Precipitation: Measurement,remote sensing,climatology and modeling

This review paper deals with four aspects of precipitation: measurement, remote sensing, climatology and modeling. The measurement of precipitation is summarized in terms of the instruments that count and measure drop sizes (defined as disdrometers) and the instruments that measure an average quantity proportional to the integrated volume of an ensemble of raindrops (these instruments are normally called rain gauges). Remote sensing of precipitation is accomplished with ground based radar and from satellite retrievals and these two approaches are separately discussed. The climatology of precipitation has evolved through the years from the traditional rain gauge data analyses to the more sophisticated data bases that result from a coalescence of data and information on precipitation that is available from several sources into amalgamated products. Recently, rain observations from both ground and space have been assimilated into regional and global numerical weather prediction models aiming at improved moisture analysis and better forecasts of extreme weather events. The current status and the main outstanding issues related to precipitation forecasting are discussed, providing a basic structure for research coordination aimed at the improvement of modeling, observation and data assimilation applicable to global and regional scales.     

Temperature projection in a tropical city using remote sensing and dynamic modeling

Recent temperature projections for urban areas have only been able to reflect the expected change due to greenhouse-induced warming, with little attempt to predict urbanisation effects. This research examines temperature changes due to both global warming and urbanisation independently and applies them differentially to urban and rural areas over a sub-tropical city, Hong Kong. The effect of global warming on temperature is estimated by regressing IPCC data from eight Global Climate Models against the background temperature recorded at a rural climate station. Results suggest a mean background temperature increase of 0.67 °C by 2039. To model temperature changes for different degrees of urbanization, long-term temperature records along with a measureable urbanisation parameter, plot ratio surrounding different automatic weather stations (AWS) were used. Models representing daytime and nighttime respectively were developed, and a logarithmic relationship between the rate of temperature change and plot ratio (degree of urbanisation) is observed. Baseline air temperature patterns over Hong Kong for 2009 were derived from two ASTER thermal satellite images, for summer daytime and nighttime respectively. Dynamic raster modeling was employed to project temperatures to 2039 in 10-year intervals on a per-pixel basis according to the degree of urbanization predicted. Daytime and nighttime temperatures in the highly urbanized areas are expected to rise by ca. 2 °C by 2039. Validation by projecting observed temperature trends at AWS, gave low average RMS errors of 0.19 °C for daytime and 0.14 °C for nighttime, and suggests the reliability of the method.     

Precipitation climatology over India: validation with observations and reanalysis datasets and spatial trends

Changing rainfall patterns have significant effect on water resources, agriculture output in many countries, especially the country like India where the economy depends on rain-fed agriculture. Rainfall over India has large spatial as well as temporal variability. To understand the variability in rainfall, spatial–temporal analyses of rainfall have been studied by using 107 (1901–2007) years of daily gridded India Meteorological Department (IMD) rainfall datasets. Further, the validation of IMD precipitation data is carried out with different observational and different reanalysis datasets during the period from 1989 to 2007. The Global Precipitation Climatology Project data shows similar features as that of IMD with high degree of comparison, whereas Asian Precipitation-Highly-Resolved Observational Data Integration Towards Evaluation data show similar features but with large differences, especially over northwest, west coast and western Himalayas. Spatially, large deviation is observed in the interior peninsula during the monsoon season with National Aeronautics Space Administration-Modern Era Retrospective-analysis for Research and Applications (NASA-MERRA), pre-monsoon with Japanese 25 years Re Analysis (JRA-25), and post-monsoon with climate forecast system reanalysis (CFSR) reanalysis datasets. Among the reanalysis datasets, European Centre for Medium-Range Weather Forecasts Interim Re-Analysis (ERA-Interim) shows good comparison followed by CFSR, NASA-MERRA, and JRA-25. Further, for the first time, with high resolution and long-term IMD data, the spatial distribution of trends is estimated using robust regression analysis technique on the annual and seasonal rainfall data with respect to different regions of India. Significant positive and negative trends are noticed in the whole time series of data during the monsoon season. The northeast and west coast of the Indian region shows significant positive trends and negative trends over western Himalayas and north central Indian region.     

