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Atmospheric Phase Correction for ALMA Phase correction & for - - PowerPoint PPT Presentation

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WVRGCAL B. Nikolic Atmospheric Phase Correction for ALMA Phase correction & for ALMA Introduction ALMA 183 GHz WVR The WVRGCAL program system The FP6 programme The WVRGCAL program B. Nikolic Results Good results Astrophysics

slide-1
SLIDE 1

WVRGCAL

  • B. Nikolic

Phase correction for ALMA

Introduction ALMA 183 GHz WVR system

The FP6 programme The WVRGCAL program Results

Good results Effect on the beam Poor results “Dry” fluctuations

Future work Summary

Atmospheric Phase Correction for ALMA & The WVRGCAL program

  • B. Nikolic

Astrophysics Group, Cavendish Laboratory, University of Cambridge http://www.mrao.cam.ac.uk/˜bn204/

ALMA Software Development Workshop NRAO/Charlottesville October 2011

slide-2
SLIDE 2

WVRGCAL

  • B. Nikolic

Phase correction for ALMA

Introduction ALMA 183 GHz WVR system

The FP6 programme The WVRGCAL program Results

Good results Effect on the beam Poor results “Dry” fluctuations

Future work Summary

Outline

Phase correction for ALMA Introduction ALMA 183 GHz WVR system The FP6 programme The WVRGCAL program Results Good results Effect on the beam Poor results “Dry” fluctuations Future work Summary

slide-3
SLIDE 3

WVRGCAL

  • B. Nikolic

Phase correction for ALMA

Introduction ALMA 183 GHz WVR system

The FP6 programme The WVRGCAL program Results

Good results Effect on the beam Poor results “Dry” fluctuations

Future work Summary

Outline

Phase correction for ALMA Introduction ALMA 183 GHz WVR system The FP6 programme The WVRGCAL program Results Good results Effect on the beam Poor results “Dry” fluctuations Future work Summary

slide-4
SLIDE 4

WVRGCAL

  • B. Nikolic

Phase correction for ALMA

Introduction ALMA 183 GHz WVR system

The FP6 programme The WVRGCAL program Results

Good results Effect on the beam Poor results “Dry” fluctuations

Future work Summary

ALMA

Recent (but already out of date) photo of ALMA with 16 antennas

slide-5
SLIDE 5

WVRGCAL

  • B. Nikolic

Phase correction for ALMA

Introduction ALMA 183 GHz WVR system

The FP6 programme The WVRGCAL program Results

Good results Effect on the beam Poor results “Dry” fluctuations

Future work Summary

ALMA as a high resolution imager

◮ ALMA is aiming to improve the routinely available

resolution at mm/sub-mm by 50× from ∼ 0.5 to ∼ 0.01 arcseconds

◮ Comparable to the improvement introduced by the

Hubble space telescope at optical wavelengths

Images of M13 from http://hubblesite.org courtesy of NASA, ESA, and the Hubble Heritage Team (STScI/AURA). Approximately scaled by eye... Do not use for science!

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SLIDE 6

WVRGCAL

  • B. Nikolic

Phase correction for ALMA

Introduction ALMA 183 GHz WVR system

The FP6 programme The WVRGCAL program Results

Good results Effect on the beam Poor results “Dry” fluctuations

Future work Summary

ALMA as a high resolution imager

◮ ALMA is aiming to improve the routinely available

resolution at mm/sub-mm by 50× from ∼ 0.5 to ∼ 0.01 arcseconds

◮ Comparable to the improvement introduced by the

Hubble space telescope at optical wavelengths To achieve this:

