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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


  1. Scanning Strategies for Imaging Arrays Attila Kovács MPI for Radioastronomy FOV Observing Strategies for Imaging Arrays SPIE 2008 -- Marseille

  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

  3. Large Arrays LABOCA SHARC-2 Poster on data reduction on Friday! Observing Strategies for Imaging Arrays SPIE 2008 -- Marseille

  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

  5. Noise Resistance Spectral Noise Locations Stationary noise (in time and in space) is characterized by its power spectrum of independent components. f + F F x x f - - + F F f y y Projections of a spectral cube Observing Strategies for Imaging Arrays SPIE 2008 -- Marseille

  6. Noise Resistance Spectral Noise Locations f + F F x x f f - - + F F f y y Correlated Noise (atmosphere, T-fluctiation) F y F f x Observing Strategies for Imaging Arrays SPIE 2008 -- Marseille

  7. Noise Resistance Spectral Noise Locations f + F F x x f f - - + F F f y y Correlated Noise (atmosphere, T-fluctiation) 1/f Noise F y F f x Observing Strategies for Imaging Arrays SPIE 2008 -- Marseille

  8. Noise Resistance Spectral Noise Locations f + F F x x f f - - + F F f y y Correlated Noise (atmosphere, T-fluctiation) 1/f Noise F Sky Noise y F f x Observing Strategies for Imaging Arrays SPIE 2008 -- Marseille

  9. Noise Resistance Spectral Noise Locations f + F F x x f f - - + F F f y y Correlated Noise (atmosphere, T-fluctiation) 1/f Noise F Sky Noise y Narrow-band Resonance (isotropic) Wide-band Resonance F f x (oriented) Observing Strategies for Imaging Arrays SPIE 2008 -- Marseille

  10. Noise Resistance Strategies Spread signals into the higher frequencies... 1/f Noise Faster Scanning Spread signals widely... Generic Noise 2-D Scanning Random Source Crossings Observing Strategies for Imaging Arrays SPIE 2008 -- Marseille

  11. Sensitivity to Large Scales Spectral Tapering (convolution theorem) S(x) ⊗ P(x) S(f) x P(f) f S: Source structure P: Point source spectrum F y F x f Observing Strategies for Imaging Arrays SPIE 2008 -- Marseille

  12. Sensitivity to Large Scales B S A L x l Scanning Wide Observing Strategies for Imaging Arrays SPIE 2008 -- Marseille

  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

  14. Design Criteria (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). Observing Strategies for Imaging Arrays SPIE 2008 -- Marseille

  15. What's Wrong with Staring? Heavily Background Limited Detector Noise Limited σ det << σ bg σ det > σ bg Dark Frame Calibration Time Dark Frame Calibration Time << = On-Source Time On-Source Time small overhead 4 x overhead!!! Space-based and airborne sub-mm optical/IR cameras and far-infrared instrumentation Ground-based sub-mm cameras Observing Strategies for Imaging Arrays SPIE 2008 -- Marseille

  16. Simulations Pattern Gallery OTF random DREAM OTF Lissajous (cross-linked) Billiard (closed) Billiard (open) raster-spiral spiral ... and other patterns... What is your favourite? http://www.submm.caltech.edu/~sharc/scanning/ Observing Strategies for Imaging Arrays SPIE 2008 -- Marseille

  17. Simulations 32 x 32 pixels http://www.submm.caltech.edu/~sharc/scanning/ Observing Strategies for Imaging Arrays SPIE 2008 -- Marseille

  18. Simulations Size Aim to cover same area 32 x 32 16 x 16 pixels pixels “Speed” 1 pixel/frame average scanning speed (1 position/frame) Observing Strategies for Imaging Arrays SPIE 2008 -- Marseille

  19. Spectral Moments m 0 : The fraction of phase space volume occupied by a point source observed with the pattern. m 1 : Resistance against canonical 1/f noise (electronics) m 2 : Resistance against 1/f 2 noise (atmopshere + temperature fluctuations) m 1 ,m 2 : Also large-scale sensitivity indicators... Observing Strategies for Imaging Arrays SPIE 2008 -- Marseille

