CRUSH IMAGES OPTIONS. @350 um Atmospheric Background is 10 7 times brighter than faint galaxies....
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Transcript of CRUSH IMAGES OPTIONS. @350 um Atmospheric Background is 10 7 times brighter than faint galaxies....
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CRUSH
IMAGES
OPTIONS
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@350 um Atmospheric Background is 107 times brighter than faint galaxies.Analogous to Observing a ~16 Magnitude star at daytime!
The Submillimeter Challenge
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Turnover to white noise regime at ~ 10 Hz
The Atmospheric Power Spectrum (5 January 2003)
Strong 1/f characteristic
Need Fast Sampling of Background(SHARC-2 has samples every 36ms)
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Differencing of Signals
100 Jy source
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Lissajous Sweep
Chopped Image has Limiting noise typically 2-3 times higher than 'state of the art' reduction.Not including deconvolution noise!!!
Simulated 4 Hz chopper with 40” throw under better than average conditions
Vesta ~5 Jy(2 min)
Blank Sky(10 min)
Chopped
Residual Sky Noise
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The Need for Speed (Sweeping)
Moving Several pixels onto the same sky position within the limiting instrumental time scale 'calibrates' pixels against one another.
The more pixels that can be thus related, the more robust the 'calibration' measurement.
'Calibrated' pixels can observe several positions on the sky within the limiting time scale, leading to high fidelity maps.
Faster Better pixel-to-pixel calibration
Larger and higher fidelity maps
Smarter and Better Crossing Sweep Patterns
Non-periodic source crossing
Move Primary to avoid changing illumination pattern
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Scanning Strategies without a Chopping Secondary
For compact and point sourcesMaximizes time coverage over a small area.
For large map making. Obtains uniform coverage over an area much larger than the array
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From Chopped Data to Discreet Modeling
Singular Value Decomposition
Difficulties with SVD
Computationally costly. (Large Matrices to invert)
Non-linearities. (Gain fitting).
Degeneracies, Singularities and Constraints
Time dependent noise
Mathematically Rigorous Maximum Entropy Solution.
Parallel SVD Effort at Goddard Space Flight Centre
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Model 1
Final SourceModel
Model N
Model 2
Iterative Reduction
Series of Maximum Likelihood Estimators.
Brightest First
Convergence via Iterating
Model 3
Advantages
Intuitive
Fast. (Linear with Data Size)
Able to Deal with Non-Linearities
Easily Configurable / Changeable
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Instrument Specific Models
=
Static Residual Pixel Offsets~ 2000 Jy
Static Residual Pixel Offsets~ 2000 Jy
Acceleration Response~ 0.2 Jy
Detector 1/f Drift Model~ 1 Jy
Electronic RowDrifts ~ 1 Jy
Source Model~ 5 Jy
Vesta 82935 January 2003Excellent Conditions
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The Format of the SHARC-2 Array
32 x 12 pixels. Nearly Nyquist Sampled.
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Maximum Likelihood Estimators
Alternatively, in terms of the Residuals:
As if residuals only contained given model...
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CRUSH Models with Maximum Likelihood Estimators
Model Name
Residual Pixel Offsets
Correlated Background Noise
Gain Modelling
Pixel Weights
Chopping Residuals.
Temperature Gradients.
Electronic Row Drifts
Detector 1/f Drifts
Time Weights
Residuals Spikes
Regional Correlations
Acceleration Response
Temporal Features
Spectral Features
Typical Flux
1,000 – 10,000 Jy
10-1000 Jy
~ 10 Jy
1-10 Jy
~1 Jy
~1 Jy
~10 mJy
~10 mJy
Typical Time
Scale
scan
10 min
scan
scan
1 chop*
1 frame
1 second
~30 seconds
~1 second
0.1-1 second
scan
all time scales
all time scales
Typical Spacial
Scale
pixel
array
pixel
pixel
pixel
array
row
pixel
array
4x4 to 8x6
pixel
pixel
pixel
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Reduction Goal
Simulated source with only white noise – this is the best any analysis could achieve
Simulated Raw Data (1/f correlated)
Partial Cleaning (50 iterations)
Deep Cleaning (200 iterations)
SHARC 1.5 Uranus Raw (Dowell)
SHARC 1.5 Uranus Reduced (Dowell)
Preliminary Simulations for the Iterative Reduction Method (Feb 2001)
SHARC 1.5 – single row of bolometers. Edge pixels used for estimating correlated noise.
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Simulations with CRUSH
Source Fluxes Recovered within 1%
100 mJy Ring surrounding compact star in 1 hour10' x 10' Billiard Ball Scan.
Imperfect cleaning offaint large scale structures
100 mJy CompactLissajous Sweepin 1 hour
Clean background on small scales
Tom Tyranowski
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Correlated Noise And Gain Fitting
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Non-Linear Response
where,
Small signal gain
Large signal gain
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Weighting
Weights Separated into a product of pixel-only weights and time-only weights.
