Netlogo+-+CCD+Simulation


 * __Netlogo CCD Simulation__**


 * Author: Scott Mayle, 2011**

netlogo ccd program - [|CCDFinal(ClassRoom).nlogo] quiz - [|CCDquiz.doc]
 * __Materials:__**

The purpose of this activity is to see what type of things need to be looked at before implementing new technology to make a measurement. I have written a simulation of how CCD works with many parameters that need to be adjusted in order to get a good image or measurement. I will briefly explain what each parameter controls and let you play with the simulator giving some scenarios to play with!


 * Setup**: This button sets up the initial conditions of the simulation and also clears everything from previous runs. It must be pressed before each run.


 * Go**: This button moves the simulation forward in time continuously until the button is deselected.


 * Go Once**: This button moves the simulation forward one step in time and stops.


 * Speed Slide bar at the top**: This slider changes the length of time each step of the simulation takes. It will probably need to be slide to a slower than normal setting to see all of the nuances of this simulation


 * Exposure-Time**: This sets the amount of time that the CCD will collect light. At the end of this time it will close a shutter and let no more light hit the CCD. __Note__: A time of 75 or greater recommended.


 * Gain**: This will change the strength of the signals red out by sensor (red box). The higher the gain the bigger the signal will appear. __Note__: This essentially multiplies the charge that was red by the set constant and should only be used to set the correct scale.


 * PixelNumber**: This bar sets the total number of pixels that the CCD is made out of. __Note__:in order to keep the physical size of the CCD relatively the same (so we do not simply collect more light with more pixels) the size of the simulation window will change as this number changes.


 * IntensityTopStar/IntensityBottomStar**: This will change the amount of light that comes out of each star independently. __Note__: If either of these are set to zero the start emits no light.


 * BackgroundLight**: This switch will turn on a set amount of background light used to simulate light pollution, light from other stars, or infrared light produced from “hot” object.


 * Counts vs Time**: This graph will produce a signal of counts as the charge passes through the sensor as time goes on. The time (x) axis of the graph will automatically readjust itself as necessary. The count (y) axis of the graph has a fixed scale. You must play with the exposure time and the gain to ensure a reasonable number of counts. The graph should reproduce the intensity of light that hit each pixel.


 * __Some Questions and Scenarios to play with:__**

Set the following parameters as follows: PixelNumber: 21 Exposure-Time: 200 IntensityTopStar: 4 IntensityBottomStar: 0 Gain: 5 BackgroundLight: Off

As the simulation is running what happens when the photons (white circles) hits the blue pixels?

Let the simulation run and after the shutter has closed (the black line near the pixels appears and no light reaches the pixels) describe in a few sentences what happens both near the pixels and on the graph (rerun the simulation if necessary).

Rerun the simulation a couple of times. Does the “image” produced in the graph stay the same after each simulation? Can you identify the star in the image? If so do the stars look the same after each run?

Now set the following parameters: PixelNumber: 21 Exposure-Time: 200 IntensityTopStar: 4 IntensityBottomStar: 4 Gain: 5 BackgroundLight: Off

Can you identify both stars?

Now set the following parameters: PixelNumber: 5 Exposure-Time: 200 IntensityTopStar: 4 IntensityBottomStar: 4 Gain: 5 BackgroundLight: Off

Describe what you observe in the graph after the shutter closes:

You should not be able to get a good image with these parameters due to saturating you sensor. If you can only change the **Gain** what should it be set at to get a good image (make sure you repeat the simulation a couple of times to avoid saturation):

Go back to **Gain** 5. If you can only change the **Time-Exposure** find the value for which you do not get any saturation: With your new found “better” setting can you identify two distinct stars in your “image”

If not which setting do you think is most important to change to remedy this?

Now set the following parameters: PixelNumber: 15 Exposure-Time: 200 IntensityTopStar: 2 IntensityBottomStar: 2 Gain: 5 BackgroundLight: Off

After running a couple of times with these parameters can you identify both stars?

Now turn the **BackgroundLight** switch on. Can you still see both stars?

Describe any other differences you see when the **BackgroundLight** is on versus off.

Now with: IntensityTopStar: 5 IntensityBottomStar: 5 BackgroundLight: On

It is your turn to play with all of the parameters to try and get the best image possible. Note the best possible image will have two very distinct peaks for each star, and fill up as much of the graph as possible without going off screen.

PixelNumber: Exposure-Time: Gain:

Which of these parameters that you tuned do you feel as though is most important to get a good image and why?

Finally set

IntensityTopStar: 10 IntensityBottomStar: 1 BackgroundLight: On

Play around with the other parameters to try and see both stars. After several tries is it possible to get a good image of both stars?

Briefly describe why you think this is.

Are there any ways you can think of other than playing with the parameters of your CCD that would give you better image of the dimmer star?

Try and come up with three things that would be important to astronomers when using a CCD that I have not included in the simulation: