Lecture 3

Question 1

A flat field, Fij

Answer 1

semiconductor material may vary, each CCD pixel respond differently to illumination

additionally the CCD may have surface spots or flaws

exposing the CCD to a uniform light source we can see this.

Question 2

< 10 DN
> 10 DN

Answer 2

underperforming
overperforming

Question 3

pixel variation corrected photo - electron is (formula)

Answer 3

Nij = Pij/ Fij

Question 4

instrumental background Bij (formula)

Answer 4

Bij = Tij + Eij

Question 5

The DN per pixel due to astronomical sources, Nij (formula)

Answer 5

Nij = (Xij - Bij) / Fij

Question 6

Cosmic ray spikes

Answer 6

if a CCD is exposed for a long time, or a CCD is in space, CRs impact it and cause pixels or groups of pixels to saturate

Question 7

How to deal with cosmic rays

Answer 7

Procedure : rank order the DN values and use the median (middle value)

Question 8

How to deal with cosmic rays if the source is changing

Answer 8

most common method is median filtering

each pixel value in an image is replaced with the median value of the immediate surrounding pixels

this also smooths out intensity variations correcting for hot pixels

Question 9

CCD quantum efficiency peaks in the optical this can be improved by

Answer 9

Anti-reflection (AR) coatings improve QE

Question 10

short wavelengths are absorbed before

Answer 10

they reach the depletion region

Question 11

Rear-side illumination

Answer 11

gives increased sensitivity

Question 12

the limited full well of a CCD pixel limits

Answer 12

CCD ‘dynamic range’ and can lead to blooming

Question 13

dynamic range

Answer 13

is the ratio between brightest and faintest sources that can be recorded

Question 14

blooming

Answer 14

photo electrons overflow from one potential well to the next along conduction paths (rows)

leads to bright streaks, which cannot be corrected in processing