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Introduction/Overview Detailed radiometer modelling System Simulations

Advanced WVR Algorithms (AWA): Recent Progress
B. Nikolic1 , J. S. Richer1 , R. E. Hills2
1

MRAO, Cavendish Lab., University of Cambridge 2 Joint ALMA Office, Santiago, Chile

ESO/Garching, 26 February 2008

B. Nikolic, J. S. Richer, R. E. Hills


Introduction/Overview Detailed radiometer modelling System Simulations

Outline

1

Introduction/Over view

2

Detailed radiometer modelling

3

System Simulations

B. Nikolic, J. S. Richer, R. E. Hills


Introduction/Overview Detailed radiometer modelling System Simulations

Outline

1

Introduction/Over view

2

Detailed radiometer modelling

3

System Simulations

B. Nikolic, J. S. Richer, R. E. Hills


Introduction/Overview Detailed radiometer modelling System Simulations

Introduction/Scope
Last meeting with TelCAL in June 07 ­ will briefly cover work since then The major focus has been a twin-track approach simulation:
Detailed simulation of radiometers (or pairs of radiometers) to analyse their performance Simulations of ALMA as a system to connect:
atmospheric conditions observing strategies and WVR performance

to metrics relevant for science obser vations.

Minor work items: WVR CDR, ar ticle for Messenger, etc.

B. Nikolic, J. S. Richer, R. E. Hills


Introduction/Overview Detailed radiometer modelling System Simulations

Twin track simulation approach (I)
Detailed radiometer modelling

Radiometer modelling Thermal noise, stability Calibration uncer tainty Unknown atmospheric parameters Retrieval algorithm Atmospheric conditions

Results Residual phase fluctuation on baselines Phase transfer accuracy (i.e., correction of path change when slewing over significant distance on sky)

Use this to Design/investigate retrieval algorithm Initial optimisation of these algorithms
B. Nikolic, J. S. Richer, R. E. Hills


Introduction/Overview Detailed radiometer modelling System Simulations

Twin track simulation approach (II)
System simulation

System simulation Results of radiometer modelling Atmospheric conditions Array configuration Phase calibration scheme (FS time cycle, distance to calibrator)

Results Point source sensitivity Resolution/image fidelity Astrometry and absolute flux calibration (especially for snapshots)

Use this to Optimise phase correction/calibration techniques Understand impact on science Constraints on scheduling
B. Nikolic, J. S. Richer, R. E. Hills


Introduction/Overview Detailed radiometer modelling System Simulations

Outline

1

Introduction/Over view

2

Detailed radiometer modelling

3

System Simulations

B. Nikolic, J. S. Richer, R. E. Hills


Introduction/Overview Detailed radiometer modelling System Simulations

Scope

Here I will show results published in ALMA memo 573, on the effect of beam mismatch between the radiometer and astronomical beams.

B. Nikolic, J. S. Richer, R. E. Hills


Introduction/Overview Detailed radiometer modelling System Simulations

Effect of beam mis-match
Astronomical beam WVR Beam

Turbulent layer w = 500 m

h = 750 m z -direction

Offset between astronomical beams and the radiometer beam for ALMA is between 4` (highest frequencies) and 9` (lowest frequencies).

B. Nikolic, J. S. Richer, R. E. Hills


Introduction/Overview Detailed radiometer modelling System Simulations

Beam shapes
Voltage response of astronomical beam Vs power response of radiometer beam
0 -10 0 -10 0 -10 0 -10 0 -10 0 -10 0 -10 0 -10 -20 -30 -30 -20 -10 0 r (m) 10 20 30 0 -10 0 -10 0 -10 0 -10 0 -10 0 -10 0 -10 0 -10 -20 -30 -30 -20 -10 0 r (m) 10 20 30

10 log(Amp)

B. Nikolic, J. S. Richer, R. E. Hills

10 log(Pwr)


Introduction/Overview Detailed radiometer modelling System Simulations

Statistical realisations of 3D turbulent screens
Illustration of sub-sections of 1 m, 10 m and 100 m thick screens

0 0 20 40 60 80 100 120

200

400

600

800

1000

0 0 20 40 60 80 100 120

200

400

600

800

1000

0 0 20 40 60 80 100 120

200

400

600

800

1000

B. Nikolic, J. S. Richer, R. E. Hills


Introduction/Overview Detailed radiometer modelling System Simulations

Beam mismatch simulations
Generate simulated time series of radiometer measurements using the power response pattern
y -direction b = 128 m