Where B is the number of Active Bolometers, and P is the number of Parameters fitted in the time interval T'
Where P is the number of fitted parameters in the time interval T
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Identifying Anomalous Pixel Behaviour
One of the Most challenging aspects of deep reductions
Removal of Residual Spikes
Flagging of Pixels with Unreasonable Gain Fits
Looking for Statistically Significant Temporal Features...
... and Spectral Features
About 300 of 384 pixels are good enough
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The Lockman Hole z ~ 2-3
Follow-up of SCUBA galaxies
4 Fields, 3-4 Hours of Grade I Each
1-sigma of ~ 5mJy depth.
3 of 4 SCUBA galaxies detected
Additional 7 objects detected above noise
SHARC-2
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Map Noise Characteristics & Detection Confidence
Perfectly Gaussian Noise
~2 Times wider than expected statistically from independent pixel noise! Detectors are NOT independent!
Positive tail Clearly indicating the presence of source flux.
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Residual Pixel-to-Pixel Covariances(Learning from the Data Themself...)
Gaussian with ca.35” FWHM
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Principal Options to CRUSH
Reduction Options
Scan Specific Options
Model Specific Options
Source Map
Gain Modelling
Frame and Pixel Weighting
Row Model
Detector Drift Model
2-D Gradient Model
Residual Spike Removal
Temporal and Spectral Feature Identification
Chopping Residual Model
Acceleration Response Model
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Options to CRUSH
crush [options] -help
http://www.submm.caltech.edu/~sharc/crush/glossary.html
A concise listing of ALL available options to crush, including their current settings.
A detailed explanation of the options, with corresponding configuration keys, and valid arguments. Cross-referenced and easily searchable. The true “CRUSH User's Guide”.
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Principal Reduction Options
Brightness Related
Miscalleneous
< 1 Jy
< 100 mJy. Similar to -faint -compact, but more aggressive.
-faint
-deep
EXTENDED_STRUCTURE = false-compact
LOAD_CONFIG = faint.cfg
LOAD_CONFIG = deep.cfg
Do not worry about filtering extended structures on the scale of the array. Instead clean aggressively...
Size Related
-rounds=
-point
-config=xxx
-altaz
ITERATIONS
LOAD_CONFIG = point.cfg
LOAD_CONFIG = xxx
ALTAZ = true
The number of iterations before final solution.
Perform pointing after reduction.
Load setting for confguration file xxx.
Reduce maps in Alt/Az coordinatesinstead of the default RA/DEC.
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Scan Specific Options
Preconditioning of Scan data
Location
The number of 36 millisecond frames to integrate data over. E.g. -average=3.
If a chopping secondary was used.
-average=
-chopped=
-scale=
-FAZO=-FZAO=
-tau=id:value
AVERAGE_FRAMES
CHOPPED_OBSERVATION = true
Scale the scan data by this factor. E.g. -scale=1.23 13852 13853
Adjust the pointing. E.g. -FAZO=-103.0 -FZAO=12.7 9712
Change the tau value to use. E.g -tau=225GHz:0.046 15224
Adjustments
-path= RAW_DATA_PATH Specify the directory where the raw data resides. E.g. -path=/home/nobody/data/SHARC2
Options affect all scans that are subsequently listed.
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Generic Options
Activation Iteration
Specify when a given model is to be activated. Several models have 'auto' setting available. When specified each model will evaluate a number of possible criteria, based on which it activates or delays. One can also explicitly activate a model at the given iteration.
-Ixxx=
XXX_T =
-xxxT=
XXX_TURN
Characteristic Time Constant
Several of the models have time constants assigned to them. Most commonly they control the time resolution of the given model. The longer the time constant, the less often a parameter is fitted for the given model.
Large ~ RobustSmall ~ Aggressive
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Options to Source Map
Pipeline Auto Configure Related
Do not allow self-activating models to activate until the given iteration. Also, if negative clipping is enabled, clip images until the specified iteration. E.g. -Ifidel=3
If EXTENDED_STRUCTURE is set true, do not self activate models that may remove extended structure until the specified number of source generations is obtained. E.g. -Iextended=4
-Ifidel=
-Iextended=
MAP_RELATIVE_EXPOSURE =
CONVOLVING_BEAM_FWHM =
-minExp=
-convolve=
MAP_FAITHFUL_TURN
EXTENDED_STRUCTURE_TURN
Map Appearance Related
Clip noisy map edges. Use exposure time relative to peak exposure to define clipping criterion. E.g. -minExp=0.1
Convolve map to beam size to get rid of unwanted high spacial frequency structure. E.g. -convolve=4.0
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Gain Fitting and Gain Adjustment Options
Gain Related
The number of initial gain iterations. Like the full pipeline iterations, except only gain and models preceding gain are solved for.
