NIKA Data Reduction

The following diagram shows the NIKA data flow from the IRAM 30m telescope to the observers' accounts.

Neel Pipeline

Go to the NIKA Main Wiki.


Offline data reduction

Data products v0

The version v0 of the NIKA first open pool products has been made by the NIKA team by the end of the pool (Feb 28,2014) and it was distributed by IRAM. The products are described here.

For each project, there are fits files containing the maps of each scan and combined scans of each object. The data processing has been oriented towards point-source extraction or diffuse emission depending on the aim of your project.

There are also logbook files and illustrative pdf files. On the main directory you will find:

Then for each object, there is a directory that contains:

To retrieve the data, please type:

scp  XXX-YY@enter.iram.es:~/observationData/nika/v0.tar.gz  /path/in/your/computer

where XXX-YY is your project number. If you get an error message, enter the following command:

ssh-keygen -R enter.iram.es

and then try to retrieve the data again.

CAVEAT: At this stage, the data offline products are not of scientific quality. The selection of scans was unfortunately rendered difficult because of an unexpected problem with the pointing data. We hope to solve that problem with post-processing steps that we did not have time to implement. Instead, scans were manually selected with some mistakes still present. The photometry is probably correct at the 20% level at 1mm and 10% level at 2mm for scans of good quality. Don't shoot. We will prepare the next version in the coming weeks. Contact your NIKA friend of project to give us your feedback.

The NIKA team

Data products v1

This version V1 of the NIKA first open pool products has been made by the NIKA team by the end of May 2014. It is distributed by IRAM. It follows the quick release done at the end of the pool (v0). The products are described here

For each project, there are fits files containing the maps of each scan and combined scans of each object. The data processing has been oriented towards point-source extraction or diffuse emission depending on the aim of your project. The main processing has improved by including more scans and dealing with internal problems more effectively.

There are also logbook files and illustrative pdf files. On the main directory you will find:

spreadsheet handler (libreoffice or excel) It gives the summary information of all the scans that could be used including opacity measurements, sky noise in Jy (per band of frequency from 1mHz to 10 Hz), camera noise NEFD (in mJy.s^1/2) and finally a flux in mJy of a point-source at the center of the map (fixed central position, fixed FWHM, Gaussian fit) with the error at both wavelengths. For pointing sources the position is allowed to vary.

Then for each object, there is a directory that contains:

scan maps and the combined scans maps.

look at them. Units in Jy/beam unless otherwise stated.

The calibration was done assuming a Gaussian main beam of 12.5 and 18.5 arcseconds (FWHM). The primary calibrator is Uranus with fluxes of 36.4 and 15.3 Jy.

For Lissajous scans (V1Liss directories), the pipeline introduces a filtering effect for point sources of about 0.70 and 0.56 (at 1 and 2mm). This effect has been corrected in the .csv files but not in the maps. Thus fluxes in Jy in the .csv files should be correct.

For you to assess the filtering effect, we have rerun the pipeline with a much less agressive decorrelation that should not affect the fluxes. For that just look at V1cLiss directories made for calibration sources only.

For OTF maps (directories V1otf): the main beam to full beam correction is by 1.56+-0.10 at 1mm and 1.35+-0.10 at 2mm. It has not been applied to the maps.

At this stage, the offline products can be used for a first scientific analysis as most of the scans have been included. The point-source photometry is probably correct at the 15% level at 1mm and 10% level at 2mm.

To retrieve the data, please type:

scp  XXX-YY@enter.iram.es:~/observationData/nika/v1.tar.gz  /path/in/your/computer

where XXX-YY is your project number. If you get an error message, enter the following command:

ssh-keygen -R enter.iram.es

and then try to retrieve the data again.

The NIKA team

Data products v2

We hope to deliver a final V2 version of the first NIKA open pool data products in the Summer including our best strategy of systematic removals. Your feedback is essential to improve the quality of the v1 data and help the NIKA team to develop the final version.

The NIKA team


Online data reduction

To start the IDL session for the real time analysis, open a terminal and type:

   $ ssh -X nikas-14@mrt-lx1
   $ ssh_sami
   > idl 

Shortly after a scan is done, the NIKA scientific data, the xml information generated by PAKO (and the AntennaIMBfits shortly after) are written on SAMI and can be processed. There are two types of observation: the “science” scans and the “calibration” scans. All scans should be reduced with the same routine (except the "focus_liss" sequence as of now, see below):

IDL> nk_rta, scan

scan is a string the format YYYYMMDDsN, e.g. '20141112s3'. Mind the simple quote, IDL does not accept double quotes when the string starts by a number.

If this is a calibration scan (pointing, focus), informations or actions to be taken by the observer appear explicitely in IDL terminal window:

cross

cross_1.png

pointliss

pointing_liss.png

  • The routine displays one map for each band, an estimation of the flux where the source is fit (red), an estimation of the flux at the center of the map (green). It also provides a quick estimate of the NEFD and the map RMS for 10arcsec equivalent pixels and the values of Tau derived by NIKA.
  • The observer should follow instructions given in the terminal, e.g.: B 2mm, : (MAP) (for PAKO) SET POINTING -4.7, 1.4

focusp

[ATTACH]

  • By default, optimize the focus at 1mm

cont_skydip

skydip_results.png

  • No action is requested from the observer other than checking that the displayed histograms look reasonable. These results will be used by the NIKA team later on offline.

focusliss

pointing_liss.png fits.png

Point source maps

Diffuse emission

  • rta_reduce, day, scan_num, /diffuse
  • to combine several scans, use combine_scans in the same way as for point source maps


Continuum/NIKA/DataReduction (last edited 2014-11-07 09:05:40 by NikaBolometer)