Global monitoring of tropospheric water vapor with GPS radio occultation aboard CHAMP

The global positioning system radio occultation (GPS RO) technique provides a powerful tool for atmospheric sounding which requires no calibration, is not affected by clouds, aerosols or precipitation, and provides an almost uniform global coverage. The paper deals with application of GPS RO measurements from CHAllenging Minisatellite Payload (CHAMP) for the retrieval of tropospheric water vapor profiles. CHAMP RO data are available since 2001 with up to 200 high resolution atmospheric profiles per day. We introduce a new direct method for water vapor retrieval from GPS RO data. Additionally, a 1Dvar algorithm is used for this purpose. The so derived CHAMP water vapor profiles are validated with radiosonde data on a global scale. Here, both methods come to statistically comparable results revealing a negative bias of less than 0.1 g/kg and a standard deviation of less than 1 g/kg specific humidity in the mid troposphere. Potentials of CHAMP RO retrievals for monitoring the mean tropospheric water vapor distribution on a global scale are presented.     

ROPP反演软件算法及其精度分析

介绍了ROPP反演软件中无线电掩星反演的算法与精度分析. 采用COSMIC卫星2008年1 月1日全天的附加相位数据, 反演得到折射率、温度、压强与湿度等参数, 并与CDAAC 相应结果进行对比. 实验结果表明, 在30km高度以下, 折射率、压强和湿度的相对 误差在2%以内, 温度误差不超过2K.      

Boundary layer aerosol retrieval from thermal infrared nadir sounding – Preliminary results

A non-empirical algorithm is presented to retrieve the optical depth in the 750–1250 cm⁻¹ spectral range, of aerosol located in the boundary layer over the ocean, from nadir high-resolution radiance spectra in the thermal infrared. The algorithm is based on a line-by-line radiative transfer forward model and used the Optimal Estimation Method for the retrieval. Its performance strongly depends on the quality of the a priori temperature and H₂O atmospheric profiles. To demonstrate the relevance of the algorithm, distributions of maritime aerosol parameters have been retrieved from IMG/ADEOS data for December 1996, using the algorithm with the LBLRTM radiative transfer code, and ERA40 (ECMWF) a priori atmospheric profiles and surface conditions.     

Spaceborne lidar measurement accuracy: Simulation of aerosol,cloud, molecular density,and temperature retrievals

Spaceborne lidar measurements and retrievals are simulated using realistic errors in signal, conventional density information, atmospheric transmission, and lidar calibration. We find that by day, independent analysis of returns at wavelengths of 0.53 and 1.06 μm yields vertical profiles (0.1- to 1-km resolution) of tenuous clouds and boundary-layer, Saharan, and strong volcanic stratospheric aerosols to accuracies of 30% or better, provided particulate optical depth does not exceed ?0.3. By night all these constituents are retrieved, plus noctilucent clouds, mesospheric aerosols, and upper tropospheric/nonvolcanic stratospheric (UT/NVS) areosols. Molecular-density uncertainties are a dominant source of error for UT/NVS retrievals.To reduce these errors and also to provide density and temperature profiles, we developed a procedure that combines returns at 0.35 and 1.06 μm. This technique significantly improves UT/NVS aerosol retrieval accuracy and also yields useful density and temperature profiles there. Strong particulate contamination limits the technique to the cloud-free upper troposphere and above.     

Towards validation of SCIAMACHY lunar occultation NO2 vertical profiles

Vertical profiles of stratospheric nitrogen dioxide (NO₂) have been retrieved from moderate resolution lunar occultation transmission spectra measured by Scanning Imaging Absorption spectroMeter for Atmospheric CHartographY (SCIAMACHY) on board the European Environmental Satellite (ENVISAT). These measurements were taken over the high southern latitude of 50°–90° during the period of 2003–2005. To assess the accuracy of the retrieved NO₂ profiles, the SCIAMACHY nighttime NO₂ profiles were compared with NO₂ profiles retrieved from sunrise solar occultation spectra measured by the Halogen Occultation Experiment (HALOE) and the Stratospheric Aerosol and Gas Experiments II (SAGE II) using a photochemical correction model. The validation results show good agreement of SCIAMACHY lunar occultation NO₂ with scaled HALOE and SAGE II profiles. The relative mean differences (rmd) with scaled HALOE profiles are within −13% to +5% and standard deviations (rms) of the relative differences are within 3–19% between 25 and 38 km. The rmd and rms with scaled SAGE II NO₂ profiles are in the range of −9 to +7 and 10–17% respectively between 22 and 39 km.     

