-- The IRAF External Package GRASP

The IRAF External Package GRASP

The Global Oscillation Network Group (GONG) is using IRAF as the software environment to support its reduction software. This software is found in the external package called GRASP (GONG Reduction and Analysis Software Package). The GONG network (with sites in the Canary Islands, Spain; Udaipur, India; Learmonth, Australia; Mauna Loa, Hawaii; Big Bear, California; and CTIO) is scheduled to begin observations in the early spring of 1995, and will provide to the Data Management and Analysis Center (DMAC) in Tucson at least one image of the sun every minute for a minimum of 3 years. Each site will be sending approximately 1.2 GB of data per week (one Exabyte tape) to the DMAC group. The GRASP package will be used to reduce this data with the major requirement of keeping cadence with the daily input.

The subpackages and tasks of GRASP are designed to support general (i.e., not only GONG) Helioseismic image data reduction and analysis. For the purposes of GONG, the tasks may be divided into three broad categories:

Daily Upstream Tasks are those programs which input the raw GONG data (3-phase intensity full disk images, 256 x 256 x 3) and output calibrated velocity, average intensity, and modulation images (256 x 256 each).
The stages through which the data flow are analogous to bias, dark and flat-field corrections applied to night-time imaging CCD data but the velocity calibration is a complicated process.
In addition, the elliptical geometry of the disk image (center, major/minor radii, ellipse angle) and the modulation transfer function (MTF) are determined for each image.
Daily Downstream Tasks are those programs which take the time series of calibrated velocity images, and produce a time series of spherical harmonic coefficients for (0 <= L <= 250).
The stages of this processing are to remap the full disk velocity images into the Heliographic coordinate system, and perform the spherical harmonic transformation (SHT). The output is 251 3-dimensional time series images: one image for each L-value, with the columns being time, the rows being azimuthal order m (0 <= m <= L), and the bands being the real and imaginary parts of SHT.
In addition power spectra of these time series will be generated for each site day of data. The spectra are examined to assure the data quality once the stamp of approval has been given; the daily spectra are discarded.
The daily time series from the six sites are then merged using the image MTF's as a weighting function.
Monthly Downstream Tasks are those programs which will take the daily time and concatenate them into monthly data sets, and produce power spectra.
The monthly data sets will be 36 days long on 18 day centers for a monthly data set size of 13.6 GB. The power spectra will be generated using a non-power-of-2 FFT producing 251 3-dimensional images: one image for each L-value, with the columns being frequency, the rows being azimuthal order m (-L <= m <= L), and the bands being the power and phase. This data set will also be 13.6 GB.
The final task performed on the monthly data sets is that of peak finding. This task is to automatically go through the 251 power spectra and fit the 10**7 line profiles to produce line frequencies, widths and amplitudes.

Over the course of the first three years of network operation, the DMAC will be archiving approximately 15 TB on Exabyte tape (like many astronomical research projects, data reduction is really data explosion) with the calibrated images, daily and monthly time series, monthly power spectra and mode-frequency tables (i.e., the peak fitting results) being the major archived data products. With the exception of the peak finding routine, the majority of the GRASP applications are I/O bound, and as such the applications have been written to be memory hogs (hold as many images in memory as possible without excessive paging/swapping) so that disk reads and writes will be at a minimum.

While much of the GRASP software was written by the GONG programming group, there has been significant software contributions by the GONG community. As a result, GRASP comprises some 43000 lines of SPP, 28000 lines of Fortran and 4000 lines of C code, demonstrating the ease of including non-IRAF applications into an IRAF applications package. GRASP is currently exported to about two dozen sites around the world, and will also be installed at the data collection sites for diagnostic use by the local operators.

The Global Oscillation Network Group (GONG) is a community-based project funded principally by the National Science Foundation and administered by the National Solar Observatory. Further information may be obtained by sending email to grasp@noao.edu.

Ed Anderson
GONG Programmer

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