NHSC Data Processing Workshop Pasadena 2 nd -9 th Feb Map-Making Basics. C. Kevin Xu (NHSC/IPAC) page 1 PACS

Transcription

1 Map-Making Basics C. Kevin Xu (NHSC/IPAC) page 1

2 Contents SPIRE mapmakers: Naïve Mapper (default) MADMapper (more complicated but not better) De-striper (still in development, not covered here) Baseline Removers: Median baseline remover module (default) Polynomial baseline for whole obs (embedded in Mappers) Polynomial baseline scan-by-scan (a Jython script) Median baseline for extended sources (a Jython script) A comprehensive baseline remover module for pipeline (still in development, not covered here) page 2

3 SPIRE Naïve Mapper Flux of a sky pixel is the simple average of all signal samplings (by all detectors) in the pixel, with no weighting for either the measurement error or the position of a sampling: Sky pixel f 4 f 5 f 3 f 1 f 2 f pixel = n i n f i signal samplings page 3

4 MADMapper & Comparison to NaïveMapper MADMapper: Maximum-Likelihood algorithm, minimize uncorrelated 1/f noise Diff. map: mapplw=madscanmapper(level1, array="plw") NaïveMapper: simple average mapplw=naivescanmapper(level1, array="plw") MADMap does not improve over the simple naïve map: no uncorr. 1/f in SPIRE!! MADmap has shadows around the central bright source, due to ringing!! page 4 C.K. Xu (SPIRE) 4

5 MADMapper & Comparison to NaïveMapper MADMapper: Maximum-Likelihood algorithm, minimize uncorrelated 1/f noise Diff. map: mapplw=madscanmapper(level1, array="plw") NaïveMapper: simple average mapplw=naivescanmapper(level1, array="plw") MADMap does not improve over the simple naïve map: no uncorr. 1/f in SPIRE!! MADmap has shadows around the central bright source, due to ringing!! page 5 C.K. Xu (SPIRE) 5

6 : why it is needed? example: PSW map without you see nothing but stripes stripes: offsets of individual detector channels on the order of ~ 0.1Jy/beam. caused by errors of Temperature Drift Correction (~ a few % ~10 Jy/beam). page 6 C.K. Xu (SPIRE) 6

7 methods in pipeline Two methods available in standard pipeline: 1. A stand-along module (default): Subtracting the median from individual scans of each detector. 2. Embedded in Mappers: Subtracting a polynomial baseline from the timeline of each channel for the entire observation. Signal (Jy/beam) Obs(uncorrected) Poly-order =1 (linear) baseline subtr., whole obs med subtr, scan-by-scan Time (second) little differences between maps from the two methods, slight advantage for method 2 in taking off slope while preserving extended signals. page 7 C.K. Xu (SPIRE) 7

8 Comparison between two methods: An example (NGC 5315, PSW) method1: scan-by-scan med difference method2: linear baseline of entire obs little differences between maps from the two methods, slight advantage for method 2 in taking off slope while preserving extended signals. page 8 C.K. Xu (SPIRE) 8

9 Scan-by-scan polynomial script Stripes caused by V bias drift (during the burp ) can be removed by scan-by-scan polynomial (see example below). Script removebaselinepoly.py is included in the workshop package. Median 5 th order polynomial 9 th order polynomial page 9 ~4.5 deg scan length 20 /sec scan speed (parallel mode) 9

10 Scan-by-scan polynomial script Stripes caused by V bias drift (during the burp ) can be removed by scan-by-scan polynomial (see example below). Script removebaselinepoly.py is included in the workshop package. Median 5 th order polynomial 9 th order polynomial page 10 ~4.5 deg scan length 20 /sec scan speed (parallel mode) 10

11 Scan-by-scan polynomial script Stripes caused by V bias drift (during the burp ) can be removed by scan-by-scan polynomial (see example below). Script removebaselinepoly.py is included in the workshop package. Median 5 th order polynomial 9 th order polynomial page 11 ~4.5 deg scan length 20 /sec scan speed (parallel mode) 11

