Assessment of FY-4A and Himawari-8 Cloud Top Height Retrieval through Comparison with Ground-Based Millimeter Radar at Sites in Tibet and Beijing

The accuracy of passive satellite cloud top height (CTH) retrieval shows regional dependence. This paper assesses the CTH derived from the FY-4A and Himawari-8 satellites through comparison with those from the ground-based millimeter radar at two sites: Yangbajing, Tibet, China (YBJ), and the Institute of Atmospheric Physics (IAP), Beijing, China. The comparison shows that Himawari-8 missed more CTHs at night than FY-4A, especially at YBJ. It is found that the CTH difference (CTHD;radar CTH minus satellite CTH) for FY-4A and Himawari-8 is 0.06 ± 1.90 km and −0.02 ± 2.40 km at YBJ respectively, and that is 0.93 ± 2.24 km and 0.99 ± 2.37 km at IAP respectively. The discrepancy between the satellites and radar at IAP is larger than that at YBJ. Both satellites show better performance for mid-level and low-level clouds than for high-level clouds at the two sites. The retrievals from FY-4A agree well with those from Himawari-8, with a mean difference of 0.08 km at YBJ and 0.06 km at IAP. It is found that the CTHD decreases as the cloud depth increases at both sites. However, the CTHD has no obvious dependence on cloud layers and fractions. Investigations show that aerosol concentration has little impact on the CTHD. For high and thin clouds, the CTHD increases gradually with the increase of the surface temperature, which might be a key factor causing the regional discrepancy between IAP and YBJ.

Cloud Top Height Retrieval Using Polarizing Remote Sensing Data of POLDER

A retrieval method of cloud top heights using polarizing remote sensing is proposed in this paper. Using the vector radiative transfer model in a coupled atmosphere-ocean system, the factors influencing the upwelling linear polarizing radiance at top-of-atmosphere are analyzed, which show that the upwelling linear polarizing radiance varies remarkably with the cloud top height, but has negligible sensitivity with cloud albedo and aerosol scattering above the cloud layer. Based on this property, a cloud top height retrieval algorithm using polarizing remote sensing was developed. The algorithm has been applied to the polarizing remote sensing data of Polarization and Directionality of the Earth's Reflectances-2 (POLDER-2). The retrieved cloud top height from POLDER-2 compares well with the Moderate Resolution Imaging Spectroradiometer (MODIS) operational product with a bias of 0.83 km and standard deviation of 1.56 km.

Verification and Correction of Cloud Base and Top Height Retrievals from Ka–band Cloud Radar in Boseong,Korea

In this study,cloud base height（CBH） and cloud top height（CTH） observed by the Ka-band（33.44 GHz） cloud radar at the Boseong National Center for Intensive Observation of Severe Weather during fall 2013（September-November） were verified and corrected.For comparative verification,CBH and CTH were obtained using a ceilometer（CL51） and the Communication,Ocean and Meteorological Satellite（COMS）.During rainfall,the CBH and CTH observed by the cloud radar were lower than observed by the ceilometer and COMS because of signal attenuation due to raindrops,and this difference increased with rainfall intensity.During dry periods,however,the CBH and CTH observed by the cloud radar,ceilometer,and COMS were similar.Thin and low-density clouds were observed more effectively by the cloud radar compared with the ceilometer and COMS.In cases of rainfall or missing cloud radar data,the ceilometer and COMS data were proven effective in correcting or compensating the cloud radar data.These corrected cloud data were used to classify cloud types,which revealed that low clouds occurred most frequently.

