Indexed on: 26 Apr '12Published on: 26 Apr '12Published in: Solar Physics
Sunspot and white light facular areas are important data for solar activity and are used, for example, in the study of the evolution of sunspots and their effect on solar irradiance. Solar Dynamic Observatory’s Helioseismic and Magnetic Imager (SDO/HMI) solar images have much higher resolution (∼0.5′′ pixel−1) than Solar and Heliospheric Observatory’s Michelson Doppler Imager (SOHO/MDI) solar images (∼2′′ pixel−1). This difference in image resolution has a significant impact on the sunspot and white light facular areas measured in the two datasets. We compare the area of sunspots and white light faculae derived from SDO/HMI and SOHO/MDI observations. This comparison helps the calibration of the SOHO sunspot and facular area to those in SDO observations. We also find a 0.22 degree difference between the North direction in SDO/HMI and SOHO/MDI images.