A method for measurement of temperature profiles in inversions from refractive transmission of sound

Abstract

A method is described for estimating temperature profiles in the lower troposphere during conditions including a surface-based or elevated inversion layer. The method uses acoustic energy transmitted over paths of the order of 10 km in length. Measurements are made at approximately 1-km intervals extending radially outward from the transmitter. The vertical temperature profile is modeled as two constant temperature gradient layers. The first layer extending from the surface to height H1 has a temperature gradient T1′ (usually negative upward). The second-layer temperature gradient T2′ is strongly positive upward. For temperature profiles of this type, ray paths arrive with a high intensity at a caustic, and no rays return to earth between the source and the caustic. The method requires that H1 be determined by some other means such as vertical acdar sounding. The T1′ and T2′ are then simultaneously determined by measuring the range to the caustic and the wave propagation time. Even if the propagation time cannot be measured, useful estimates of T2′ can be obtained from observations of H1 and the caustic distance. For a ground-based inversion no caustic occurs. However, the temperature profile can be determined by measuring the wave propagation time. Since horizontal wind shear produces the same effect on ray paths as a vertical temperature gradient, the proposed method obtains the sum of the effects of the wind shear and the temperature gradient. In conditions including significant wind shear, corrections for it must be made.