Field measurements of spatially-filtered turbulence have been made in the atmospheric surface layer, using the technique of Tong and colleagues at The Pennsylvania State University. This technique employs horizontal arrays of sonic anemometers placed in a line transverse to the mean wind direction to spatially average the turbulence fields in the crosswind direction and Taylor's hypothesis to average the turbulence in the streamwise direction. The field program, executed in September 2000, used four configurations with different sonic spacings to investigate the properties of resolved and sub-filter-scale turbulence as a function of filter size, measurement height, and atmospheric stability. This paper will discuss the measurement design and the accuracy of the empirical spatial filters. Companion papers will discuss the properties of spatially-resolved and sub-filter-scale turbulence fields and the implications for Large Eddy Simulation.