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Why is there a spectral baseline ripple in Total Power observations of Bright Targets? - Knowledgebase / Offline Data Reduction and/or CASA - ALMA Science

Why is there a spectral baseline ripple in Total Power observations of Bright Targets?

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During planet observations with the ALMA TP array, significant ripples often appear in the spectral baselines with characteristic periods of approximately 200 - 300 MHz. The exact origin of these ripples is under investigation, but one possibility is that standing waves could be formed within the TP-array system during signal transmission. These waves may be amplified when observing with strong astronomical sources, in particular planets. The current single-dish pipeline does not account for fully remove these high-order standing waves, resulting in visible ripples in the final data cubes. Delivered MOUS affected by this issue will be set to SEMIPASS in the QA2 process.

Updates on this matter will be provided as more information becomes available.