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Subsections


7.3 High-Level Scientific Data Products

Once data have been assembled, poor quality parts traced, transient models calculated and ideal calibration components identified, it is possible to calculate and analyse fluxes in photometric units. The most important data products are the images calculated for every OBS-mode SCD that are given in the CMAP file. The other products are based on further analysis of CMAP images. The products contain cross references to be able to trace the path of the analysis, CMAP[1].OBSINDEX(*) to CCIM ; CMOS[1].MAPINDEX(*) to CMAP; CPSL[1].MAPINDEX(*) to CMAP; and CSSP[1].PSLINDEX(*,*) to CPSL.


7.3.1 ISOCAM basic imaging $\Longrightarrow$CMAP

The flux maps in physical units given in CMAP 3-row FLUX, FLUX_ERR, EXPOSURE images for each OBS-mode SCD are calculated from all good-quality transient-corrected data available with the reference (J2000) celestial coordinates of the SCD, which were taken from the IRPH for prime or CRPH for parallel data, with no corrections made for pointing jitter. After dark-current and detector and optical flat-field corrections have been applied in detector units using the best calibration components available as reported in the CUFF: 


     LW Drkm       TINT
     Tried:          15
     Got:            15
     LW Dflt       EWHL    FCVF    SWHL    PFOV    TINT
     Tried:         308     140      88     360      15
     Got:           308     125     220     192      36
     LW Oflt       PFOV    EWHL    FCVF    SWHL    TINT
     Tried:         360     308     140      88      15
     Got:           360     308     140      88      15
conversion to Jansky units is made using the appropriate sensitivity factor from CCGLWSPEC or CCGSWSPEC: 

     LW Spec       FCVF    EWHL
     Tried:         140     308
     Got:           140     308
The FLUX_ERR errors are calculated by a quadratic combination of the variance of the data within the SCD with errors in the calibration data. The usual non-uniformity of the EXPOSURE images is mainly because of the randomness of the impact of glitches. Each image is labelled with several auxiliary data, many of which conform to FITS conventions such as CMAP[1].MJD-OBS(*) and CMAP[1].MJD-END(*). Others specify wavelength and bandwidth, for example. Finally, a summary of each CMAP 3-row image is reported in the CUFF: 

     CMAP(181:183) 1996-11-11(15:13:01) to 1996-11-11(15:13:56)
     RA(J2000)=20 22 24.033 : DEC(J2000)=+40 31 31.08 : ROLL(J2000)=249.30
     14.0-15.8 micron LW RPID=[20,4] image of [32*32] [6"] pixels
     <FLUX>=0.58mJy/arcsec^2  <FLUX_ERR>=0.31mJy/arcsec^2  <EXPOSURE>=45.5s
     CCIM(OBS:DRK:FLT)=(190:0:0)


7.3.2 ISOCAM combination imaging $\Longrightarrow$CMOS

There were 3 ways in which CMAP images could be combined to give the more complex 3-row images in the CMOS, which is produced if, and only if, more than one direction was observed in a fixed optical configuration, namely raster pointing mode observations; beam-switch observations; and solar system tracking observations.


7.3.2.1 Raster pointing mode observations

The most usual was the compensation for the restricted ISOCAM field of view offered by the pointing system's raster capability in which a rectangular array of celestial coordinates were surveyed at a fixed instrumental configuration allowing the component images to be combined into a single mosaic of larger extent. The raster orientation and 2-D step sizes were at the observer's discretion with no guarantee that the component maps were conveniently aligned. In some cases, observers chose raster step sizes that were small enough for there to be a good deal of redundancy in overlapping areas of sky with the intention of minimising any systematic errors due to transient effects or calibration uncertainties. Rasters with very small step sizes less than a few pixels were often known as microscans although their treatment did not differ from other rasters in AAC, ignoring the ambitions of some users who may have have had super-resolution in mind. The reference coordinate frame of the 3-row CMOS images is arbitrary and AAC's choice was to use a direction as near as possible to the centre of the raster that optimised the alignment between the component maps, whose pixel size was preserved. Finally, the pixels of the resultant mosaic were calculated from a weighted average of contributing component pixels, taking any misaligment into account using the area of overlap. In some CAM parallel rasters performed therefore for the benefit of observers using other instrument, the raster steps size were bigger than the component CMAP images which did not overlap at all, causing only partial coverage of the resultant CMOS that is criss-crossed with stripes of undefined flux. Not unexpectedly, rasters of this type were the largest of all, reaching $1500\times1500$ pixels. A summary of each raster's CMOS 3-row image is reported in the CUFF: 