Land remote sensing technology and methodology

Remote sensing is a tool for gathering information about the Earth's surface and monitoring how it changes. A large number of remote sensing systems have been developed that exploit different parts of the electromagnetic spectrum and that produce data in different formats at varying scales and costs. These data may be acquired for virtually any place on Earth. A body of manual and automated techniques have evolved for processing and interpreting remote sensing data. The selections of a remote sensing system and of the techniques by which data are processed are driven by information requirements of varying detail and constrained by cost.     

Cloud vertical distribution from radiosonde,remote sensing,and model simulations

Knowledge of cloud vertical structure is important for meteorological and climate studies due to the impact of clouds on both the Earth’s radiation budget and atmospheric adiabatic heating. Yet it is among the most difficult quantities to observe. In this study, we develop a long-term (10 years) radiosonde-based cloud profile product over the Southern Great Plains and along with ground-based and space-borne remote sensing products, use it to evaluate cloud layer distributions simulated by the National Centers for Environmental Prediction global forecast system (GFS) model. The primary objective of this study is to identify advantages and limitations associated with different cloud layer detection methods and model simulations. Cloud occurrence frequencies are evaluated on monthly, annual, and seasonal scales. Cloud vertical distributions from all datasets are bimodal with a lower peak located in the boundary layer and an upper peak located in the high troposphere. In general, radiosonde low-level cloud retrievals bear close resemblance to the ground-based remote sensing product in terms of their variability and gross spatial patterns. The ground-based remote sensing approach tends to underestimate high clouds relative to the radiosonde-based estimation and satellite products which tend to underestimate low clouds. As such, caution must be exercised to use any single product. Overall, the GFS model simulates less low-level and more high-level clouds than observations. In terms of total cloud cover, GFS model simulations agree fairly well with the ground-based remote sensing product. A large wet bias is revealed in GFS-simulated relative humidity fields at high levels in the atmosphere.     

城市遥感研究进展

城市遥感是当前遥感技术应用的一个重要领域.随着我国新型城镇化过程的推进,遥感技术将在城市生态建设、国土空间开发、资源环境承载能力监测等方面发挥重要作用,成为城市规划管理重要的信息源.本文在总结国内外城市遥感研究内容的基础上,重点对城市遥感若干重要方向的发展进行了分析,在此基础上构建出一个地理学视角的城市遥感研究框架,结合典型实例从结构与格局、要素与作用、变化与过程、功能与响应4个方面进一步探讨了城市遥感研究的发展.最后,结合国家需求和技术发展,对城市遥感今后的发展从数据源、研究对象、应用主题、研究目标、技术方法等方面进行了展望.     

卫星遥感数据库系统

介绍了系统的总体设计构思、原理与功能特点,开发了系统技术说明,建立了一套适合黑龙江省的卫星遥感数据库系统,可对遥感资料进行现代化管理。     

On the radiative properties of ice clouds: Light scattering,remote sensing,and radiation parameterization

Presented is a review of the radiative properties of ice clouds from three perspectives: light scattering simulations, remote sensing applications, and broadband radiation parameterizations appropriate for numerical models. On the subject of light scattering simulations, several classical computational approaches are reviewed, including the conventional geometric-optics method and its improved forms, the finite-difference time domain technique, the pseudo-spectral time domain technique, the discrete dipole approximation method, and the T-matrix method, with specific applications to the computation of the singlescattering properties of individual ice crystals. The strengths and weaknesses associated with each approach are discussed.With reference to remote sensing, operational retrieval algorithms are reviewed for retrieving cloud optical depth and effective particle size based on solar or thermal infrared(IR) bands. To illustrate the performance of the current solar- and IR-based retrievals, two case studies are presented based on spaceborne observations. The need for a more realistic ice cloud optical model to obtain spectrally consistent retrievals is demonstrated. Furthermore, to complement ice cloud property studies based on passive radiometric measurements, the advantage of incorporating lidar and/or polarimetric measurements is discussed.The performance of ice cloud models based on the use of different ice habits to represent ice particles is illustrated by comparing model results with satellite observations. A summary is provided of a number of parameterization schemes for ice cloud radiative properties that were developed for application to broadband radiative transfer submodels within general circulation models(GCMs). The availability of the single-scattering properties of complex ice habits has led to more accurate radiation parameterizations. In conclusion, the importance of using nonspherical ice particle models in GCM simulations for climate studies is proven.     

