Traditionally, surface weather observations have been made by human observers. It has been their difficult task to estimate subjective elements such as sky cover (in tenths) and the heights of clouds (often to the nearest 100 ft). Automation has moved slowly to replace subjective methods in the field and, even then, usually only in special areas such as runway visual range (RVR) and runway visibility (RVV). Recent work has demonstrated that automated observations of other subjective elements are feasible and are already operational at two points in the United States.

The paper reviews the concepts of RVR and RVV, and discusses in detail new methods for the automation of cloud and visibility observations. The automated observations are compared with human products made at the same time and location. The paper points out the difficulties of assessing the success of objective techniques in comparison with subjective methods.