Scanning Strategies for Imaging Arrays Attila Kovcs MPI for - - PowerPoint PPT Presentation

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Scanning Strategies for Imaging Arrays Attila Kovcs MPI for - - PowerPoint PPT Presentation

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Scanning Strategies for Imaging Arrays Attila Kovcs MPI for Radioastronomy FOV Observing Strategies for Imaging Arrays SPIE 2008 -- Marseille Chopping Differential Signals Fast switching of detectors between source and blank sky. Analyze

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SLIDE 1

FOV

Scanning Strategies for Imaging Arrays

Attila Kovács MPI for Radioastronomy

Observing Strategies for Imaging Arrays SPIE 2008 -- Marseille

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SLIDE 2

Chopping

Differential Signals

Fast switching of detectors between source and blank sky. Analyze difference signals. E.g. 45” switching at 4 Hz for SHARC Problems Differencing Noise (2x observing time) Insensitivity to Certain Spatial Components Duty Cycle Striping (Imperfect Sky Removal)

Observing Strategies for Imaging Arrays SPIE 2008 -- Marseille

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SLIDE 3

Large Arrays

SHARC-2 LABOCA

Observing Strategies for Imaging Arrays SPIE 2008 -- Marseille

Poster on data reduction on Friday!

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SLIDE 4

Observing Mode Wish List

Noise Resistance (esp. 1/f) Large-Scale Sensitivity Coverage Dynamic Range Feasibility of Implementation

Observing Strategies for Imaging Arrays SPIE 2008 -- Marseille

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SLIDE 5

Noise Resistance

Spectral Noise Locations

+ +

f F

  • F

x y

f f F

y

F

x

Stationary noise (in time and in space) is characterized by its power spectrum of independent components. Projections of a spectral cube

Observing Strategies for Imaging Arrays SPIE 2008 -- Marseille

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SLIDE 6

+ +

f F

  • F

x y

f f F

y

F

x

f f F

y

F

x

Correlated Noise (atmosphere, T-fluctiation)

Noise Resistance

Spectral Noise Locations

Observing Strategies for Imaging Arrays SPIE 2008 -- Marseille

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SLIDE 7

+ +

f F

  • F

x y

f f F

y

F

x

f f F

y

F

x

Correlated Noise (atmosphere, T-fluctiation) 1/f Noise

Noise Resistance

Spectral Noise Locations

Observing Strategies for Imaging Arrays SPIE 2008 -- Marseille

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SLIDE 8

+ +

f F

  • F

x y

f f F

y

F

x

f f F

y

F

x

Correlated Noise (atmosphere, T-fluctiation) 1/f Noise Sky Noise

Noise Resistance

Spectral Noise Locations

Observing Strategies for Imaging Arrays SPIE 2008 -- Marseille

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SLIDE 9

+ +

f F

  • F

x y

f f F

y

F

x

f f F

y

F

x

Narrow-band Resonance (isotropic) Correlated Noise (atmosphere, T-fluctiation) 1/f Noise Sky Noise Wide-band Resonance (oriented)

Noise Resistance

Spectral Noise Locations

Observing Strategies for Imaging Arrays SPIE 2008 -- Marseille

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SLIDE 10

1/f Noise Spread signals into the higher frequencies...

Faster Scanning

Generic Noise Spread signals widely...

2-D Scanning Random Source Crossings

Noise Resistance

Strategies

Observing Strategies for Imaging Arrays SPIE 2008 -- Marseille

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SLIDE 11

Sensitivity to Large Scales

Fx Fy f f Spectral Tapering (convolution theorem) S(x) ⊗ P(x) S(f) x P(f) S: Source structure P: Point source spectrum

Observing Strategies for Imaging Arrays SPIE 2008 -- Marseille

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SLIDE 12

Sensitivity to Large Scales

L x l S A B

Scanning Wide

Observing Strategies for Imaging Arrays SPIE 2008 -- Marseille

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SLIDE 13

Dynamic Range

Ground-Based, High-Background Instrumentation DOCTOR'S WARNING! Avoid observing modes where changing of background can dwarf astronomical signals. Calibrator Blades Secondary Movement

Observing Strategies for Imaging Arrays SPIE 2008 -- Marseille

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SLIDE 14

Design Criteria

Observing Strategies for Imaging Arrays SPIE 2008 -- Marseille

(1) Faster is Better! (2) 2D Scanning. (3) Random Source Crossings in Time-streams. (non-repeating patterns...) (4) Wide Strokes matching the Largest Faint Structures. (5) Scanning with Primary (for ground-based submm). (6) Connected Patterns (settling time overheads). (7) No Sharp Turns (acceleration overload).

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SLIDE 15

What's Wrong with Staring?

Detector Noise Limited σdet > σbg Heavily Background Limited σdet << σbg

Dark Frame Calibration Time

<<

On-Source Time

4 x overhead!!!

Dark Frame Calibration Time

=

On-Source Time

small overhead

Ground-based sub-mm cameras Space-based and airborne sub-mm and far-infrared instrumentation

  • ptical/IR cameras

Observing Strategies for Imaging Arrays SPIE 2008 -- Marseille

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SLIDE 16

Simulations

Pattern Gallery

http://www.submm.caltech.edu/~sharc/scanning/

Observing Strategies for Imaging Arrays SPIE 2008 -- Marseille

DREAM OTF OTF (cross-linked) Lissajous Billiard (closed) Billiard (open) spiral raster-spiral random ... and other patterns... What is your favourite?

