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A special issue of Remote Sensing (ISSN 2072-4292). This special issue belongs to the section "Atmospheric Remote Sensing".

Deadline for manuscript submissions: closed (29 February 2020) | Viewed by 52579

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Special Issue Editors

Dr. Phillip M. Stepanian

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Guest Editor

Plains Institute, University of Oklahoma, Norman, OK, USA
Interests: aeroecology; biometeorology; global change; radar polarimetry

Prof. Dr. Jeffrey F. Kelly

E-Mail Website
Guest Editor

Plains Institute, University of Oklahoma, Norman, OK 73019, USA
Interests: aeroecology; phenology; animal movement; migration, ornithology

Special Issue Information

Dear Colleagues,

The past decade has seen rapid growth in the application of radar technology toward animal research, motivated in part by advances in analysis techniques, data accessibility, and hardware capabilities. Radar observations have enabled new discoveries relating to animal behavior, spatial ecology, phenology, and migration, as well as facilitated novel applications in pest surveillance, aviation hazard monitoring, ecological forecasting, and wildlife conservation. Still, these exciting advancements represent a small fraction of the potential value still to be realized from radar applications.

This Special Issue on “Radar Aeroecology” invites original research papers focusing on concepts, methods, applications, and empirical findings associated with radar surveillance of animals in the airspace. The scope of these studies can include field or laboratory measurements of birds, bats, or insects made from atmospheric, marine, or purpose-built ecological radar units operating at millimeter to meter wavelengths. We also encourage technical contributions relating to the electromagnetic scattering properties of individual organisms, ecologically-focused radar design and engineering, target classification methods, and validation studies.

We look forward to your contribution to this Special Issue on “Radar Aeroecology”.

Dr. Phillip M. Stepanian
Prof. Jeffrey F. Kelly
Guest Editors

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Keywords

aeroecology
animals
bats
birds
ecology
insects
migration
polarimetry
radar
wildlife

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Published Papers (11 papers)

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Editorial

Jump to: Research, Other

2 pages, 164 KiB

Open AccessEditorial

Radar Aeroecology

by Jeffrey F. Kelly and Phillip M. Stepanian

Remote Sens. 2020, 12(11), 1768; https://doi.org/10.3390/rs12111768 - 30 May 2020

Cited by 2 | Viewed by 1861

Abstract

Aeroecology is an emerging discipline founded by Tom Kunz and colleagues in the early 2000s to address the challenges of studying animal flight in the lower atmosphere [...] Full article

(This article belongs to the Special Issue Radar Aeroecology)

Research

Jump to: Editorial, Other

18 pages, 2044 KiB

Open AccessArticle

Insect Target Classes Discerned from Entomological Radar Data

by Zhenhua Hao, V. Alistair Drake, John R. Taylor and Eric Warrant

Remote Sens. 2020, 12(4), 673; https://doi.org/10.3390/rs12040673 - 18 Feb 2020

Cited by 12 | Viewed by 3477

Abstract

Entomological radars employing the ‘ZLC’ (zenith-pointing linear-polarized narrow-angle conical scan) configuration detect individual insects flying overhead and can retrieve information about a target’s trajectory (its direction and speed), the insect’s body alignment and four parameters that characterize the target itself: its radar cross section, two shape parameters and its wingbeat frequency. Criteria have previously been developed to distinguish Australian Plague Locusts Chortoicetes terminifera, large moths, medium moths and small insects using the target-character parameters. Combinations of target characters that occur frequently, known as target ‘classes’, have also been identified previously both through qualitative analyses and more objectively with a 4D peak-finding algorithm applied to a dataset spanning a single flight season. In this study, fourteen years of radar observations from Bourke, NSW (30.0392°S, 145.952°E, 107 m above MSL) have been used to test this approach and potentially improve its utility. We found that the previous criteria for assigning targets to classes require some modification, that classes identified in the previous studies were frequently present in other years and that two additional classes could be recognized. Additionally, by incorporating air-temperature information from a meteorological model, we have shown that different classes fly in different temperature ranges. By drawing on knowledge concerning migrant species found in the regional areas around the radar site, together with morphological measurements and radar cross-section data for proxy species, we have made tentative identifications of the insect taxa likely to be contributing to each class. Full article

