Oxygen sounding thermal profiler for ALMA

Transcription

1 Oxygen sounding thermal profiler for ALMA Bojan Nikolic & Emily Curtis Cavendish Laboratory, University of Cambridge August 2010 OSF Nikolic & Curtis (University of Cambridge) O2 sounder for ALMA August / 26

2 Outline Principle of operation 1 Principle of operation 2 The Radiometrics oxygen sounder 3 Outputs 4 Role of temperature profiling in ALMA calibration Phase correction Amplitude calibration Nikolic & Curtis (University of Cambridge) O2 sounder for ALMA August / 26

3 Principle of operation Atmospheric transmission at the ALMA site 1 PWV = 1 mm Atmosperhic transmision Frequency(GHz) Nikolic & Curtis (University of Cambridge) O2 sounder for ALMA August / 26

4 Principle of operation Atmospheric transmission at the ALMA site 1 PWV = 1 mm Atmosperhic transmision Band 3 Band 4 Band 6 Band 8 Band 9 Band Band 1 Band 2 Band 5 Band Frequency(GHz) Nikolic & Curtis (University of Cambridge) O2 sounder for ALMA August / 26

5 Principle of operation The three most important components: 1 Water vapour: 2 Oxygen (O 2 ) 3 Ozone (O 3 ) Nikolic & Curtis (University of Cambridge) O2 sounder for ALMA August / 26

6 Principle of operation The three most important components: (1) Water Tx ν (GHz) Nikolic & Curtis (University of Cambridge) O2 sounder for ALMA August / 26

7 Principle of operation The three most important components: (2) Oxygen Tx ν (GHz) Nikolic & Curtis (University of Cambridge) O2 sounder for ALMA August / 26

8 Principle of operation The three most important components: (3) Ozone Tx ν (GHz) Nikolic & Curtis (University of Cambridge) O2 sounder for ALMA August / 26

9 Principle of operation Relationship between absorption and emission Tx ν (GHz) Nikolic & Curtis (University of Cambridge) O2 sounder for ALMA August / 26

10 Principle of operation Relationship between absorption and emission Atmospheric brightness (Kelvin) ν (GHz) Nikolic & Curtis (University of Cambridge) O2 sounder for ALMA August / 26

11 Principle of operation Effect of pressure on the oxygen absorption 1 Atmosperhic transmision pressure = 500 mbar pressure = 400 mbar pressure = 300 mbar pressure = 200 mbar pressure = 100 mbar Frequency(GHz) Nikolic & Curtis (University of Cambridge) O2 sounder for ALMA August / 26

12 Principle of operation Effect of pressure on the oxygen absorption Atmosperhic brightness pressure = 500 mbar pressure = 400 mbar pressure = 300 mbar pressure = 200 mbar pressure = 100 mbar Frequency(GHz) Nikolic & Curtis (University of Cambridge) O2 sounder for ALMA August / 26

13 Principle of operation Example: changing the tropospheric lapse rate Atmosperhic brightness Lapse = 0 K/km Lapse = -3 K/km Lapse = -6 K/km Lapse = -9 K/km Lapse = -12 K/km Frequency(GHz) Nikolic & Curtis (University of Cambridge) O2 sounder for ALMA August / 26

14 Principle of operation Example: changing the tropospheric lapse rate Atmosperhic brightness Lapse = 0 K/km Lapse = -3 K/km Lapse = -6 K/km Lapse = -9 K/km Lapse = -12 K/km Frequency(GHz) Nikolic & Curtis (University of Cambridge) O2 sounder for ALMA August / 26

15 Outline The Radiometrics oxygen sounder 1 Principle of operation 2 The Radiometrics oxygen sounder 3 Outputs 4 Role of temperature profiling in ALMA calibration Phase correction Amplitude calibration Nikolic & Curtis (University of Cambridge) O2 sounder for ALMA August / 26

16 The Radiometrics oxygen sounder Radiometrics oxygen sounder Nikolic & Curtis (University of Cambridge) O2 sounder for ALMA August / 26

17 The Radiometrics oxygen sounder Radiometrics oxygen sounder: concept The Sky Calibration load Noise Diode LO Chain 50to60 GHz LO Signal Agile Freq. Synth LNA Filter Detection, Sampling & Readout Readout via RS422 Nikolic & Curtis (University of Cambridge) O2 sounder for ALMA August / 26

18 Calibration The Radiometrics oxygen sounder Calibration is critically important! 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 Noise diode injection of known signal (100+ times/second) 2 Observing the internal ambient load (once every 10 seconds) 3 Observing the external liquid nitrogen calibration load (once every 6 months) Nikolic & Curtis (University of Cambridge) O2 sounder for ALMA August / 26

19 The Radiometrics oxygen sounder Inverting the measurements to obtain temperature profile Have Sky brightness measurements at 14 frequencies Want Temperature as function of height above ground 1 Not a one-to-one problem 2 Need to include information about what temperature profiles are plausible 3 Radiometrics software is based on a neural-network approach 4 Linear approximation methods have also been used Nikolic & Curtis (University of Cambridge) O2 sounder for ALMA August / 26

