High-Resolution Observations of Insects in the Atmospheric Boundary Layer
Journal of Atmospheric and Oceanic Technology
High spatial and temporal resolution S-band radar observations of insects in the atmospheric boundary layer (ABL) are described. The observations were acquired with a frequency-modulated continuous-wave (FMCW) radar during the 2002 International H 2 0 Project (IHOP_2002) held in Oklahoma in the months of May and June 2002. During the observational period the boundary layer was convective with a few periods of rain. Rayleigh scattering from particulate scatterers (i.e., insects) dominates the
... s) dominates the return; however, Bragg scattering from refractive index turbulence is also significant, especially at the top of the afternoon boundary layer. There is a strong diurnal signal in the insect backscatter: minima in the morning and at dusk and maxima at night and midafternoon. Insect number densities and radar cross sections (RCSs) are calculated. The RCS values range from less than 10 Ϫ12 m 2 to greater than 10 Ϫ7 m 2 and likewise have a strong diurnal signal. These are converted to equivalent reflectivity measurements that would be reported by typical meteorological radars. The majority of reflectivity measurements from particulate scatterers ranges from Ϫ30 to Ϫ5 dBZ; however, intense point scatterers (Ͼ10 dBZ ) are occasionally present. The results show that although insects provide useful targets for characterization of the clear-air ABL, the requirements for continuous monitoring of the boundary layer are specific to time of day and range from Ϫ20 dBZ in the morning to Ϫ10 to Ϫ5 dBZ in the afternoon and nocturnal boundary layer (NBL).