光束发散角对星载激光测高仪森林回波的影响  

Impact of beam divergence angle on forest echo from satellite laser altimeter

作　　者：王虹[1,2] 马跃 李松[1] 张智宇[1] 黄科 易洪[1] 

机构地区：[1]武汉大学电子信息学院,湖北武汉430072 [2]昆明理工大学理学院,云南昆明650051

出　　处：《红外与毫米波学报》2018年第1期112-118,共7页Journal of Infrared and Millimeter Waves

基　　金：对地高分辨率观测系统国家科技重大专项(11-Y20A12-9001-17/18;42-Y20A11-9001-17/18);国家自然科学基金(41506210;11574240);中国博士后科学基金项目(2016M600612);中央高校基本科研业务费专项资金(2015212020201)资助的课题;测绘地理信息公益性行业科研专项(201512010)~~

摘　　要：植被树高是生物量评估和森林生态监测的重要参数,但是大区域的植被树高数据获取困难.由大光斑星载激光测高系统森林回波可反演大区域植被树高,然而大坡度山区的植被和地面回波混叠严重,难以准确提取波形参数反演植被树高.为此建立森林目标回波的解析模型,推导出从混叠回波中分离植被和地面回波的必要条件,指出导致回波混叠的因素除了目标粗糙度和坡度,还有发射脉冲的发散角.分析了地表粗糙度和地形坡度对植被冠层回波的展宽效应及其对波形分解的影响,通过比较实测GLAS波形和仿真回波波形,验证了压缩光束发散角可降低森林回波对大坡度地形的敏感性.对于卫星轨道高度在500~600 km之间时,激光测高仪光束发散角一般在40~60μrad,更有利于森林植被树高的反演.所得结论为提高大坡度山地森林树高反演精度,从星载激光测高仪的系统设计角度提供了有意义的参考.Vcgctation hcight is an important parameter for biomass assessment and ecosystem structure monitoring. However, vegetation height data over large areas are difficult to obtain. Vegetation heights can be retrieved by using large-footprint satellite altimeter system GLAS waveforms, but the current method can only be used in relatively flat forest regions because over sloping mountainous areas, the effects of ground and canopy are mixing on the waveforms and cannot be distinguished. By establishing analytical model of forest target echo, the separation requirement of vegetation echo and ground echo from aliasing waveforms is derived. It is pointed out that the factors of leading to echo aliasing in addition to target roughness and slope, and beam divergence angle is also a factor. The broadening effect and waveform decomposition related to the beam divergence angle, surface roughness and topography slope is analyzed. By using the waveform simulation and GLAS actual waveforms, it is verified to de- crease beam divergence angles can reduce the sensitivity of forest echo to sloping mountainous terrains and be more conducive to the retrieval of canopy heights. For laser altimeter to carry on satellite in the orbit of 500 - 600 km, the beam divergence angles is 40 - 60 μrad better. The result provides a meaningful reference for designing of satellite laser altimeter system for the retrieval of canopy heights over high sloping terrains.

关 键 词：星载激光测高仪 光束发散角 光斑直径 森林回波 

分 类 号：TP79[自动化与计算机技术—检测技术与自动化装置]