FULL-DISK HELIOSEISMIC IRIS RAW DATA CALIBRATION

The IRIS helioseismometer measures the full disk line of sight velocit y of the Sun. In fact, it makes a photometric measurement using two mo nochromatic spectral windows located on the wings of the D1 solar line . This is a non-linear measurement. Before a scientific exploitation o f the IRIS data, the instrumental signal must be converted from non-li near photometric data into calibrated line of sight velocity. In this process, it is necessary to extract the small component due to the sol ar surface motions from the much larger contributions of the Earth spi n, the Earth orbit, the gravitational redshift, the D1 line distortion s produced by solar activity and even some telluric atmospheric effect s.This paper describes the calibration method which is now used for pr e-processing the IRIS data. It is the result of several iterations, an d the use of one and a half years of IRIS data from one instrument, at Teide Observatory. It is certainly the best possible method to date, given the quality of the current data, and it can be regarded as valid over all the entire p-mode frequency range, and down to 100 muHz or s o in the g-mode range. At lower frequencies, calibration, solar noise and merging techniques cannot be completely separated, and possible fu rther improvements are still under investigation.