Michelle – How to Take Read Noise Measurements

Michelle – How to Take Read Noise Measurements

1) Log into Ohi as "observer"

2) Launch a terminal

3) Run up the michelle DM screens if you want (you don't need to) by 
typing "michelleMenu&" and choosing the mich_oper screen.

4) From a terminal, type "engMichelleSim &". You'll get a gaia display 
and a little gui where you can enter an exec name, load it and run it.

5) In the gui, enter "readnoise" as the exec name (without the "s) and 
hit the load button.

6) When you're ready, hit the "Run" button. This exec will set all the 
relevant mechanisms and then take 20 bias frames. It will *not* open 
the window cover! It will also enable and disable the array, so you 
don't need to worry about that.

NB. You will need to know the number of the first and last frame you 
took. Getting the last frame no. is easy, it will say so in the 
terminal you launched engMichelleSim from. It will look like this:

DTK:OOS_Michelle:.. getHeaders end 130

DTK:OOS_Michelle:.. ready  

DTK:OOS_Michelle:.. endObs  130

i.e., frame 130 was the last frame you took. To find the first frame 
number, simply subtract 19 (e.g., in this case, the first frame was 

You can also get the same info from the WFG serial console.

7) You can run the exec as many times as you want. When finished, hit 
the exit button and then choose "Cleanup & Exit". Note that if someone 
is running the OMP observing software in Hilo, this will crash their 
system! You might have to close the gaia window yourself.


OK, that's how to take the data. They will appear in the directory 
/ukirtdata/raw/eng/michelle/utdate where "utdate" is the current UT 
date in the format 20040206 (year, month, day). Remember the UT date 
changes at 2pm every day here! If the UT date changes, simply restart from 
point 1 below.

To find the read noise, you will need to log onto ohi or kauwa as 
observer and launch a terminal. Then:

1) In the terminal, type "oracdr_michelle_eng"

2) In the same terminal, type:

	oracdr -list a:b -log sf -nodisplay DIFFERENCE_STATS

where a = the first frame number and b = the final frame number (111 
and 130 from the example above). You must write DIFFERENCE_STATS in 

Ignore all the error messages! The data reduction is set up to reduce 
data taken at night with the OMP system, not the Michelle engineering 
interface, but it still seems to give the correct result.

After a lot of scrolling, you will see something like the following:

"Average standard deviation for group is 5640.359 electrons."

This is the average read noise in electrons averaged over the 20 
frames you took.

If you take more data, you don't have to do all setenv stuff again 
(unless the UT date changes). All you have to do is run the "oracdr 
-list a:b -log sf -nodisplay DIFFERENCE_STATS" command again and 
change the first and last frame numbers.