IRAC Instrument Handbook - IRSA - California Institute of Technology

List of Figures 191
IRAC Instrument Handbook
THOSE SIX REGIONS. THE BOX SIZE IS INCREMENTALLY INCREASED UNTIL THE BOX
LENGTH IS MANY HUNDREDS OF PIXELS. FOR REFERENCE THE SOLID LINE SHOWS
THE EXPECTED LINEAR RELATION. ...................................................................................61
FIGURE 4.11. NOISE AS A FUNCTION OF EXPOSURE TIME (NUMBER OF FRAMES) IN
CHANNEL 1. THE RESULTS FROM THE WARM MISSION DATA ARE SHOWN WITH X’S
AND THE EXPECTED BEHAVIOR WITH THE SOLID LINE. THE RESULTS FROM THE
CRYOGENIC MISSION ARE SHOWN WITH OPEN SQUARES AND THE EXPECTED
BEHAVIOR WITH THE DASHED LINE. .................................................................................63
FIGURE 4.12. NOISE AS A FUNCTION OF EXPOSURE TIME (NUMBER OF FRAMES) IN
CHANNEL 2. THE RESULTS FROM THE WARM MISSION DATA ARE SHOWN WITH X’S
AND THE EXPECTED BEHAVIOR WITH THE SOLID LINE. THE RESULTS FROM THE
CRYOGENIC MISSION ARE SHOWN WITH OPEN SQUARES AND THE EXPECTED
BEHAVIOR WITH THE DASHED LINE. .................................................................................64
FIGURE 4.13: POSITION OF A STAR IN THE X (LEFT) AND Y (RIGHT) AXES OF IRAC DURING
A LONG (8 HR) OBSERVATION. THE ~ 3000 SEC OSCILLATION IS SUPERPOSED ON A
SLOW DRIFT OF THE STAR TRACKER TO TELESCOPE ALIGNMENT...............................67
FIGURE 5.1: DATA FLOW FOR PROCESSING A RAW IRAC SCIENCE DCE INTO A BCD THAT
IS DESCRIBED IN THIS CHAPTER. .......................................................................................70
FIGURE 5.2: INSBPOSDOM WORKS ONLY ON THE TWO INSB ARRAYS (CHANNELS 1 & 2)
AND REVERSES THE SENSE OF INTENSITIES.....................................................................72
FIGURE 5.3: DIAGRAM OF THE WRAPPING OF NEGATIVE VALUES DUE TO TRUNCATION
OF THE SIGN BIT. ..................................................................................................................73
FIGURE 5.4: APPLICATION OF IRACWRAPCORR TO CHANNEL 1 DATA. THE MANY
APPARENTLY “HOT” PIXELS ARE ACTUALLY WRAPPED NEGATIVE VALUES, WHICH
ARE DETECTED ON THE BASIS OF THEIR VASTLY EXCEEDING THE PHYSICAL
SATURATION VALUE FOR THE DETECTORS, AND CORRECTED BY SUBTRACTING THE
APPROPRIATE VALUE. REAL HOT PIXELS DO NOT EXCEED THE PHYSICAL
SATURATION VALUE, AND HENCE ARE NOT CHANGED. ................................................75
FIGURE 5.5: ILLUSTRATION OF BIT TRUNCATION USED BY IRAC FOR GROUND
TRANSMISSION, NECESSITATING IRACNORM. THE INTERNALLY STORED 24-BIT
WORD IN TRUNCATED TO 16 BITS, WITH A SLIDING WINDOW SET BY THE BARREL
SHIFT VALUE. ILLUSTRATED IS THE CASE FOR ABARREL=4..........................................75
FIGURE 5.6: CORRECTION OF CABLE-INDUCED BANDWIDTH ERROR BY IRACEBWC. THE
ILLUSTRATED DATA SHOW A COSMIC RAY HIT...............................................................78
FIGURE 5.7: FIRST-FRAME EFFECT. DARK COUNTS AS A FUNCTION OF INTERVAL
BETWEEN FRAMES. THIS FIGURE IS FOR A 30 SECOND EXPOSURE FRAME. .................79
FIGURE 5.8: CORRECTION OF PSEUDO-MUXBLEED FOR CHANNEL 1. SHOWN IS A BRIGHT
SOURCE WITHIN A CALIBRATION AOR AND A BACKGROUND OF SOURCES UNDER
THE MUXBLEED LIMIT. ........................................................................................................80
FIGURE 5.9: TRANSPOSITION OF AN IRAC CHANNEL 1 DARK IMAGE BY THE IMFLIPROT
MODULE. ................................................................................................................................85
FIGURE 5.10. AN IMAGE SHOWING ALL FOUR READOUT CHANNEL IMAGES SIDE BY SIDE.
THESE HAVE BEEN OBTAINED BY REARRANGING THE COLUMNS IN THE ORIGINAL