A new wind vector algorithm for C-band SAR

Ocean wind speed and wind direction are estimated simultaneously using the normalized radar cross sections or' corresponding to two neighboring (25-km) blocks, within a given synthetic aperture radar (SAR) image, having slightly different incidence angles. This method is motivated by the methodology used for scatterometer data. The wind direction ambiguity is removed by using the direction closest to that given by a buoy or some other source of information. We demonstrate this method with 11 EN-VISAT Advanced SAR sensor images of the Gulf of Mexico and coastal waters of the North Atlantic. Estimated wind vectors are compared with wind measurements from buoys and scatterometer data. We show that this method can surpass other methods in some cases, even those with insufficient visible wind-induced streaks in the SAR images, to extract wind vectors.

Equivalent-barotropic definition of tropospheric mean temperature

An equivalent-barotropic (EB) description of the tropospheric temperature field is derived from the geostrophic empirical mode (GEM) in the form of a scalar function Gamma(p, phi), where p is pressure and phi is 300-850-mb thickness. Baroclinic parameter phi plays the role of latitude at each longitudinal section. Compared with traditional Eulerian-mean methods, GEM defines a mean field in baroclinic streamfunction space with a time scale much longer than synoptic variability. It prompts an EB concept that is only based on a baroclinic field. Monthly GEM fields are diagnosed from NCEP-NCAR reanalysis data and account for more than 90% of the tropospheric thermal variance. The circumglobal composite of GEM fields exhibits seasonal, zonal, and hemispheric asymmetries, with larger rms errors occurring in winter and in the Northern Hemisphere (NH). Zonally asymmetric features and planetary deviation from EB are seen in the NH winter GEM. Reconstruction of synoptic sections and correlation analysis reveal that the tropospheric temperature field is EB at the leading order and has a 1-day phase lag behind barotropic variations in extratropical regions.

Influence of mean water depth and a subsurface sandbar on the onset and strength of wave breaking

Wave breaking in the open ocean and coastal zones remains an intriguing yet incompletely understood process, with a strong observed association with wave groups. Recent numerical study of the evolution of fully nonlinear, two-dimensional deep water wave groups identified a robust threshold of a diagnostic growth-rate parameter that separated nonlinear wave groups that evolved to breaking from those that evolved with recurrence. This paper investigates whether these deep water wave-breaking results apply more generally, particularly in finite-water-depth conditions. For unforced nonlinear wave groups in intermediate water depths over a flat bottom, it was found that the upper bound of the diagnostic growth-rate threshold parameter established for deep water wave groups is also applicable in intermediate water depths, given by k(0) h greater than or equal to 2, where k(0) is the mean carrier wavenumber and h is the mean depth. For breaking onset over an idealized circular arc sandbar located on an otherwise flat, intermediate-depth (k(0) h greater than or equal to 2) environment, the deep water breaking diagnostic growth rate was found to be applicable provided that the height of the sandbar is less than one-quarter of the ambient mean water depth. Thus, for this range of intermediate-depth conditions, these two classes of bottom topography modify only marginally the diagnostic growth rate found for deep water waves. However, when intermediate-depth wave groups ( k(0) h greater than or equal to 2) shoal over a sandbar whose height exceeds one-half of the ambient water depth, the waves can steepen significantly without breaking. In such cases, the breaking threshold level and the maximum of the diagnostic growth rate increase systematically with the height of the sandbar. Also, the dimensions and position of the sandbar influenced the evolution and breaking threshold of wave groups. For sufficiently high sandbars, the effects of bottom topography can induce additional nonlinearity into the wave field geometry and associated dynamics that modifies the otherwise robust deep water breaking-threshold results.

Outer wave number spectrum and statistical distribution of apparent wave number vector

Based on the ray theory and Longuet-Higgins's linear,model of sea waves, the joint distribution of wave envelope and apparent wave number vector is established. From the joint distribution, we define a new concept, namely the outer wave number spectrum, to describe the outer characteristics of ocean waves. The analytical form of the outer wave number spectrum, the probability distributions of the apparent wave number vector and its components are then derived. The outer wave number spectrum is compared with the inner wave number spectrum for the average status of wind-wave development corresponding to a peakness factor P = 3. Discussions on the similarity and difference between the outer wave number spectrum and inner one are also presented in the paper. (C) 2002 Elsevier Science Ltd. All rights reserved.

