膜下滴灌模式下种植密度对棉田蒸散发规律影响研究     

王小军 《沙漠与绿洲气象(新疆气象)》2020,14(1):138-143

为探求绿洲棉区膜下滴灌条件下不同种植密度棉田蒸散发规律，运用大型称重式蒸渗仪对膜下滴灌棉田蒸散过程连续监测，结果表明：在不同种植密度条件下，棉花的日蒸散量曲线都表现为单峰曲线，不同生育时期一膜六行（30株/m2）种植的棉田蒸散量比一膜四行（20株/m2）大，花铃期棉田的蒸散发强度最大，一膜四行、一膜六行分别为4.76mm/d、5.94mm/d。同时，一膜六行种植的叶面积指数大于一膜四行种植,株高小于一膜四行种植。花铃期棉田的蒸散发量与日平均气温（p<0.01）和空气相对湿度(p<0.01)具有很好的相关性，与日平均风速和日平均水汽压的关系不大。  相似文献   

Using unmanned underwater vehicles as research platforms in coastal ocean studies     

Kendall L.Carder  David K.Costello 《中国海洋大学学报(英文版)》2003,2(2):211-217

The advantages of using unmanned underwater vehicles in coastal ocean studies are emphasized. Two types of representative vehicles, remotely operated vehicle (ROV) and autonomous underwater vehicle (AUV) from University of South Florida, are discussed. Two individual modular sensor packages designed and tested for these platforms and field measurement results are also presented. The bottom classification and albedo package, BCAP, provides fast and accurate estimates of bottom albedos, along with other parameters such as in-water remote sensing reflectance. The real-time ocean bottom optical topographer, ROBOT, reveals high-resolution 3-dimentional bottom topography for target identification. Field data and results from recent Coastal Benthic Optical Properties field campaign, 1999 and 2000, are presented. Advantages and limitations of these vehicles and applications of modular sensor packages are compared and discussed.  相似文献   

Decreasing Reference Evapotranspiration in a Warming Climate—A Case of Changjiang (Yangtze) River Catchment During 1970–2000   总被引：1，自引：0，他引：1  

许崇育  龚乐冰  姜彤  陈德亮 《大气科学进展》2006,23(4):513-520

This study deals with temporal trends in the Penman-Monteith reference evapotranspiration estimated from standard meteorological observations, observed pan evaporation, and four related meteorological variables during 1970–2000 in the Yangtze River catchment. Relative contributions of the four meteorological variables to changes in the reference evapotranspiration are quantified. The results show that both the reference evapotranspiration and the pan evaporation have significant decreasing trends in the upper, the middle as well as in the whole Changjiang (Yangtze) River catchment at the 5% significance level, while the air temperature shows a significant increasing trend. The decreasing trend detected in the reference evapotranspiration can be attributed to the significant decreasing trends in the net radiation and the wind speed.  相似文献   

Study on NDVI- T _s space by combining LAI and evapotranspiration     

Han Lijuan  Wang Pengxin  Yang Hua  Liu Shaomin  Wang Jindi 《中国科学D辑(英文版)》2006,49(7):747-754

This paper focuses on interpreting the different spatial relationships between NDVI and T _s, a triangular or a trapezoid, and on analyzing transformation conditions, the physical and ecological meanings of the vegetation index-surface temperature space as well. Further, we use the Temperature-Vegetation Dryness Index (TVDI) to explain the existent meaning of a triangular space after NDVI reaches its saturated state by employing the relationships between NDVI, LAI and evapotranspiration. The specific relations between NDVI and T _s are useful for describing, validating and updating land surface models.  相似文献   

A Comparison between a Modified Counter Propagation Network and an Extended Self-Organizing Map in Remotely Sensed Data Classification     

Yongliang Chen  Micha I. Pazner  Wei Wu 《Mathematical Geology》2007,39(6):559-574

A modified counter propagation network model and an extended self-organizing map model have the same three-layer network architecture while employing slightly different learning rules. Their network architecture comprises an input layer, a Kohonen layer and an output layer. The neurons between two neighboring layers are fully connected and the neighboring neurons within the Kohonen layer also have neighborhood connections. The modified counter propagation network model employs the Kohonen algorithm to train the Kohonen layer while using the Widrow–Hoff rule to train the output layer. However, the extended self-organizing map model applies a modified Kohonen’s learning rule to train both the Kohonen layer and the output layer. This paper compares the performances of these two models in supervised classification of remotely sensed data. The training results show that compared to the extended self-organizing map model, the modified counter propagation model has faster learning speed but larger output errors. The classification results indicate that the extended self-organizing map model has a faster classification speed and a much higher classification precision than the modified counter propagation model.  相似文献   

基于神经网络的遥感影像分类方法研究     

吴芳 《测绘科技情报》2007,(2)

本文在研究BP神经网络和模糊理论的基础上,提出了传统BP算法的一种改进方法和基于模糊系统的神经网络遥感影像分类方法。通过试验表明:基于模糊技术的神经网络分类方法要优于BP神经网络方法,取得了令人满意的效果。  相似文献   

