This is a list of "features" that might appear in NICMOS science data, even after pipeline calibration. Most of these are well-known imperfections of HgCdTe detectors which are also present in ground-based data taken with similar detectors. However, since NICMOS data has a much lower thermal background than ground-based instruments, these features stand out more clearly.
Many of the items in the list are driven by small temperature variations of the on-chip electronics. Because the calibration reference files are taken at slightly different temperature, the pipeline correction is not 100% accurate.
The NICMOS group provides a set of tools that improve the data quality significantly over the pipeline calibration by using temperature information in the science data headers. In the near future, NICMOS will take advantage of "On-the-Fly Recalibration" (OTFR) which is likely to incorporate these new tools so that many of the items in the list below will be corrected in the pipeline output.
The following references may prove useful in identifying and dealing with anomalies:
| Amplifier Glow | ||
|
A pattern of light, due to the reaout amplifiers, that is highest in the corners and decreases towards the center of the detector | |
| Bad ('Photometrically Challenged') Central Column | ||
|
The central row/column of apparent decreased sensitivity | |
| Bias Jumps (Bands) | ||
|
Wide bands (tens of pixels across) of fluctuating bias levels | |
| Cosmic Ray Persistence | ||
|
Spatially correlated persistent images from cosmic ray hits incurred during SAA passages | |
| Cosmic Rays | ||
|
Possible effects of very energetic cosmic ray hits | |
| Count-rate Non-Linearity | ||
|
NICMOS Count-rate Dependent Non-linearity | |
| Dark Current | ||
|
The linear component of the NICMOS dark current | |
| Electronic Bars | ||
|
Narrow stripes (a few pixels across) occurring at corresponding positions in all four quadrants | |
| Electronic Ghosts (Mr. Staypuft, Ringing & Streaking) |
||
|
Electronic ghost images and bands appearing at points in the other three quadrants which correspond to the position of a bright source in one quadrant | |
| Flat Fields | ||
|
Sensitivity patterns for all three NICMOS cameras | |
| High Noise Region | ||
|
Sensitivity variations resulting in noise modulations across the detector | |
| Hot and Cold Pixels | ||
|
Pixels with abnormally high or low sensitivities | |
| Image Persistence | ||
|
Excess dark current observed immediately after the observation of a bright target | |
| Optical Ghosts | ||
|
Optical ghosts in the NIC1 polarizers | |
| Particulate Contaminates (GROT) | ||
|
Small spots of reduced sensitivity, generally extending only over a pixel or two | |
| Residual Bias (Pedestal) | ||
|
A DC offset which remains in an image after the dark current has been removed, producing an inverse flat field pattern in calibrated data | |
| Shading | ||
|
A time-dependent bias that changes across a quadrant as the pixels are sequentially read out | |
| Space Junk | ||
|
An example of the effects of space junk | |
| Super Shading | ||
|
An intermittent phenomenon similar to shading but with an increased amplitude | |
| Vignetting | ||
|
A decrease in observed brightness along the bottom edge of all three NICMOS cameras | |
NICMOS Anomalies & Image Artifacts Documentation
Advisories:
Important updates, discoveries and developments
that could potentially affect NICMOS observations,
calibration, or data analysis.
Memo Describing the 'Bars' Phenomenon
FAQs:
Frequently Asked Questions.
Performance Summaries:
Status reports reflecting the current
understanding of instrument characteristics,
performance and calibration.
Handbooks:
The NICMOS Instrument Handbook is the primary
guide regarding the characteristics and use of
the instrument. The HST Data Handbook is the
primary guide for calibration, reduction and analysis
of NICMOS data.
Instrument Science Reports:
ISRs are technical reports written by members
of the NICMOS Group about various aspects of the
instrument and data. They usually contain in-depth
information about specific topics.
E. Bergeron and M. Dickenson 06 Oct 2003
C. Skinner 01 Dec 1995
Papers and Proceedings:
Selected NICMOS related published papers and workshop
proceedings.
Tutorials:
Cookbook style instructions, prescribed procedures, and
helpful tips.
Space Telescope Analysis Newsletters:
STANs contain useful information regarding
calibration and data reduction.
NICMOS STScI Analysis Newsletter 22
New NICMOS Exposure Time Calculator
Synthetic DARKs for NIC1
Release of the Visual Target Tuner
NICMOS Group 31 May 2000 (html)
NICMOS STScI Analysis Newsletter 19
Temperature dependent synthetic dark image generator
Polarizer Data Analysis Software
NICMOS Histroy Tool
NICMOS Group 30 Sep 1999 (html)
NICMOS STScI Analysis Newsletter 17
Dealing With NICMOS Image Anomalies: Current Situation and Future Goals
Data header errors
NICMOS Group 01 Mar 1999 (html)
NICMOS STScI Analysis Newsletter 8
Cosmic ray persistence
NIC3 pointed flats
NICMOS Group 01 Feb 1998 (html)
NICMOS STScI Analysis Newsletter 2
Focus update
Advice on the use of ORIENT, PATTERN-ORIENT, and POS TARG for Cycle 7
The Mr. Staypuft anomaly
The 'non-zero zeroth read problem'
NICMOS Group 31 May 1997 (html)