User Tools

Site Tools


ao:cic_analysis

CIC Analysis

Clock Induced Charge Analysis

This recipe from Mike Ireland:

1) Take at least 10 frames with chosen settings, which is a high gain
mode and with shutter closed
(definitely above a gain of 200 electrons, preferably 500 electrons)
2) Compute a median dark and subtract it.
3) Compute a robust standard deviation, e.g.
stdev = 1.48*sqrt(median(data^2))
4) Compute the number of elements above a threshold e.g.
threshold = 3.5*sigma
length(where(data > threshold))/length(data)

5) Finally, there is a correction you could do which is to divide
the final number by:
exp(-threshold / em_gain_in_dn)

[but to do step 5, you need the EM gain. As long as gain is high, this
correction is small]



Further clarification from Mike:

yes by median dark I mean a bias frame. But computed by taking the median of
lots of bias frames.

Threshold should be a single number, equal to 3.5 times the readout noise.

Data is a bias-subtracted data cube. Use one slice or all slices for better
statistics, but definitely not a sum or average.



My analysis procedure:

Each data cube contains 500 images in rapid succession. I only use
the first 30 images of each data cube for analysis. I sum the 30
images and divide by 30 to get the bias frame. I subtract the bias
frame from each of the 30 images. I then cast the entire 512x512x30
data cube into a 1-D vector, use that vector to generate a robust
standard deviation scalar quantity (1.48*sqrt(median(vector^2)) –
finding the median is the most computationally intensive step), troll
the vector for any values that exceed the robust standard deviation by
a factor of 3.5, divide that number by the total length of the 1-D
vector, and divide by the gain correction factor
(exp(-1.0*thresh/gain)).

Two observations:

1) The vertical shift delay makes a difference in the measured CIC. I
don't understand why this would be the case. If one expects this,
wouldn't we need to know the value used by Andor in their literature?

2) The higher the gain, the larger the clock induced charge. To me,
this would imply that I'm not applying the correction factor correctly
– being called a correction factor implies that its application would
compensate for the differences in the gains.



The summary file:

File Temperature Gain Vertical Shift CIC Fraction

… 0000.fits -50.0000 300 3.30000e-06 0.00426411
… 0001.fits -50.0000 300 3.30000e-06 0.00390681
… 0002.fits -80.0000 300 1.70000e-06 0.00133295
… 0003.fits -80.0000 300 9.00000e-07 0.000842734
… 0005.fits -80.0000 300 5.00000e-07 0.000698496
… 0006.fits -80.0000 300 3.00000e-07 0.000715206
… 0007.fits -80.0000 500 3.30000e-06 0.00416787
… 0008.fits -80.0000 500 1.70000e-06 0.00221594
… 0009.fits -80.0000 500 9.00000e-07 0.00149811
… 0010.fits -80.0000 500 5.00000e-07 0.00114543
… 0011.fits -80.0000 500 3.00000e-07 0.00101927
… 0012.fits -80.0000 800 3.30000e-06 0.00643356
… 0013.fits -80.0000 800 1.70000e-06 0.00335487
… 0014.fits -80.0000 800 9.00000e-07 0.00227567
… 0015.fits -80.0000 800 5.00000e-07 0.00174591
… 0016.fits -80.0000 800 3.00000e-07 0.00155108
… 0017.fits -80.0000 100 3.30000e-06 0.000628299
… 0018.fits -80.0000 100 1.70000e-06 0.000518980



Sample FITS header (in case I overlooked something):

