Calibration of spectral channels for VELC onboard ADITYA-L1 and preparing data pipeline

Abstract

ADITYA-L1 will be India’s first space mission dedicated to solar studies. The Visible Emission Line Coronagraph (VELC) is one of the prime payloads onboard ADITYA L1. VELC will perform simultaneous imaging, spectroscopy and spectropolarimetry of the solar corona, starting at a heliocentric distance of 1.05Ro. There are three spectral channels at 5303 Å (Fe XIV), 7892 Å (Fe XI) and 10747 Å (Fe XIII) in VELC. High cadence simultaneous spectroscopy and imaging will be a novel feature of the instrument. In this project, as a test case, we have analyzed a ground-based, multi-slit total solar eclipse spectral data, taken at 5303 Å and 6374 Å (Fe X). This data has been taken by an IIA team as part of a total solar eclipse expedition to Chile in July 2010, which is described in Samanta et al., 2016. The various data processing techniques employed are adapted into the next section of the project where the development of the data pipeline is discussed. Some of the major stages of the data pipeline are detailed in this project. To create the data pipeline, techniques in existing pipelines in other space missions were studied. Further, the variation of Signal to Noise Ratio (SNR) with different solar phenomena and under different instrumental conditions are discussed. To do the SNR analysis, we made use of the CHIANTI atomic database, which is used to calculate the parameters of different emission lines and the background continuum (Landi et al., 2012). The scatter photon numbers are estimated and CHIANTI simulations are carried out to infer the dependence of SNR on the slit width and exposure of the instrument. The spectral channel data is simulated to produce synthetic spectra for different solar conditions. One is the quiet-Sun case, without many large-scale solar activities, and another is the CME-case, where CME represents Coronal Mass Ejection. In these cases, we have developed the spectral images as will be seen by different channels of VELC. These synthetic spectra will be useful in the creation of the observation plan and the preparation of the data pipeline.