Sensitivity analysis for air temperature profile estimation methods around the tropopause using simulated Aqua/AIRS data

A sensitivity analysis is performed to investigate potential improvements to the accuracy of air temperature profile retrievals near the tropopause. A simple inversion method is employed to identify and remove redundant spectral channels from the retrievals using simulated data for the high-spectral resolution sounder AIRS (Atmospheric Infrared Sounder) on the Aqua satellite. Bayesian optimal theory and inverse technique are applied for the atmospheric temperature profile retrievals, and the 15 μm CO₂ absorption bands (620–750 cm⁻¹) are chosen for this study. Sequentially elimination of redundant channels is directly integrated into the inverse scheme for the temperature profile, in order to accurately retain the valuable channels and remove all the redundant channels, for accurate retrieval of the temperature profile. Also, the tropopause and troposphere are treated differently in the inverse scheme to improve the retrieval accuracy in the tropopause. Results of a sensitivity analysis based on this method, for the Tropical and Middle-Latitude Summer models simulated by MODTRAN4.0, show that the estimated accuracies are improved by 2 K around the tropopause, and are only changed by less than 0.2 K in the troposphere.     

北京上空高分辨率气球探空观测的温度垂直波数谱

使用分辨率为10 m的温度剖面检查2.90～8.01 km和14.65～19.76 km高度范围内归一化温度扰动谱的谱特性,并且将它们与模式谱比较.结果表明,在波数9.8×10-4～2.5×10-2m-1范围内,对流层的垂直波数谱有约-1.9的平均谱斜率;低平流层的垂直波数谱有约-2.2的平均谱斜率.这两个平均谱斜率大大偏离了目前饱和谱模式和普适大气谱模式表示的-3.0和-2.4谱斜率,并且认为是目前气球测量中曾经观测到的最平谱斜率.在波数9.8×10-4～2.5×10-2m-1范围内,对流层和低平流层的平均谱振幅比饱和谱模式的谱振幅分别大24倍和5倍,这也与饱和谱模式以及目前文献中的观测结果有很大不同.这些较大平均谱振幅与最平的平均谱斜率一道共同表明,观测的温度谱并不遵循目前的饱和谱模式和普适大气谱模式.      

The potential for radiometric retrievals of halocarbon concentrations from the MIPAS-E instrument

Halocarbons, such as CFC-11, CFC-12 and HCFC-22, are important trace gases in the atmosphere through their role as greenhouse gases and their influence on stratospheric ozone chemistry. This paper focuses on an initial study using integration of spectral radiance measurements from a spaceborne limb sounding Fourier Transform Spectrometer (FTS) to retrieve these compounds in the upper troposphere and lower stratosphere (UTLS). The instrument employed in this study is the Michelson Interferometer for Passive Atmospheric Sounding onboard ENVISAT (MIPAS-E) which obtains spectral data in the altitude range of 6–68 km at an unapodized spectral resolution of 0.025 cm⁻¹. We have used optimal estimation techniques to retrieve vertical information for these compounds using a radiometric approach.

It is shown that significant retrieval information is obtained at up to five measured levels in the UTLS for CFC-11, up to six for CFC-12 and up to two levels for HCFC-22. An initial error analysis indicates significant sensitivity of our retrievals to variability in operationally retrieved pressure and temperature data. For each halocarbon, gain, offset and spectroscopic uncertainties generally each contribute less than 10% to the total error. Finally, tracer correlations are used to compare the datasets to equivalent relationships derived here from version 2 ATMOS data with very good agreements for CFC-12 but with more variability in the CFC-11 comparisons.     

K波段微波高光谱辐射计的晴空定标方法

K波段微波高光谱辐射计应用于大气探测方向,能够减少地表至对流层内的大气廓线误差和提高廓线的垂直分辨率.针对平均辐射温度在宽大气频谱和不同天空仰角下存在浮动的问题,结合所统计的北京地区往年廓线数据和晴空条件下的Liebe大气吸收模型（1993）,提出了一种微波高光谱下改进的晴空定标方法.相比于传统的晴空定标方法,该方法利用先验的气象数据对定标过程进行优化计算,有利于提高平均辐射温度的预测精度.误差分析结果表明当K波段微波高光谱辐射计采用改进的晴空定标方法时,能够有效减少平均辐射温度对其定标误差的影响.      

