SSC Home Page
Spitzer Science Center
 SSC Home -  Active Mission -  Overview -  IRAC -  IRS -  MIPS -  Data Archive -  Data Analysis & Tools
Knowledgebase: IRAC
What is the pixel phase effect and do I need to worry about it?
Posted by Seppo Laine on 29 January 2009 12:00 PM
The pixel phase effect is due to the varying sensitivity of a pixel across its area. The sensitivity is usually highest in the center of the pixel. This effect is seen most clearly in channel 1 data, but appears to exist at a detectable level in channel 2 as well. If your data are well dithered and sample a variety of pixel phases (the object is centered on various parts of pixels), this effect will probably average out mostly (in cases of a dozen or more dithers). With significantly fewer than a dozen or so dithers you need to apply a correction to each BCD. See the IRAC calibration files web page and also the list of contributed IRAC software under the Data Analysis and Tools web pages for more information and useful correction codes for the pixel phase effect. This effect can be as large as 4% (from the largest downward correction to the largest upward correction) in the cryogenic data and 7% - 8% in the warm IRAC data.