Elin Malmqvist

Effective Parameterization of Laser Radar Observations of Atmospheric Fauna

The pace at which the worlds ecosystems and biodiversity of, e.g., pollinators decline is currently at a rate where it is challenging to document. In recent years, our group has made an effort to bridge the disciplines of laser remote sensing and biophotonics, and we have developed lidar methods for inventorying the biosphere. Here, we present an effective method for extracting fauna observations from atmospheric lidar data and reducing the observations to a set of descriptive parameters. Kilohertz-lidar data are used, the essential steps are walked through and a glimpse of the obtainable data product is presented.

The Scheimpflug lidar method

The recent several years we developed the Scheimpflug lidar method. We combined an invention from the 19th century with modern optoelectronics such as diode lasers and CMOS array from the 21st century. The approach exceeds expectations of background suppression, sensitivity and resolution beyond known from time-of-flight lidars. We accomplished multiband elastic atmospheric lidars for resolving single particles and aerosol plumes from 405 nm to 1550 nm. We pursued hyperspectral differential absorption lidar for molecular species. We demonstrated a simple method of inelastic hyperspectral lidar for profiling aquatic environments and vegetation structure. Not least, we have developed polarimetric Scheimpflug lidar with multi-kHz sampling rates for remote modulation spectroscopy and classification of aerofauna. All these advances are thanks to the Scheimpflug principle. Here we give a review of how far we have come and shed light on the limitations and opportunities for future directions. In particular, we show how the biosphere can be resolved with unsurpassed resolution in space and time, and share our expectation on how this can revolutionize ecological analysis and management in relation to agricultural pests, disease vectors and pollinator problematics.

The bat–bird–bug battle: daily flight activity of insects and their predators over a rice field revealed by high-resolution Scheimpflug Lidar

We present the results of, to our knowledge, the first Lidar study applied to continuous and simultaneous monitoring of aerial insects, bats and birds. It illustrates how common patterns of flight activity, e.g. insect swarming around twilight, depend on predation risk and other constraints acting on the faunal components. Flight activity was monitored over a rice field in China during one week in July 2016, using a high-resolution Scheimpflug Lidar system. The monitored Lidar transect was about 520 m long and covered approximately 2.5 m3. The observed biomass spectrum was bimodal, and targets were separated into insects and vertebrates in a categorization supported by visual observations. Peak flight activity occurred at dusk and dawn, with a 37 min time difference between the bat and insect peaks. Hence, bats started to feed in declining insect activity after dusk and stopped before the rise in activity before dawn. A similar time difference between insects and birds may have occurred, but it was not obvious, perhaps because birds were relatively scarce. Our observations are consistent with the hypothesis that flight activity of bats is constrained by predation in bright light, and that crepuscular insects exploit this constraint by swarming near to sunset/sunrise to minimize predation from bats.

Scheimpflug Lidar for combustion diagnostics

A portable Lidar system developed for large-scale (~1-20 m) combustion diagnostics is described and demonstrated. The system is able to perform remote backscattering measurements with range and temporal resolution. The range resolution is obtained by sharply imaging a part of the laser beam onto a CMOS-array or ICCD detector. The large focal depth required to do this is attained by placing the laser beam, the collection optics and the detector in a so-called Scheimpflug configuration. Results from simulations of the range capabilities and range resolution of the system are presented and its temporal resolution is also discussed. Various applications, important for combustion diagnostics, are also demonstrated, including Rayleigh scattering thermometry, aerosol detection and laser-induced fluorescence measurements. These measurements have been carried out using various continuous-wave GaN diode lasers, emitting in the violet-blue (405 - 450 nm) wavelength regime. It is anticipated that Scheimpflug Lidar will provide a useful and versatile diagnostic tool for combustion research, not only for fundamental studies, but in particular for applications at industrial sites.

OH-Thermometry with Photofragmentation Laser-Induced Fluorescence

A technique that increases the temperature range and the sensitivity of OH-LIF thermometry is proposed. OH-excitation scans, acquired through photofragmentation laser-induced fluorescence of H2O2, are used to determine 2-D-temperatures in H2O2-vapor and in an HCCI-engine.

CW-laser radar for combustion diagnostics

A CW-laser radar system developed for combustion diagnostics is described. It is based on triangulation to attain range information. Some initial results from measurements in sooting flames are shown and some future perspectives are discussed.