Identifying coronal holes from synoptic maps of SOHO/EIT and SDO/AIA EUV images

Coronal holes are regions of open magnetic field lines and the source of fast solar wind. Understanding the evolution of coronal holes is critical for solar magnetism as well as for accurate space weather forecasts. Long-term occurrence gives fundamentally important information for solar dynamo and space climate studies. Solar wind models are highly sensitive to the size and location of the holes on solar disk.
Coronal holes are best seen in images of coronagraphs at the solar limb. However, coronal holes are difficult to determine on the solar surface since they appear differently in different wavelengths. The size, shape, intensity and contrast of any given hole are not the same when using different observing filters.
We study here the synoptic EUV images at wavelengths of 195 Å and 193 Å measured by SOHO/EIT and SDO/AIA instruments, respectively. We aim to identify the coronal holes from these images using an automated routine based on the statistical properties of the measured pixel intensities and a dynamical division of images into sub-images. We present here the method and the first results obtained for coronal hole properties from these two databases. We compare the results with other methods based on different routines.