ocr: MDI The goal of the MDI Michelson Doppler Imager) instrument, is to obtain observations to allow the SOI (Solar Oscillations Investiga- tion) team to infer the structure and dynamics of the Sun's interior, This can be done by measuring the properties of internal acoustic waves as they perturb the photosphere. Long-term, continuous sta- ble observations free of atmospheric disturbances are required. Global helioseismology uses the trequencies of trapped acoustic waves to infer the global internal structure and rotation. Time-dis- tance helioseismology measures the travel time of acoustic waves ...
