Webb Office Hours Session 2: February 22, 2024
Q&A's:
Q1: Where are the Webb Office Hours procedures and guidelines?
A1: Webb Office Hours. Type your question into the WebEx chat. We will asynchronously copy questions from the chat to this main page and work through them as a group. If you have images to share please give WebEx permission to share your screen (you may need to log out and log back in again to enable this feature.)
Q2: What is "effective integration time?" There seem to be many different flavors of time in the documentation, e.g., "photon gathering time."
A2: Consider an integration with three groups up the ramp, each group combining four frames on board before downlink, i.e., 1 1 1 1 2 2 2 2 3 3 3 3. The time associated with each downlinked group is the average of the times of the four individual frames that were combined, e.g., 1, 1, 1, 1. The total time spent gathering photons is 12 frame times. The effective integration time is the time interval between the first (1) and last group (3), which is only 8 frame times. To calculate flux, divide the flux difference by effective integration time, not by the photon gathering time.
Consider an integration with three groups up the ramp, each group consisting of a single frame. Assume the time to read all pixels in a single frame is 10 seconds. Photons are gathered for a total of 30 seconds, starting with the first pixel in the first frame and ending with the last pixel in the last frame. The first pixel is read at t=0, t=10, and t=20, so the effective integration time is only 20 seconds. The last pixel is read at t=10, t=20, and t=30, so the effective integration time is again only 20 seconds. When multiple frames are combined into a group on board before downlink, the downlinked
- EFFINTTM "Effective integration Time in units of seconds."
- "(NGROUPS-1)*TGROUP+(TGROUP0) where TGROUP and TGROUP0 are calculated"