Compute phase fluctuation using the complex voltage response pattern of the antenna Find accuracy as function of beam offset, atmospheric proper ties, baseline length

x-direction Wind direction

B. Nikolic, J. S. Richer, R. E. Hills


Introduction/Overview Detailed radiometer modelling System Simulations

Error due to beam mismatch
Turbulent layer at 250 m
0.2 0.2 0.1 0.1

Turbulent layer at 750 m



0.02

0 5 10 15 (arcmin) 20 25 30

0.05

0.05

0.02

0.01

0.01

0

5

10

15 (arcmin)

20

25

30

Fractional error due to the mismatch between the astronomical and water vapour radiometer beams. For each layer height, the error for four layer thickness have been calculated: thin-screen (solid line), 10 m thick layer (dashed line), 100 m thick layer (dotted line) and 500 m thick layer (dash-dot-dash line).
B. Nikolic, J. S. Richer, R. E. Hills


Introduction/Overview Detailed radiometer modelling System Simulations

Outline

1

Introduction/Over view

2

Detailed radiometer modelling

3

System Simulations

B. Nikolic, J. S. Richer, R. E. Hills


Introduction/Overview Detailed radiometer modelling System Simulations

Simulation framework

1 2

Use casa to generate uv tracks and data Simulate effects of the atmosphere:
Kolmogorov three-dimensional phase screens

3

Produces corrupted uv data A separate calibration stage
Fast switching calibration WVR phase correction (in the future)

Produces corrupted+calibrated uv data.
4

Finally use casa or Obit for imaging

B. Nikolic, J. S. Richer, R. E. Hills


Introduction/Overview Detailed radiometer modelling System Simulations

Configurations

50

500

5000

y (m)

y (m)

0

0

y (m)

0

-50

-500

-5000

-1000

-50

0 x (m)

50

-1000

-500

0 x (m)

500

-5000

0 x (m)

5000

B. Nikolic, J. S. Richer, R. E. Hills


Introduction/Overview Detailed radiometer modelling System Simulations

Statistical realisations of 3D turbulent screens
Illustration of sub-sections of 1 m, 10 m and 100 m thick screens

0 0 20 40 60 80 100 120

200

400

600

800

1000

0 0 20 40 60 80 100 120

200

400

600

800

1000

0 0 20 40 60 80 100 120

200

400

600

800

1000

B. Nikolic, J. S. Richer, R. E. Hills


Introduction/Overview Detailed radiometer modelling System Simulations

Corrupted UV phases

50

40

1

antenna #

30 (rad) 20 -1 10 0 0 20 40 60 80 time (integration #) 100 120 140 0 1 0

B. Nikolic, J. S. Richer, R. E. Hills


Introduction/Overview Detailed radiometer modelling System Simulations

Simple results: no calibration, long integration
Peak: 2 Jy Peak: 1.66 Jy

B. Nikolic, J. S. Richer, R. E. Hills


Introduction/Overview Detailed radiometer modelling System Simulations

Simple results: no calibration, long integration
Peak: 0.98 Jy Peak: 0.45 Jy

B. Nikolic, J. S. Richer, R. E. Hills


Introduction/Overview Detailed radiometer modelling System Simulations

Simple results: no calibration, snapshot
Sequence of snapshots separated by about 3 minutes in time

B. Nikolic, J. S. Richer, R. E. Hills


Introduction/Overview Detailed radiometer modelling System Simulations

Simple results: no calibration, snapshot
Sequence of snapshots separated by about 3 minutes in time

B. Nikolic, J. S. Richer, R. E. Hills


Introduction/Overview Detailed radiometer modelling System Simulations

Simple results: no calibration, snapshot
Sequence of snapshots separated by about 3 minutes in time

B. Nikolic, J. S. Richer, R. E. Hills


Introduction/Overview Detailed radiometer modelling System Simulations

Simple results: no calibration, snapshot
Sequence of snapshots separated by about 3 minutes in time

B. Nikolic, J. S. Richer, R. E. Hills


Introduction/Overview Detailed radiometer modelling System Simulations

Simple results: no calibration, snapshot
Sequence of snapshots separated by about 3 minutes in time

B. Nikolic, J. S. Richer, R. E. Hills


Introduction/Overview Detailed radiometer modelling System Simulations

Simple results: no calibration, snapshot
Sequence of snapshots separated by about 3 minutes in time

B. Nikolic, J. S. Richer, R. E. Hills


Introduction/Overview Detailed radiometer modelling System Simulations

Uncalibrated: point source sensitivity
Compact configuration
1

0.5

S 0.2 0.1 0.05

0.1

0.2

0.5 rms (rad)

1

2

5

Point source sensitivity (relative to no atmospheric phase fluctuations) as function of phase rms on a 300 m baseline, for four thicknesses of the turbulent layer and no phase correction.
B. Nikolic, J. S. Richer, R. E. Hills