The change of cloud top height over East Asia during 2000–2018

In order to know how regional averaged cloud top height(CTH)responded to the past climatic change,the spatial and temporal variations of CTH based on MODIS data(MOD03_08_v6.0)from March 2000 to February 2018 are analyzed.The results show that the CTH in East Asia was higher in the southwest and lower in the northeast.The annual mean CTH was found to increase in East Asia at the rate of 0.020 km per year,of which,0.035 km per year over the eastern land and 0.034 km per year over the eastern sea.The CTH changes statistically correlated with the sea surface temperature changes over the eastern sea(r=0.68),which indicates that the CTH changes may be affected by the underlying surface.Statistically significant increasing trend of annual mean CTH was found in the latitude zone of 30°–40°N.Furthermore,CTH showed decreasing trends of about−0.030 km per year in the Middle-Lower Yangtze River Basin,Tarim Basin,Turpan Basin and northeastern Sichuan Basin in summer since more low cloud formations benefited to the decrease of CTH.In winter,the decreasing trend of CTH was found over the north of 40°N,whereas the increasing trend was found over the south of 40°N in East Asia.

Evaluation of Cloud Top Height Retrievals from China’s Next-Generation Geostationary Meteorological Satellite FY-4A

To evaluate the validity of cloud top height (CTH) retrievals from FY-4A, the first of China's next-generation geostationary meteorological satellite series, the retrievals are compared to those from Himawari-8, CloudSat, Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO), and Moderate Resolution Imaging Spectroradiometer (MODIS) operational products from August to October 2017. Regarding CTHs from CloudSat, CALIPSO, and MODIS as truth, the results show that the performance of FY-4A CTH retrievals is similar to that of Himawari-8. Both FY-4A and Himawari-8 retrieve reasonable CTH values for single-layer clouds, but perform poorly for multi-layer clouds. The mean bias error (MBE) shows that the mean value of FY-4A CTH retrievals is smaller than that of Himawari-8 for single-layer clouds but larger for multi-layer clouds. For ice crystal clouds, both FY-4A and Himawari-8 obtain the underestimated CTHs. However, there is a tendency for FY-4A and Himawari-8 to overestimate the CTH values of CloudSat and CALIPSO mainly for low level liquid water clouds. The temperature inversion near the tops of water clouds may result in an overestimation of CTHs. According to the MBE change with altitude, FY-4A and Himawari-8 overestimate the CTHs mainly for clouds below 3 km, and the overestimation is slightly more apparent in Himawari-8 data than that in FY-4A values. As the cloud optical thickness (COT) increases, the CTH bias of FY-4A CTH retrievals gradually decreases. Two typical cases are analyzed to illustrate the differences between different satellites' CTH retrievals in detail.

利用CloudSat资料分析青藏高原、高原南坡及南亚季风区云高度的统计特征量

云与辐射的相互作用对全球的天气和气候变化过程有着重要的影响,不同高度的云有着不同的辐射强迫,获得云体高度及其在时空上的变化对研究全球气候的变化有着重要意义。本文利用云卫星上的云廓线雷达(CloudSat/CPR)2006年6月—2007年12月期间的资料,对比分析了青藏高原、高原南坡和南亚季风区域不同云类的云顶、云底高度和云厚统计量。结果表明,在所研究区域单位面积上的云顶和云底高度变化具有一定的时空连续性,不同云类的云顶和云底高度存在不同的变化范围,且随着季节的改变均有明显的变化;同时各区域不同云类的云体厚度在夏季较大,冬季较小;各区域不同云类所占的比例(云量)也具有一定的季节变化规律。

FY-4B与FY-4A云顶性质产品精度的一致性评估

风云四号(FY4)气象卫星是我国第二代静止气象卫星,FY4B云顶温度、云顶高度和云顶压强的反演算法与FY4A相同,为了方便用户更好地应用FY4B云顶产品,本文利用美国EOS/MODIS极轨气象卫星和日本第二代静止气象卫星Himawari-8云产品检验FY4A和FY4B反演的云顶产品精度的一致性,结果表明,FY4B云顶产品与FY4A具有很好的一致性,其中B星多层云的较大误差主要是由于云分类将卷云错判成了多层云所致。从全样本的检验结果可以看出FY4B云顶参数产品的精度与FY4A精度大体相当,两者的差异主要来自于通道光谱特征的改变、定标精度及所用的辐射传输模式的不同。

