24 um Dark Verification

Principal: James Muzerolle
Deputy: Karl Gordon
Data Monkey(s): Kate Su, Casey Papovich
Priority: Necessary
Downlink Priority: Normal
Analysis Time: 24 hours
Last Updated:

Objective

Verify expected counts in dark current measurements with different exposure times.

Description

Point to the 24 µm dark position, acquire dark measurements at 3, 4, 10, and 30 seconds, and compare the resulting counts.

Data Collected

Darks will be obtained using the standard 24 µm dark IERs, which acquire 101, 77, 35, and 13 DCEs at 3, 4, 10, and 30 second exposure times, respectively, in SUR mode.

Data Reformatting Requirements

Array Data Desired:

24 µm

Data Reformatting Option:

SPECIAL

Special Instructions:
The entire collection of DCEs corresponding to each exposure time should be packed into one fits file with extensions. Four files should be generated: one with 101 DCEs, one with 77, one with 35, and one with 13, corresponding to the 3, 4, 10, and 30-second exposures IERs.

Task Dependencies

None

Calibration Dependencies

None

Output and Deliverable Products

This task serves as a check of our planned use of ONLY 10-second darks during routine calibration, which assumes that either the dark current is extremely small (0-2 DN/sec), or else there is a significant scattered light component that does not vary with exposure time.

Data Analysis

The data will be processed as normally with the DAT: mips_sloper without dark subtraction (-b), mips_caler with no flat fielding (no flag; here, mips_caler is only needed to provide correct input into mips_enhancer), and mips_enhancer (with -f to specify the input *.cal.fits file with extensions) to combine multiple DCEs into dark current calibration images at each exposure time. The IDL script "get_rdnoise.pro", which is contained in the DAT distribution, can be used to measure and compare the counts in these images. This script will output both the dark current (i.e., the signal on the array, in e/s) and the read noise (not important here). Note that the boost frames will appear to have lower counts than the rest. If there is minimal scattered light, typical counts should be ~0-2 DN/sec (0-10 e/s), with lots of zeroes at the longest exposure times. However, the scattered light may well be dominant, in which case the median count rates should be the same regardless of exposure time.

Software Requirements

Actions Following Analysis

If count rates are NOT the same for each exposure time, check the following. Check that counts are at or near levels seen in ground testing (see the 24um read noise log). There is likely to be some scattered light, so counts will probably be higher than in the ground test darks; this needs to be quantified. Check for unexpected image structure such as large-scale gradients or pattern noise. Check for evidence of latency from a previous bright source on the array.

Failure Modes and Responses

If dark count rates taken under nominal conditions are anomalous (e.g., because of latency from a previously exposed bright source), this test should probably be repeated.