◮ ALMA will observe at λ ∼ 350 µm on baselines up to

15 km long

◮ Will need to correct for the effects of the troposphere

slide-7
SLIDE 7

WVRGCAL

  • B. Nikolic

Phase correction for ALMA

Introduction ALMA 183 GHz WVR system

The FP6 programme The WVRGCAL program Results

Good results Effect on the beam Poor results “Dry” fluctuations

Future work Summary

Atmospheric Phase Fluctuations

R(t) The turbulent troposphere Astronomical wavefront Corrupted astronomical wavefront

slide-8
SLIDE 8

WVRGCAL

  • B. Nikolic

Phase correction for ALMA

Introduction ALMA 183 GHz WVR system

The FP6 programme The WVRGCAL program Results

Good results Effect on the beam Poor results “Dry” fluctuations

Future work Summary

Atmospheric Phase Fluctuations

R(t) The turbulent troposphere Astronomical wavefront Corrupted astronomical wavefront

slide-9
SLIDE 9

WVRGCAL

  • B. Nikolic

Phase correction for ALMA

Introduction ALMA 183 GHz WVR system

The FP6 programme The WVRGCAL program Results

Good results Effect on the beam Poor results “Dry” fluctuations

Future work Summary

Atmospheric Phase Fluctuations

R(t) The turbulent troposphere Astronomical wavefront Corrupted astronomical wavefront

slide-10
SLIDE 10

WVRGCAL

  • B. Nikolic

Phase correction for ALMA

Introduction ALMA 183 GHz WVR system

The FP6 programme The WVRGCAL program Results

Good results Effect on the beam Poor results “Dry” fluctuations

Future work Summary

Path fluctuations due to the atmosphere

−750 −500 −250 250 500 750 δL(µm) δL(µm) 6 6.2 6.4 6.6 6.8 7 7.2 t (hours UT) t (hours UT) 0.009

Path fluctuation on a baseline of ∼ 500 m inferred from ALMA observations of a quasar at λ = 3.3 mm.

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SLIDE 11

WVRGCAL

  • B. Nikolic

Phase correction for ALMA

Introduction ALMA 183 GHz WVR system

The FP6 programme The WVRGCAL program Results

Good results Effect on the beam Poor results “Dry” fluctuations

Future work Summary

Outline

Phase correction for ALMA Introduction ALMA 183 GHz WVR system The FP6 programme The WVRGCAL program Results Good results Effect on the beam Poor results “Dry” fluctuations Future work Summary

slide-12
SLIDE 12

WVRGCAL

  • B. Nikolic

Phase correction for ALMA

Introduction ALMA 183 GHz WVR system

The FP6 programme The WVRGCAL program Results

Good results Effect on the beam Poor results “Dry” fluctuations

Future work Summary

Water Vapour cm/mm/sub-mm lines

1 mm precipitable water vapour

50 100 150 200 250 300 Tb (K) Tb (K) 200 400 600 800 1000 ν (GHz) ν (GHz)

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SLIDE 13

WVRGCAL

  • B. Nikolic

Phase correction for ALMA

Introduction ALMA 183 GHz WVR system

The FP6 programme The WVRGCAL program Results

Good results Effect on the beam Poor results “Dry” fluctuations

Future work Summary

Water Vapour cm/mm/sub-mm lines

1 mm precipitable water vapour

50 100 150 200 250 300 Tb (K) Tb (K) 200 400 600 800 1000 ν (GHz) ν (GHz)

22 GHz Water Line – previous WVR systems 183 GHz Water Line – ALMA WVR system

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SLIDE 14

WVRGCAL

  • B. Nikolic

Phase correction for ALMA

Introduction ALMA 183 GHz WVR system

The FP6 programme The WVRGCAL program Results

Good results Effect on the beam Poor results “Dry” fluctuations

Future work Summary

The 183 GHz Water Vapour Line

Blue rectangles are nominal WVR filters

50 100 150 200 250 Tb (K) Tb (K) 175 177.5 180 182.5 185 187.5 190 ν (GHz) ν (GHz)

