Monitoring aerial insect biodiversity: a radar perspective

Abstract

In the current biodiversity crisis, populations of many species have alarmingly declined, and insects are no exception to this general trend. Biodiversity monitoring has become an essential asset to detect biodiversity change but remains patchy and challenging for organisms that are small, inconspicuous or make (nocturnal) long-distance movements. Radars are powerful remote-sensing tools that can provide detailed information on intensity, timing, altitude and spatial scale of aerial movements and might therefore be particularly suited for monitoring aerial insects and their movements. Importantly, they can contribute to several essential biodiversity variables (EBVs) within a harmonized observation system. We review existing research using small-scale biological and weather surveillance radars for insect monitoring and outline how the derived measures and quantities can contribute to the EBVs ‘species population’, ‘species traits’, ‘community composition’ and ‘ecosystem function’. Furthermore, we synthesize how ongoing and future methodological, analytical and technological advancements will greatly expand the use of radar for insect biodiversity monitoring and beyond. Owing to their long-term and regional-to-large-scale deployment, radar-based approaches can be a powerful asset in the biodiversity monitoring toolbox whose potential has yet to be fully tapped. This article is part of the theme issue ‘Towards a toolkit for global insect biodiversity monitoring’.

Towards a toolkit for global insect biodiversity monitoring

“…Radars emit electromagnetic beams that are reflected by objects in the air, and based on their echoes, these objects can be characterized. A variety of radar systems exists that differ in specifications, in the level of detail they provide on aerial objects and in spatio-temporal resolution [ 55 ]: small-scale radars can identify individual animals and characterize their body shape, size, wing beat frequency and other characteristics, but cover only relatively small aerial volumes [ 56 ]. By contrast, weather radar networks survey the atmosphere above areas stretching several hundreds to thousands of square kilometres but provide fewer and coarser characteristics of the biological targets detected [ 57 ].…”

“…The contributions in this theme issue show-case several of these developments and demonstrate the potential of radars for contributing macroecological patterns to insect monitoring: First, Bauer et al [ 55 ] review the use of radar for insect monitoring. Then, Drake et al [ 60 ] develop biodiversity metrics that can complement the biomass and abundance measures from radar reflections, thereby enhancing the information that can be gained from radar monitoring.…”

Derivation of aerial insect concentration with a 94 GHz FMCW cloud radar

“…The correlation is particularly strong during the day and crepuscular evening (R=0.86) and least strong in crepuscular morning. Bauer et al (2024) define 'abundance and biomass estimates' as an essential biodiversity variable. Although the absolute values of detected insect concentrations by both instruments differ by several orders of magnitude, we investigated whether the ratio of detected insect concentrations between both measurements is constant through time and height.…”

“…Scanning radars further have the potential to cover spatially large regions. During recent years, the deployment of specialized radar-based detection methods for aerial fauna has become more prevalent, especially for movements of up to several hundred meters up in the air (e.g., Hu et al 2016, Lukach et al 2022, Wainwright et al 2023, Haest et al 2024b, Bauer et al 2024). To study larger flying animals, like birds and bats, radar instruments with wavelengths of a few up to several centimeters, like X-band (λ = 2.5-3.75 cm; e.g.…”

“…S-band, and more rarely also C-Band (Mäkinen et al 2022), weather radars have been shown useful to study high-density insect movements (Tielens and Kelly 2024), including specific events like mayfly emergences (Stepanian et al 2020, Kwakye et al 2023). X-Band radars have repeatedly been shown useful to study larger individual insects (Chapman et al 2011, Hu et al 2016, Gao et al 2020, Haest et al 2024b, Bauer et al 2024), but mostly miss insects with smaller radar cross sections (Riley 1985), which, in fact, are often more abundant. Ku-Band (λ = 1.67-2.4 cm), K-Band (λ = 1.11-1.67 cm) and Ka-Band (λ = 0.75-1.11 cm) radars have seen some use for entomological purposes (e.g., Cai et al 2019), however, almost no studies have been published on W-Band radar insect detection.…”