I am doing an undergraduate project on the use of LIDAR data for DEM generation and flood modelling. I currently have 2 LiDAR datasets for a broad area and a survey data set for a much narrower area within that. These data sets were captured at times before and after a major flood event. I need to carry out a series of comparisons of heights between the DEMs (average height difference between DTMs, a map showing the scale of elevation differences across the subject area). What would be the best geoprocessing functions to use for this purpose (I have created terrain datasets but ideally I would be working in raster format)? Also is there any way of checking up on the progress of a geoprocessing function prior to its completion? Just sometimes I execute a function but there is no evidence on the screen as to what is happening to a while later when it is completed.