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SLIDE 15

WVRGCAL

  • B. Nikolic

Phase correction for ALMA

Introduction ALMA 183 GHz WVR system

The FP6 programme The WVRGCAL program Results

Good results Effect on the beam Poor results “Dry” fluctuations

Future work Summary

WVR in the ALMA receiver cabin

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SLIDE 16

WVRGCAL

  • B. Nikolic

Phase correction for ALMA

Introduction ALMA 183 GHz WVR system

The FP6 programme The WVRGCAL program Results

Good results Effect on the beam Poor results “Dry” fluctuations

Future work Summary

Sky brightness observed by WVRs

50 100 150 200 250 TB (K) TB (K) 6 6.25 6.5 6.75 7 7.25 t (hours UT) t (hours UT) 50 100 150 200 250 TB (K) TB (K) 6 6.25 6.5 6.75 7 7.25 t (hours UT) t (hours UT) 50 100 150 200 250 TB (K) TB (K) 6 6.25 6.5 6.75 7 7.25 t (hours UT) t (hours UT)

Observed brightness temperatures of WVR

  • n the three antennas

involved in this test

  • bservation. The four

colours in each panel are the four channels

  • f the WVRs.
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SLIDE 17

WVRGCAL

  • B. Nikolic

Phase correction for ALMA

Introduction ALMA 183 GHz WVR system

The FP6 programme The WVRGCAL program Results

Good results Effect on the beam Poor results “Dry” fluctuations

Future work Summary

Correlation between WVRs and paths

−1 −0.5 0.5 1 ∆TB,1 (K) ∆TB,1 (K) −200 −100 100 200 300 δL(µm) δL(µm) 2 4 6 8 −1.5 −1 −0.5 0.5 1 1.5 ∆TB,2 (K) ∆TB,2 (K) −200 −100 100 200 300 δL(µm) δL(µm) 2 4 6 8 −1 −0.5 0.5 1 ∆TB,3 (K) ∆TB,3 (K) −200 −100 100 200 300 δL(µm) δL(µm) 2 4 6 8 −0.5 0.5 1 ∆TB,4 (K) ∆TB,4 (K) −200 −100 100 200 300 δL(µm) δL(µm) 2 4 6 8

slide-18
SLIDE 18

WVRGCAL

  • B. Nikolic

Phase correction for ALMA

Introduction ALMA 183 GHz WVR system

The FP6 programme The WVRGCAL program Results

Good results Effect on the beam Poor results “Dry” fluctuations

Future work Summary

Outline

Phase correction for ALMA Introduction ALMA 183 GHz WVR system The FP6 programme The WVRGCAL program Results Good results Effect on the beam Poor results “Dry” fluctuations Future work Summary

slide-19
SLIDE 19

WVRGCAL

  • B. Nikolic

Phase correction for ALMA

Introduction ALMA 183 GHz WVR system

The FP6 programme The WVRGCAL program Results

Good results Effect on the beam Poor results “Dry” fluctuations

Future work Summary

About the FP6 programme

◮ ‘European Union Framework 6 Programme for

Enhancement of ALMA Early Science’

◮ Aim to enhance ALMA over-and-above the already

planned/funded capabilities

◮ Funded entirely separately from ALMA ◮ Wide range of community groups (universities + ESO

+ IRAM)

◮ “No drag” on the project

◮ Proposal to the EC in March 2004, work packages

commenced Mid-2006

◮ Six Band-5 receivers, OTF interferometry software,

and (this talk) Advanced Radiometric Phase Correction Techniques

◮ Similarities to the ALMA Development programme

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SLIDE 20

WVRGCAL

  • B. Nikolic

Phase correction for ALMA

Introduction ALMA 183 GHz WVR system

The FP6 programme The WVRGCAL program Results

Good results Effect on the beam Poor results “Dry” fluctuations

Future work Summary

WP 5: Advanced Radiometric Phase Correction Techniques

◮ The project recognised that significant R&D would be

required for effective phase correction

◮ EC funding provided an opportunity to retain

involvement of groups with lots of expertise in phase correction

◮ Enhancement:

◮ Offline phase correction (vs on-line correction in the

baseline project)

