1) Total noise (Dark Shot Noise + Dark Fixed Pattern Noise + Read Noise) vs Signal
2) Dark Fixed Pattern Noise vs Signal
3) Dark Shot Noise vs Signal
1) Camera conversion gain (e- / DN)
2) Read noise ( in DN or absolute units such as e-)
3) DSNU factor
4) Full well capacity (if you take long enough exposures)
5) And the data can permit you to calculate the dark current Quality factor (the room temperature dark current/unit-area) and doubling temperature
The next thing is to difference pairs of identical dark frames. This results in removal of the Dark Fixed Pattern noise and the standard deviation of this difference is equal to sqrt(2) * the remaining noise, which is Dark Shot Noise and Read noise in a quadrature sum.
Using the expression for the quadrature adding of
uncorrelated noise sources, you can compute the Dark Fixed Pattern Noise for
each Signal level in a separate column
Then the Total Noise, the quadrature sum of the Dark Shot Noise and Read Noise, and the Dark Fixed Pattern noise can be plotted on LOG LOG scale versus Signal. The units will be in DN (also known as ADU in the amateur astronomy community). A sample Excel Spreadsheet layout is shown below:
The Y intercept of the Total Noise is the Read Noise. Once the read noise is known you can again use the quadrature formula to isolate the Dark Shot Noise and that is added to the DTC plot: again plotting noise against signal. The final plot will look like this:
The Kadc (camera gain) is measured directly as well: it is the X intercept of the Slope = ½ portion of the Dark Shot Noise Curve. It will have dimensions of e- / DN. If the dark integrations are long enough, you can observe full well being approached as the slope of the curves will show a change on the high signal level end of the curves.
If you record the integration times and temperatures
when the data is collected you can also calculate the Dark Figure of Merit (a
room temperature measurement of e-/sec/pixel) or (e-/sec/cm^2) and that number
can be used along with the energy gap equation to
predict the dark current at any operating temperature. The energy gap equation is more accurate than the doubling temperature method but that can give good results over a comparatively small temperature excursion from the reference temperature.
Additionally if you have dark integrations at other temperatures and exposure times you can calculate the doubling temperature as well. So there are a number of important parameters that can be learned from these plots.
1) Read Noise
2) Signal Shot Noise
3) Signal Fixed Pattern Noise
4) Camera gain (Kadc)
5) Full Well
6) The effectiveness of flat fielding (are you improving the image by applying flats or not?)
7) And a host of other parameters of interest.
Photon transfer curve (taken with light on)
Using a similar approach but with the light on and taking flat fields, a Photon Transfer Curve can be created. This tool is useful for measuring camera linearity, full well capacity, camera gain, Photo Response Non-Uniformity, and various noise sources, charge skimming and so on.
The procedure is nearly identical except instead of working with Dark Frames, you take pairs of identical flat fields with varying exposure from bias frames to full well.
8 February 2008
this sensor was deployed initially in early 2006. Since that time it has aged significantly due to cumulative radiation damage. to see its cosmetics and to see the impact of cooling on the cosmetics see this page:
This sensor has very high noise as shown on this graph. Compare with the DTCs for the Grade 1 KAF6303 and the TK1024 to see the differences. To use the sensor effectively requires a combination of deep cooling and shorter exposures. The longer the exposure the deeper the cooling needs to be to prevent the very high DFPN from making the image noisy. Even though the DFPN can be subtracted out, the resulting images are noisier when there was significant DFPN prior to removal. By cooling more and by knowing the dark current generation rate, a cooling level can be established to make the DFPN so small as to be insignificant.
Operating it at -25C gives moderately noisy images even with 10 minute