Based on the scenario below, if I propose to use a "survey" to gauge employee engagement, why is the survey the most useful tool for gauging organizational climate?

The Office of Personnel Management [OPM] conducts an annual Federal Employee Viewpoint Survey with the goal of determining the level of federal employee engagement. A high engagement rate correlates with high morale and high productivity. On the other hand, a low engagement rate correlates with low morale and low productivity. Assume that you serve as the Director of a federal government agency and that you are challenged to increase the employee engagement rate toward improving agency performance,