Mean sea surface heights of the South and East China Seas from ocean circulation model and geodetic leveling

The mean sea surface heights (sea surface topography) of the South China, East China, Yellow and Bohai Seas are derived from an ocean general circulation model and surface air pressure. The circulation model covers the global oceans, with fine grid (1/6degrees) covering the East Asian marginal seas and coarse grid (31) covering the rest part of the global oceans. The result shows that the China 1985 National Altitude Datum is 24.7 cm above the me-an sea surface height of the world oceans. The mean sea surface in the coastal ocean adjacent to China is higher in the south than in the north. Intercomparison of the model results with the geodetic leveling measurements at 28 coastal tidal stations shows a standard deviation of 4.8 cm and a fitting coefficient of 95.3%. After correction through linear regression, the standard deviation is reduced to 4.5 cm. This indicates that the accuracy of model results is sufficient for practical application. Based on the model results, the mean sea surface heights for the study area with a resolution of 1/6 degree are given. This result also links the mean sea levels at islands with those on the mainland coast and gives the mean sea surface heights at tidal stations in the Taiwan Island, the Dongsha Islands, the Yisha Islands and the Nansha Islands relative to the China 1985 National Altitude Datum.

Wind-vector estimation for RADARSAT-1 SAR images: Validation of wind-direction estimates based upon geometry diversity

In this letter, a new wind-vector algorithm is presented that uses radar backscatter sigma(0) measurements at two adjacent subscenes of RADARSAT-1 synthetic aperture radar (SAR) images, with each subscene having slightly different geometry. Resultant wind vectors are validated using in situ buoy measurements and compared with wind vectors determined from a hybrid wind-retrieval model using wind directions determined by spectral analysis of wind-induced image streaks and observed by colocated QuikSCAT measurements. The hybrid wind-retrieval model consists of CMOD-IFR2 [applicable to C-band vertical-vertical (W) polarization] and a C-band copolarization ratio according to Kirchhoff scattering. The new algorithm displays improved skill in wind-vector estimation for RADARSAT-1 SAR data when compared to conventional wind-retrieval methodology. In addition, unlike conventional methods, the present method is applicable to RADARSAT-1 images both with and without visible streaks. However, this method requires ancillary data such as buoy measurements to resolve the ambiguity in retrieved wind direction.

卫星高度计资料在海洋潮汐研究中的应用

本文依据收集到的392个地面验潮站8个主要分潮（M2、S2、K1、O1、N2、K2、P1及Q1）的调和常数，对现有7个全球大洋潮汐模式的准确度进行了检验，结果显示各模式在深海区域均达到了比较高的准确度，相互之间差别也不大。经验模式GOT00和CSR4.0、同化模式NAO99、反演同化模式TPXO7.0、数值同化模式FES2002和FES2004的M2分潮均方根偏差在3 cm左右，其它分潮（S2、K1、O1、N2、K2、P1及Q1）大约在1～2 cm。本文还依据中国近海18个岛屿的调和常数对其中的5个大洋潮汐模式的准确度进行了检验，结果表明，M2分潮均方根偏差在6～14 cm，明显高于大洋部分的偏差，其中日本国家天文台的潮汐模式NAO99在中国近海的结果相对较准确。 我们利用1992年8月至2008年8月的TOPEX/POSEIDON和JASON-1(T/P-J)卫星高度计资料，对沿卫星轨道的302816个站点进行了14个分潮的潮汐调和分析，得到了全球大洋潮汐的8个主要分潮以及2个气象分潮Sa、Ssa的经验同潮图。主要结果有：（1）各分潮在卫星上升轨道与下降轨道的交叉点(约7000个)相关性分析表明：M2分潮的振幅和迟角的相关系数很高（分别为0.9965和0.9961）；S2，K1，O1和Sa分潮也有较好的相关性（相关系数为0.94～0.99）；（2）该结果与392地面个验潮站吻合较好，其中M2分潮的振幅、迟角和向量的均方根偏差分别为：1.73 cm，2.340和2.93 cm；S2，K1和O1分潮的振幅、迟角和向量的均方根偏差为1 cm左右，5.250～7.270和1.5～2.1 cm，该精度与最近几年国际上的主要大洋潮汐模式的准确度相近；（3）首次通过卫星资料获得了Sa、Ssa分潮的同潮图。周期为1年的Sa分潮与大洋105个地面站相比，振幅、迟角和向量的均方根偏差分别为1.50 cm、18.360和2.16 cm。在此基础上，进一步分析了构成Sa、Ssa气象分潮的两个主要因素（海水密度以及海面气压）在全球的分布。 在T/P-J等卫星资料无法覆盖到南大洋和北冰洋，本文利用Princeton Ocean Model（POM）进行了数值模拟，模拟结果与162个地面实测站（其中南大洋30个，北冰洋132个）的观测比较一致。基于卫星资料分析的结果和数值模拟结果合并得到了全球大洋的8个主要分潮同潮图。在此基础上通过全球潮汐能量耗散的计算得到潮能通量的分布，并得到全球M2、S2、K1和O1分潮的潮汐能量耗散率为2.431TW、0.401TW、0.336TW和0.176TW。 本文还利用卫星资料对南海潮汐进行了研究，在中国南海，获得了主要的半日潮、全日潮、四分日分潮和长周期分潮（M2，S2，N2，K2，K1，O1，P1，Q1，M4, MS4，Sa, Ssa）的经验同潮图。与南海沿岸94个地面验潮站的数据符合得比较好，M2，S2，K1及O1等4个主要分潮的平均振幅差为2～4 cm，均方根偏差分别是9～11 cm.其它4个主要分潮N2，K2，P1，Q1的平均振幅差为1～2 cm，均方根偏差为2～4 cm。此外，本文还利用卫星高度计资料潮汐分析结果沿卫星轨道进行高通滤波，分离得出中国近海的M2，S2，K1及O1分潮的内潮信息。