◮ Advanced modelling of the atmosphere and inference

  • f phase correction coefficients

◮ Investigation of various physical effects (ALMA

Memos #573, 582, 590, 592)

◮ Documentation (!) (ALMA Memos #587, 588, 593)

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SLIDE 21

WVRGCAL

  • B. Nikolic

Phase correction for ALMA

Introduction ALMA 183 GHz WVR system

The FP6 programme The WVRGCAL program Results

Good results Effect on the beam Poor results “Dry” fluctuations

Future work Summary

Outline

Phase correction for ALMA Introduction ALMA 183 GHz WVR system The FP6 programme The WVRGCAL program Results Good results Effect on the beam Poor results “Dry” fluctuations Future work Summary

slide-22
SLIDE 22

WVRGCAL

  • B. Nikolic

Phase correction for ALMA

Introduction ALMA 183 GHz WVR system

The FP6 programme The WVRGCAL program Results

Good results Effect on the beam Poor results “Dry” fluctuations

Future work Summary

Offline radiometric phase correction

Advantages:

  • 1. Opportunity to inspect, flag, manipulate the data
  • 2. Can have several tries at correction (different

parameters/strategies)

  • 3. Opportunity to identify and correct any issues with

WVR data

  • 4. Can use information from forward as well as backward

in time

  • 5. Simplifies data taking & processing

Disadvantages:

  • 1. Need to record data at one second dump time (faster

than intrinsic limit at most frequency/baseline length combinations)

slide-23
SLIDE 23

WVRGCAL

  • B. Nikolic

Phase correction for ALMA

Introduction ALMA 183 GHz WVR system

The FP6 programme The WVRGCAL program Results

Good results Effect on the beam Poor results “Dry” fluctuations

Future work Summary

WVRGCAL: Inputs/Outputs

Inputs: All directly from the measurement set

  • 1. WVR data (recorded as if an auto-correlation)
  • 2. Pointing table
  • 3. SPWs, scan intents, field/source info
  • 4. (Ground meteorological, WVRs SPWs)

Outputs:

  • 1. CASA “T” Jones gain calibration table
  • 2. Diagnostic print out
  • 3. (Calculated Path information in HDF5 format)
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SLIDE 24

WVRGCAL

  • B. Nikolic

Phase correction for ALMA

Introduction ALMA 183 GHz WVR system

The FP6 programme The WVRGCAL program Results

Good results Effect on the beam Poor results “Dry” fluctuations

Future work Summary

Using WVRGCAL

◮ A separate, pure C++ executable ◮ Fully callable and scriptable from CASA

1 # Python /CASA 2 wvrgcal ( ” uid X02 X545f3 X1 .ms” , ” uid X02 X545f3 X1 .W” , 3 t o f f s e t =−1.0, s e g f i e l d =True )

  • r call the executable directly

1 # Python /CASA 2 ! wvrgcal uid X02 X545f3 X1 .ms uid X02 X545f3 X1 .W − −t o f f s e t \ 3 −1.0 − −s e g f i e l d