地基云雷达与FY-4A卫星云顶高度联合反演方法

基于地基毫米波云雷达与FY-4A卫星对云顶同步观测的特点,分析云雷达垂直顶空观测的云顶高度与FY-4A卫星AGRI载荷通道数据之间关系,提出了地基云雷达与FY-4A卫星云顶高度联合反演方法,实现云雷达安装点周边区域卫星云顶高度的融合反演,并对反演结果进行验证分析。结果表明,AGRI载荷的第11~14通道值与云雷达观测云顶高度呈线性相关,且卫星通道值与云雷达观测云顶高度比值呈现冬季最小、春秋季次之、夏季最大的季节性变化特点;星地融合反演云顶高度与云雷达观测云顶高度相关系数0.84,融合后比融合前均方根误差减小了0.7 km,提高了卫星云顶高度的反演精度。

基于CloudSat卫星资料的新疆三大山区不同类型云高特征研究

作为空中水资源的重要组成部分,云在地球水循环过程和气候系统中扮演着重要角色,不同高度的云因其物理特性和动力过程的不同而对人工增水作业具有不同的指示意义.采用2007年1月至2008年12月的美国宇航局(NASA)云卫星(CloudSat)2B-CLDCLASS资料,从不同类型云的高度分布特征分析了新疆阿尔泰山、天山和昆仑山区的云水资源情况.结果表明:各个季节三大山区高层云所占比例均较大,在20%以上,其中,天山山区和昆仑山区雨层云所占比例也较大,在15%以上.三大山区不同云的云顶和云底高度年变化趋势基本一致,昆仑山区各类型云的平均云顶和云底的高度最大,阿尔泰山区的最低.

毫米波雷达在台风外围云系研究中的应用

为评估台风条件下毫米波雷达的探测表现,利用上海2018年和2019年4个台风影响期间的毫米波雷达数据,结合雨滴谱仪、静止卫星、S波段天气雷达等资料,探讨了利用毫米波雷达研究台风外围云系的可能性。结果表明:毫米波雷达探测台风外围区域具有良好的性能,对于云降水结构的垂直探测具有一定应用潜力;在降水强度低于5 mm·h^(-1)时雷达对于云顶高度的探测较为准确;提出一种融化层亮带判别方法,亮带识别结果与探空观测一致。对比毫米波雷达与S波段天气雷达降水强度反演,结果显示利用毫米波雷达衰减特征能够实现降水强度廓线的反演,但需要对存在显著雨滴碰并增长的降水进行识别并订正,可为毫米波雷达探测台风外围云系提供参考依据。

Comparison between MODIS-derived Day and Night Cloud Cover and Surface Observations over the North China Plain

Satellite and human visual observation are two of the most important observation approaches for cloud cover. In this study, the total cloud cover （TCC） observed by MODIS onboard the Terra and Aqua satellites was compared with Synop meteorological station observations over the North China Plain and its surrounding regions for 11 years during daytime and 7 years during nighttime. The Synop data were recorded eight times a day at 3-h intervals. Linear interpolation was used to interpolate the Synop data to the MODIS overpass time in order to reduce the temporal deviation between the satellite and Synop observations. Results showed that MODIS-derived TCC had good consistency with the Synop observations; the correlation coefficients ranged from 0.56 in winter to 0.73 in summer for Terra MODIS, and from 0.55 in winter to 0.71 in summer for Aqua MODIS. However, they also had certain differences. On average, the MODIS-derived TCC was 15.16% higher than the Synop data, and this value was higher at nighttime （15.58%-16.64%） than daytime （12.74%-14.14%）. The deviation between the MODIS and Synop TCC had large seasonal variation, being largest in winter （29.53%-31.07%） and smallest in summer （4.46%-6.07%）. Analysis indicated that cloud with low cloud-top height and small cloud optical thickness was more likely to cause observation bias. Besides, an increase in the satellite view zenith angle, aerosol optical depth, or snow cover could lead to positively biased MODIS results, and this affect differed among different cloud types.

