Frequency domain interferometry in the planetary boundary layer: first results

A 915 MHz boundary layer radar (BLR) is currently being used with frequency domain interferometry (FDI) and a Radio Acoustic Sounding System (RASS) to study the nocturnal jet. FDI is a technique by which the range resolution of an existing radar can be increased by using a pair of alternating transmitter frequencies. It is hoped that by using FDI, turbulent layers that exist at the shear regions of the nocturnal jet can be resolved within the resolution volume of the radar. The RASS is used to estimate the virtual temperature profile of the atmosphere from the local speed of sound. Using FDI and RASS will provide greater detail and hopefully an understanding of jet formation. Nocturnal jets are a low-level wind maximum that are common in the Great Plains region of the United States. Wind speeds in the jet can occasionally reach velocities in excess of 25 ms^-1. The jet occurs at an altitude of approximately 500 m and normally forms during the night in calm surface wind and clear sky conditions. The jet can generate severe turbulence and wind shear which can be hazardous to unsuspecting aircraft