◮ Error status is returned ◮ Not a CASA task

Can not do inp(wvrgcal) and go

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SLIDE 25

WVRGCAL

  • B. Nikolic

Phase correction for ALMA

Introduction ALMA 183 GHz WVR system

The FP6 programme The WVRGCAL program Results

Good results Effect on the beam Poor results “Dry” fluctuations

Future work Summary

WVRGCAL diagnostic output I

Input WVR data information : − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − Timestamp Ant . # [ Chn 0 , Chn 1 , Chn 2 , Chn 3] Elevation STATE ID 4.82415e+09 [203.95 , 112.95 , 64.03 , 47.10] 0.879331 10 4.82415e+09 [185.27 , 97.06 , 54.25 , 39.98] 1.2491 2 4.82415e+09 [182.96 , 95.22 , 53.27 , 39.28] 1.32064 22 4.82415e+09 [201.12 , 110.41 , 62.78 , 46.28] 0.89608 2 4.82415e+09 [202.65 , 111.75 , 63.32 , 46.64] 0.948044 26 Calculating the c o e f f i c i e n t s now . . . done ! Retrieved parameters − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − Evidence PWV PWV Error dTdL dTdL dTdL dTdL 4.06901e−25 1.05784 0.0113119 8.00164 8.40131 5.14256 3.53637 4.37288e−23 1.03764 0.00938764 11.32 9.62416 5.4269 3.65468 1.38594e−23 1.03341 0.00833841 11.7391 9.76709 5.46462 3.67295 6.67496e−24 1.0291 0.00994679 8.4328 8.58773 5.23842 3.60326 4.39244e−24 1.09548 0.0111935 8.18877 8.4811 5.17959 3.56128

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SLIDE 26

WVRGCAL

  • B. Nikolic

Phase correction for ALMA

Introduction ALMA 183 GHz WVR system

The FP6 programme The WVRGCAL program Results

Good results Effect on the beam Poor results “Dry” fluctuations

Future work Summary

WVRGCAL diagnostic output II

Antenna /WVR information : − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − # Name WVR? Flag? RMS (um) Disc (um) DA41 Yes No 162 26.4 1 DA42 Yes No 199 30.7 2 DV02 Yes No 153 30.9 3 DV03 Yes No 171 22.9 4 DV05 Yes No 159 21.3 5 DV06 Yes No 180 24.6 6 DV08 Yes No 145 34.2 7 DV11 Yes No 192 25.1 8 DV12 Yes No 192 24 9 DV13 Yes No 171 24.4 10 DV14 Yes No 158 20.1 11 PM01 Yes No 184 27.3 12 PM02 Yes No 173 23.1 13 PM03 Yes No 172 25.7 14 PM04 Yes No 149 24.2 Expected performance − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − ∗ Estimated WVR thermal c o n t r i b u t i o n to path f l u c t u a t i o n s ( micron per antenna ) : 5.34387 ∗ Greatest Estimated path f l u c t u a t i o n i s ( micron on a baseline ) : 168.165 ∗ Rough estimate path error due to c o e f f i c i e n t error ( micron on a baseline ) : 1.13354

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SLIDE 27

WVRGCAL

  • B. Nikolic

Phase correction for ALMA

Introduction ALMA 183 GHz WVR system

The FP6 programme The WVRGCAL program Results

Good results Effect on the beam Poor results “Dry” fluctuations

Future work Summary

Software architecture

CASA dependent code Better I/O Core algorithms LibAir package GSL Boost CASA HDF5 BNMin1: inference /

  • ptimisation

LibAIR Core LibAIR I/O for CASA LibAIR I/O for HDF5 SWIG LibAIR Python bindings wvrgcal: main user- facing application msdump: Extract data from MS to HDF5

◮ High level of modularity, computation/data

input-output/user interfaces separated

◮ Uses CASA as a C++ library (the way it was intended)

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SLIDE 28

WVRGCAL

  • B. Nikolic

Phase correction for ALMA

Introduction ALMA 183 GHz WVR system

The FP6 programme The WVRGCAL program Results

Good results Effect on the beam Poor results “Dry” fluctuations

Future work Summary

WVRGCAL summary

◮ Takes a measurement set and produces calibration

table

◮ User can view, apply, modify the calibration table

using standard CASA tools (applycal, accum, calsmooth, calplot)

