A2704 430 MHz mapping oct12
image of what's been done (jpeg)
field with sources removed (jpeg)
Links to Sections and Plots:
The steps in processing the data
Map positions raw data
positions for each field (.ps) (.pdf).
Plot: where all 28
fields fit into the final combined map (.ps) (.pdf).
The individual maps by field
The average maps for each field
Mosaicing the 28 fields together
Notes on the fields:
The final mosaiced maps
A2704 mapped 13 overlapping fields at 430 MHz
using the gregorian. Data was sampled at 1 hz. Each field was
covered in the ra and then the dec direction for basket weaving. The
12.5 MHz bands with 2048 channels were used to computed the total
Data was taken oct12-dec12. The a2125 and
a2415 data was then included in the final combined map.
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The steps in processing the data were:
The steps in
processing the data (top)
- see a2125 steps in making
- Mosaic these fields together with the a2415 and a2125 fields
(28 fields total).
The plots shows the sampled
map positions for each field take for a2704 (.ps) (.pdf).
The next plot shows where all 28 fields
fit into the final combined map (.ps) (.pdf).
- Pages 1-3 shows the az,za positions for each field
- Page 4 has the ra/dec sampled positions for each field (labels
are not very helpful).
- each field is plotted in a different color.
- an index (0..27) is plotted on top of each field for
- The list at the bottom of the plot, maps index number of field
name, and average ra, dec 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
explained in a2125.
Plots of Tsys for fields A thru M
- Create a model of the za dependence of Tsys using the x102
data (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
is 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
0 of tsysRemoved should be ok, but the scaleFactor of
tsysRemoved will still be off (since we didn't scale it by the
change in the cal values).
- Plot (TsysA/TsysB -1) before
fitting or corrections (.ps) (.pdf)
- The data has been converted from correlator counts
to kelvins using the cals (after cal fitting).
- Top: TsysA/TsysB-1 vs za
- 2nd: TsysA/TsysB -1 vs az
- bottom:TsysA/TsysB -1 by field
- dashed green lines separate fields.
- Cal scale factors by field
- These values are computed from the cals on every
strip. they convert from correlator counts to Kelvins.
- black (polA) ,red(polB) after cal fitting
- green(polA), blue(polB) before cal fitting
- Cal fitting takes adjacent cals (with no
attenuation changes) and does a linear fit to the measured
scaling factor ( throwing out outliers). The fit is then
used to convert correlator counts to kelvins rather than the
- If there are no outliers than the blue,green
overlay the black, red traces.
Some of these things will be
fixed 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 simultaneously
- We left them separate here to see if the ra, or
dec scans had any outliers.
residuals by field (rascans and decscans together)(.ps)
- Same as above plots but the scaling fit is done
with ra and dec strips together. This is how the images
- Black is polA, red is polB.
- The scale factor and errors are included in the
title for each plot.
After removing Tsys and scaling to janskies, each
field 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
difference map after basketweaving.
- Grid spacing was 3 arcminutes.
- The gridding function used a gaussian with a fwhm of 5.5 (it
was repeated 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
The average maps for each field (.gif) show the results.
- The basket weaving will try an remove offsets in strips.
The 28 fields from A2704,a2415, a2125 were
combined into a single image. The processing to do this was:
The plots below show the pairwise difference of the overlap regions
of the maps.
- take each pair of overlapping maps.
- Interpolate the first map of each pair to the grid
position of the second (within the overlap region).
- compute mapRaDif=(map2 - interpolated Map1) in the
- Fit a linear polynomial to the differences as a function of
the ra position
- Correct the two maps by subtracting half the difference from
map2 and adding half the difference to map 1
- Repeat steps 1 5 with the corrected fields, using the dec
overlap of the pairwise maps.
- 21feb11: changed so that 1-6 only corrects 20% of the
difference. It then iterates 1-6 5 times. This gets rid of jumps
caused by the correction.
- the units are Janskies (multiply by 10 to get kelvins).
- Pages 1-6. 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 6-13. Overlap in dec direction with map1 -
map2Interpolated plotted vs dec.
- Each set is the start of iteration i (i=1 to 5). the last one
is when everything is done. The set shows how the correction
progresses with a correction factor of 20% per iteration.
The final mosaiced maps (.gif):
The final mosaiced maps with positions (.gif)
- The x,y positions are just grid points along the ra,dec
- This used a 5.5 arcmin gridding function. The final resolution
is about 14 arcminutes.
Notes on the fields. (top)
- Field K. PolB data is zero. Looks like the interim correlator
sbc3 dropped out.
- I copied polA into Polb so the software wouldn't complain.
- Field L. Need to re observe topmost (highest dec) 8 strips.
- You can see a horizontal line in two strips (each starting
at the same side of the map.
- The cals for two of the strips look like they were sitting
on a source. Can't use interpolation since the adjacent strips
were not taken at the same time.
Instabilities in polA.
Spectral ripples were seen in polA during
various nights. This type of problem has plagued polA 430gr for
multiple years (more
info..). It doesn't look like this caused a problem in the
total power measurements. I thinkt he ripple problem was finally
identified. it was the filter in front of the dewar. It had a
loose connection in inside the filter. There was also a problem
with one of the elbow connectors. The teflon insert was not always
seating properly... so we would get different results after taking
things apart, and reassembling..