(This article belongs to the Special Issue Radar Aeroecology)

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20 pages, 5469 KiB

Open AccessArticle

Insect Monitoring Radar: Maximizing Performance and Utility

by V. Alistair Drake, Shane Hatty, Colin Symons and Haikou Wang

Remote Sens. 2020, 12(4), 596; https://doi.org/10.3390/rs12040596 - 11 Feb 2020

Cited by 19 | Viewed by 4625

Abstract

Autonomously-operating radars employing the ‘ZLC configuration’ have been providing long-term datasets of insect flight activity to heights of about 1 km since the late 1990s. A unit of this type operating in Australia has recently received a major upgrade. The aim of the project was to maximize the utility of the radar to entomologists and aeroecologists by providing larger and more continuous datasets and extending observations to 2.5 km. The upgrade was achieved primarily by incorporating modern digital technology, which has enabled much improved data-acquisition, control performance, and data-archiving capacity; by implementing a more comprehensive observing protocol; and by replacing fixed electronic signal-acquisition gates with specially developed software that identifies insect echoes and applies a narrow moving gate that follows them. The upgraded version provides an approximately five-fold increase in hourly sample sizes, a doubling of the duration of observations (from 12 to 24 h per day) and a doubling of the height range over which observations are made. The design considerations (incentives and constraints) that informed the various subsystem implementations are identified, and the necessary compromises are discussed. Observations of the development of a layer echo during a migration by two different insect types are presented as a demonstration of the upgraded unit’s capabilities. Full article

(This article belongs to the Special Issue Radar Aeroecology)

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Graphical abstract

21 pages, 1583 KiB

Open AccessArticle

Broad-Scale Weather Patterns Encountered during Flight Influence Landbird Stopover Distributions

by Hannah L. Clipp, Emily B. Cohen, Jaclyn A. Smolinsky, Kyle G. Horton, Andrew Farnsworth and Jeffrey J. Buler

Remote Sens. 2020, 12(3), 565; https://doi.org/10.3390/rs12030565 - 8 Feb 2020

Cited by 18 | Viewed by 6771

Abstract

The dynamic weather conditions that migrating birds experience during flight likely influence where they stop to rest and refuel, particularly after navigating inhospitable terrain or large water bodies, but effects of weather on stopover patterns remain poorly studied. We examined the influence of broad-scale weather conditions encountered by nocturnally migrating Nearctic-Neotropical birds during northward flight over the Gulf of Mexico (GOM) on subsequent coastal stopover distributions. We categorized nightly weather patterns using historic maps and quantified region-wide densities of birds in stopover habitat with data collected by 10 weather surveillance radars from 2008 to 2015. We found spring weather patterns over the GOM were most often favorable for migrating birds, with winds assisting northward flight, and document regional stopover patterns in response to specific unfavorable weather conditions. For example, Midwest Continental High is characterized by strong northerly winds over the western GOM, resulting in high-density concentrations of migrants along the immediate coastlines of Texas and Louisiana. We show, for the first time, that broad-scale weather experienced during flight influences when and where birds stop to rest and refuel. Linking synoptic weather patterns encountered during flight with stopover distributions contributes to the emerging macro-ecological understanding of bird migration, which is critical to consider in systems undergoing rapid human-induced changes. Full article

(This article belongs to the Special Issue Radar Aeroecology)

