ABSTRACT
Imaging........................................... 446 6.4. Illustrations of Fluorescence Lidar Applications ..... 447
6.4.1. Marine Monitoring ........................................ 447 6.4.2. Vegetation Monitoring................................... 450
6.4.3. Historical Monuments................................... 456 6.5. Discussion .................................................................. 461 Acknowledgments................................................................ 461 References............................................................................ 462
6.1. INTRODUCTION
Our perception of the world is largely based on our vision, where colors are perceived as a result of the different reflectance properties of materials. Sunlight, or the sky, has a well-defined spectral distribution and when impinging on a surface, those parts of the spectrum that match some transition of the molecules are absorbed, leaving the others the freedom to scatter and eventually reach our eye. Through the interaction with the different types of cones in the retina and the subsequent processing in the brain, the perception of color occurs. The eye is sensitive to a very limited range of the electromagnetic spectrum: from 400 to 700 nm. A grass lawn being identified as green is due to chlorophyll absorption in the blue and red spectral regions, while the red color of blood is the result of strong hemoglobin absorption all through the visible spectrum up to 600 nm. Outside the visible range, selective absorption occurs, in the ultraviolet (UV) and infrared (IR) ranges, but here the features must be recorded by different types of electronic detectors. Satellite remote sensing using whiskbroom or pushbroom multispectral sensors is widely used for earth resource monitoring and classification.1,2
It is well known that the fluorescence phenomenon can provide information in addition to that obtained by absorptive or reflective spectroscopy. Things that are hidden to the naked eye or normal photography are revealed using fluorescence techniques. The use of fluorescence in microscopy,3 forensic science,4 art inspection,5 and tissue diagnostics6 is well known. All these applications are carried out in indoor controlled environments, although sometimes competing background light, for example, operation lamps, make pulsed excitation and time-gated detection necessary.7