Estimation of vertically integrated water vapor in Hungary using MODIS imagery

Information about the amount and spatial structure of atmospheric water vapor is essential in understanding meteorology and the Earth environment. Space-borne remote sensing offers a relatively inexpensive method to estimate atmospheric water vapor in the form of integrated water vapor (IWV). The research activity reported in the present paper is based on the data acquired by the HRPT/MODIS (High Resolution Picture Transmission, MODerate resolution Imaging Spectroradiometer) receiving station established in Budapest (Hungary) by the Space Research Group of the Eötvös Loránd University. Integrated water vapor is estimated by the remotely sensed data of the MODIS instrument with different methods and also by the operational numerical weather prediction model of the European Centre for Medium-Range Weather Forecasts (ECMWF). Radiosonde data are used to evaluate the accuracy of the different IWV fields though it has been pointed out that the in situ data also suffers from uncertainties. It was found that both the MODIS and the ECMWF based fields are of good accuracy. The satellite data represent finer scale spatial structures while the ECMWF data have a relatively poor spatial resolution. The high quality IWV fields have proved to be useful for radiative transfer studies such as the atmospheric correction of other satellite data from times different than the overpass times of satellites Terra/Aqua and the forecast times of the model data. For this purpose the temporal variability of IWV is scrutinized both using ECMWF and MODIS data. Taking advantage of Terra and Aqua overpasses, the mean rate of change of IWV estimated by the near infrared method was found to be 0.47 ± 0.45 kg m⁻² h⁻¹, while it was 0.13 ± 0.65 kg m⁻² h⁻¹ based on the infrared method. The numerical weather prediction model’s analysis data estimated −0.01 ± 0.13 kg m⁻² h⁻¹ for the mean growth rate, while using forecast data it was 0.24 ± 0.18 kg m⁻² h⁻¹. MODIS data should be used when available for the estimation of the IWV in other studies. If no satellite data are available, or available data are only from one overpass, ECMWF based IWV can be used. In this case the analysis fields (or the satellite field) should be used for temporal extrapolation but the rate of change should be calculated from the forecast data due to its higher temporal resolution.     

瑞利激光雷达反演中层大气温度算法

瑞利激光雷达是探测中层大气温度的重要设备,具有高时空分辨率且不存在探测盲区的优点.为充分利用激光雷达探测到的原始数据,改进了传统的Chanin-Haunchecorne方法,采用由均匀搜索生成温度初值的方式反演大气温度.位于北京延庆（40.3°N,116.2°E）的瑞利激光雷达具有589nm和532nm两个通道,将589nm通道用于计算,532nm通道作为参考.在150~250K区间等间隔选取多个温度初值,利用589nm通道反演60~70km高度范围内的大气温度廓线和大气密度廓线,利用参考密度廓线选取准确的温度初值,反演得到准确的大气温度廓线.将589nm通道和532nm通道反演的温度廓线相比较,发现二者具有较高的一致性.改进后的方法有效利用了信噪比较差的光信号,使589nm通道的温度探测上限从60km提高到70km.      

太阳活动突发过程对临近空间大气影响的模拟

空间天气对地球及近地空间具有重要影响,大的空间天气事件对中上层大气动力学和成分具有不同的影响。利用全大气耦合模式WACCM,针对太阳耀斑、太阳质子、地磁暴三类事件,以太阳活动平静期2015年5月10-14日的GEOS-5数据为模式背景场,通过F_10.7、离子产生率、Kp及Ap指数设置,分别模拟三类事件对临近空间大气温度、密度和臭氧的影响。结果表明耀斑事件在三类事件中对临近空间大气温度和密度的影响最为显著。平流层大气温度增加是由耀斑辐射增强引起平流层臭氧吸收紫外辐射发生的光化学反应所致,耀斑事件引起平流层和低热层温度增加约为2～3 K,低热层大气相对密度增加在6%以内;太阳质子事件及磁暴事件主要影响低热层,但太阳质子事件和磁暴事件对低热层温度扰动不大于1 K。     

