A Proposal to Compare Ground-Based Photometric Images with Irradiance Data from SOHO G.A. Chapman and S.R. Walton California State University, Northridge The solar irradiance is being measured on the SoHO spacecraft by VIRGO at several wavelength bands, unimaged, and by MDI with images in the wing of the Ni 676.8 nm line. VIRGO measures total irradiance as well as spectral irradiance in several wavelength bands. MDI obtains images without the complications of the earth's atmosphere. These data are unique in the history of solar irradiance measurements. We propose to collaborate with the PI teams in comparing these data with full-disk ground-based photometric images. The ground-based images will be obtained from the San Fernando Observatory (SFO), Big Bear Solar Observatory (BBSO), and when available, the National Solar Observatory (NSO) [in particular, the Precision Solar Photometric Telescope (PSPT)]. The SFO images come from two full-disk photometric telescopes, one producing images having 512x512 pixels and the other having 1024x1024 pixels. They both have filters in red and blue bands as well as in the Ca II K-line. The 1024x1024 images are obtained using two K-line filters, one with a bandpass of 1 nm and the other 0.3 nm. These instruments are described in Chapman, et al. (1996). Images from SFO, BBSO and the NSO/PSPT have a very similar pixel size and will be combined to create a set of ground-based images from which sunspot deficits and facular excesses will be determined. These deficits and excesses will be compared with the spacecraft irradiance fluctuations to determine, in detail, the causes of solar variability. This determination will help in our understanding of the flow of energy in the outer part of the convection zone of the sun.