◮ Choose to apply the correction in combination with

  • ther calibrations, self-cal, etc
slide-29
SLIDE 29

WVRGCAL

  • B. Nikolic

Phase correction for ALMA

Introduction ALMA 183 GHz WVR system

The FP6 programme The WVRGCAL program Results

Good results Effect on the beam Poor results “Dry” fluctuations

Future work Summary

Outline

Phase correction for ALMA Introduction ALMA 183 GHz WVR system The FP6 programme The WVRGCAL program Results Good results Effect on the beam Poor results “Dry” fluctuations Future work Summary

slide-30
SLIDE 30

WVRGCAL

  • B. Nikolic

Phase correction for ALMA

Introduction ALMA 183 GHz WVR system

The FP6 programme The WVRGCAL program Results

Good results Effect on the beam Poor results “Dry” fluctuations

Future work Summary

First application – February 2010

Courtesy of Al Wooten

02:41:16.8 02:52:48.0 03:04:19.2 03:15:50.4 03:27:21.6 Time 50 100 150 Phase of Corrected Data (deg)

This was an observation switching between two quasars. Blue: uncorrected phase; red: corrected phase

slide-31
SLIDE 31

WVRGCAL

  • B. Nikolic

Phase correction for ALMA

Introduction ALMA 183 GHz WVR system

The FP6 programme The WVRGCAL program Results

Good results Effect on the beam Poor results “Dry” fluctuations

Future work Summary

Outline

Phase correction for ALMA Introduction ALMA 183 GHz WVR system The FP6 programme The WVRGCAL program Results Good results Effect on the beam Poor results “Dry” fluctuations Future work Summary

slide-32
SLIDE 32

WVRGCAL

  • B. Nikolic

Phase correction for ALMA

Introduction ALMA 183 GHz WVR system

The FP6 programme The WVRGCAL program Results

Good results Effect on the beam Poor results “Dry” fluctuations

Future work Summary

Data-set A002 Xb9f5d X1: Long baseline

Red: uncorrected phase; Blue: corrected phase

−500 −400 −300 −200 −100 100 Degrees Degrees 500 1000 1500 2000 Time (s) Time (s)

slide-33
SLIDE 33

WVRGCAL

  • B. Nikolic

Phase correction for ALMA

Introduction ALMA 183 GHz WVR system

The FP6 programme The WVRGCAL program Results

Good results Effect on the beam Poor results “Dry” fluctuations

Future work Summary

Data-set A002 Xa0705 X1

Another example, only short baselines

−60 −40 −20 20 Degrees Degrees 250 500 750 1000 1250 1500 Time (s) Time (s)

slide-34
SLIDE 34

WVRGCAL

  • B. Nikolic

Phase correction for ALMA

Introduction ALMA 183 GHz WVR system

The FP6 programme The WVRGCAL program Results

Good results Effect on the beam Poor results “Dry” fluctuations

Future work Summary

March dataset X1849a5 X191

Very wet weather, ∼ 600 m baseline

slide-35
SLIDE 35

WVRGCAL

  • B. Nikolic

Phase correction for ALMA

Introduction ALMA 183 GHz WVR system

The FP6 programme The WVRGCAL program Results

Good results Effect on the beam Poor results “Dry” fluctuations

Future work Summary

Best result – minimum phase errors

This is for short baselines and very rare! (A002 X219601 X5c7)

◮ Uncorrected phase ∼ 14 micron (< 3 min timescale) ◮ WVR-corrected phase ∼ 7 micron ◮ → This is almost good enough for mid-infrared

interferometry!

−20 −10 10 20 Degrees Degrees 200 400 600 800 1000 Time (s) Time (s)

slide-36
SLIDE 36

WVRGCAL

  • B. Nikolic

Phase correction for ALMA

Introduction ALMA 183 GHz WVR system

The FP6 programme The WVRGCAL program Results

Good results Effect on the beam Poor results “Dry” fluctuations

Future work Summary

Outline

Phase correction for ALMA Introduction ALMA 183 GHz WVR system The FP6 programme The WVRGCAL program Results Good results Effect on the beam Poor results “Dry” fluctuations Future work Summary

slide-37
SLIDE 37

WVRGCAL

  • B. Nikolic

Phase correction for ALMA

Introduction ALMA 183 GHz WVR system

The FP6 programme The WVRGCAL program Results

Good results Effect on the beam Poor results “Dry” fluctuations

Future work Summary

Inner ALMA pad positions

From http: //www.alma.cl/˜dbarkats/pad_position_plotter/plots/ALMA_pad_viewer_zoom2.html

