Development and implementation of a multiscale biomass model using hyperspectral vegetation indices for winter wheat in the North China Plain

Crop monitoring during the growing season is important for regional management decisions and biomass prediction. The objectives of this study were to develop, improve and validate a scale independent biomass model. Field studies were conducted in Huimin County, Shandong Province of China, during the 2006–2007 growing season of winter wheat (Triticum aestivum L.). The field design had a multiscale set-up with four levels which differed in their management, such as nitrogen fertilizer inputs and cultivars, to create different biomass conditions: small experimental fields (L1), large experimental fields (L2), small farm fields (L3), and large farm fields (L4). L4, planted with different winter wheat varieties, was managed according to farmers’ practice while L1 through L3 represented controlled field experiments. Multitemporal spectral measurements were taken in the fields, and biomass was sampled for each spectral campaign. In addition, multitemporal Hyperion data were obtained in 2006 and 2007. L1 field data were used to develop biomass models based on the relation between the winter wheat spectra and biomass: several published vegetation indices, including NRI, REP, OSAVI, TCI, and NDVI, were investigated. A new hyperspectral vegetation index, which uses a four-band combination in the NIR and SWIR domains, named GnyLi, was developed. Following the multiscale concept, the data of higher levels (L2 through L4) were used stepwise to validate and improve the models of the lower levels, and to transfer the improved models to the next level. Lastly, the models were transferred and validated at the regional scale using Hyperion images of 2006 and 2007. The results showed that the GnyLi and NRI models, which were based on the NIR and SWIR domains, performed best with R² > 0.74. All the other indices explained less than 60% model variability. Using the Hyperion data for regionalization, GnyLi and NRI explained 81–89% of the biomass variability. These results highlighted that GnyLi and NRI can be used together with hyperspectral images for both plot and regional level biomass estimation. Nevertheless, additional studies and analyses are needed to test its replicability in other environmental conditions.     

2007年冬季沈阳典型大气污染源PM10排放模拟

选取沈阳市区9个典型的大气污染源冬季的PM10排放浓度资料,利用MM5耦合CALPUFF对2007年12月至2008年2月沈阳城市区域气象场和排放PM10浓度分布进行月平均数值模拟.结果表明:冬季沈阳地区受高压控制,北风较强,并经过增强、减弱的过程,多呈现对大气污染物扩散不利的天气形势.高空为偏西风且风速较大时,地面和...     

1961—2020年辽宁省暖冬现象气候特征分析

利用1961—2020年辽宁省56个气象站冬季逐日气温数据,根据国家标准《暖冬等级》,以1990—2020年为气候值作为参考,综合采用气候倾向率、IDW、滑动t检验突变分析以及小波分析等方法,分析辽宁省近60 a冬季平均气温的时空变化趋势,单站暖冬及区域暖冬事件的气候变化特征。结果表明：近60 a来辽宁省冬季平均气温以0.3℃/10 a的速率升高,辽宁中部和东部地区变暖趋势最为显著;20世纪90年代前的30 a属于偏冷时段,但增温效应强于后30 a,冬季平均气温在1987年前后出现了明显的由冷转暖的突变,1971年出现了相对较弱的冷暖转变;1988年后逐年单站暖冬事件的发生整体比1961—1987年出现单站暖冬事件明显增多。发生频次较高的地区分布在辽宁中部和东南部地区,为16—20次;近60 a来共有16次区域暖冬事件,21世纪后的20 a内共出现9次区域暖冬事件,占总数的60%;区域暖冬事件以准22 a和2—3 a为振荡周期。     

江苏省冬季气温、降水年代际异常及相关分析

利用NCEP/NCAR再分析资料和江苏省冬季气温、降水资料,运用带通滤波、经验正交分解(EOF)和相关分析等方法,分析了江苏省冬季气候年代际异常及同期气温与降水的相关特征.结果表明:江苏省冬季气候的年代际变化具有很好的空间一致性,表现为全省整体偏暖(偏冷)和偏涝(偏旱)的趋势;冬季气候存在明显的年代际突变,时间在1980s中期前后,平均气温从偏冷时期向偏暖时期转换,降水由偏少期向偏多时期转换.通过冬季同期降水和气温的相关分析发现,降水和气温具有一定的正相关性,而他们的年代际分量的正相关性更为显著,这与冬季大气环流场和海温场的年代际变化有密切的关系.     