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Graphical abstract

31 pages, 4150 KiB

Open AccessArticle

Discrimination of Biological Scatterers in Polarimetric Weather Radar Data: Opportunities and Challenges

by Sidney Gauthreaux and Robert Diehl

Remote Sens. 2020, 12(3), 545; https://doi.org/10.3390/rs12030545 - 6 Feb 2020

Cited by 25 | Viewed by 4149

Abstract

For radar aeroecology studies, the identification of the type of scatterer is critically important. Here, we used a random forest (RF) algorithm to develop a variety of scatterer classification models based on the backscatter values in radar resolution volumes of six radar variables (reflectivity, radial velocity, spectrum width, differential reflectivity, correlation coefficient, and differential phase) from seven types of biological scatterers and one type of meteorological scatterer (rain). Models that discriminated among fewer classes and/or aggregated similar types into more inclusive classes classified with greater accuracy and higher probability. Bioscatterers that shared similarities in phenotype tended to misclassify against one another more frequently than against more dissimilar types, with the greatest degree of misclassification occurring among vertebrates. Polarimetric variables proved critical to classification performance and individual polarimetric variables played central roles in the discrimination of specific scatterers. Not surprisingly, purposely overfit RF models (in one case study) were our highest performing. Such models have a role to play in situations where the inclusion of natural history can play an outsized role in model performance. In the future, bioscatter classification will become more nuanced, pushing machine-learning model development to increasingly rely on independent validation of scatterer types and more precise knowledge of the physical and behavioral properties of the scatterer. Full article

(This article belongs to the Special Issue Radar Aeroecology)

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19 pages, 3135 KiB

Open AccessArticle

Artificial Light at Night is Related to Broad-Scale Stopover Distributions of Nocturnally Migrating Landbirds along the Yucatan Peninsula, Mexico

by Sergio A. Cabrera-Cruz, Emily B. Cohen, Jaclyn A. Smolinsky and Jeffrey J. Buler

Remote Sens. 2020, 12(3), 395; https://doi.org/10.3390/rs12030395 - 26 Jan 2020

Cited by 23 | Viewed by 5440

Abstract

The distributions of birds during migratory stopovers are influenced by a hierarchy of factors. For example, in temperate regions, migrants are concentrated near areas of bright artificial light at night (ALAN) and also the coastlines of large water bodies at broad spatial scales. However, less is known about what drives broad-scale stopover distributions in the tropics. We quantified seasonal densities of nocturnally migrating landbirds during spring and fall of 2011–2015, using two weather radars on the Yucatan peninsula, Mexico (Sabancuy and Cancun). We tested the influence of environmental predictors in explaining broad-scale bird stopover densities. We predicted higher densities in areas (1) closer to the coast in the fall and farther away in spring and (2) closer to bright ALAN and with lower ALAN intensity in both seasons. We found that birds were more concentrated near the coastline in the fall and away from it in spring around Cancun but not Sabancuy. Counter to our expectations, we detected increased bird densities with increased distance from lights in spring around Sabancuy, and in both seasons around Cancun, suggesting avoidance of bright areas during those seasons. This is the first evidence of broad-scale bird avoidance of bright areas during stopover. Full article

(This article belongs to the Special Issue Radar Aeroecology)

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17 pages, 27398 KiB

Open AccessArticle

Monitoring and Characterizing Temporal Patterns of a Large Colony of Tadarida brasiliensis (Chiroptera: Molossidae) in Argentina Using Field Observations and the Weather Radar RMA1

by Lourdes Boero, Denis Poffo, Verónica Damino, Sabrina Villalba, Rubén M. Barquez, Andrés Rodríguez, Matías Suárez and Hernán Mario Beccacece