Atmosphere sounding by GPS radio occultation: First results from TanDEM-X and comparison with TerraSAR-X

On 21 June 2010 the TerraSAR-X satellite was joined by the TanDEM-X satellite. A Global Positioning System (GPS) radio occultation (RO) experiment using the twin satellites has been carried out to estimate the precision of GPS atmospheric soundings. For the Day Of Year (DOY) 330–336, 2011, we analyze phase and amplitude data recorded by GPS receivers separated by a few hundred meters in a low earth orbit and derive collocated atmospheric refractivity profiles. In the altitude range 10–20 km the standard deviation between TerraSAR-X and TanDEM-X refractivity does not exceed 0.15%. The standard deviation is rapidly increasing for lower and higher altitudes; close to the surface and at an altitude of 30 km the standard deviation reaches 0.8% and 0.5%, respectively. Systematic deviations between TerraSAR-X and TanDEM-X refractivity in the considered altitude range (0–30 km) are negligible. The results confirm the anticipated high precision of the GPS RO technique. However, the difference in the retrieved refractivity in the lower troposphere for different Open Loop (OL) signal tracking parameters, altered onboard TanDEM-X for DOY 49–55, 2012, calls for an in depth analysis. At the moment we can not exclude that a potential bias in the OL Doppler model introduces a bias in our retrieved refractivity at altitudes <8$<8$ km.     

A comprehensive study on middle atmospheric thermal structure over a tropic and sub-tropic stations

The general characteristics of middle atmospheric thermal structure have been studied by making use of the Rayleigh lidar data collected over the period of about four years (1998–2001). Here, the data has been used from two different stations in the Indian sub-continent in tropics (Gadanki; 13.5°N, 79.2°E) and in sub-tropics (Mt. Abu; 24.5°N, 72.7°E). The observed monthly mean temperature profiles are compared with different model atmospheres (CIRA-86 and MSISE-90). We observed, the mean temperature profiles have closer agreement with MSISE-90 than CIRA-86. The temperature profiles measured by lidar and HALOE satellite overpass nearby lidar site are generally in agreement with each other. The systematic and statistical errors in deriving temperature are found to be uniform for both the stations, as 1 K at 50 km, 3 K at 60 km and 10 K at 70 km. The special features of mesospheric temperature inversion (MTI) and double stratopause structure (DBS) are also addressed for both the stations.     

大气电场综合观测设备的设计

大气电场反映了地球近地表大气对气象活动、太阳活动与地质活动的综合响应。实现大气电场与气象参数及地磁活动指数等参数的综合测量,对雷电活动、地质灾害和磁暴活动等的研究具有重要意义。 设计开发了一种大气电场综合观测设备,能够同时测量包含温度、相对湿度、风速和大气电场等多个参数,在大气电场探测原理的基础上给出了大气电场综合观测设备的详细设计和电场标定过程。 通过对该设备在北京市十三陵台站实测数据的分析,与中国科学院国家空间科学中心FAMEMS-DF02电场仪以及中国气象网发布的气象数据进行对比,结果表明各气象参数99%的时刻对应误差不超过±10%,平均误差不超过±3%,而电场数据的平均误差为±0.166 kV·m–1。      

太赫兹火星大气临边探测仿真研究

对火星大气进行连续高分辨率观测是研究火星大气物理和化学过程的重要手段.太赫兹临边探测技术通过测量火星大气中的风和光化学循环中的重要气体（CO，O₃，H₂O，H₂O₂等）提高对火星的认知.针对火星大气遥感的探测需求，分析了300～1000GHz频段的频谱特征.针对探测卫星对于载荷质量、功耗等参数的要求，提出一个560GHz频段的火星大气太赫兹临边探测仪设计方案，并利用辐射传输模型ARTS中的行星工具箱进行仿真.仿真结果显示:火星大气温度的反演精度优于4K，其中45km高度以下优于2K；H₂O丰度的反演精度在90km以下优于50%，30km以下优于2%；H₂O₂的反演精度在40km以下优于50%；O₃的反演精度在50km以下优于60%；大气风速度的反演精度在65km以上优于5m·s-1，最高可以达到2m·s-1.研究结果表明，利用太赫兹波段的吸收谱线可以很好地探测火星大气中各成分的丰度、变化趋势以及中高层大气的风，可为后续火星表面及大气探测提供参考.      