中国东部水分收支的初步分析   总被引：7，自引：6，他引：7  

张文君  周天军  宇如聪 《大气科学》2007,31(2):329-345

利用中国160站降水资料、中国气象局提供的探空资料、NCEP/NCAR提供的再分析资料(简称NCEP资料)和ECMWF提供的再分析资料(简称ERA40资料), 根据水汽平衡方程, 估算了1990～1999年中国东部的陆表水分收支, 分析了华北、 长江流域和华南三个典型区域的陆表水分收支, 同时对NCEP、ERA40资料在东亚地区的陆表水分收支进行评估。结果表明, 在中国东部区域, 年平均和夏季是水汽汇区, 冬季降水与蒸发基本平衡；华北在年平均、夏季以及冬季均为水汽源区；长江流域在年平均、夏季及冬季均为水汽汇区；华南在年平均和冬季为弱水汽汇区, 夏季为水汽源区。两套再分析资料基本揭示出了上述特征。就区域平均的蒸发和降水的年际变化而言, 两套再分析资料的结果与观测都存在显著相关, 但估算的蒸发NCEP好于ERA40； 相对于气候态的定量比较而言, 由两套再分析资料得到的陆表水分收支距平(即降水减去蒸发的距平)的年际变化基本与观测一致。  相似文献   

Water balance change for a re-vegetated xerophyte shrub area/Changement du bilan hydrique d’une zone replantée d’arbustes xérophiles     

《水文科学杂志》2013,58(2)

Abstract

Abstract Water balances for a re-vegetated xerophyte shrub (Caragana korshinskii) area were compared to that of a bare surface area by using auto-weighing type lysimeters during the 1990–1995 growing seasons at the southeast Tengger Desert, Shapotou, China. The six-year experiment displayed how major daily water balance components might vary for a bare and a re-vegetated sand dune area. Evapotranspiration from the C. korshinskii lysimeter represented a major part of the water balance. The average annual ET/P ratios varied between 69 and 142%. No seepage was observed for the vegetated lysimeter. For the bare lysimeter, on the other hand, 48 mm or 27% of observed rainfall per year occurred as seepage. These results suggest that re-vegetating large sandy areas with xerophytic shrubs could reduce soil water storage by transpiration. Also, the experimental results indicate that re-vegetating large sandy areas could significantly change groundwater recharge conditions. However, from a viewpoint of desert ecosystem reconstruction, it appears that natural rainfall can sustain xerophytic shrubs such as C. korshinskii which would reduce erosion loss of sand. However, re-vegetation has to be balanced with recharge/groundwater needs of local populations.  相似文献   

Development of a continuous soil moisture accounting procedure for curve number methodology and its behaviour with different evapotranspiration methods     

N. Kannan  C. Santhi  J. R. Williams  J. G. Arnold 《水文研究》2008,22(13):2114-2121

The curve number (CN) method is widely used for rainfall–runoff modelling in continuous hydrologic simulation models. A sound continuous soil moisture accounting procedure is necessary for models using the CN method. For shallow soils and soils with low storage, the existing methods have limitations in their ability to reproduce the observed runoff. Therefore, a simple one‐parameter model based on the Soil Conservation Society CN procedure is developed for use in continuous hydrologic simulation. The sensitivity of the model parameter to runoff predictions was also analysed. In addition, the behaviour of the procedure developed and the existing continuous soil moisture accounting procedure used in hydrologic models, in combination with Penman–Monteith and Hargreaves evapotranspiration (ET) methods was also analysed. The new CN methodology, its behaviour and the sensitivity of the depletion coefficient (model parameter) were tested in four United States Geological Survey defined eight‐digit watersheds in different water resources regions of the USA using the SWAT model. In addition to easy parameterization for calibration, the one‐parameter model developed performed adequately in predicting runoff. When tested for shallow soils, the parameter is found to be very sensitive to surface runoff and subsurface flow and less sensitive to ET. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

Estimation of seasonal crop water consumption in a vineyard using Bowen ratio‐energy balance method     

B. Z. Zhang  S. Z. Kang  L. Zhang  T. S. Du  S. E Li  X. Y. Yang 《水文研究》2007,21(26):3635-3641

Information about seasonal crop water consumption is useful to develop the appropriate irrigation scheme. Measurements of energy balance components using the Bowen ratio method were made for a complete growing season at a vineyard in the arid region of northwest China. Vine in the experiment was furrow‐irrigated using a trellis system. The measured evapotranspiration was compared with estimates using the soil water balance method. It is shown that the Bowen ratio method provided accurate estimates of evapotranspiration from the vineyard and this requires that the Bowen ratio system is appropriately installed. The energy balance components showed typical diurnal pattern with peaks that occurred around the midday, except for the ground heat flux which delayed its peak by 2–3 h. The sensible heat flux was greater than the latent heat flux and followed the net radiation closely. The ratio of the latent heat flux to net radiation was low in the early growing season and increased over time. Under the limited irrigation experienced in the vineyard, the latent heat flux was controlled by available soil moisture and the total evapotranspiration in the growing season was 253 mm. The seasonal progression of the crop coefficient is similar to that reported in the literature, with the maximum occurring during the month of September. The crop coefficient can be estimated as a non‐linear function of day of year (DOY) and used to estimate evapotranspiration from vineyards in the region. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献