     CMOS(1:3)     1996-11-11(14:13:39) to 1996-11-11(16:08:57)
     RA(J2000)=20 22 18.000 : DEC(J2000)=+40 09 40.01 : ROLL(J2000)=249.28
     14.0-15.8 micron LW image of [480*296] [6"] pixels
     <FLUX>=0.82mJy/arcsec^2  <FLUX_ERR>=0.15mJy/arcsec^2  <EXPOSURE>=72.8s


7.3.2.2 Beam-switch observations

In a simulation of traditional IR observational methods, there was a special CAM03 AOT designed for beam-switch in which component images of a fixed designated source field were interleaved with images of one or more reference offset fields which were supposed to provide a reliable background estimate. The combination image written to the CMOS in this case is the difference between the source and a background estimate. During the mission it was soon discovered that it would make sense to swap the order of source and reference images although it did not prove possible to alter some of the on-board software accordingly, so that the attached beam-switch labels are the wrong way round. AAC makes an effort to identify this condition by trapping negative fluxes in the combination image, in which case suitable action is taken and reported thus in the CUFF: 


     Reversing source and reference positions
The beam-switch configuration, the component CMAPs and the resultant CMOS 3-row images are reported in the CUFF as in the following example extracts which shows an observation with 4 sequences with <4> background fields at two wavelengths. The first CMOS has the badly illuminated column [1] trimmed from the final image. 

     T=5315s C03 4*<4> beam-switch observation of N4038_BS_4REF
     RA(J2000)=12 01 53.781 : DEC(J2000)=-18 52 42.51 : ROLL(J2000)=118.03

     146370023<UTK<146426926 Badly illuminated column [1]

     CMAP(1:3)   5.1-8.3 micron LW On<1> image of [32*32] [6"] pixels
     CMAP(4:6)   5.1-8.3 micron LW Off<1> image of [32*32] [6"] pixels
     CMAP(7:9)   5.1-8.3 micron LW On<2> image of [32*32] [6"] pixels
     CMAP(10:12) 5.1-8.3 micron LW Off<2> image of [32*32] [6"] pixels
     CMAP(13:15) 5.1-8.3 micron LW On<3> image of [32*32] [6"] pixels
     CMAP(16:18) 5.1-8.3 micron LW Off<3> image of [32*32] [6"] pixels
     CMAP(19:21) 5.1-8.3 micron LW On<4> image of [32*32] [6"] pixels
     CMAP(22:24) 5.1-8.3 micron LW Off<4> image of [32*32] [6"] pixels
     CMAP(25:27) 5.1-8.3 micron LW On<1> image of [32*32] [6"] pixels
     CMAP(28:30) 5.1-8.3 micron LW Off<1> image of [32*32] [6"] pixels
     CMAP(31:33) 5.1-8.3 micron LW On<2> image of [32*32] [6"] pixels
     CMAP(34:36) 5.1-8.3 micron LW Off<2> image of [32*32] [6"] pixels
     CMAP(37:39) 5.1-8.3 micron LW On<3> image of [32*32] [6"] pixels
     CMAP(40:42) 5.1-8.3 micron LW Off<3> image of [32*32] [6"] pixels
     CMAP(43:45) 5.1-8.3 micron LW On<4> image of [32*32] [6"] pixels
     CMAP(46:48) 5.1-8.3 micron LW Off<4> image of [32*32] [6"] pixels

     CMAP(49:51) 5.1-8.3 micron LW On<1> image of [32*32] [6"] pixels
     CMAP(52:54) 5.1-8.3 micron LW Off<1> image of [32*32] [6"] pixels
     CMAP(55:57) 5.1-8.3 micron LW On<2> image of [32*32] [6"] pixels
     CMAP(58:60) 5.1-8.3 micron LW Off<2> image of [32*32] [6"] pixels
     CMAP(61:63) 5.1-8.3 micron LW On<3> image of [32*32] [6"] pixels
     CMAP(64:66) 5.1-8.3 micron LW Off<3> image of [32*32] [6"] pixels
     CMAP(67:69) 5.1-8.3 micron LW On<4> image of [32*32] [6"] pixels
     CMAP(70:72) 5.1-8.3 micron LW Off<4> image of [32*32] [6"] pixels
     CMAP(73:75) 5.1-8.3 micron LW On<1> image of [32*32] [6"] pixels
     CMAP(76:78) 5.1-8.3 micron LW Off<1> image of [32*32] [6"] pixels
     CMAP(79:81) 5.1-8.3 micron LW On<2> image of [32*32] [6"] pixels
     CMAP(82:84) 5.1-8.3 micron LW Off<2> image of [32*32] [6"] pixels
     CMAP(85:87) 5.1-8.3 micron LW On<3> image of [32*32] [6"] pixels
     CMAP(88:90) 5.1-8.3 micron LW Off<3> image of [32*32] [6"] pixels
     CMAP(91:93) 5.1-8.3 micron LW On<4> image of [32*32] [6"] pixels
     CMAP(94:96) 5.1-8.3 micron LW Off<4> image of [32*32] [6"] pixels

