Onboard Automated CME Detection Algorithm for the Visible Emission Line Coronagraph on ADITYA-L1

Abstract

ADITYA-L1 is India's first space mission to study the Sun from Lagrangian 1 position. Visible Emission Line Coronagraph (VELC) is one of the seven payloads in ADITYA-L1 mission scheduled to be launched around 2020. One of the primary objectives of the VELC is to study the dynamics of coronal mass ejections (CMEs) in the inner corona. This will be accomplished by taking high resolution (≈ 2.51 arcsec pixel −1 ) images of corona from 1.05 R -3 R at high cadence of 1 s in 10Å passband centered at 5000Å. Due to limited telemetry at Lagrangian 1 position we plan to implement an onboard automated CME detection algorithm. The detection algorithm is based on the intensity thresholding followed by the area thresholding in successive difference images spatially re-binned to improve signal to noise ratio. We present the results of the application of this algorithm on the data from existing coronagraphs such as STEREO/SECCHI COR-1, which is space based coronagraph, and K-Cor, a ground based coronagraph, because they have field of view (FOV) nearest to VELC. Since, no existing space-based coronagraph has FOV similar to VELC, we have created synthetic coronal images for VELC FOV after including photon R. Patel ritesh.patel@iiap.res.in V. Pant vaibhav@iiap.res.in Amareswari K. Patel R. et al.noise and injected CMEs of different types. The performance of CME detection algorithm is tested on these images. We found that for VELC images, the telemetry can be reduced by a factor of 85% or more keeping CME detection rate of 70% or above at the same time. Finally, we discuss the advantages and disadvantages of this algorithm. The application of such onboard algorithm in future will enable us to take higher resolution images with improved cadence from space and also reduce the load on limited telemetry at the same time. This will help in better understanding of CMEs by studying their characteristics with improved spatial and temporal resolutions.

A Simple Radial Gradient Filter for Batch-Processing of Coronagraph Images

“…Figure 1c shows a uniform background image made using the radial profile shown in Figure 1b. As the instrument background and scatter remains nearly uniform from Equator to polar regions (Morgan and Habbal, 2007;Patel et al, 2018), this will serve to normalise such contributors of the radial gradient along with inherent coronal-intensity variation.…”

Characterizing Spectral Channels of Visible Emission Line Coronagraph of Aditya-L1

“…The constant factor in Eq. 3 is obtained using the procedure for conversion followed by Patel et al (2018). The scatter is assumed to be circularly symmetric and is added to the synthetic spectra obtained using CHIANTI in Eq.…”

“…This implies that even though exposure of more than 1 s could be set for the visible channels, it should be less than a second for the IR channel for CME observations to occur without saturating the detector. For this, when the CME is detected onboard using the onboard CME detection logic (Patel et al, 2018), the spectroscopic channel will be configured with a predetermined set of exposures. We plan to use the flag provided by the onboard CME detection algorithm for the continuum channel of VELC to change the IR observation to the low-gain mode with a reduced exposure time for CME observations.…”

Characterizing Spectral Channels of Visible Emission Line Coronagraph of Aditya-L1

“…The pixel scale for the continuum channel is 2.5 arcsec pixel −1 . The constant factor in the Equation 3 is obtained using the procedure for conversion followed in Patel et al (2018). The scatter is assumed to be circularly symmetric and is added to the synthetic spectra obtained using CHIANTI in Equation 2.…”