slide-38
SLIDE 38

WVRGCAL

  • B. Nikolic

Phase correction for ALMA

Introduction ALMA 183 GHz WVR system

The FP6 programme The WVRGCAL program Results

Good results Effect on the beam Poor results “Dry” fluctuations

Future work Summary

The effect of WVR correction on the ALMA synthesised beam

No phase correction WVR phase correction

Short observation with very inhomogeneous uv distribution –

  • ne antenna was on a long north baseline and others were

close together in a cluster

slide-39
SLIDE 39

WVRGCAL

  • B. Nikolic

Phase correction for ALMA

Introduction ALMA 183 GHz WVR system

The FP6 programme The WVRGCAL program Results

Good results Effect on the beam Poor results “Dry” fluctuations

Future work Summary

Outline

Phase correction for ALMA Introduction ALMA 183 GHz WVR system The FP6 programme The WVRGCAL program Results Good results Effect on the beam Poor results “Dry” fluctuations Future work Summary

slide-40
SLIDE 40

WVRGCAL

  • B. Nikolic

Phase correction for ALMA

Introduction ALMA 183 GHz WVR system

The FP6 programme The WVRGCAL program Results

Good results Effect on the beam Poor results “Dry” fluctuations

Future work Summary

Data-set A002 Xba2ed X1

Short baselines, leak-through phase fluctuations (offset in coefficients due to time-constant cloud?)

−20 −15 −10 −5 5 10 Degrees Degrees 500 1000 1500 2000 Time (s) Time (s)

Very short baseline (A0-A1), essentially no phase fluctuations to correct

slide-41
SLIDE 41

WVRGCAL

  • B. Nikolic

Phase correction for ALMA

Introduction ALMA 183 GHz WVR system

The FP6 programme The WVRGCAL program Results

Good results Effect on the beam Poor results “Dry” fluctuations

Future work Summary

Data-set A002 Xba2ed X1

Short baselines, leak-through phase fluctuations (offset in coefficients due to time-constant cloud?)

−30 −20 −10 10 Degrees Degrees 500 1000 1500 2000 Time (s) Time (s)

Also a very short baseline (A0-A2), some atmospheric-like phase fluctuation seen and corrected

slide-42
SLIDE 42

WVRGCAL

  • B. Nikolic

Phase correction for ALMA

Introduction ALMA 183 GHz WVR system

The FP6 programme The WVRGCAL program Results

Good results Effect on the beam Poor results “Dry” fluctuations

Future work Summary

Data-set A002 Xba2ed X1

Short baselines, leak-through phase fluctuations (offset in coefficients due to time-constant cloud?)

−80 −60 −40 −20 20 40 Degrees Degrees 500 1000 1500 2000 Time (s) Time (s)

Slightly longer baseline (A0-A3): atmospheric phase fluctuations clearly seen, corrected somewhat but clear “leak-through”

slide-43
SLIDE 43

WVRGCAL

  • B. Nikolic

Phase correction for ALMA

Introduction ALMA 183 GHz WVR system

The FP6 programme The WVRGCAL program Results

Good results Effect on the beam Poor results “Dry” fluctuations

Future work Summary

Outline

Phase correction for ALMA Introduction ALMA 183 GHz WVR system The FP6 programme The WVRGCAL program Results Good results Effect on the beam Poor results “Dry” fluctuations Future work Summary