     CMAP(97:99)   11.6-17.0 micron LW On<1> image of [32*32] [6"] pixels
     CMAP(100:102) 11.6-17.0 micron LW Off<1> image of [32*32] [6"] pixels
     CMAP(103:105) 11.6-17.0 micron LW On<2> image of [32*32] [6"] pixels
     CMAP(106:108) 11.6-17.0 micron LW Off<2> image of [32*32] [6"] pixels
     CMAP(109:111) 11.6-17.0 micron LW On<3> image of [32*32] [6"] pixels
     CMAP(112:114) 11.6-17.0 micron LW Off<3> image of [32*32] [6"] pixels
     CMAP(115:117) 11.6-17.0 micron LW On<4> image of [32*32] [6"] pixels
     CMAP(118:120) 11.6-17.0 micron LW Off<4> image of [32*32] [6"] pixels
     CMAP(121:123) 11.6-17.0 micron LW On<1> image of [32*32] [6"] pixels
     CMAP(124:126) 11.6-17.0 micron LW Off<1> image of [32*32] [6"] pixels
     CMAP(127:129) 11.6-17.0 micron LW On<2> image of [32*32] [6"] pixels
     CMAP(130:132) 11.6-17.0 micron LW Off<2> image of [32*32] [6"] pixels
     CMAP(133:135) 11.6-17.0 micron LW On<3> image of [32*32] [6"] pixels
     CMAP(136:138) 11.6-17.0 micron LW Off<3> image of [32*32] [6"] pixels
     CMAP(139:141) 11.6-17.0 micron LW On<4> image of [32*32] [6"] pixels
     CMAP(142:144) 11.6-17.0 micron LW Off<4> image of [32*32] [6"] pixels

     CMAP(145:147) 11.6-17.0 micron LW On<1> image of [32*32] [6"] pixels
     CMAP(148:150) 11.6-17.0 micron LW Off<1> image of [32*32] [6"] pixels
     CMAP(151:153) 11.6-17.0 micron LW On<2> image of [32*32] [6"] pixels
     CMAP(154:156) 11.6-17.0 micron LW Off<2> image of [32*32] [6"] pixels
     CMAP(157:159) 11.6-17.0 micron LW On<3> image of [32*32] [6"] pixels
     CMAP(160:162) 11.6-17.0 micron LW Off<3> image of [32*32] [6"] pixels
     CMAP(163:165) 11.6-17.0 micron LW On<4> image of [32*32] [6"] pixels
     CMAP(166:168) 11.6-17.0 micron LW Off<4> image of [32*32] [6"] pixels
     CMAP(169:171) 11.6-17.0 micron LW On<1> image of [32*32] [6"] pixels
     CMAP(172:174) 11.6-17.0 micron LW Off<1> image of [32*32] [6"] pixels
     CMAP(175:177) 11.6-17.0 micron LW On<2> image of [32*32] [6"] pixels
     CMAP(178:180) 11.6-17.0 micron LW Off<2> image of [32*32] [6"] pixels
     CMAP(181:183) 11.6-17.0 micron LW On<3> image of [32*32] [6"] pixels
     CMAP(184:186) 11.6-17.0 micron LW Off<3> image of [32*32] [6"] pixels
     CMAP(187:189) 11.6-17.0 micron LW On<4> image of [32*32] [6"] pixels
     CMAP(190:192) 11.6-17.0 micron LW Off<4> image of [32*32] [6"] pixels

     +--------+---------+---------+--------+--------+---------+---------+--------+
 
     CMOS(1:3)     1996-01-10(14:05:49) to 1996-01-10(14:45:20)
     RA(J2000)=12 01 53.781 : DEC(J2000)=-18 52 42.52 : ROLL(J2000)=118.04
     5.1-8.3 micron LW image of [31*32] [6"] pixels
     <FLUX>=0.05mJy/arcsec^2  <FLUX_ERR>=0.02mJy/arcsec^2  <EXPOSURE>=365.0s
 
     CMOS(4:6)     1996-01-10(14:47:35) to 1996-01-10(15:27:06)
     RA(J2000)=12 01 53.782 : DEC(J2000)=-18 52 42.52 : ROLL(J2000)=118.05
     11.6-17.0 micron LW image of [32*32] [6"] pixels
     <FLUX>=0.07mJy/arcsec^2  <FLUX_ERR>=0.11mJy/arcsec^2  <EXPOSURE>=361.2s


7.3.2.3 Solar system tracking observations

A modified pointing system raster mode allowed the tracking of fast-moving objects such as comets and asteroids. Using a known ephemeris, the object's path across the sky was simulated in a series of short duration 1-D raster steps designed to keep the object at fixed detector coordinates. AAC calculates the series of CMAPs as usual, labelled with changing celestial coordinates and then combines them into a single resultant CMOS 3-row image in detector coordinates. In the following example, 4 component CMAP 3-row images starting at RPID=[6,1] make the final $32\times43$ CMOS which is labelled with nominal celestial coordinates as opposed to a more rigorous object-centred system. 