  20. Random Observing Strategies for Imaging Arrays SPIE 2008 -- Marseille

  21. Random m 0 = 1.000 m 1 = 1.000 m 2 = 1.000 Observing Strategies for Imaging Arrays SPIE 2008 -- Marseille

  22. DREAM Dutch Real-Time Acquisition Mode Observing Strategies for Imaging Arrays SPIE 2008 -- Marseille

  23. DREAM Dutch Real-Time Acquisition Mode m 0 = 0.0018 m 1 = 0.0018 m 2 = 0.0019 Observing Strategies for Imaging Arrays SPIE 2008 -- Marseille

  24. Lissajous Used for SHARC-2 FoV mapping since 2003. Irrational x and y Edge-heavy frequencies lead to coverage non-repeating, open patterns Observing Strategies for Imaging Arrays SPIE 2008 -- Marseille

  25. Lissajous m 0 = 0.129 m 1 = 0.126 m 2 = 0.125 Observing Strategies for Imaging Arrays SPIE 2008 -- Marseille

  26. Billiard Scan a.k.a. 'PONG' and 'box-scan' Used for SHARC-2 large-field mapping since 2003 (Borys & Dowell). Rational x and y Irrational x and y frequencies lead to frequencies lead to closed patterns non-repeating, open patterns Observing Strategies for Imaging Arrays SPIE 2008 -- Marseille

  27. Billiard Scan (closed) a.k.a. 'PONG' and 'box-scan' m 0 = 0.097 m 0 = 0.091 m 1 = 0.089 m 1 = 0.068 m 2 = 0.086 m 2 = 0.058 Observing Strategies for Imaging Arrays SPIE 2008 -- Marseille

  28. On-The-Fly (OTF) Scanning a.k.a. 'Serpentine' or 'Raster Scan' Cross-linked at 90 deg Directional Sensitivity for better large scale sensitivity to Large Scales... in both directions Observing Strategies for Imaging Arrays SPIE 2008 -- Marseille

  29. On-The-Fly (OTF) Scanning a.k.a. 'Serpentine' or 'Raster Scan' m 0 = 0.035 m 0 = 0.018 m 1 = 0.035 m 1 = 0.018 m 2 = 0.035 m 2 = 0.018 Observing Strategies for Imaging Arrays SPIE 2008 -- Marseille

  30. Archimedian Spirals Used at the APEX telescope in Chile for LABOCA Mapping Observing Strategies for Imaging Arrays SPIE 2008 -- Marseille

  31. Archimedian Spirals m 0 = 0.061 m 0 = 0.080 m 1 = 0.056 m 1 = 0.073 m 2 = 0.054 m 2 = 0.070 Observing Strategies for Imaging Arrays SPIE 2008 -- Marseille

  32. Score Card Observing Strategies for Imaging Arrays SPIE 2008 -- Marseille

  33. Score Card Observing Strategies for Imaging Arrays SPIE 2008 -- Marseille

  34. Large Fields What's the best strategies for fields > FoV? All at once... Little by little... Observing Strategies for Imaging Arrays SPIE 2008 -- Marseille

  35. 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!!! Observing Strategies for Imaging Arrays SPIE 2008 -- Marseille

  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

  37. Lissajous SHARC-2 SMM J163631.47 +405546.9 Observing Strategies for Imaging Arrays SPIE 2008 -- Marseille

  38. Billiard Protostars in Cygnus X F . Motte Observing Strategies for Imaging Arrays SPIE 2008 -- Marseille

  39. Billiard Protostars in Cygnus X FoV F . Motte Observing Strategies for Imaging Arrays SPIE 2008 -- Marseille

  40. Billiard Protostars in Cygnus X FoV F . Motte Observing Strategies for Imaging Arrays SPIE 2008 -- Marseille

  41. Raster of Spirals Centaurus A NGC 253 LABOCA Observing Strategies for Imaging Arrays SPIE 2008 -- Marseille

  42. Raster of Spirals Observing Strategies for Imaging Arrays SPIE 2008 -- Marseille

  43. Cross-Linked OTF The Galactic Centre Region by LABOCA from the ATLASGAL survey FOV Jy/beam Observing Strategies for Imaging Arrays SPIE 2008 -- Marseille

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