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SLIDE 17

Simulations

32 x 32 pixels http://www.submm.caltech.edu/~sharc/scanning/

Observing Strategies for Imaging Arrays SPIE 2008 -- Marseille

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SLIDE 18

Simulations

32 x 32 pixels 16 x 16 pixels Aim to cover same area 1 pixel/frame average scanning speed (1 position/frame)

Size “Speed”

Observing Strategies for Imaging Arrays SPIE 2008 -- Marseille

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SLIDE 19

Spectral Moments

m0: The fraction of phase space volume occupied by a point source observed with the pattern. m1: Resistance against canonical 1/f noise (electronics) m2: Resistance against 1/f2 noise (atmopshere + temperature fluctuations) m1,m2: Also large-scale sensitivity indicators...

Observing Strategies for Imaging Arrays SPIE 2008 -- Marseille

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SLIDE 20

Observing Strategies for Imaging Arrays SPIE 2008 -- Marseille

Random

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SLIDE 21

m0 = 1.000 m2 = 1.000 m1 = 1.000

Observing Strategies for Imaging Arrays SPIE 2008 -- Marseille

Random

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SLIDE 22

Observing Strategies for Imaging Arrays SPIE 2008 -- Marseille

DREAM

Dutch Real-Time Acquisition Mode

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SLIDE 23

m0 = 0.0018 m2 = 0.0019 m1 = 0.0018

Observing Strategies for Imaging Arrays SPIE 2008 -- Marseille

DREAM

Dutch Real-Time Acquisition Mode

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SLIDE 24

Observing Strategies for Imaging Arrays SPIE 2008 -- Marseille

Lissajous

Used for SHARC-2 FoV mapping since 2003. Edge-heavy coverage Irrational x and y frequencies lead to non-repeating,

  • pen patterns
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SLIDE 25

m0 = 0.129 m2 = 0.125 m1 = 0.126

Observing Strategies for Imaging Arrays SPIE 2008 -- Marseille

Lissajous

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SLIDE 26

Observing Strategies for Imaging Arrays SPIE 2008 -- Marseille

Billiard Scan

a.k.a. 'PONG' and 'box-scan'

Used for SHARC-2 large-field mapping since 2003 (Borys & Dowell). Irrational x and y frequencies lead to non-repeating,

  • pen patterns

Rational x and y frequencies lead to closed patterns

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SLIDE 27

m0 = 0.091 m2 = 0.058 m1 = 0.068

Observing Strategies for Imaging Arrays SPIE 2008 -- Marseille

Billiard Scan (closed)

a.k.a. 'PONG' and 'box-scan'

m0 = 0.097 m2 = 0.086 m1 = 0.089

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SLIDE 28

Observing Strategies for Imaging Arrays SPIE 2008 -- Marseille

On-The-Fly (OTF) Scanning

a.k.a. 'Serpentine' or 'Raster Scan'

Directional Sensitivity to Large Scales... Cross-linked at 90 deg for better large scale sensitivity in both directions

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SLIDE 29

m0 = 0.018 m2 = 0.018 m1 = 0.018

Observing Strategies for Imaging Arrays SPIE 2008 -- Marseille

On-The-Fly (OTF) Scanning

a.k.a. 'Serpentine' or 'Raster Scan'

m0 = 0.035 m2 = 0.035 m1 = 0.035

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SLIDE 30

Observing Strategies for Imaging Arrays SPIE 2008 -- Marseille

Archimedian Spirals

Used at the APEX telescope in Chile for LABOCA Mapping

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SLIDE 31

m0 = 0.061 m2 = 0.054 m1 = 0.056

Observing Strategies for Imaging Arrays SPIE 2008 -- Marseille

m0 = 0.080 m2 = 0.070 m1 = 0.073

Archimedian Spirals

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SLIDE 32

Observing Strategies for Imaging Arrays SPIE 2008 -- Marseille

Score Card

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SLIDE 33

Observing Strategies for Imaging Arrays SPIE 2008 -- Marseille

Score Card

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SLIDE 34

Observing Strategies for Imaging Arrays SPIE 2008 -- Marseille

Large Fields

What's the best strategies for fields > FoV?

All at once... Little by little...

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SLIDE 35

Observing Strategies for Imaging Arrays SPIE 2008 -- Marseille

Large Fields

What's the best strategies for fields > FoV?

All at once... Little by little...

The answer does not depend on field size. It depends entirely on the pattern chosen!!!

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SLIDE 36

Conclusions

  • I. Recipes for Designing Better Patterns
  • II. Rankings:

(1) Random (2) Lissajous, Billiard, Spirals (3) Cross-Linked OTF

  • III. Evaluate you own pattern at

http://www.submm.caltech.edu/~sharc/scanning

Observing Strategies for Imaging Arrays SPIE 2008 -- Marseille

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SLIDE 37

SMM J163631.47 +405546.9

Lissajous

SHARC-2

Observing Strategies for Imaging Arrays SPIE 2008 -- Marseille

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SLIDE 38

F . Motte

Protostars in Cygnus X

Observing Strategies for Imaging Arrays SPIE 2008 -- Marseille

Billiard

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SLIDE 39

F . Motte

Observing Strategies for Imaging Arrays SPIE 2008 -- Marseille

Protostars in Cygnus X

Billiard

FoV

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SLIDE 40

F . Motte

Observing Strategies for Imaging Arrays SPIE 2008 -- Marseille

Protostars in Cygnus X

Billiard

FoV

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SLIDE 41

Centaurus A NGC 253

Observing Strategies for Imaging Arrays SPIE 2008 -- Marseille

Raster of Spirals

LABOCA

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SLIDE 42

Raster of Spirals

Observing Strategies for Imaging Arrays SPIE 2008 -- Marseille

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SLIDE 43

Cross-Linked OTF

Observing Strategies for Imaging Arrays SPIE 2008 -- Marseille

Jy/beam

FOV

The Galactic Centre Region by LABOCA from the ATLASGAL survey