On Turbulence Measurements with Phased Array Radar

Isotropic and homogeneous turbulence can be characterized via the eddy dissipation rate ε and a correlation scale length, Λ. Weather radars have been used to estimate ε (assuming a fixed length scale) in precipitation from the Doppler spectrum width, which is a measure of the spread of radial velocities within the radar resolution volume. Pointed herein are differences between turbulence measurements by conventional pencil bean antenna and electronically steering phased array radar (PAR) antennas. Differences are caused by the shape and orientation of the beam cross section on phased array antenna because these depend on the pointing direction. A formalism applicable to pencil beams of circular cross section is extended to elliptic beam cross sections. For lateral dimensions of the radar resolution volume larger than its range extent an approximate formula is suggested for computing ε. Eddy dissipation rate computed along a radial pointing at a 40° of an all-digital PAR is presented.