新疆自然区划单元土地利用/覆盖分布图谱研究

Under the direction of Geo-informatic Tupu theory, based on comprehensive natural division in Xinjiang and 1:100000 land use and land cover vector data in 2000 from resource and environment database of CAS, the paper gave out some distribution Tupu of land resource types in different regions of Xinjiang. GIS tools such as ARCTOOLS and ARCV1EW were used to clip the unit of each natural division. Some useful conclusions were established. Then the lower reaches of Tarim River were selected as typical area to analyze the ecological environment evolvement from 2000 to 2004 since the beginning of ecological water delivering. The comprehensive space-time analysis provided a method to monitor the effect dynamically. The main contents of the thesis are listed as follows: (1) Similarities and differences between North Xinjiang and South Xinjiang, 6 second-classified regions and 37 third-classified regions. The conclusion of each region emphasized the percentage of area of main land types, characteristic description and distribution of cultivated land > woodlands grassland-, water area^ urban and rural land and unused land. (2) Thematic Tupu of each region. It concluded artificial oasis Tupu, the proportion between dense-grass% moderate-grass and sparse-grass, pattern of land resources and the land use degree. The artificial oasis mean cultivated land^ woodland^ urban & rural land and other construction land. The proportion of grassland disclosed the quality of all grassland and showed the development of them. Pattern of land resources and the land use degree gave out the detailed development direction and development degree of each region. (3) Ecological environment evolvement of the lower reaches of Tarim River. The effects of each ecological water delivering were compared.

社会形势预警的几种建模方法比较

Based on social survey data conducted by local research group in some counties executed in the nearly past five years in China, the author proposed and solved two kernel problems in the field of social situation forecasting: i) How can the attitudes’ data on individual level be integrated with social situation data on macrolevel; ii) How can the powers of forecasting models’ constructed by different statistic methods be compared? Five integrative statistics were applied to the research: 1) algorithm average (MEAN); 2) standard deviation (SD); 3) coefficient variability (CV); 4) mixed secondary moment (M2); 5) Tendency (TD). To solve the former problem, the five statistics were taken to synthesize the individual and mocrolevel data of social situations on the levels of counties’ regions, and form novel integrative datasets, from the basis of which, the latter problem was accomplished by the author: modeling methods such as Multiple Regression Analysis (MRA), Discriminant Analysis (DA) and Support Vector Machine (SVM) were used to construct several forecasting models. Meanwhile, on the dimensions of stepwise vs. enter, short-term vs. long-term forecasting and different integrative (statistic) models, meta-analysis and power analysis were taken to compare the predicting power of each model within and among modeling methods. Finally, it can be concluded from the research of the dissertation: 1) Exactly significant difference exists among different integrative (statistic) models, in which, tendency (TD) integrative models have the highest power, but coefficient variability (CV) ones have the lowest; 2) There is no significant difference of the power between stepwise and enter models as well as short-term and long-term forecasting models; 3) There is significant difference among models constructed by different methods, of which, support vector machine (SVM) has the highest statistic power. This research founded basis in all facets for exploring the optimal forecasting models of social situation’s more deeply, further more, it is the first time methods of meta-analysis and power analysis were immersed into the assessments of such forecasting models.