next up previous contents
Next: Flat fielding Up: Reducing Science Data Previous: Ghost removal

Dark subtraction

One subtracts the dark frame from all images. Since the zero level offset (or bias) is a function of the flux and since the bias is somewhat variable, this subtraction is not perfect. The residual is removed in the subsequent steps.

The behavior of the bias as a function of the flux and DIT is very complex. We are investigating ways to model the bias so that this step is more precise.

Christopher Lidman