Library of rough hailstone backscattering coefficients at 2.8 GHz.

The rough hailstone scattering library is created to fill the need for results of non-spheroidal hailstone backscattering characteristics. The listed backscattering coefficients at the S-band (2.8 GHZ) are specifically tailored for computing the polarimetric variables. The National Weather Service's radar operates in this band; hence the library is pertinent to those studying hail in the USA. The library contains several axis ratios and a range of hail sizes from 5 mm to 100 mm. Moreover, hailstone surface roughness is expressed as a percentage of the equatorial diameter. Our computational electromagnetic approach to modeling hailstones is compared with typically employed simpler methods. The polarimetric variables calculated using our models can be compared to observations. Furthermore, we illustrate the potency of the CEM approach to hydrometeors with extreme axis ratios for which simpler methods (i.e., the T-matrix) fail.

Nocturnal city lighting elicits a macroscale response from an insect outbreak population.

Anthropogenic environmental change affects organisms by exposing them to enhanced sensory stimuli that can elicit novel behavioural responses. A pervasive feature of the built environment is artificial nocturnal lighting, and brightly lit urban areas can influence organism abundance, distribution and community structure within proximate landscapes. In some cases, the attractive or disorienting effect of artificial light at night can draw animals into highly unfavourable habitats, acting as a macroscale attractive ecological sink. Despite their significance for animal ecology, identifying cases of these phenomena and determining their effective scales and the number of organisms impacted remains challenging. Using an integrated set of remote-sensing observations, we quantify the effect of a large-scale attractive sink on nocturnal flights of an outbreak insect population in Las Vegas, USA. At the peak of the outbreak, over 45 million grasshoppers took flight across the region, with the greatest numbers concentrating over high-intensity city lighting. Patterns of dusk ascent from vegetated habitat toward urban areas suggest a daily pull toward a time-varying nocturnal attractive sink. The strength of this attractor varies with grasshopper density. These observations provide the first macroscale characterization of the effects of nocturnal urban lighting on the behaviour of regional insect populations and demonstrate the link between insect perception of the built environment and resulting changes in spatial and movement ecology. As human-induced environmental change continues to affect insect populations, understanding the impacts of nocturnal light on insect behaviour and fitness will be vital to developing robust large-scale management and conservation strategies.

Declines in an abundant aquatic insect, the burrowing mayfly, across major North American waterways.

Seasonal animal movement among disparate habitats is a fundamental mechanism by which energy, nutrients, and biomass are transported across ecotones. A dramatic example of such exchange is the annual emergence of mayfly swarms from freshwater benthic habitats, but their characterization at macroscales has remained impossible. We analyzed radar observations of mayfly emergence flights to quantify long-term changes in annual biomass transport along the Upper Mississippi River and Western Lake Erie Basin. A single emergence event can produce 87.9 billion mayflies, releasing 3,078.6 tons of biomass into the airspace over several hours, but in recent years, production across both waterways has declined by over 50%. As a primary prey source in aquatic and terrestrial ecosystems, these declines will impact higher trophic levels and environmental nutrient cycling.

Characterizing animal anatomy and internal composition for electromagnetic modelling in radar entomology.

The use of radar as an observational tool in entomological studies has a long history, and ongoing advances in operational radar networks and radio-frequency technology hold promise for advances in applications such as aerial insect detection, identification and quantification. Realizing this potential requires increasingly sophisticated characterizations of radio-scattering signatures for a broad set of insect taxa, including variability in probing radar wavelength, polarization and aspect angle. Although this task has traditionally been approached through laboratory measurement of radar cross-sections, the effort required to create a comprehensive specimen-based library of scattering signatures would be prohibitive. As an alternative, we investigate the performance of electromagnetic modelling for creating such a database, focusing particularly on the influence of geometric and dielectric model properties on the accuracy of synthesized scattering signatures. We use a published database which includes geometric size measurements and laboratory-measured radar cross-sections for 194 insect specimens. The insect anatomy and body composition were emulated using six different models, and radar cross-sections of each model were obtained through electromagnetic modelling and compared with the original laboratory measurements. Of the models tested, the prolate ellipsoid with an internal dielectric of homogenized chitin and hemolymph mixture best replicates the measurements, providing an appropriate technique for further modelling efforts.

Electromagnetic Model Reliably Predicts Radar Scattering Characteristics of Airborne Organisms.

The radar scattering characteristics of aerial animals are typically obtained from controlled laboratory measurements of a freshly harvested specimen. These measurements are tedious to perform, difficult to replicate, and typically yield only a small subset of the full azimuthal, elevational, and polarimetric radio scattering data. As an alternative, biological applications of radar often assume that the radar cross sections of flying animals are isotropic, since sophisticated computer models are required to estimate the 3D scattering properties of objects having complex shapes. Using the method of moments implemented in the WIPL-D software package, we show for the first time that such electromagnetic modeling techniques (typically applied to man-made objects) can accurately predict organismal radio scattering characteristics from an anatomical model: here the Brazilian free-tailed bat (Tadarida brasiliensis). The simulated scattering properties of the bat agree with controlled measurements and radar observations made during a field study of bats in flight. This numerical technique can produce the full angular set of quantitative polarimetric scattering characteristics, while eliminating many practical difficulties associated with physical measurements. Such a modeling framework can be applied for bird, bat, and insect species, and will help drive a shift in radar biology from a largely qualitative and phenomenological science toward quantitative estimation of animal densities and taxonomic identification.