A2415 430 MHz mapping aug09
image of fields mapped to 22feb11
26oct10: links to images removed till jun11 when data becomes
to see images
image of what's
been done (jpeg)
field with sources
Links to Sections and Plots:
The steps in processing the data
Map positions raw data
positions for each field (.ps) (.pdf).
The individual maps by field
average maps for each field (.gif)
Mosaicing the 11 + 4 maps
Notes on the fields:
final mosaiced maps (.gif):
A2415 mapped 9 overlapping fields at 430 MHz using the
gregorian. Data was sampled at 1 hz. Each field
covered in the ra and then the dec direction for basket weaving. The
MHz bands with 2048 channels were used to computed the total power.
After processing the data the polA data showed instabilities, so the
maps,images were only made with the polB data. The 4 maps made for
a2125 were also included in the mosaicing.
Data was taken aug-dec09 and dec10. The a2125
data was then included in the final combined map.
|a2125 fields (_05 added to
|00:50:38 , 23:31:00
||00:34:42 , 28:31:00
||00:50:55 , 32:01:00
||00:34:25 , 32:01:00
The steps in processing the data were:
The steps in
- see a2125 steps in making
- Mosaic the 11 + 4 fields together.
- Mosaicking was done on a pair wise basis looking at the ra
dec overlaps. This is not the optimum method but ...
The plots shows the sampled
map positions for each field (.ps) (.pdf).
- Pages 1-3 shows the az,za positions for each field
- Page 4 has the ra/dec sampled positions for each field.
Removing Tsys (top)
We need to remove Tsys (excluding the sky
contribution since that is what we want to measure). This is
Plots of Tsys for fields 1 thru 14.
- Create a model of the za dependence of Tsys using the x102
(tsysX102M). Normalize this so tsysX102M(za=10) is 1.
- For each map (ra,dec strips processed together):
- fit for the scale factor TsysData(za)=tsysX102M(za)*scale
- TsysRemoved= TsysData(za) - tsysX102M(za)*scale .. this
done separately for pola, polb.
- If the actual Tsys changes over time ,this should help correct
- If the cal Values change (without remeasuring them), then the
of tsysRemoved should be ok, but the scaleFactor of tsysRemoved
still be off (since we didn't scale it by the change in the cal
- Plot (TsysA/TsysB -1) before
data has been converted from correlator counts to kelvins
cals (after cal fitting).
TsysA/TsysB-1 vs za
TsysA/TsysB -1 vs az
-1 by field
green lines separate fields.
- Cal scale factors by field
values are computed from the cals on every strip. they
correlator counts to Kelvins.
(polA) ,red(polB) after cal fitting
blue(polB) before cal fitting
fitting takes adjacent cals (with no attenuation changes)
and does a
linear fit to the measured scaling factor ( throwing out
fit is then used to convert correlator counts to kelvins
the individual measurements.
there are no outliers than the blue,green overlay the black,
Some of these things will be
by the basket weaving.
- Global fitting of all the
- Fitting Tsys by Field.
- When the images are made,
Tsys is removed
from the ra and dec scans simulataneously
- We left them separate here to see if the
ra, or dec scans had any outliers.
residuals by field
(rascans and decscans together).
as above plots but the scaling fit is done with ra and dec
together. This is how the images are made.
is polA, red is polB.
scale factor and errors are included in the title for each
- Fields11A,12,3 Some fields that
mesh well (.ps)
page shows the Tsys-fit (by map) plotted vs rahr and dec to
there is any obvious bad data.
is pola, red is polB
decstrips vs ra. raHr 1.51 -> end polA has slope to it.
- Since i didn't use polA, shouldn't matter.
2 ra strips vs dec.
- decs 26->26.6 polB is low. This will
be part of the overlap with Field14 below it.
4: decstrips vs ra
- ra 1.27 -> 1.37 hrs, PolB is high and
polA is low. This is part of the overlap with Field 4
(to the right).
- Page 3: Field3
4 dec strips vs ra.
- looks like a jump at middle of map: ra
1.15 hours. Both polA and B go from low to high
After removing Tsys and scaling to janskies, each
was gridded. The process was:
- grid the ra driven and dec driven maps separately to the same
basketweave the two maps. Create an average map and a
map after basketweaving.
- Grid spacing was 3 arcminutes.
- The gridding function used a gaussian with a fwhm of 5.5 (it
with a gaussian of 11 aminutes).
- The gridding function extended out to about 30 arcminutes.
- A sin projection was used to project onto the 2-d
average maps for each field (.gif) show the results.
- The basket weaving will try an remove offsets in strips.
The 11 fields from a2415 plus the 4 fields of
were to be combined into a single
The processing to do this was:
The plots below show the pairwise difference of the overlap regions
- take each pair of overlapping maps.
- Interpolate the first map of each pair to the grid
second (within the overlap region).
- compute mapRaDif=(map2 - interpolated Map1) in the
- Fit a linear polynomial to the differences as a function of
- Correct the two maps by subtracting half the difference from
half the difference to map 1
- Repeat steps 1 5 with the corrected fields, using the dec
of the pairwise maps.
- 21feb11: changed so that 1-6 only corrects 20% of the
It then interates 1-6 5 times. This gets rid of jumps caused by
- the units are Janskies (multiply by 10 to get kelvins).
- Pages 1-3. Overlap in ra direction with
map1-map2Interpolated plotted vs ra.
- The red line is the fit vs ra.
- Page 2, frame 2 Field12 - Field11A vs ra has a large
offset and slope
- Pages 3-7. Overlap in dec direction with map1 -
plotted vs dec.
- Each set is the start of iteration i (i=1 to 5). the last one
when everything is done. The set shows how the correction
progresses with a correction factor of 20% per iteration.
final mosaiced maps (.gif):
The final mosaiced maps with positions
- The x,y positions are just grid points along the ra,dec
- This used a 5.5 arcmin gridding function. The final resolution
Notes on the fields. (top)
- Trouble with PolA 2009 data.
- There were large jumps in polA. see 10aug09
- Ended up just using polB when making final map (but it is
- Dec10: TsysField11A, TsysField14
- Looking at the globally fit data, TsysA - TsysFit has a
of -9Kelvins for these 2 fields
taken in dec10.
- TsysB11a -TsysFit is +4K
- Must be that calA has changed since the calibration fit
- Field11A,Field12 dec overlap.
- there is an offset in the dec overlap of these fields of .1
and a slope of about .2 Jy across the map. This is removed
during the mosaicing.
- Field 12.
- Dec strips at low ra , polA is low and polB is high.