SIMPLE = T / file does conform to FITS standard
BITPIX = -32 / number of bits per data pixel
NAXIS = 3 / number of data axes
NAXIS1 = 512 / length of data axis 1
NAXIS2 = 512 / length of data axis 2
NAXIS3 = 500 / length of data axis 3
EXTEND = T / FITS dataset may contain extensions
COMMENT FITS (Flexible Image Transport System) format is defined in 'Astronomy
COMMENT and Astrophysics', volume 376, page 359; bibcode: 2001A&A…376..359H
HEAD = 'DU897_BV' / Head model
ACQMODE = 'Kinetics' / Acquisition mode
ACT = 0.0246 / Integration cycle time
KCT = 0.0246 / Kinetic cycle time
NUMACC = 1 / Number of integrations
NUMKIN = 500 / Series length
READMODE= 'Image ' / Readout mode
IMGRECT = '1, 512, 512, 1' / Image format
HBIN = 1 / Horizontal binning
VBIN = 1 / Vertical binning
SUBRECT = '1, 512, 512, 1' / Subimage format
DATATYPE= 'Counts ' / Data type
XTYPE = 'Pixel number' / Calibration type
XUNIT = 0 / Calibration units
TRIGGER = 'Internal' / Trigger mode
CALIB = '0,1,0,0 ' / Calibration
DLLVER = '4.21.30006.0' / Software Version
EXPOSURE= 1.0E-05 / Total Exposure Time
TEMP = -50. / Temperature
READTIME= 5.882353E-08 / Pixel readout time
OPERATN = 0 / Type of system
GAIN = 300 / Gain
EMREALGN= 0 / EM Real Gain
VCLKAMP = 0 / Vertical Clock Amplitude
VSHIFT = 3.3E-06 / Vertical Shift Speed
OUTPTAMP= 'Electron Multiplying' / Output Amplifier
PREAMP = 3. / Pre Amplifier Gain
SERNO = 7103 / Serial Number
UNSTTEMP= -999. / Unstabilized Temperature
BLCLAMP = T / Baseline Clamp
PRECAN = 0 / Prescans
FLIPX = 0 / Horizontally Flipped
FLIPY = 0 / Vertically Flipped
CNTCVTMD= 0 / Count Convert Mode
CNTCVT = 1 / Count Convert
DTNWLGTH= 550. / Detection Wavelength
SNTVTY = 5.44053 / Sensitivity
SPSNFLTR= 0 / Spurious Noise Filter Mode
THRSHLD = 0. / Threshold
PCNTENLD= 0 / Photon Counting Enabled
NSETHSLD= 0 / Number of Photon Counting Thresholds
PTNTHLD1= 0. / Photon Counting Threshold 1
PTNTHLD2= 0. / Photon Counting Threshold 2
PTNTHLD3= 0. / Photon Counting Threshold 3
PTNTHLD4= 0. / Photon Counting Threshold 4
AVGFTRMD= 0 / Averaging Filter Mode
AVGFCTR = 1 / Averaging factor
FRMCNT = 1 / Frame Count
USERTXT1= ' ' / User text
USERTXT2= ' ' / User text
USERTXT3= ' ' / User text
USERTXT4= ' ' / User text
DATE = '2012-07-06T01:22:34' / file creation date (YYYY-MM-DDThh:mm:ss)
FRAME = '2012-07-06T01:22:34.000' / Start of Frame Exposure
ESHTMODE= -1 / Electronic Shuttering Mode
END



If anyone wishes to do further reduction, the data can be found in my home
directory ( ~nils/tmp/andor/andor_cic_tests ) on the office side network.



In comparison with the literature included with the camera, we are very close. The CIC number with the camera tests was done at an EM gain of 1000x, 10 MHz horizontal, and 0.5 usec vertical shift. For our tests, we did 300x, 500x, and 800x, 17 MHz horizontal with varying vertical shifts. The relevant entries from above are:

… 0005.fits -80.0000 300 5.00000e-07 0.000698496
… 0010.fits -80.0000 500 5.00000e-07 0.00114543
… 0015.fits -80.0000 800 5.00000e-07 0.00174591

These match well with the value of 0.00108 events per pixel measured by Andor. My conclusion – the camera meets spec.


2012-09-11:

CIC tests using subregions:

All tests done using an EM gain of 1000x, a temperature of -75C, a readout rate of 10MHz, a 0.5 usec vertical shift rate, and a 90×90 region of interest.

Lower left corner of ROI
Preamp gain
CIC
(1,1)
3
0.00578088
(1,1)
2
0.00447576
(1,1)
1
0.00284685
(211,1)
3
0.00581897
(211,1)
2
0.00419993
(211,1)
1
0.00273999
(211,211)
3
0.00609663
(211,211)
2
0.00490706
(211,211)
1
0.00275234



2012-09-26:

CIC tests on the six cameras delivered 2012-09-24:

201209xx_camera_shipment

ao/cic_analysis.txt · Last modified: 2018/07/07 12:56 by jones