|MELNIKOV, VALERY - University Of Oklahoma|
|ISTOK, MICHAEL - National Oceanic & Atmospheric Administration (NOAA)|
Submitted to: Journal of Atmospheric and Ocean Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/28/2014
Publication Date: 4/1/2015
Citation: Melnikov, V.M., Istok, M.J., Westbrook, J.K. 2015. Asymmetric radar echo patterns from insects. Journal of Atmospheric and Ocean Technology. 32(4):659-674.
Interpretive Summary: Radar echoes have long detected migratory flights of insects, but often have been unable to classify the relevant species or measure important flight characteristics. New techniques are needed to monitor and estimate flight displacements of migratory insects. Algorithms developed to analyze measurements from the network of National Weather Service radars revealed mean insect body size, heading, air speed, and body tilt (pitch angle). Taken together, these radar-derived parameters provided useful information to classify the migrating insects. These findings will lead to the development of sophisticated algorithms that automatically classify and estimate migratory pathways of flying insects, which is critically needed for early detection of pest infestations and spread of diseases vectored by insects.
Technical Abstract: Radar echoes from insects, birds, and bats in the atmosphere exhibit both symmetry and asymmetry in polarimetric patterns. Symmetry refers to similar magnitudes of polarimetric variables at opposite azimuths, and asymmetry relegates to differences in these magnitudes. Asymmetry can be due to different species observed at different azimuths. It is shown in this study that asymmetric patterns can also be caused by insects of the same species that are oriented the same way. A model for scattering of simultaneously transmitted horizontally and vertically polarized radar waves by insects is developed. The model reproduces the main features of asymmetric patterns in differential reflectivity, the copolar correlation coefficient, and differential phase. It is shown that asymmetry in the patterns can be caused by same insects oriented not strictly horizontally. The radar differential phase in transmit between horizontally and vertically polarized waves plays a critical role in formations of the asymmetric patterns. The width-to-length ratios of insects’ bodies and their orientation angles are retrieved from matching the model output with radar data.