冬奥会张家口赛区一次降水相态特征分析

利用冬奥会气象观测站网资料、ERA5的0.25°×0.25°高分辨率再分析资料、常规探空资料以及激光雷达和风廓线雷达资料,从环流形势、温湿度和微物理特征以及雷达特征等方面对2020年11月17-19日冬奥会张家口赛区一次明显的雨转雪天气过程进行分析。结果表明：低层前期的暖湿西南气流,为降水提供好的水汽和能量条件,后期强的干冷平流为相态转换提供有利条件。赛区出现雨转雪时,700 hPa温度低于-2℃,同时850 hPa温度低于2℃。零度层高度的快速下降是相态转换的重要温度判据,0℃线降到距地面400 m左右赛区降水相态已经转变为纯雪,低层风向的转向对赛场的雨雪相态转换有一定的指示意义。随着高空云冰和雪水含量逐渐增加,其出现最大值后,雨雪相态开始转换。降雪时激光雷达最大探测高度比降雨时有明显的降低,风廓线雷达低层风场的变化和雨雪相态关系密切,风廓线雷达探测的垂直速度变化也能反映雨雪相态的转换。     

High salinity winter outflow from a mega inverse-estuary—the Great Australian Bight

Conductivity-temperature-depth (CTD) observations taken in the Great Australian Bight (GAB) during ORV Franklin cruise Fr 07/94 in July 1994 indicated the presence of a dense bottom layer at the head of the GAB, which flowed along the sea floor towards the shelf-break as a gravity current The north central region of the GAB was stratified with a maximum salinity difference of between 0.4 and 0.5. The outflow was confined to the shelf and was directed in a south-easterly direction with little evidence of cross-shelf transport. The flow exhibited a well-defined bottom interface evident from the head of the GAB to near the mouth of Spencer Gulf (SG), where the surface-bottom salinity difference was about 0.3. The mean thickness of the outflow was about 15 m. An estimate of the speed of the outflow at the discharge over the shelf-break was made using the zero entrainment assumption. This yielded a speed of <16 cm s⁻¹, which remarkably was consistent with near bottom current meter measurements (16 cm s⁻¹) on the continental shelf edge, reported south of the Eyre Peninsula. A mass budget analysis indicated that the outflow, which probably is partially maintained by the gravity current and partly by a wind-driven circulation would exist over the period, July–December, with a peak transport of about 10⁶ m³s⁻¹ (1 Sverdrup) which is approximately twenty times that of the bottom outflow from the adjoining Spencer Gulf.     

辽宁冬季气温时空分布特征及其预测概念模型

分析了1961—2004年辽宁冬季平均气温的时空分布特征。结果表明：辽宁冬季平均气温具有明显的南高北低、从沿海向内陆逐渐降低的趋势;冬季平均气温呈线性递增趋势,递增率为0.56 ℃/10 a,与全球气候变暖趋势一致。辽宁冬季气温存在3—5 a和24 a的周期,于1986 a前后发生了一次明显突变,突变前气温呈下降趋势,且以5 a左右的短周期波动为主,突变后开始显著的增温变化,并以10 a以上的长周期变化为主。在此基础上,分析了影响辽宁冬季气温异常的物理因子,建立了辽宁冬季冷暖的预测概念模型。     

北亚洲大陆冬季地表感热通量对我国江淮梅雨的影响

利用1979—2008年NCEPⅡ月平均地表感热通量再分析资料、江苏省气象台整编的江淮出入梅日期和全国753个测站逐日降水资料,分析了亚洲北部(60°～135°E,32°～75°N,简称北亚洲)大陆冬季地表感热通量对我国江淮梅雨的影响及其可能机制。结果表明,北亚洲大陆地表在冬季总体为感热冷源,对大气起到强冷却作用。通过定义WSH指数来表征北亚洲大陆冬季地表感热冷源的强度,该指数值越小,冷源越强;反之,冷源越弱。当冬季北亚洲大陆地表感热冷源偏强时,夏季梅雨锋北侧的冷空气强度大范围加强,东北冷涡增强,且冷空气向南输送增强;7月高空副热带西风急流位置偏南,南亚高压呈青藏高压型;江淮流域上升运动增强,且该流域上空高层变干、低层变湿,大气层结的不稳定度增加,对流活动增强,有利于梅雨降水,出梅偏晚。冬季地表感热冷源偏弱时,情况则相反。因此,冬季北亚洲大陆地表感热通量的异常对汛期江淮梅雨的预测具有一定的指示意义。     

东亚冬季风指数的分类和比较

在回顾了2009年以前定义过的冬季风指数的基础上,按照定义要素的不同,进行了分类及序列延长计算,并将现有的冬季风指数分为海陆气压差类(4个)、高压特征类(3个)、风场特征类(9个)、环流特征类(4个)和综合类(2个)。研究了这些冬季风指数的年际及年代际变化趋势及其周期变化,分析了各指数之间的相关性,以及冬季风指数对中国冬季大陆气温变化的指示性。结果表明:东亚冬季风存在缓慢减弱的变化趋势,主要呈现出准6a,准11a和准17a的周期振荡特征。同类别指数之间的相关性要优于不同类别的。东亚冬季风指数与中国冬季大陆气温相关性普遍好的地区主要在河套及内蒙古中部、华南和东南沿海、四川盆地等。     

浅谈GPS技术在"竿影日照图"测量中的应用

按照规划原理的要求,利用GPS定位技术测定本地区“竿影日照图”,用以规范和指导城市规划中建筑物、构筑物等的日照间距问题,同时对GPS观测中的体会加以总结。