The desired gain convergence if GAIN_ITERATIONS is set to 'auto'. The fainter the source, the better the convergence that is required.
-gainRounds=
-gainGoal=
TAU_ADJUST=true/false-tauAdjust-notauAdjust
GAIN_ITERATIONS
GAIN_CONVERGENCE_GOAL
Fast Line-of-Sight Opacity Adjustment
Allow/Disallow for fast (real-time) adjustment of the extinction around the mean extinction value (explicitly defined or obtained from Mai-Tau) base on the background power variations.
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Weighting and Flagging
Weight Related
Set the time scales over which pixel weights are to be determined. Max should be set such that it is smaller than beam crossing time.
-pWeightT=min-max
MIN_DEGREES_OF_FREEDOM
DESPIKE_LEVEL
REJECT_SPIKE_FRACTION
MAX_TEMPORAL_FEATURE
MAX_SPECTRAL_FEATURE
-minDOF=
-spikeLevel=
-spikeRatio=
-maxTemporal=
-maxSpectral=
PIXEL_WEIGHT_T
Flagging Related
The minimu degrees of freedom that must remain per pixel for the pixel to remain active.
Remove residual spikes above the specified significance level.
Flag pixels that have a higher fraction of spikes to data point.
Flag pixels with temporal features above the spec'd significance level.
Flag pixels with spectral features above the spec'd significance level.
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Output Related Options
Gain Related
-outpath=
-name=
-precess=
-resolution=
REDUCED_MAP_PATH
REDUCED_MAP_EPOCH
MAP_RESOLUTION
The output directory in which to place files that are automatically names as [SourceName].[Scan1#]. ... .[ScanN#].fits.E.g. -outpath=/home/nobody/reduced
The name of the output file including absolute path. E.g. -name=/home/nobody/reduced/mysource.fits
The coordinate epoch in which the reduced map is written. CRUSH does precession!!! E.g. -epoch=1950.0
The map resolution. The setting 'auto' defaults to 1/3 Cassegrain detector pixel size, ~1”.62, but one can set this to any desired value really.
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CRUSH Tips
Reduce as much data at once as you possibly can. Coadd later. Increase the memory allocated to the Java VM.
Reduce Data together that were taken with different Position Angles and Scanning Angles.
If default reduction is 'funny'.
Try different brightness. (-bright, -faint, -deep)
Adjust gain convergence criterion.
Try -compact if emission is not on the scale of the array.
Adjust specific model time-scales.
Try to identify problematic scans. Act on them!
Trade Extended flux for Flatter Baselines.
Check on Pointing.
Use Mai-Tau.
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Observing Tips
Choose Appropriate Scanning Pattern
Size (smaller patterns yield cleaner data)
Coverage (Lissajous vs Billiard Ball)
Speed (Faster = Better)
Orientation (not along rows!!!)
Feasibility.
Chopping / Not Chopping...
Point Often on Nearby object (esp. in ZA)
Calibrate Often on known calibrator
Check on Beam Quality every night
Use DSOS (Dish Surface Optimization System)
Keep Detailed Logs
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The Data Structure
* Free FITS viewing software FV
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Primary Image: Flux Distribution
“Measurement Flux”As would be seen by detector if there was no atmospheric absorbtion Natural units are Voltage (nV, V)
Pseudo flux units(Jy/beam, Jy/sr, Jy/arcsec**2)
Response to 1 Jy source
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Aperture Flux
For some Aperture
With default crush pixelization(1/3 Cassegrain Pixel Size)
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Peak Flux – (Flux Inside a Beam)
Where, the typical 350um valuesfor SHARC-2 are,
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Smoothing with a Beam
Define Smoothing as
Where, the a typical smoothing beam will be a Gaussian of the form:
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Second Image: RMS
“Measurement Uncertainty”Uncertainty of the Detector Measurement
“Map Uncertainty”The Uncertainty of the Flux value on the map.
For default pixelization...
...and Gaussian Beam
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Flux Uncertainty inside an Aperture
With default crush pixelization(1/3 Cassegrain Pixel Size)
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Excess Noise and Non-Independent Pixels
Correlated Pixel Noise
Some Linear Quantity A
The Uncertainty on A
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Excess Noise Determination
From Map Chi-Squared (No source)
From Map NoiseDistribution Gaussian Fit upper limit
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Crush Suite of Utilities
imagetoolAiming to be a comprehensive image manipulation tool. Scaling, rms scaling, map units, regridding, smoothing, filtering and clipping. Under development...
show (via imagetool)Display tool that allows quick view of images with some limited capabilities such as PSF fitting, image toggle, units on the fly etc.
coaddProduce maps out of multiple images.
jiggle Shift maps on the fly to determine alignment
covarseeA visualization tool for pixel-to-pixel covariance matrixes.
histogramMap signal-to-noise Histrogram generator. Useful for determining excess noise + quick diagnostic
deconvolveObtain super-resolution. Undocumented...