Remote Sens. 2020, 12(2), 210; https://doi.org/10.3390/rs12020210 - 8 Jan 2020

Cited by 10 | Viewed by 4344

Abstract

Migratory colonies of up to thousands or millions of Brazilian free-tailed bats (Tadarida brasiliensis) are present in temperate areas of America. The monitoring of these massive colonies is crucial to know their conservation status and to evaluate the important ecosystem services that they provide. The objectives of this study were to characterize and to monitor, with an interdisciplinary approach, one of the largest bat colonies in South America, located in La Calera (Córdoba, Argentina). This study includes eight years of field observations inside of their shelter and outside when the colony emerged. Moreover, these observations were complemented with one year of weather radar detections using the Radar Meteorológico Argentino 1 (RMA1). To determine if a detection is a true or false massive emergence of bats, an algorithm was designed. We observed that this large colony of T. brasiliensis is maternal and migratory, just like others in South and North America. This colony arrives in early spring and births occur two months later, migrations occur in early autumn, meanwhile the shelter is empty or inhabited only by a small group of individuals during the cold seasons. The colony was estimated at 900,000 individuals before births occurred. The radar detection was coincident with field observations, when a simultaneous emergence was observed, as well as in the monitoring throughout the year. This represents the first study made in South America using radar technology for monitoring a bat colony. We here demonstrate that RMA1 is a powerful tool for monitoring this colony in the long term, and even to alert possible changes in permanence in time or in the number of individuals. Full article

(This article belongs to the Special Issue Radar Aeroecology)

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24 pages, 10530 KiB

Open AccessArticle

A Geostatistical Approach to Estimate High Resolution Nocturnal Bird Migration Densities from a Weather Radar Network

by Raphaël Nussbaumer, Lionel Benoit, Grégoire Mariethoz, Felix Liechti, Silke Bauer and Baptiste Schmid

Remote Sens. 2019, 11(19), 2233; https://doi.org/10.3390/rs11192233 - 25 Sep 2019

Cited by 17 | Viewed by 6516

Abstract

Quantifying nocturnal bird migration at high resolution is essential for (1) understanding the phenology of migration and its drivers, (2) identifying critical spatio-temporal protection zones for migratory birds, and (3) assessing the risk of collision with artificial structures. We propose a tailored geostatistical model to interpolate migration intensity monitored by a network of weather radars. The model is applied to data collected in autumn 2016 from 69 European weather radars. To validate the model, we performed a cross-validation and also compared our interpolation results with independent measurements of two bird radars. Our model estimated bird densities at high resolution (0.2° latitude–longitude, 15 min) and assessed the associated uncertainty. Within the area covered by the radar network, we estimated that around 120 million birds were simultaneously in flight (10–90 quantiles: 107–134). Local estimations can be easily visualized and retrieved from a dedicated interactive website. This proof-of-concept study demonstrates that a network of weather radar is able to quantify bird migration at high resolution and accuracy. The model presented has the ability to monitor population of migratory birds at scales ranging from regional to continental in space and daily to yearly in time. Near-real-time estimation should soon be possible with an update of the infrastructure and processing software. Full article

(This article belongs to the Special Issue Radar Aeroecology)

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19 pages, 2354 KiB

Open AccessArticle

Radar Measurements of Morphological Parameters and Species Identification Analysis of Migratory Insects

by Cheng Hu, Shaoyang Kong, Rui Wang and Fan Zhang

Remote Sens. 2019, 11(17), 1977; https://doi.org/10.3390/rs11171977 - 22 Aug 2019

Cited by 12 | Viewed by 3632

Abstract

Migratory insect identification has been concerning entomology and pest managers for a long time. Their nocturnal behavior, as well as very small radar cross-section (RCS), makes individual detection challenging for any radar network. Typical entomological radars work at the X-band (9.4 GHz) with a vertical pencil beam. The measured RCS can be used to estimate insect mass and wingbeat frequency, and then migratory insects can be categorized into broad taxon classes using the estimated parameters. However, current entomological radars cannot achieve species identification with any higher precision or confidence. The limited frequency range of current insect radars have precluded the acquisition of more information useful for the identification of individual insects. In this paper, we report an improved measurement method of insect mass and body length using a radar with many more measurement frequencies than current entomological radars. The insect mass and body length can be extracted from the multi-frequency RCSs with uncertainties of 16.31% and 10.74%, respectively. The estimation of the thorax width and aspect ratio can also be achieved with uncertainties of 13.37% and 7.99%, respectively. Furthermore, by analyzing the statistical data of 5532 insects representing 23 species in East China, we found that the correct identification probabilities exceed 0.5 for all of the 23 species and are higher than 0.8 for 15 of the 23 species under the achievable measurement precision of the proposed technique. These findings provide promising improvements of individual parameter measurement for entomological radars and imply a possibility of species identification with higher precision. Full article