Stability classification by acoustic remote sensing

Two different Doppler acoustic sounders have been operated at the Kernforschungszentrum Karlsruhe (KfK) since 1982. It has been investigated whether meteorological data from these sounders can be used for dispersion modeling and monitoring in the environment of pollutant-emitting plants. Data from the sounders and from a 200 m high meteorological tower have been sampled continuously for intercomparison.Two schemes of stability classification are presented. They are based on 30-min mean values of the following meteorological data measured by the acoustic sounders: (a) standard deviation σ_w of the vertical wind speed and horizontal wind speed u, at a height of 100 m; and (b) standard deviation σ_φ of the vertical wind direction at a height of 100 m and vertical profile of the backscattered amplitude A_w.The class limits applied in these schemes are determined by “statistical equivalence” with a standard classification scheme. This standard scheme is based on σ_φ, measured by a vector vane at the 100 m level of the tower. Statistical equivalence in this context means that the frequency distributions of the classes are approximately equal at the same site and during the same period.The reliability of these schemes is investigated and compared to the standard scheme by correlation analysis. Finally, the schemes are compared with other commonly applied classification methods.     

大气微波辐射起伏及其遥感

本文讨论了大气微波辐射起伏的机制。推导出利用大气氧气微波辐射起伏统计特征,探测大气温度结构常数分布与风分布的遥感方程。对遥感方程核函数的基本性质进行了讨论。     

GNSS remote sensing of the Australian tropopause

Radio occultation (RO) techniques that use signals transmitted by Global Navigation Satellite Systems (GNSS) have emerged over the past decade as an important tool for measuring global changes in tropopause temperature and height, a valuable capacity given the tropopause??s sensitivity to temperature variations. This study uses 45,091 RO data from the CHAMP (CHAllenging Minisatellite Payload, 80 months), GRACE (Gravity Recovery And Climate Experiment, 23 months) and COSMIC (Constellation Observing System for Meteorology, Ionosphere, and Climate, 20 months) satellites to analyse the variability of the tropopause??s height and temperature over Australia. GNSS RO temperature profiles from CHAMP, GRACE, and COSMIC are first validated using radiosonde observations provided by the Bureau of Meteorology (Australia). These are compared to RO soundings from between 2001 and 2007 that occurred within 3 h and 100 km of a radiosonde. The results indicate that RO soundings provide data of a comparable quality to radiosonde observations in the tropopause region, with temperature deviations of less than 0.5 ± 1.5 K. An analysis of tropopause height and temperature anomalies indicates a height increase over Australia as a whole of ca. 4.8 ± 1.3 m between September 2001 and April 2008, with a corresponding temperature decrease of ?0.019 ± 0.007 K. A similar pattern of increasing height/decreasing temperature was generally observed when determining the spatial distribution of the tropopause height and temperature rate of change over Australia. Although only a short period has been considered in this study, a function of the operating time of these satellites, the results nonetheless show an increase in the height of the tropopause over Australia during this period and thus may indicate regional warming. Several mechanisms could be responsible for these changes, such as an increase in the concentration of greenhouse gases in the atmosphere, and lower stratospheric cooling due to ozone loss, both of which have been observed during the last decades.     

光谱地质遥感研究进展

地质遥感是最能体现与发挥光谱遥感技术特点与优势的应用领域之一.本文从矿物岩石光谱模拟、矿物岩石光谱特征分析、遥感光谱仪技术指标的优化设计、辐射定标与数据辐射校正、地表光谱反演、信息提取、信息产品验证、地质应用8个方面总结了最新的研究进展,并对目前光谱遥感地质应用存在的问题和发展趋势进行了深入的论述.     

