Return from insects in the clear-air convective boundary layer

The Microwave Remote Sensing Laboratory (MIRSL) at the University of Massachusetts operated its S- band Frequency Modulated Continuous Wave (FMCW) radar during the International H20 Project (IHOP_2002) over the months of May and June 2002. The radar operates at very high spatial and temporal resolutions, 2.4 m and 5 s, respectively, which allows the segregation of scatter from different scattering mechanisms. Rayleigh scattering from particulate scatterers (i.e. dust and insects) dominated the return, however Bragg scattering from turbulence was also significant, especially at the top of the afternoon convective bounday layer (CBL). Scattering from insects was isolated using a 5x5 median high-pass filter. The majority of reflectivity measurements from particulate scatterers ranged from -30 dBZ to -10 dBZ, however intense point-scatterers (> 0 dBZ) skewed the distribution which resulted in mean values much greater than the median values. There is a strong diurnal signal in the backscatter: minima in the morning and at dusk and a maximum mid-afternoon and in the nocturnal boundary layer. The strong diurnal signal suggests that with targeted allocation of radar resources return from insects can be used to monitor the clear-air CBL of the central Great Plains of North America.