Transcript Brief Overview of the Chop/Nod Spectrometer Pipeline and Data

PACS IFU Spectrometer
Overview, Spectrometer Products
and Processing Philosophy
Phil Appleton
on Behalf of PACS Team
PACS Spectrometer:
The First IFU to L2!
PACS Integral Field Spectrometer
(Poglitch et al. 2010)
5x5 pixels
1 pixel = 9.4”
FOV 47”x47”
SLICER
MIRRORS
Simultaneous Blue and Red
Coverage via diachroic
GeGa Two
(25 x 16)
arrays
Stressed
and unstressed
Blue (55-98 m)
Selectable band
(3rd and 2nd Order)
GeGa
detectors
Red (102-210m)
1st order
PACS—Some Optical Components
Calibration grey-body
source (common
with Photometer)
Lithrow-mounted Grating recieves elliptical
beam from anomorphic collimator
Filter wheel
assembly
Chopper (common)
max 6 arcmin throw
8.5 grooves/mm
2720 grooves
Diffraction grating
spectrometer with high- and lowstressed Ge:Ga detector arrays
Grating: diffraction element used in 3 orders
The Ge:Ga Photoconductor Arrays
Stressed (R) and unstressed (B) photoconductors
cooled to 1.65K in a 5 + 5 linear segments of 16
form the basic 25 spatial modules with 16 spectral
pixels.
The photoconductors are
read-out at 256Hz via
cold amplifier/multiplexer
(CRE) CMOS circuit held
at 3-5K.
A complete assembled
Ge:Ga detector assembly.
Data is read out in 32 samples
and slopes are fitted onboard
to produce samples of 1/8s
each for storage and transmission
to the ground.
Spectrometer Astronomical Observing
Templates (AOTs)
Signal modulation
Techniques
•
Line Spectroscopy AOT: observation of individual narrow lines:
PIPELINE
– Chopping/nodding
STANDARD (SLICED) PIPELINE
– Pointed, dithered and mapping modes
(optional special pointed)
pipeline)
– For isolated sources and rasters ≤ 6 arcmin
– Variable grating sampling for faint and bright linesUnchopped mode
-
Signal modulation
Techniques
Range
definition
•
•
UNCHOPPED PIPELINE (Under dev)
– For mapping observations of crowded fields
– ON and OFF Source position provided
Range Spectroscopy AOT: observation of extended ranges, broad lines or continuum STANDARD (SLICED)
PIPELINE
– Range scan (same concept as Line Spectroscopy) for broad lines
– SED mode for continuum-like spectral scans covering huge range
– Chopping/nodding
– Pointed, dithered and mapping modes
– For isolated sources and rasters ≤ 6 arcmin
–
Unchopped mode
– For mapping observations of crowded fields
– Optional off-position
UNCHOPPED PIPELINE (Under dev)
Example of Chop/nod AOT blocks
START
observation
On-target slew
Nod
slew
Nodding “A” position
Nodding “B” position
Calib.
Line1 x 1
Line2 x 1
Line3 x 2
Line1 x 1
Line2 x 1
Line3 x 2
87 sec
184 sec
184 sec
344 sec
184 sec
184 sec
344 sec
Repeat N times (number of cycles)
984 sec
= grating up-down scan
… move to next raster position
END
observation
and repeat
Pointing layout example of a nodding raster
observation:
Nod “A”
Nod “B”
Chopping/nodding pattern
Spectrometer Data
• PACS raw data is integration
ramps with typically
– 1/8 second reset interval (32
readouts) for bright sources/lines
– the dynamic range can be adjusted
by four integration capacitors
• On-board averaging is required to
fit within the allowed downlink
telemetry rate
– 32 readouts averaged
– several “raw” ramps are downloaded
in their entirety to provide “saturation”
information. The raw pixels cycle
through
the array with time.
PACS raw ramps
9
Spectrometer Pipeline
Level 0 first processing
Level 0
PACS data,
House Keeping
Pointing
Flag Data
Permanently Bad pixels (few)
When grating or chopper moving
Saturated data
When glitches present
Open and dummy channels (spec 0, 18)
Convert DNs to Volts/s
Assign observing block labels
(e. g. Nod positions, grating scan direction,
calibration block, scan mode)
Assign RA/Dec > pixel
Level 0.5
Uncalibrated Data Frame
10
Steps to Calibrated Frame
Level 0.5
Wavelength Calibration
Nonlinearities and Spatial Distortions
Apply RSRF
Flat Field correction
Subtract On and Off Chop and
Convert to Jy
Transient Corrections
Under investigation
Level 1 Calibrated Data Frames
(25 x 16 x time = grating movement)
11
What are Level 1 Frames?
Calibrated Frame is time history
of spectral scan as seen by each pixel
16 spectral
FRAMES
Time
25 spatial pix
12
RAMPS → FRAMES
averaged ramps provide frames
25 spatial pixels
Level 0 -1 and 2 Products
PACS PIPELINE
SINGS
CUBE BUILDING
FRAMES
RAW
background
Level 0
To Level 0.5
Projected
to 3” x 3”
pixels
To calibrated L1 FRAMES
CALIBRATION PRODUCTS
similar to B. Ali’s talk
CALIBRATED
FRAME
PACSCUBE
CUBE
Level 1
REBINNED
CUBE
PROJECTED
CUBE
Level 2
Level 2
Spectral Cubes
Level 2 Spectral Cube
15
PACS SPECTROMETER Pipeline uses
SLICED FRAMES and CUBES
The concept of slicing was introduced because of
the many dimension of data in a given AOR.
The slices can be processed sequentially
Possible Slicing “Dimensions”
1) Calibration block needed to
have a separate slice.
2) Raster Mapping
(Cube every IFU pointing).
3) In Chop-Nod you have
NodA and NodB for every
demanded position.
4) More than one line can
be observed in one AOR.
5) Might want the option of separating
the up and down scans of the grating
6) In unchopped mode “On” and “Off”
How is this accomplished
in HIPE 6.0 RC2 build
Observational
Context
e. g. ( 2 x 1 raster and 2
line obs)
perform Level
0.0-0.5
pipeline steps
CALBLOCK
REMOVED
NODA/NODB
LINE 1
slicedFrame[0]
slicedFrame[1]
slicedFrame[2]
slicedFrame[3]
LINE 1 and 2
LINE 2
slicedFrame[0] A
slicedFrame[1] B
slicedFrame[2] A
slicedFrame[3] B
slicedFrames =
SlicedFrames(level0.fitted.getCamera
(camera).product)
CalBlock
APPLY SLICING RULE by
raster/Nod Position/LINE_ID
slicedFrame[0]
slicedFrame[1]
slicedFrame[3]
slicedFrame[5]
slicedFrame[7]
= cal block
slicedFrame[2]
slicedFrame[4]
slicedFrame[6]
slicedFrame[8]
perform Level 0.5-1.0
pipeline steps
convert all raster
frames and
nod frames into sliced
cubes
for that line ID
Manually select
given line
by line ID
FINAL LINE Projected CUBES
SpecProject
LINE1
GRID RASTERS
ONTO WCS
SpecProject
Line 2
Rebinned cubes
gathered into
LIST Context
Level 1-2
pipeline
Make sliced
rebinned
cubes
for for all
rasters and nods
for given line ID
repeat for line 2 ...3...etc