20 The Radiometrics oxygen sounder The sounder within ALMA AOS Radiometrics Sounder RS422 Perle IOLAN TCP/IP over Ethernet Linux Control Local files ALMA SOAP Interface SW Nikolic & Curtis (University of Cambridge) O2 sounder for ALMA August / 26

21 Outline Outputs 1 Principle of operation 2 The Radiometrics oxygen sounder 3 Outputs 4 Role of temperature profiling in ALMA calibration Phase correction Amplitude calibration Nikolic & Curtis (University of Cambridge) O2 sounder for ALMA August / 26

22 Outputs Brightness of the sky as function of time 300 At radio frequencies 320 In the infrared Tsky (K) 150 Tir (K) GMT Time (hours) GMT Time (hours) Nikolic & Curtis (University of Cambridge) O2 sounder for ALMA August / 26

23 Outputs Temperature profile of the atmosphere 10 8 Height above AOS (km) Temperature (K) Nikolic & Curtis (University of Cambridge) O2 sounder for ALMA August / 26

24 Outputs Temperature profile of the atmosphere Height (km) Temperature (K) GMT Time (hours) Nikolic & Curtis (University of Cambridge) O2 sounder for ALMA August /

25 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 every 5 minutes the observed sky brightness, retrieved profile & infrared signal Long-term understanding of weather at the site 3 Science data Store observed sky brightness, retrieved profile & infrared signal Calibration of science data! Nikolic & Curtis (University of Cambridge) O2 sounder for ALMA August / 26

26 Outline Role of temperature profiling in ALMA calibration 1 Principle of operation 2 The Radiometrics oxygen sounder 3 Outputs 4 Role of temperature profiling in ALMA calibration Phase correction Amplitude calibration Nikolic & Curtis (University of Cambridge) O2 sounder for ALMA August / 26

27 Outline Role of temperature profiling in ALMA calibration Phase correction 1 Principle of operation 2 The Radiometrics oxygen sounder 3 Outputs 4 Role of temperature profiling in ALMA calibration Phase correction Amplitude calibration Nikolic & Curtis (University of Cambridge) O2 sounder for ALMA August / 26

28 Role of temperature profiling in ALMA calibration Phase correction Atmospheric Phase Fluctuations Nikolic & Curtis (University of Cambridge) O2 sounder for ALMA August / 26

29 Role of temperature profiling in ALMA calibration Phase correction Atmospheric Phase Fluctuations Nikolic & Curtis (University of Cambridge) O2 sounder for ALMA August / 26

30 Role of temperature profiling in ALMA calibration Phase correction Atmospheric Phase Fluctuations Nikolic & Curtis (University of Cambridge) O2 sounder for ALMA August / 26

31 Role of temperature profiling in ALMA calibration Phase correction Atmospheric Phase Fluctuations Nikolic & Curtis (University of Cambridge) O2 sounder for ALMA August / 26

32 Role of temperature profiling in ALMA calibration Phase correction Phase fluctuations as function of time δl(µm) t (hours UT) Nikolic & Curtis (University of Cambridge) O2 sounder for ALMA August / 26

33 Role of temperature profiling in ALMA calibration Phase correction WVR in the ALMA receiver cabin Nikolic & Curtis (University of Cambridge) O2 sounder for ALMA August / 26

34 Role of temperature profiling in ALMA calibration Phase correction with WVRs Phase correction δl(µm) Nikolic & Curtis (University of Cambridge) O2 sounder for ALMA August / 26

35 Role of temperature profiling in ALMA calibration Phase correction Converting WVR output to path estimate We need to estimate the temperature of the water vapour: 1 Convert sky brightness to quantity of water vapour [ ] T B T 1 exp( κc) 2 Convert quantity of water vapour to path delay [ n α P d + β P w + γ P w T T T 2 ] P w : Partial pressure of the water vapour T : Temperature of the water vapour Nikolic & Curtis (University of Cambridge) O2 sounder for ALMA August / 26

36 Outline Role of temperature profiling in ALMA calibration Amplitude calibration 1 Principle of operation 2 The Radiometrics oxygen sounder 3 Outputs 4 Role of temperature profiling in ALMA calibration Phase correction Amplitude calibration Nikolic & Curtis (University of Cambridge) O2 sounder for ALMA August / 26

37 Role of temperature profiling in ALMA calibration Amplitude calibration Amplitude calibration Atmospheric absorption Atmospheric brightness (Kelvin) ν (GHz) Nikolic & Curtis (University of Cambridge) O2 sounder for ALMA August / 26

38 Role of temperature profiling in ALMA calibration Amplitude calibration Amplitude calibration Atmospheric absorption 1 PWV = 1 mm Atmosperhic transmision Frequency(GHz) Nikolic & Curtis (University of Cambridge) O2 sounder for ALMA August / 26

39 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 Frequency(GHz) Nikolic & Curtis (University of Cambridge) O2 sounder for ALMA August / 26