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 2010 1 / 26
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 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 50 100 200 500 1000 Frequency(GHz) Nikolic & Curtis (University of Cambridge) O2 sounder for ALMA August 2010 3 / 26
Principle of operation Atmospheric transmission at the ALMA site 1 PWV = 1 mm Atmosperhic transmision 0.8 0.6 0.4 Band 3 Band 4 Band 6 Band 8 Band 9 Band 10 0.2 0 Band 1 Band 2 Band 5 Band 7 50 100 200 500 1000 Frequency(GHz) Nikolic & Curtis (University of Cambridge) O2 sounder for ALMA August 2010 3 / 26
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 2010 4 / 26
Principle of operation The three most important components: (1) Water 1 0.8 0.6 Tx 0.4 0.2 0 50 100 200 500 1000 ν (GHz) Nikolic & Curtis (University of Cambridge) O2 sounder for ALMA August 2010 4 / 26
Principle of operation The three most important components: (2) Oxygen 1 0.8 0.6 Tx 0.4 0.2 0 50 100 200 500 1000 ν (GHz) Nikolic & Curtis (University of Cambridge) O2 sounder for ALMA August 2010 4 / 26
Principle of operation The three most important components: (3) Ozone 1 0.8 0.6 Tx 0.4 0.2 0 50 100 200 500 1000 ν (GHz) Nikolic & Curtis (University of Cambridge) O2 sounder for ALMA August 2010 4 / 26
Principle of operation Relationship between absorption and emission 1 0.8 0.6 Tx 0.4 0.2 0 50 100 200 500 1000 ν (GHz) Nikolic & Curtis (University of Cambridge) O2 sounder for ALMA August 2010 5 / 26
Principle of operation Relationship between absorption and emission 300 250 Atmospheric brightness (Kelvin) 200 150 100 50 0 50 100 200 500 1000 ν (GHz) Nikolic & Curtis (University of Cambridge) O2 sounder for ALMA August 2010 5 / 26
Principle of operation Effect of pressure on the oxygen absorption 1 Atmosperhic transmision 0.8 0.6 0.4 0.2 pressure = 500 mbar pressure = 400 mbar pressure = 300 mbar pressure = 200 mbar pressure = 100 mbar 0 45 50 55 60 65 70 Frequency(GHz) Nikolic & Curtis (University of Cambridge) O2 sounder for ALMA August 2010 6 / 26
Principle of operation Effect of pressure on the oxygen absorption Atmosperhic brightness 300 250 200 150 100 pressure = 500 mbar pressure = 400 mbar pressure = 300 mbar pressure = 200 mbar pressure = 100 mbar 50 0 45 50 55 60 65 70 Frequency(GHz) Nikolic & Curtis (University of Cambridge) O2 sounder for ALMA August 2010 6 / 26
Principle of operation Example: changing the tropospheric lapse rate Atmosperhic brightness 300 250 200 150 100 Lapse = 0 K/km Lapse = -3 K/km Lapse = -6 K/km Lapse = -9 K/km Lapse = -12 K/km 50 0 45 50 55 60 65 70 Frequency(GHz) Nikolic & Curtis (University of Cambridge) O2 sounder for ALMA August 2010 7 / 26
Principle of operation Example: changing the tropospheric lapse rate Atmosperhic brightness 300 250 200 150 100 Lapse = 0 K/km Lapse = -3 K/km Lapse = -6 K/km Lapse = -9 K/km Lapse = -12 K/km 50 0 45 50 55 60 65 70 Frequency(GHz) Nikolic & Curtis (University of Cambridge) O2 sounder for ALMA August 2010 7 / 26
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 2010 8 / 26
The Radiometrics oxygen sounder Radiometrics oxygen sounder Nikolic & Curtis (University of Cambridge) O2 sounder for ALMA August 2010 9 / 26
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 2010 10 / 26
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 2010 11 / 26
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 2010 12 / 26
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 2010 13 / 26
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 2010 14 / 26
Outputs Brightness of the sky as function of time 300 At radio frequencies 320 In the infrared 300 250 280 200 260 Tsky (K) 150 Tir (K) 240 220 100 200 180 50 18 19 20 21 22 23 24 GMT Time (hours) 160 18 19 20 21 22 23 24 GMT Time (hours) Nikolic & Curtis (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 & Curtis (University of Cambridge) O2 sounder for ALMA August 2010 16 / 26
Outputs Temperature profile of the atmosphere 20100817 10 336 Height (km) 8 6 4 2 318 300 282 264 246 228 210 Temperature (K) 0 18 19 20 21 22 23 24 GMT Time (hours) Nikolic & Curtis (University of Cambridge) O2 sounder for ALMA August 2010 16 / 26 192
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 2010 17 / 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 2010 18 / 26
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 2010 19 / 26
Role of temperature profiling in ALMA calibration Phase correction Atmospheric Phase Fluctuations Nikolic & Curtis (University of Cambridge) O2 sounder for ALMA August 2010 20 / 26
Role of temperature profiling in ALMA calibration Phase correction Atmospheric Phase Fluctuations Nikolic & Curtis (University of Cambridge) O2 sounder for ALMA August 2010 20 / 26
Role of temperature profiling in ALMA calibration Phase correction Atmospheric Phase Fluctuations Nikolic & Curtis (University of Cambridge) O2 sounder for ALMA August 2010 20 / 26
Role of temperature profiling in ALMA calibration Phase correction Atmospheric Phase Fluctuations Nikolic & Curtis (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 δl(µm) 0 250 500 750 6 6.2 6.4 6.6 6.8 7 7.2 t (hours UT) Nikolic & Curtis (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 & Curtis (University of Cambridge) O2 sounder for ALMA August 2010 22 / 26
Role of temperature profiling in ALMA calibration Phase correction with WVRs Phase correction 300 200 100 δl(µm) 0 100 200 300 300 Nikolic & Curtis (University of Cambridge) O2 sounder for ALMA August 2010 23 / 26
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 1 10 6 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 2010 24 / 26
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 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 50 100 200 500 1000 ν (GHz) Nikolic & Curtis (University of Cambridge) O2 sounder for ALMA August 2010 26 / 26
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 50 100 200 500 1000 Frequency(GHz) Nikolic & Curtis (University of Cambridge) O2 sounder for ALMA August 2010 26 / 26
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 50 100 200 500 1000 Frequency(GHz) Nikolic & Curtis (University of Cambridge) O2 sounder for ALMA August 2010 26 / 26