     T=456s C01 tracking observation of 214015 WILSON-HA
     RA(J2000)=00 46 47.583 : DEC(J2000)=+06 31 16.19 : ROLL(J2000)=246.40
 
     CMAP(1:3) 1997-01-28(14:51:08) to 1997-01-28(14:51:58)
     RA(J2000)=00 46 47.651 : DEC(J2000)=+06 31 16.59 : ROLL(J2000)=246.40
     8.6-15.4 micron LW RPID=[6,1] image of [32*32] [1.5"] pixels
     <FLUX>=1.67mJy/arcsec^2  <FLUX_ERR>=0.12mJy/arcsec^2  <EXPOSURE>=29.3s
      
     CMAP(4:6) 1997-01-28(14:51:58) to 1997-01-28(14:52:38)
     RA(J2000)=00 46 47.787 : DEC(J2000)=+06 31 17.38 : ROLL(J2000)=246.40
     8.6-15.4 micron LW RPID=[7,1] image of [32*32] [1.5"] pixels
     <FLUX>=1.66mJy/arcsec^2  <FLUX_ERR>=0.11mJy/arcsec^2  <EXPOSURE>=29.8s
      
     CMAP(7:9) 1997-01-28(14:52:38) to 1997-01-28(14:53:29)
     RA(J2000)=00 46 47.922 : DEC(J2000)=+06 31 18.17 : ROLL(J2000)=246.40
     8.6-15.4 micron LW RPID=[8,1] image of [32*32] [1.5"] pixels
     <FLUX>=1.66mJy/arcsec^2  <FLUX_ERR>=0.11mJy/arcsec^2  <EXPOSURE>=39.5s

 
     CMAP(10:12) 1997-01-28(14:53:29) to 1997-01-28(14:54:09)
     RA(J2000)=00 46 48.058 : DEC(J2000)=+06 31 18.95 : ROLL(J2000)=246.40
     8.6-15.4 micron LW RPID=[9,1] image of [32*32] [1.5"] pixels
     <FLUX>=1.67mJy/arcsec^2  <FLUX_ERR>=0.12mJy/arcsec^2  <EXPOSURE>=29.1s

     +--------+---------+---------+--------+--------+---------+---------+--------+
 
     CMOS(1:3)     1997-01-28(14:51:08) to 1997-01-28(14:54:09)
     RA(J2000)=00 46 47.583 : DEC(J2000)=+06 31 16.19 : ROLL(J2000)=246.40
     8.6-15.4 micron LW image of [32*32] [1.5"] pixels
     <FLUX>=1.66mJy/arcsec^2  <FLUX_ERR>=0.06mJy/arcsec^2  <EXPOSURE>=127.6s


7.3.3 The CMAP point source survey $\Longrightarrow$CPSL

A search is made through all the CMAP images for point sources. The simple method employed detects sources by modelling the observed spatial flux distribution in appropriately sized detection cells using maximum likelihood statistics. The models combine the best-available source PSFs, as reported in the CUFF, and a flat background. The shape of the PSF generally also depends on source position as well as on the instrumental configuration. Knowledge of the noise is vital because an underestimate would lead to the detection of many spurious sources while an overestimate causes weak sources to be missed. AAC adopts an empirical approach by creating an equivalent counts map in which the amplitude of the Poisson noise matches the observed variance of the data. Candidates are first identified assuming a single point source at the centre of pixels after which the models become more sophisticated. As many sources as required are included for a successful fit with all the parameters adjusted simultaneously. The best-fit source positions are chosen by considering the sub-pixel PSF resolution available in the CCGLWPSF and CCGSWPSF files. After final consistency checks, parameters of the detected sources are exported to the CPSL and summarized in the CUFF.


7.3.4 Point source spectra $\Longrightarrow$CSSP

If, and only if, observations were made at more than one wavelength, the CPSL point sources are rearranged in order to create the CSSP, which contains the flux spectra of the various objects detected which are cross-identified by their celestial coordinates. If an object was not detected at a particular wavelength the corresponding flux is assigned the conventional NULL value while a mean value is calculated for multiple detections.

next up previous contents index
Next: 7.4 Browse Products Up: 7. ISOCAM Auto-Analysis Previous: 7.2 Instrumental Procedures and
ISO Handbook Volume II (CAM), Version 2.0, SAI/1999-057/Dc