Robust Insect Mass Estimation with Co-Polarization Estimators for Entomological Radar

Insect mass could be estimated by estimators calculated by the radar cross Section (RCS) measured by entomological radar, which is essential for the statistics of migratory biomass and classification of insects. In order to obtain the insect mass through radar, the RCS of various insects is measured in the microwave anechoic chamber by a specially designed system containing dual-polarization antennas, which point at insects in the measurement process, and the mapping between RCS and the insect mass is constructed and applied to entomological radar. However, insects might deviate from beam center in practice, and the echo intensity will decrease. The decrease cannot be compensated for radar without angle measurement capability. Through the study of insect scattering matrix (SM), it is found that co-polarization estimators, such as co-polarization ratio (CR) and co-polarization phase (CP), are echo intensity independent and correlated with insect mass. Therefore, a co-polarization estimator calculation method driven by model and data is elaborately designed, and an estimation method for insect mass is given on the basis of the co-polarization estimators. Analyses present that the method is suitable for insects below 200 mg, and the mean relative mass estimation error is lower than 30% in X-band and 20% in Ku-band. The effectiveness and robustness of this method is verified by measuring 39 individual insects with a Ku-band fully polarimetric radar (FPR) in field. The proposed methods provide a way to estimate insect mass for entomological radar without angle measurement capability.