The primary method used to measure the flow of Niagara Falls is through direct measurement. This involves gauging and measuring the total volume of water flowing over the falls in a given period of time, usually measured in cubic feet per second (cfs). Indirect methods such as radar-based technologies can be used to measure surface flow and overall water velocity. Further information on water flow levels can be obtained through various types of remote sensing techniques such as satellite imagery and aerial photography. These methods are able to detect changes in sedimentation levels or any other physical changes that may affect the amount of water flowing over Niagara Falls.