Two methods of measuring atmospheric turbulence as it affects free space optical communications are presented. Each method yields a value of the structure constant of refractive index fluctuations, Cn2. A scintillometer is used as the basis or 'truth' for measurements taken by the first method by fitting data from the other instrument to the simultaneous scintillometer data. The first method utilizes a device conceived at New Mexico Tech using microphones to measure a pressure differential. This device was altered to provide both pressure and temperature measurements at two points separated by a specific distance. A thermocouple was added beside each microphone to provide temperature data, and the data collection method was altered. The device currently measures two pressure and temperature gradients. Also, the Naval Research Laboratory conducted the first efforts to quantify and calibrate the data collected by the device. Second, measurements are made from the angle of arrival of light from a laser transmitted across 16.4 km of the Chesapeake Bay. The variance of the angle of arrival over time is obtained from the variance of the centroid location of the focused light on a position-sensing detector. The same measurement is made over the same path using a halogen spotlight, a CCD camera, and a video tracker. The angle of arrival variance is used to calculate Cn2. The microphone/thermocouple apparatus took measurements over land alongside the scintillometer. Results from both methods are provided.© (2002) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.