Vis Stacked Frame Product

Data product name

VisStackedFrame

Data product custodian

VIS

Data model tag

9.0.2

Name of the Schema file

euc-test-vis-VisStackedFrame.xsd

Schema documentation tag

emphasis:Documentation for data product element DpdVisStackedFrame:

Output of the Science Pipeline for the StackedFrame. The VIS PF provides stacked images which individual VIS dither is combined using SWarp with the option COMBINE TYPE=WEIGHTED

Documentation for data product element Header:

The generic header of the product.

Data product elements

Header of type: sys:genericHeader

Data of type: vis:visStackedFrame

Parameters of type: ppr:genericKeyValueParameters

Processing Element(s) creating/using the data product

Processing function using the data product

MER processing function.

Detailed description of the data product

The VIS processing function provides a Stackedframe product consisting of 3 FITS files; a stacked VIS image, and the corresponding PSF model and background.

The stacked VIS image is the combined result of calibrated VIS individual dither(s) using SWarp with the option “COMBINE TYPE=WEIGHTED”, i.e. the output flux F over i images is given by:

F = \frac{\sum \omega_i p_i f_i}{\sum \omega_i}

where f_i is the flux in each calibrated VIS individual image, p_i the flux scaling factor (currently set to 1 for all images) and, as for a calibrated frame, w_i the individual weight for each image expressed in terms of relative inverse variance, w_j \propto \frac{1}{{\sigma_{j}}^{2}} , where \sigma_j is the standard deviation (or “RMS” of the j_th pixel).

The tangent point ([Calabretta & Greisen 2002]_) of the output image is computed by SWarp software with the option “CENTER_TYPE all”. Therefore, the size of this image and its tangent point is for the moment not pre-defined, and can vary based on the coverage of the input dithers. The output tangent point is approximately equal to the geometric average of the tangent point of the input images.

The input data products (SCI, RMS, and FLG) are resampled to constant pixel scale over the focal plane of 0.1” / pixel. The images are background subtracted with a sliding window using the following parameters BACK_SIZE=64 and BACK_FILTERSIZE=3.

We will now describe the content of each extension of the stacked VIS image:

SCI extension

The fluxes in each pixel of the SCI extension are rescaled to have a zero point of 23.9 AB magnitudes with an effective exposure time of 1s.

RMS extension

As for the calibrated VIS individual images, the RMS map contains standard deviation at each pixel in the corresponding Science image, expressed as the absolute standard deviation.

FLG extension

For the stacked images, the value of the Flagmap is 0 for good data, 1 otherwise. Flags are stored as eight-bit unsigned integers.

Calabretta & Greisen 2002] Calabretta, M. R. & Greisen, E. W. 2002, A&A, 395, 1077

Primary Header:

SIMPLE		/
BITPIX		/
NAXIS		/
EXTEND		/
END

Extension Header: