顾及地形起伏的无人机影像覆盖分析方法     

张衡  李骁  叶朋飞 《测绘通报》2020,(1):102-106

使用无人机实施测绘航空摄影时，由于无人机相对航高较低，地面起伏会对无人机影像的分辨率、覆盖范围、重叠度造成较大的影响，影像成果会出现分辨率不足、重叠度不够、覆盖漏洞等缺陷。针对这一情况，本文提出了一种利用数字微分正解法的计算方法，借助DEM准确计算每张影像的覆盖范围，并使用FME软件高效生成全部影像的覆盖范围。经过实际使用，验证了该方法可以在航线设计阶段准确预测并分析全部影像的覆盖范围、重叠度，因此可及时发现设计问题并调整航线。该方法可以有效减少因地形起伏造成的影像覆盖缺陷，减少返工现象，从整体上提高了作业效率。  相似文献   

Seasonal variations in prey selection by estuarine black-headed gulls (Larus ridibundus)     

D.J. Curtis  C.G. Galbraith  J.C. Smyth  D.B.A. Thompson 《Estuarine, Coastal and Shelf Science》1985,21(1):75-90

The number of black-headed gulls (Larus ridibundus) in the Clyde Estuary is large. In summer the average density has reached 1350 gulls km^?2 and in winter 180 gulls km^?2. This paper compares prey selection and feeding efficiency in gulls during summer and winter on tidal flats, and considers how seasonal differences may be adaptations to cope with seasonal changes in prey availability.Gross and net rates of energy intake were highest in summer because gulls captured more of the polychaete N. diversicolor than the amphipod C. volutator. In winter, gulls selected for C. volutator and therefore an energetically less profitable diet. Throughout the year gulls selected more C. volutator relative to N. diversicolor than expected on energetic grounds and so apparently did not maximize potential net rate of energy intake.Gulls used three techniques to capture prey and made most intensive use of the ‘crouch’ technique. Crouching gulls attained a much higher net rate of energy intake than ‘upright’ or ‘paddling’ gulls.A log-linear model showed that (a) season, water depth and gull density determined feeding technique and (b) feeding technique and season independently determined foraging success and prey selection. Thus gull density and water depth acted on prey selection through imposed variations in feeding technique.Reasons for gulls selecting energetically unprofitable C. volutator and for the use of several distinct feeding techniques are discussed.  相似文献   

Particulate organic matter in the coastal and estuarine waters of Goa and its relationship with phytoplankton production     

X.N. Verlencar  S.Z. Qasim 《Estuarine, Coastal and Shelf Science》1985,21(2):235-243

In the coastal and estuarine waters of Goa, particulate organic carbon (POC) varied from 0.52 to 2.51 mg l^?1 and from 0.28 to 5.24 mg l^?1 and particulate phosphorus (PP) varied from 0.71 to 5.18 μg l^?1 and from 0.78 to 20.34 μg l^?1, respectively. The mean values of chlorophyll and primary productivity were 1.94 mg m^?3 and 938.1 mg C m^?2 day^?1 in the coastal waters and 4.3 mg m^?3 and 636.5 mg C m^?1 day^?1 in the estuarine waters, respectively.$\text{POC}\text{chl}$ ratios were low in June and October even when POC values were quite high. The POC in surface waters was linearly correlated with the chlorophyll content. Also PP increased when chlorophyll and primary productivity remained high. The results suggest that the phytoplankton was sharply increasing and contributed to POC and PP content. The percentage of detritus calculated from the intercept values of chlorophyll on POC varied from 46 to 76% depending on season. Results indicate that the major portion of POC and PP during postmonsoon (October–January) is derived from phytoplankton production while the allochthonous matter predominate during monsoon (June–September).  相似文献   

基于遥感技术对黄河口水色与岸线季相变化特征研究     

马安青  胡泓  袁道伟  胡婷 《中国海洋大学学报(自然科学版)》2008,38(1):151-156

使用Landsat-5 TM 2004年11月24日与2005年5月13日黄河口遥感影像,配合准同期外业实测资料,进行黄河口水体水色物质叶绿素a与悬浮泥沙的动态反演与河口岸线解译.研究表明由于秋末与春初黄河上游来水物质含量的差异,上述悬浮指标值存在显著的季相差异.根据样值与光谱特征建立的反演模型得出的反演值与实测值有平均在0.85以上的相关关系,具有很好的反演效果.岸线解译成果表明,黄河口岸线演变迅速,在河流平枯水量时期仍然具有较强的变化,岸线推进尤以新河口附近显著.这表明,使用遥感手段是进行河口生态环境质量监测的有效手段,是进行岸线动态变化研究的一种基本技术支撑手段.  相似文献   

棉兰老涡旋的数值模拟     

李荣凤  曾庆存  季仲贞 《热带海洋学报》1991,(4)

用一个水平分辨率比较高的非线性正压模式,对热带西太平洋海域里的海流进行了数值模拟。计算海流与观测结果颇相一致。结果表明:赤道以北、棉兰老岛以东附近海域中,棉兰老冷涡在一年的大部分时间里都得到发展,但是其范围、强度和中心位置在各个月份并不相同,显示出很强的季节变化;在哈马黑拉岛东北海域,6月份突然出现了一个反气旋式的涡旋;这个涡旋8月份发展得最强,一直持续到10月份,在11月份就消亡了。  相似文献   

Vertical and seasonal distribution of eight Clausocalanus species (Copepoda: Calanoida) in oligotrophic waters   总被引：1，自引：0，他引：1  

Peralba  Aurea; Mazzocchi  Maria Grazia 《ICES Journal of Marine Science》2004,61(4):645-653

  相似文献   

关于南海暖水季节和年际变化的研究   总被引：1，自引：3，他引：1  

王启 《中国海洋大学学报(自然科学版)》2003,33(6):821-824

阐述了研究南海暖水的意义 ,综述了关于南海暖水的现状 ,提出了关于南海暖水季节和年际变化方面应该研究的问题  相似文献   

崇明东滩沉积环境探讨   总被引：8，自引：0，他引：8  

刘清玉  戴雪荣  何小勤 《海洋地质前沿》2003,19(12):1-4

为探讨崇明东滩的沉积环境，了解崇明东滩的植被、水动力等对沉积的影响，对崇明进行了为期一年的实地观测和采样实验分析研究，研究结果表明：①沉积物中含有细砂、粉砂、黏土，其中粉砂是主要组分。塑造滩地的动力以潮汐作用为主，波浪作用居于次要地位；②沉积物的平均粒径自北线断面向南线断面、自高潮向低潮滩有逐渐变粗、分选变差的趋势，且平均粒径具有明显的季节变化；③潮滩季节性冲淤变化主要是与不同季节水文条件的差异性、潮滩植被季节变化及风暴天气等有关。  相似文献   

Influence of Current Width Variation on the Annual Mean Transport of the East Sakhalin Current: A Simple Model     

Yoichi?ShimadaEmail author  Atsushi?Kubokawa  Kay?I.?Ohshima 《Journal of Oceanography》2005,61(5):913-920

Recent observations suggest that the annual mean southward transport of the East Sakhalin Current (ESC) is significantly larger than the annual mean Sverdrup transport. Motivated by this observational result, transport of a western boundary current has been investigated using a simple numerical model with a western slope. This transport is defined as the instantaneous barotropic transport integrated from the western boundary to the offshore point where the barotropic velocity vanishes. The model, forced by seasonally varying wind stress, exhibits an annual mean of the western boundary current transport that is larger than that of the Sverdrup transport, as observed. The southward transport from October to March in the model nearly equals the instantaneous Sverdrup transport, while the southward transport from April to September decreases slowly. Although the Sverdrup transport in July vanishes, the southward transport in summer nearly maintains the annual mean Sverdrup transport, because the barotropic Rossby wave cannot intrude on the western slope. This summer transport causes the larger annual mean. Although there are some uncertainties in the estimation of the Sverdrup transport in the Sea of Okhotsk, the seasonal variation of the southward transport in the model is qualitatively similar to the observations.  相似文献   

夏季南海上层环流动力机制的数值研究   总被引：10，自引：0，他引：10  

蔡树群  苏纪兰  甘子钧  刘秦玉 《海洋学报》2002,24(1):1-7

通过利用一个分区性的正压-斜压衔接模式来探讨夏季南海的上层环流特征及其动力机制,结果表明:夏季期间,由于风生环流的不稳定性促使在东沙群岛附近的气旋涡的强度及位置发生变化,并间接导致黑潮侵入南海北部的程度变化以及气旋涡南侧的反气旋式环流、西沙群岛西南侧的气旋涡的强度和范围出现波动现象;在南海南部的北向西边界流由于离岸的西南季风所驱动在中南半岛中部沿岸脱离岸线往东北方向的流动,导致沿岸的水体大量流失而在沿岸形成一支南向补偿流并在西沙群岛西南侧诱生一气旋涡,而上述的离岸西边界流则作顺时针方向流动,从而在南海南部形成反气旋式大环流;在南沙海槽附近出现的局地气旋涡和万安滩附近的气旋涡分别受β效应、底形效应的作用而形成.  相似文献