NICMOS Anomalies

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.

The NICMOS 'Pedestal' Effect
This memo describes our current understanding of the "pedestal" effect in NICMOS images.
NICMOS Group 10 Aug 1998 (html)

Memo Describing the 'Bars' Phenomenon
This memo describes the artifact (bars), its probable source, how to avoid it in upcoming observations, and what to do about it if it appears in your data.
NICMOS Group 04 Nov 1997 (pdf)

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.

NICMOS ISR 2003-010: Removal of Cosmic Ray persistence From Science Data using the Post-SAA Darks
Latent or persisten images of cosmic ray hits following HST transits of the South Atlantic Anomaly (SAA) can signicantly increase the noise in subsequent NICMOS science images. By taking a pair of DARK exposures immediately following the exit of the SAA, a map of the persistent signal can be made and then used to subtract this signal from the impacted images in that orbit, thereby recovering much of the original S/N. We here describe an algorithm to do this
E. Bergeron and M. Dickenson 06 Oct 2003 (pdf)

NICMOS ISR-99-010: NICMOS Temperature-Specific Darks
The various components of NICMOS dark images have been modeled and combined to make synthetic dark calibration files which are intended for use with observations in a temperature range from 61 to ~75 K.
B. Monroe 09 Nov 1999 (pdf)

NICMOS ISR-99-009: NICMOS Dark Current Anomaly: Models and Test Plans
The NICMOS dark current anomaly (the "bump") was a transient enhancement of the detector dark current observed during the on-orbit warmup of the instrument after its cryogen depletion in January 1999. We summarize our current understanding of the mechanism which causes the effect, and summarize plans to test the most likely scenario.
T. Boeker 25 Oct 1999 (pdf)

NICMOS ISR-99-008: GROT in NICMOS Cameras
Grot is exhibited as small areas of reduced sensitivity, most likely due to flecks of anti-reflective paint scraped off the optical baffles as they were forced against each other. This paper characterizes grot associated with all three cameras. The main products of this analysis are grot masks for each of the cameras.
M. Sosey 20 Sep 1999 (pdf)

NICMOS ISR-1999-012 NICMOS Calibration Lamp Stability
Characterizes the output, over its lifetime, of NICMOS internal calibration lamp number 1.
L. Bergeron 01 Mar 1999 (pdf)

NICMOS ISR-99-002: Color Dependence of NICMOS Flatfields
We report two methods for obtaining color dependent flat fields for NICMOS data. Programs to produce both types of flatfield are described, along with the reference data necessary.
A. Storrs 26 Feb 1999 (pdf)

NICMOS ISR-98-011: NIC1 Narrow-band Earth Flats
We have created a set of 8 NIC1 narrow-band flats by combining images of streaked Earth flats. The processing of the flats, preliminary image analysis of the combined flats, and photometric analysis using a solar analog (P330E) and a white dwarf (G191) are discussed. We also discuss several new anomalies found in the data.
D. Gilmore 22 Jul 1998 (pdf)

NICMOS ISR-98-003: NICMOS Camera 3 Pointed Flats
This report describes the NICMOS Camera 3 pointed flat fields program.
A. Schultz 12 Mar 1998 (pdf)

NICMOS ISR-98-002: First NICMOS On-Orbit Flat-Fields: Results from SMOV Data
This ISR presents the first set of on-orbit flat-field images obtained for NICMOS.
D. Calzetti 05 Mar 1998 (pdf)

NICMOS ISR-98-001: Cosmic Ray Persistence in NICMOS Data
In this report, we discuss the implications of cosmic ray persistence for the overall quality of NICMOS data, quantify the tradeoff between data quality and timing of observations relative to SAA passages, and discuss possible strategies to minimize the problem.
J. Najita 25 Feb 1998 (pdf)

NICMOS ISR-032: NICMOS SAA Contour Test: Results from SMOV data
This Instrument Science Report presents the results of the analysis of the South Atlantic Anomaly (SAA) contour test executed in June 1997.
D. Daou 31 Dec 1997 (pdf)

NICMOS ISR-026: Characteristics of NICMOS Detector Dark Observations
This ISR describes the characteristics of the dark current for the NICMOS detectors. We then describe a recipe for generating `synthetic' dark current calibration reference files, which could be used to generate darks for any arbitrary sequence of MULTIACCUM reads, and present results of a comparison of such a synthetic dark with observed data.
C. Skinner 14 Oct 1997 (pdf)

NICMOS ISR-024: Persistence in NICMOS: Results from On-Orbit data
This ISR presents the results of the analysis of NICMOS persistence data taken as part of the Servicing Mission Orbital Verification (SMOV).
D. Daou 12 Sep 1997 (pdf)

NICMOS ISR-023: Persistence in NICMOS: Results from Thermal Vacuum Data
This ISR presents an analysis of the System Level Thermal Vacuum (SLTV) persistence tests performed with NICMOS.
D. Daou 16 Jun 1997 (pdf)

NICMOS ISR-022: Cosmic Rays on NICMOS: Results from On-Orbit Data
NICMOS dark frames obtained during SMOV are used to derive the sensitivity of the detectors to cosmic ray hits.
D. Calzetti 07 Jun 1997 (pdf)

NICMOS ISR-019: Cosmic Rays on NICMOS: Results from Thermal Vacuum Data
The analysis of NICMOS data obtained during the System Level Thermal Vacuum Test in August 1996 has yielded some information on the sensitivity of the NICMOS detectors to cosmic ray hits.
D. Calzetti 27 Nov 1996 (pdf)

NICMOS ISR-95-006: Effects of the NICMOS Array Flat-field Response on Observations.
In this report we use the results obtained from our detailed flat-field response tests to analyze numerically the likely effect of this behaviour on NICMOS photometry and imaging.
C. Skinner 01 Dec 1995 (pdf)

NICMOS ISR-95-005: Characterisation of NICMOS Array Flat-field Response.
This ISR describes the likely flat-field performance of the NICMOS array detectors. A series of tests of one of the flight spare arrays are described, and then the results of these are presented, along with some initial analysis.
C. Skinner 02 Nov 1995 (pdf)

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)