Atomic Physics

Faculty of Engineering, LTH

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Fluorescence LIDAR

Studies on birds

Birds, with their special advantage of being able to fly, can travel long distances in a relatively short period of time. This has made it possible for them to migrate and live at different habitats depending on season and in this way also to effectively spread genes. Every year, millions of birds travel thousands of kilometers, e.g., between Europe and Africa heading for seasonal breeding places. 

Still, the seasonal habitats of different species of birds have not been completely mapped but this would be of great interest to get a more thorough picture of the global gene flow. Birds are especially important in this aspect due to the large land areas they cover and travel. The spread of diseases is another central aspect, with the bird flue, which in the 90’s was found also to spread to humans, as a striking example of the importance of bird migration research. 

Questions that still are lacking complete answers are among others how, exactly, the times of travel are chosen, how the geography and winds affect the flights and, generally, how the habitats are selected and found year after year.

A number of remote sensing techniques for studying birds in flight have been developed and used. Examples are tracking radars, infrared cameras and ceilometers. Observing flying birds at day time with binoculars of course provides important information. All these methods are though limited by different factors; unfortunately making it very difficult to distinguish between species, especially during night time when binoculars are impossible to use for this purpose. With radar, which is very effective in locating birds, a few species like the Common Swift (Sw. tornseglare), might be recognized with the help of their specific wing beat frequency, but this method cannot provide any classification help in the general case. The flying heights, which are often exceeding 1 km makes even visual classification difficult, even at daytime. The fact that many birds actually prefer to fly at nighttime thanks to beneficial conditions with, e.g., a less turbulent atmosphere and less risk of being caught by predators makes bird classification at night time even more important. 

Fluorescence lidar may provide a great contribution to the extra information needed to classify birds remotely. The fluorescence induced when the laser light hits the feathers of a bird is observed from a remote distance. Basically, the fluorescence gives information about the colour of a bird, and together with, e.g., radar, both the species and number of passing birds could be established. 

Studies on insects

Analogous to birds, the beautiful insects damselflies, being ectotherms, are forced to change their habitats according to global temperature changes. It has turned out that these animals consistently have moved their living locations northwards during the last years. The damselflies are therefore possible effective natural probes for climate changes. With remote investigations, the risk of disturbing the natural behavior of the animals is also decreased.

The site at Klingavälsån is a position where much research has been done on these insects, by among others scientists from the Animal Ecology group in Lund. The purpose of the corresponding measurements was to try to observe several different features of the damselflies, e.g., where they are mostly located at and around the river and how they are affected by weather and time of day, i.e., when they start to fly in the morning and when they stop in the evening (they are generally not flying at night). One aim was also to try to discriminate between different species and genders, similar to the studies on birds.

Cultural heritage

With fluorescence lidar, ultraviolet laser pulses are directed towards a solid target where fluorescence is induced. The fluorescence light could, instead of being detected by a multi-detector setup be analyzed in its full spectrum using a spectrometer. The laser beam is then scanned over an area to gather the entire spectrum in each point. When analyzing the spectral shapes, a function can be applied that yields a value in each point, which can be displayed in a false-color coded picture. In this manner different features of the spectra can be focused on and this may represent different characteristics of the target. In the examples at the Coliseum in Rome and at Öveds kloster, stone building material is examined with fluorescence lidar.

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