Tomographic determination of the spatial distribution of water vapor using GPS observations

With the advent of the GPS navigation system, a promising ground based technique has been introduced which makes it possible to estimate the amount of water vapor in the troposphere from operational GPS networks at relatively low additional costs. While the estimation of the integrated amount is currently well established, the determination of the spatial water vapor distribution and its temporal variation are still a major challenge. To account for the vertical resolution, several tomographic approaches were pursued. We developed the software package AWATOS (atmospheric water vapor tomography software) which is based on the assimilation of double differenced GPS observations. Applying a least-squares inversion, the inhomogeneous spatial distribution of water vapor is determined. An extensive investigation has been carried out in Switzerland. GPS measurements are performed by the dense permanent Swiss national GPS network AGNES of the Swiss Federal Office of Topography (swisstopo). A total of 40 equally distributed water vapor profiles have been estimated on an hourly basis. For the purpose of validation, 22 radiosonde profiles were used at the GPS and meteorological station Payerne. Furthermore, data of the numerical weather model aLMo (alpine model in Switzerland, MeteoSwiss) were compared with the tomographic results. An overall good agreement of the three methods with an rms of better than 1.6 g/m³ absolute humidity was achieved. The results show that AGNES can be used as a dedicated network for the purpose of GPS-tomography, using a horizontal resolution of approximately 50 km and height layers of 300–500 m thickness in the lower troposphere.     

Progress in tropospheric ammonia retrieval from the MIPAS satellite instrument

The Michelson Interferometer for Passive Atmospheric Sounding is a polar orbiting high resolution mid-infrared emission limb sounder with a nominal vertical resolution of 3 km. Work to extend the list of routinely retrieved species led to the examination of ammonia, NH₃. In this paper, we explore the feasibility of upper tropospheric retrievals around 6-km altitude, discussing appropriate methods. We demonstrate a weak north to south gradient outside the error bars, using co-addition to improve signal-to-noise and compare these first results with a model.     

密闭空间内氢气和二氧化碳甲醇化系统的非均相模型及反应特性

在载人密闭空间内通过电解水方式为乘员供氧会产生副产物氢气（H₂）。此外,乘员还呼出二氧化碳（CO₂）。将H₂和CO₂催化合成甲醇（CH₃OH）是消除载人密闭空间内富余H₂和CO₂的最优方式之一。对其开展反应过程建模及反应特性研究有助于进行反应过程的控制,更好地维持载人密闭空间内的大气平衡。本文采用微元法建立了H₂和CO₂催化合成甲醇的物料计算模型和温度一维非均相模型,研究了不同反应压力、冷却介质温度以及入口反应气体中CO₂与CO比值等反应条件下的反应特性变化规律。结果显示,反应压力的增加、冷却介质的温升以及入口气体中CO₂与CO比值的减小均能促进各反应速率增加,进而使得H₂和CO₂消除量增加、甲醇合成率上升以及催化剂和反应气体最高温度上升。在保证反应速率增加且催化剂最高温度不超过合理反应温度区间的最大值573.15 K时需维持反应压力不大于8 MPa,冷却介质温度不高于538.15 K以及CO₂与CO比值不小于1。      

基于SABER的平流层顶温度的时空特征分析

利用SABER探测器2002—2017年超过一个太阳活动周的数据，以大气垂直方向上40～60km的最大温度作为平流层顶温度（T_sp），分析50°S—50°N T_sp的时空分布特征.结果表明:T_sp具有明显的纬度特征和季节特征，在赤道和南北半球夏季温度较高，而在南北半球冬季的40°—50°纬度附近温度有最低值.再利用EOF方法分析T_sp，发现其第一模态的解释率达91%，且时间系数与平流层顶高度相关性最大，为-0.75，与平流层顶臭氧体积混合比相关性约0.49，与日地距离相关性为0.44，与太阳活动性（太阳活动指数，太阳黑子数）的相关性约0.33.依据该相关关系，进一步分析各变量原始场，发现T_sp和平流层顶臭氧体积混合比的纬度变化近似相反；与日地距离的季节变化有明显的负相关，约-0.81，且这种相关性与日地距离有弱的正相关关系；年平均T_sp在2002—2017年的变化约为2K，与F_10.7的相关系数为0.6，在南北纬20°附近与太阳活动指数F_10.7的相关性最大，约0.74.