Introduction/Overview Detailed radiometer modelling System Simulations

Uncalibrated: point source sensitivity
Medium configuration
1

0.5

S 0.2 0.1 0.05

0.1

0.2

0.5 rms (rad)

1

2

5

Point source sensitivity (relative to no atmospheric phase fluctuations) as function of phase rms on a 300 m baseline, for four thicknesses of the turbulent layer and no phase correction.
B. Nikolic, J. S. Richer, R. E. Hills


Introduction/Overview Detailed radiometer modelling System Simulations

Uncalibrated: point source sensitivity
Extended configuration
1

0.5

S 0.2 0.1 0.01

0.02

0.05

0.1

0.2 rms (rad)

0.5

1

2

5

Point source sensitivity (relative to no atmospheric phase fluctuations) as function of phase rms on a 300 m baseline, for four thicknesses of the turbulent layer and no phase correction.
B. Nikolic, J. S. Richer, R. E. Hills


Introduction/Overview Detailed radiometer modelling System Simulations

Snapshot observation sensitivity variance
Compact configuration
1

S

2

-S /S

0.1

2

0.01

0.001 0.01

0.02

0.05

0.1

0.2 rms (rad)

0.5

1

2

5

Standard deviation of relative point source sensitivity as function of phase rms on a 300 m baseline, for four thicknesses of the turbulent layer and no phase correction.
B. Nikolic, J. S. Richer, R. E. Hills


Introduction/Overview Detailed radiometer modelling System Simulations

Snapshot observation sensitivity variance
Medium configuration
1

S

2

-S /S

0.1

2

0.01

0.001 0.01

0.02

0.05

0.1

0.2 rms (rad)

0.5

1

2

5

Standard deviation of relative point source sensitivity as function of phase rms on a 300 m baseline, for four thicknesses of the turbulent layer and no phase correction.
B. Nikolic, J. S. Richer, R. E. Hills


Introduction/Overview Detailed radiometer modelling System Simulations

Snapshot observation sensitivity variance
Extended configuration
1

S

2

-S /S

0.1

2

0.01

0.001 0.01

0.02

0.05

0.1

0.2 rms (rad)

0.5

1

2

5

Standard deviation of relative point source sensitivity as function of phase rms on a 300 m baseline, for four thicknesses of the turbulent layer and no phase correction.
B. Nikolic, J. S. Richer, R. E. Hills


Introduction/Overview Detailed radiometer modelling System Simulations

Fast switching phase calibration
50 40 1

antenna #

30 (rad) 20 -1 10 0 0 50 1 40 0.5 20 40 60 80 time (integration #) 100 120 140 0 1 30 (rad) 20 -0.5 10 -1 0 0 20 40 60 80 time (integration #) 100 120 140 0 1 0 0

antenna #

B. Nikolic, J. S. Richer, R. E. Hills


Introduction/Overview Detailed radiometer modelling System Simulations

Fast switching phase calibration (compact conf.)
50 1.5 1 40 0.5 antenna # 30 (rad) 20 10 -1.5 0 0 50 20 40 60 80 time (integration #) 1 100 120 140 0 1 40 30 (rad) 20 -0.5 10 -1 0 0 20 40 60 80 time (integration #) 100 120 140 0 1 0 0 -0.5 -1

0.5

antenna #

B. Nikolic, J. S. Richer, R. E. Hills


Introduction/Overview Detailed radiometer modelling System Simulations

Fast-switching calibration: point source sensitivity
Compact configuration
1

0.5

S 0.2 0.1 0.1

0.2

0.5

1 rms (rad)

2

5

10

Relative point source sensitivity, perfect fast-switching calibration with a 15 s duty cycle, 1.5 degree offset to calibrator, calibration transfer from lower frequency band.
B. Nikolic, J. S. Richer, R. E. Hills


Introduction/Overview Detailed radiometer modelling System Simulations

Fast-switching calibration: point source sensitivity
Medium configuration
1

0.5

S 0.2 0.1 0.1

0.2

0.5

1 rms (rad)

2

5

10

Relative point source sensitivity, perfect fast-switching calibration with a 15 s duty cycle, 1.5 degree offset to calibrator, calibration transfer from lower frequency band.
B. Nikolic, J. S. Richer, R. E. Hills


Introduction/Overview Detailed radiometer modelling System Simulations

Fast-switching calibration: point source sensitivity
Extended configuration
1

0.5

S 0.2 0.1 0.1

0.2

0.5

1 rms (rad)

2

5

10

Relative point source sensitivity, perfect fast-switching calibration with a 15 s duty cycle, 1.5 degree offset to calibrator, calibration transfer from lower frequency band.
B. Nikolic, J. S. Richer, R. E. Hills