12 Scan-by-scan polynomial script Stripes caused by V bias drift (during the burp ) can be removed by scan-by-scan polynomial (see example below). Script removebaselinepoly.py is included in the workshop package. Median 5 th order polynomial 9 th order polynomial The longer the scan, the higher the degree page 12 ~4.5 deg scan length 20 /sec scan speed (parallel mode) 12

13 Scan-by-scan polynomial script Stripes caused by V bias drift (during the burp ) can be removed by scan-by-scan polynomial (see example below). Script removebaselinepoly.py is included in the workshop package. Median 5 th order polynomial 9 th order polynomial page 13 ~4.5 deg scan length 20 /sec scan speed (parallel mode) 13 replace this

14 Scan-by-scan polynomial script Stripes caused by V bias drift (during the burp ) can be removed by scan-by-scan polynomial (see example below). Script removebaselinepoly.py is included in the workshop package. Median 5 th order polynomial 9 th order polynomial page 14 ~4.5 deg scan length 20 /sec scan speed (parallel mode) 14

15 an off-line script for extended sources Median removal does a poor job for observations of extended sources (over-subtraction because the source bias the median high) Remedy: an off-line script removebaselineextendsource.py (provided by NHSC) Median source-masked med subtr. diff. map data inside the circle are masked in med. calculation page 15 15

16 an off-line script for extended sources Median removal does a poor job for observations of extended sources (over-subtraction because the source bias the median high) Remedy: an off-line script removebaselineextendsource.py (provided by NHSC) Median source-masked med subtr. diff. map data inside the circle are masked in med. calculation page 16 16

17 an off-line script for extended sources Median removal does a poor job for observations of extended sources (over-subtraction because the source bias the median high) Remedy: an off-line script removebaselineextendsource.py (provided by NHSC) Median source-masked med subtr. diff. map Do it with SPIA data inside the circle are masked in med. calculation page 17 17

18 an off-line script for extended sources Median removal does a poor job for observations of extended sources (over-subtraction because the source bias the median high) Remedy: an off-line script removebaselineextendsource.py (provided by NHSC) Median source-masked med subtr. diff. map data inside the circle are masked in med. calculation page 18 18

19 Scan-by-scan polynomial script Stripes caused by V bias drift (during the burp ) can be removed by scan-by-scan polynomial (see example below). Script removebaselinepoly.py is included in the workshop package. Median 5 th order polynomial 9 th order polynomial Scan length: ~4.5 deg Scan speed: 20 /sec (parallel mode) page 19 19

20 Scan-by-scan polynomial script Stripes caused by V bias drift (during the burp ) can be removed by scan-by-scan polynomial (see example below). Script removebaselinepoly.py is included in the workshop package. Median 5 th order polynomial 9 th order polynomial Scan length: ~4.5 deg Scan speed: 20 /sec (parallel mode) page 20 20

21 Scan-by-scan polynomial script Stripes caused by V bias drift (during the burp ) can be removed by scan-by-scan polynomial (see example below). Script removebaselinepoly.py is included in the workshop package. Median 5 th order polynomial 9 th order polynomial Scan length: ~4.5 deg Scan speed: 20 /sec (parallel mode) page 21 21

22 Scan-by-scan polynomial script Stripes caused by V bias drift (during the burp ) can be removed by scan-by-scan polynomial (see example below). Script removebaselinepoly.py is included in the workshop package. 5 th order polynomial 9 th order polynomial Median The baseline longer removal the scan, The higher the degree Scan length: ~4.5 deg Scan speed: 20 /sec (parallel mode) page 22 22

23 Scan-by-scan polynomial script Stripes caused by V bias drift (during the burp ) can be removed by scan-by-scan polynomial (see example below). Script removebaselinepoly.py is included in the workshop package. Median User s Script 5 th order polynomial 9 th order polynomial replace this block with: scans=removebaselinepoly(level1,polydegree=9) Scan length: ~4.5 deg Scan speed: 20 /sec (parallel mode) page 23 23

24 Scan-by-scan polynomial script Stripes caused by V bias drift (during the burp ) can be removed by scan-by-scan polynomial (see example below). Script removebaselinepoly.py is included in the workshop package. Median 5 th order polynomial 9 th order polynomial Scan length: ~4.5 deg Scan speed: 20 /sec (parallel mode) page 24 24