared signal Use to identify unstable weather & clouds

2

Monitor database
Store ever y 5 minutes the obser ved sky brightness, retrieved profile & infrared signal Long-term understanding of weather at the site

3

Science data
Store obser ved sky brightness, retrieved profile & infrared signal Calibration of science data!

Nikolic & Cur tis (University of Cambridge)

O2 sounder for ALMA

August 2010

17 / 26


Role of temperature profiling in ALMA calibration

Outline

1

Principle of operation The Radiometrics oxygen sounder Outputs Role of temperature profiling in ALMA calibration Phase correction Amplitude calibration

2

3

4

Nikolic & Cur tis (University of Cambridge)

O2 sounder for ALMA

August 2010

18 / 26


Role of temperature profiling in ALMA calibration

Phase correction

Outline

1

Principle of operation The Radiometrics oxygen sounder Outputs Role of temperature profiling in ALMA calibration Phase correction Amplitude calibration

2

3

4

Nikolic & Cur tis (University of Cambridge)

O2 sounder for ALMA

August 2010

19 / 26


Role of temperature profiling in ALMA calibration

Phase correction

Atmospheric Phase Fluctuations

Nikolic & Cur tis (University of Cambridge)

O2 sounder for ALMA

August 2010

20 / 26


Role of temperature profiling in ALMA calibration

Phase correction

Atmospheric Phase Fluctuations

Nikolic & Cur tis (University of Cambridge)

O2 sounder for ALMA

August 2010

20 / 26


Role of temperature profiling in ALMA calibration

Phase correction

Atmospheric Phase Fluctuations

Nikolic & Cur tis (University of Cambridge)

O2 sounder for ALMA

August 2010

20 / 26


Role of temperature profiling in ALMA calibration

Phase correction

Atmospheric Phase Fluctuations

Nikolic & Cur tis (University of Cambridge)

O2 sounder for ALMA

August 2010

20 / 26


Role of temperature profiling in ALMA calibration

Phase correction

Phase fluctuations as function of time
0.009 750

500

250 L (µ m)

0 -250 -500 -750 6

6.2

6.4

6.6 t (hours UT)

6.8

7

7.2

Nikolic & Cur tis (University of Cambridge)

O2 sounder for ALMA

August 2010

21 / 26


Role of temperature profiling in ALMA calibration

Phase correction

WVR in the ALMA receiver cabin

Nikolic & Cur tis (University of Cambridge)

O2 sounder for ALMA

August 2010

22 / 26


Role of temperature profiling in ALMA calibration

Phase correction

Phase correction with WVRs

300 200 100 L (µ m) 0 -100 -200 -300

Nikolic & Cur tis (University of Cambridge)

300

O2 sounder for ALMA

August 2010

23 / 26


Role of temperature profiling in ALMA calibration

Phase correction

Conver ting WVR output to path estimate
We need to estimate the temperature of the water vapour:
1

Conver t sky brightness to quantity of water vapour TB T 1 - exp(-c )

2

Conver t quantity of water vapour to path delay n - 1 10
-6



Pd T

+

Pw T

+

P T

w 2

Pw : Par tial pressure of the water vapour T : Temperature of the water vapour

Nikolic & Cur tis (University of Cambridge)

O2 sounder for ALMA

August 2010

24 / 26


Role of temperature profiling in ALMA calibration

Amplitude calibration

Outline

1

Principle of operation The Radiometrics oxygen sounder Outputs Role of temperature profiling in ALMA calibration Phase correction Amplitude calibration

2

3

4

Nikolic & Cur tis (University of Cambridge)

O2 sounder for ALMA

August 2010

25 / 26


Role of temperature profiling in ALMA calibration

Amplitude calibration

Amplitude calibration
Atmospheric absorption
300

250 Atmospheric brightness (Kelvin)

200

150

100

50

0 50 100 200 (GHz)
Nikolic & Cur tis (University of Cambridge) O2 sounder for ALMA August 2010 26 / 26

500

1000


Role of temperature profiling in ALMA calibration

Amplitude calibration

Amplitude calibration
Atmospheric absorption
1 PWV = 1 mm

Atmosperhic transmision

0.8

0.6

0.4

0.2

0 50 100 200 Frequency (GHz)
Nikolic & Cur tis (University of Cambridge) O2 sounder for ALMA August 2010 26 / 26

500

1000


Role of temperature profiling in ALMA calibration

Amplitude calibration

Amplitude calibration
Atmospheric absorption
1 PWV = 0.5 mm PWV = 1 mm PWV = 1.5 mm

Atmosperhic transmision

0.8

0.6

0.4

0.2

0 50 100 200 Frequency (GHz)
Nikolic & Cur tis (University of Cambridge) O2 sounder for ALMA August 2010 26 / 26

500

1000