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 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. To conserve downlink bandwidth, some detector readout patterns average measurements for a pixel from multiple frames. In this case, the effective time for a downlinked measurement of a pixel is the average of the measurement times in the frames that were combined on board. In this scenario, the effective integration time for a pixel is the time associated with the last group in an integration minus the time associated with the first group.
Effective integration time is provided in the JWST Header keyword: EFFINTTM "Effective integration Time in units of seconds."