(This article belongs to the Special Issue Radar Aeroecology)

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Other

Jump to: Editorial, Research

14 pages, 4656 KiB

Open AccessLetter

High-Resolution Spatial Distribution of Bird Movements Estimated from a Weather Radar Network

by Bart Kranstauber, Willem Bouten, Hidde Leijnse, Berend-Christiaan Wijers, Liesbeth Verlinden, Judy Shamoun-Baranes and Adriaan M. Dokter

Remote Sens. 2020, 12(4), 635; https://doi.org/10.3390/rs12040635 - 14 Feb 2020

Cited by 17 | Viewed by 7763

Abstract

Weather radars provide detailed information on aerial movements of organisms. However, interpreting fine-scale radar imagery remains challenging because of changes in aerial sampling altitude with distance from the radar. Fine-scale radar imagery has primarily been used to assess mass exodus at sunset to study stopover habitat associations. Here, we present a method that enables a more intuitive integration of information across elevation scans projected in a two-dimensional spatial image of fine-scale radar reflectivity. We applied this method on nights of intense bird migration to demonstrate how the spatial distribution of migrants can be explored at finer spatial scales and across multiple radars during the higher flying en-route phase of migration. The resulting reflectivity maps enable explorative analysis of factors influencing their regional and fine-scale distribution. We illustrate the method’s application by generating time-series of composites of up to 20 radars, achieving a nearly complete spatial coverage of a large part of Northwest Europe. These visualizations are highly useful in interpreting regional-scale migration patterns and provide detailed information on bird movements in the landscape and aerial environment. Full article

(This article belongs to the Special Issue Radar Aeroecology)

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9 pages, 3264 KiB

Open AccessFeature PaperLetter

Coupling Atmospheric and Biological Remote Sensing to Investigate Boundary-Layer Evolution and Animal Flight Behavior as Affected by the 2017 North American Solar Eclipse

by Phillip M. Stepanian and Charlotte E. Wainwright

Remote Sens. 2020, 12(4), 591; https://doi.org/10.3390/rs12040591 - 11 Feb 2020

Cited by 1 | Viewed by 2671

Abstract

The daytime atmospheric boundary layer is characterized by vertical convective motions that are driven by solar radiation. Lift provided by thermal updrafts is sufficiently ubiquitous that some diurnal birds and arthropods have evolved specialized flight behaviors to soar or embed in these atmospheric currents. While the diel periodicity of boundary-layer dynamics and animal flight has been characterized, rare disruptions to this cycle provide a chance to investigate animal behavioral responses to boundary layer motion and photoperiod that are disjointed from their expected circadian rhythm. To analyze these interactions, we couple radar-derived animal observations with co-located lidar measurements of the convective boundary layer over north-central Oklahoma, USA during the solar eclipse of 21 August 2017. Analysis of animal flight behavior confirmed that ascending and descending flight effort did change in the time period encompassing the solar eclipse, however, the response in behavior was coincident with proximate changes in boundary-layer turbulence. Both the animal behavioral response and decrease in atmospheric turbulence lagged changes in solar irradiance by approximately 30 min, suggesting that changes in flight activity were not cued by the eclipse directly, but rather by the modification of vertical air motions caused by the eclipse. Full article

(This article belongs to the Special Issue Radar Aeroecology)

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