Balloon Intercomparison Campaigns: Results of remote sensing measurements of HCl

All of the techniques used to measure stratospheric HCl during the two BIC campaigns involved high resolution infrared spectroscopy. The balloon-borne instruments included five different spectrometers, three operating in the solar absorption mode and two in emission (at distinctly different wavelengths). Ground-based and aircraft correlative measurements were made close to the balloon locations, again by near-infrared spectroscopy.Within this set of results, comparisons between different techniques (absorption vs emission) viewing the same airmass (i.e., on the same gondola) were possible, as were comparisons between the same technique used on different gondolas spaced closely in time and location. The final results yield a mean profile of concentration of HC1 between 18 and 40 km altitude; an envelope of ±15% centered on this profile encompasses all of the results within one standard deviation of their individual mean values. The absolute accuracy of the final profile is estimated to be no worse than 10%. It is concluded also that the measurement techniques for HCl have reached a level of performance where a precision of 10% to 15% can be confidently expected.     

Measuring crop residue cover using remote sensing techniques

Summary Crop residues are managed under conservation tillage programs to leave as much as possible on the surface for minimization soil erosion and for improving water quality. Because current methods for measuring crop residue cover are tediuous and somewhat subjective, there is a need for new methods to measure residue cover that are rapid, accurate, and objective. We discuss the potential for discriminating crop residues from soils using reflectance and fluorescence techniques and examine experimentally the changes in wheat residue fluorescence during weathering. The fluorescence of crop residue was a board band phenomenon with emissions extending from 420 to 600 nm for excitation of 350–420 nm. Soils had low intensity broad band emissions over the 400–690 nm region for excitations of 300–600 nm. We found that the fluorescence intensities for the crop residues were much greater than the fluorescence of the soils, but as the crop residues decompose, their blue-green fluorescence intensities approach the fluorescence of the soils. We conclude that fluorescence techniques are less ambiguous and better suited for discriminating crop residues from soils than the reflectance methods. However, the potential problems, that must be addressed to implement the fluorescence technique, are (i) adequate excitation energy must be supplied to induce fluorescence and (ii) the fluorescence signal is small relative to normal, ambient sunlight. Nevertheless, if properly implemented, we believe that the fluorescence techniques can be used to quantify crop residue cover in the field.With 7 Figures     

Ocean feedback to tropical cyclones: climatology and processes

This study presents the first multidecadal and coupled regional simulation of cyclonic activity in the South Pacific. The long-term integration of state-of the art models provides reliable statistics, missing in usual event studies, of air–sea coupling processes controlling tropical cyclone (TC) intensity. The coupling effect is analyzed through comparison of the coupled model with a companion forced experiment. Cyclogenesis patterns in the coupled model are closer to observations with reduced cyclogenesis in the Coral Sea. This provides novel evidence of air–sea coupling impacting not only intensity but also spatial cyclogenesis distribution. Storm-induced cooling and consequent negative feedback is stronger for regions of shallow mixed layers and thin or absent barrier layers as in the Coral Sea. The statistical effect of oceanic mesoscale eddies on TC intensity (crossing over them 20 % of the time) is also evidenced. Anticyclonic eddies provide an insulating effect against storm-induced upwelling and mixing and appear to reduce sea surface temperature (SST) cooling. Cyclonic eddies on the contrary tend to promote strong cooling, particularly through storm-induced upwelling. Air–sea coupling is shown to have a significant role on the intensification process but the sensitivity of TCs to SST cooling is nonlinear and generally lower than predicted by thermodynamic theories: about 15 rather than over 30 hPa °C^?1 and only for strong cooling. The reason is that the cooling effect is not instantaneous but accumulated over time within the TC inner-core. These results thus contradict the classical evaporation-wind feedback process as being essential to intensification and rather emphasize the role of macro-scale dynamics.     

微波链路测量降水研究综述

利用微波链路测量降水是降水测量的最新技术,具有作用于近地面大气、时空分辨率高等优势。文章总结了微波链路测量降水方法的发展现状和技术难点,结合微波通信的实际应用,分析了频段的选择依据、雨衰减量的精确测量和正演模型的精确建模需要考虑的因素,指出降水起始时间的准确识别和区域化反演算法是解决该方法实用化问题的关键技术,为利用微波链路测量降水的进一步研究提供了借鉴。     

On lidar application for remote sensing of the atmosphere

This paper introduces some advanced subjects on lidar remote sensing of the atmosphere, emphasizing recent studies and developments in lidar application for measuring ozone, cloud, aerosol, atmospheric temperature, moisture, pressure and wind.