slide-44
SLIDE 44

WVRGCAL

  • B. Nikolic

Phase correction for ALMA

Introduction ALMA 183 GHz WVR system

The FP6 programme The WVRGCAL program Results

Good results Effect on the beam Poor results “Dry” fluctuations

Future work Summary

Evidence for ‘dry’ fluctuations

Baseline length ∼ 100 m

8.0 8.2 8.4 8.6 8.8 9.0 9.2

0.10 0.05

0.00 0.05 0.10

slide-45
SLIDE 45

WVRGCAL

  • B. Nikolic

Phase correction for ALMA

Introduction ALMA 183 GHz WVR system

The FP6 programme The WVRGCAL program Results

Good results Effect on the beam Poor results “Dry” fluctuations

Future work Summary

Outline

Phase correction for ALMA Introduction ALMA 183 GHz WVR system The FP6 programme The WVRGCAL program Results Good results Effect on the beam Poor results “Dry” fluctuations Future work Summary

slide-46
SLIDE 46

WVRGCAL

  • B. Nikolic

Phase correction for ALMA

Introduction ALMA 183 GHz WVR system

The FP6 programme The WVRGCAL program Results

Good results Effect on the beam Poor results “Dry” fluctuations

Future work Summary

Remaining work

  • 1. Long baselines? (Hardest part still left to do!)
  • 2. + High frequencies (dispersion? phase wraps?)
  • 3. Local geography? (Altitude differences, ridges,

moisture accumulation)

  • 4. Quality assurance? (Lots of data, all to be reduced by

ALMA staff!) Cycle 0 and further...

  • 5. Project scheduling? (Will this observation work in this

weather?)

  • 6. Interpolation for the ACA?

But will require some new source of funding!

slide-47
SLIDE 47

WVRGCAL

  • B. Nikolic

Phase correction for ALMA

Introduction ALMA 183 GHz WVR system

The FP6 programme The WVRGCAL program Results

Good results Effect on the beam Poor results “Dry” fluctuations

Future work Summary

Outline

Phase correction for ALMA Introduction ALMA 183 GHz WVR system The FP6 programme The WVRGCAL program Results Good results Effect on the beam Poor results “Dry” fluctuations Future work Summary

slide-48
SLIDE 48

WVRGCAL

  • B. Nikolic

Phase correction for ALMA

Introduction ALMA 183 GHz WVR system

The FP6 programme The WVRGCAL program Results

Good results Effect on the beam Poor results “Dry” fluctuations

Future work Summary

Summary

  • 1. WVR phase correction for ALMA is working
  • 2. WVRGCAL reduces phase errors in all

measurements, often by a large factor

  • 3. WVRs are in continuous use, WVRGCAL is currently

used for all Science Verification and Early Science projects

  • 4. Writing C++ programs using CASA is quite possible,

not a “drag” on either the project or the developer

  • 5. Delivery from a software development project!
  • 6. External groups can work successfully and

productively with the ALMA project

slide-49
SLIDE 49

WVRGCAL

  • B. Nikolic

Phase correction for ALMA

Introduction ALMA 183 GHz WVR system

The FP6 programme The WVRGCAL program Results

Good results Effect on the beam Poor results “Dry” fluctuations

Future work Summary

Some lessons

  • 1. Our group was involved in the entire lifecycle of the

WVR system for ALMA:

◮ Initial research of the technique (JCMT-CSO

interferometer)

◮ Prototyping of hardware ◮ Review of production hardware ◮ Commissioning and testing ◮ Software development

It is intellectually satisfying and very efficient to be able to do this...

  • 2. Knowledge of C++ was essential for this work (CASA

Python bindings are minimal)

  • 3. Don’t start the software too early!
  • 4. Open mailing list, open source publicly available

source code: not overwhelmed!

slide-50
SLIDE 50

WVRGCAL

  • B. Nikolic

Phase correction for ALMA

Introduction ALMA 183 GHz WVR system

The FP6 programme The WVRGCAL program Results

Good results Effect on the beam Poor results “Dry” fluctuations

Future work Summary

What could we have differently?

  • 1. One programmer project –

Maintenance? Support? Bug fixes? Better to involve ALMA staff early on (but would be against the boundary condition!)

  • 2. A lot of emphasis on sophisticated computation

In fact in the beginning basic computation + thorough data checking and diagnostics were most important