Advancement of laser-induced fluorescent (LIF) lidar

Abstract

ABSTRACTSince LIF lidar has a higher sensitivity in detecting very thin oil spill,chlorophyll,gebstoff in water,it becomes auseful tool for monitoring marine environment and primary productive forces.Researches indicate especially that it is theunique technique in discriminating the sort of oil spill as comparing to the passive optical and the active microwave remotesensing techniques.In this paper we summarize the state-of -art of LIF lidar technique such as laser sources, optics andreturn analysis.Then we discuss its potential power in wider opplication aspects.Some suggestions for developing LIF lidarwill be provided and assessed.Keywords: Laser, fluoresent,lidar,oil spill1.INTRODUCTIONOn statistics a number of million tons of crude oil and it's refine products were drained into the sea per year due tonatural and artificial leakge,marine accidents and illegal emission.It pulluted directely wide marine areas and coasts . Inaddition to it the industrial and life pallutants will lead marine biological chain to broke and want of biological resources.Thus we must pay more attention to both resource exploition and enviromental protection at the same time.Considering primaryly enforcing the law and monitoring marine emission,since 70's several developed countries beganto develop new techniques to monitor oil spill.Microwave radiometer was used to detect the large area and thiker oilspill,UV/IR scanning radiometer can image the oil spill distribution with high spatial resolving power,camara or video wasused to identify the ship draining and LIF lidar will discriminate the sort of oil spill mainly. An airborne system of oil spillmonitoring will consist of several instruments mentioned above.Theory indicated that the spectral features of laser induced fluorescence have obvious differences for different oil andits intensity dependes on the thickness of oil spills.Many experimental results of shipborne or airborne lidar systems provedthat LIF lidar could be a unique effective technique to detect and classify oil spill.Even though classification capability issensitive to interferentes from a number of factors and its results depend on data processing method as well as priorknowledge of factors.Some LIF lidar systems developed by European and North American countries have been supplied as acommercial instrument.Lasting researches show that chlorophyll,gebstoff in water, some rocks and minerals,vagetation and soils possessobvious and detectable fluorescence while they are illuminated by ultraviolet laser. Their fluorescent spectral features relatedirectly to matter structure ,mechanisms of light energy interreaction,environmental condition and etc. At present theimportant appilication of LIF lidar focuses in marine environment and primary productivity. Some practical lidar systemshave been developed ,which potential capability in those fields might be affirmed From technical and economic pionts ofview LIF lidar is still a complex, high cost and difficult to operate equipment.It is necessary to improve continuously lidarperfomances,to adopt the advanced elements,devices,unit technique as well as new data processing methods in order to makelidar system inexpensive, reliable and multiuseful.2.PHYSICAL BASISS