Near-earth turbulence and coherence measurements at Aberdeen Proving Ground, Md.

Turbulence measurements were made at Aberdeen Proving Ground, Maryland, for five separate 24-h periods in August, 1971 to obtain data in support of laser beam propagation through the near-earth atmosphere. Twelve MRI bivanes were used to measure the three components of the wind in both line and space arrays, with bivanes at heights of 1 and 3 m above the surface. The site description, instrument layout and calibration, surface roughness and surface modifications are presented. Selected horizontal wind observations from the micrometeorological observations at Aberdeen Proving Ground, are analyzed in terms of coherence statistics. When plotted against the dimensionless frequency, Δf, coherence estimates follow a curve of the form exp (−aΔf) moderately well, but with considerable random scatter.The decay parameter “a” appears to be independent of height from 1 to 3 m, and varies only slightly with Richardson number in the range from −0.07 to +0.05. Its dependence on α, the angle between the mean wind direction and sensor line, is much more pronounced, however, with values of “a” in the crosswind direction (α = 90°) averaging about 3 times larger than those in the downwind direction (α = 0°). This is found for both the longitudinal (u) and lateral (ν) wind components, although lateral decay parameters were only about 60% as large as longitudinal ones.There is some evidence to suggest that decay parameters depend on the ratioΛ1/Λ2 whereΛ1 is the longitudinal length scale, andΛ2 is the lateral length scale, and also with surface roughness,z0, in both the downwind and crosswind directions.