基于资源三号多光谱影像的云顶高度估计

通常来说,云对于高分辨率光学卫星影像来说是一种无效区域,需要避免成像并消除。然而,对于气象分析来说,云顶高度的估计在大气运动和天气预报等领域都具有十分重要的意义。基于资源三号测绘卫星多光谱影像波段之间的视差,文章提出了一种高精度云顶高度的估计方法。在严格分析云顶高度估计的误差因素即内方位元素误差、外方位元素误差、匹配误差、云移动、DEM误差等影响的基础上,提出了相应的优化与补偿方法。由于内方位元素误差对每列影像的影响相同,提出了基于无云区域估计内方位元素误差的方法;鉴于每行影像的外方位元素误差相同,提出了基于无云区域估计外方位元素误差的方法;考虑到多光谱波段之间相近的成像几何,通过相位相关的方法获取高精度的视差;在假设云静止的条件下,云顶高度估计的理论精度为96 m。通过阿兹劳和乌兹别克斯坦两个地区的多光谱影像进行实验,验证该方法的可行性。该方法还可进一步应用于云的检测。

基于毫米波云雷达的黄河流域内蒙古段云宏观特征分析

云是地-气系统的重要组成部分,云宏观特征不仅与地-气系统的辐射收支及区域气候变化密切相关,还直接影响云降水过程模式预报的准确性,鉴于此本文基于2020年8月至2021年7月呼和浩特地区毫米波云雷达观测数据,对黄河流域内蒙古段云出现频率及垂直结构进行统计分析。结果表明:该地区多以晴空为主,全年晴空廓线超过了云雷达总采样廓线的70.00%,相比而言,云出现频率较小,6月最高值也仅为43.84%。云类型以中高云为主,云底高度多出现在3.00~4.00 km之间,云层较薄,厚度介于0.50~1.00 km的云出现频率最高。云宏观属性存在明显的季节变化和日变化特征,春季和夏季云的出现频率较高,分别为39.71%和35.77%,冬季云的出现频率最小,春、夏、秋季午后云出现频率明显高于上午时段。

基于FY-4A和气象条件的梵净山云海识别及特征分析

探究云海的时间变化特征,能够为当地生态旅游以及经济发展提供科学参考.以梵净山为例,基于FY-4A的云顶高度产品获取了有效的云顶高度数据,并分别按不同的判别规则提取梵净山景区范围内的云海日与金顶周边的可观赏性云海日,分析其季、月、时段的变化特征以及与温度和湿度的相关关系,并基于以上结果调取地面视频监测资料开展验证工作.结果表明:①2020年梵净山出现云海的天数总计85 d,月均7 d,其中在金顶周边可观赏到的云海天数为62 d,占云海总日数72.9%,月均5 d;②无论是云海还是可观赏性云海,季节特征为“春秋多,夏冬少”,其中可观赏性云海主要集中在2-4月,凌晨4点至上午8点期间频率最高;③当相对湿度高且平均温度较低时,云海形成的概率较高,当相对湿度过高或者平均温度过低时云海均不易形成.因此,山间冬末春初时节,湿度增加,水汽充足,清晨与傍晚极易形成云海景观,是前往梵净山观赏云海的最佳时期.

毫米波云雷达与探空测云数据对比分析

应用中国气象局大气探测综合试验基地2015年8—12月数据,对Ka波段毫米波云雷达与L波段探空云底高、云顶高及云垂直结构的探测进行对比分析,从分析结果可以看出,毫米波云雷达发射的电磁波能够穿透厚度较大的云层,探测出云垂直结构,所探测的云底高和云顶高与L波段探空结果保持良好的一致性。进一步分析一些云底、云顶高度差异较大的个例,得知与探空气球的漂移造成地域偏差和L波段探空相对湿度探测的误差相关。研究结果表明,Ka波段毫米波云雷达不仅探测能力强,探测精度也较高,是地基云探测的一种有效手段。

基于毫米波雷达、无线电掩星和探空仪资料的云边界高度对比研究

为准确评估基于相对湿度廓线法反演云边界高度的有效性,以CloudSat和CALIPSO联合探测结果为基准,对2008年1月至2009年1月COSMIC无线电掩星和探空仪的云底高与云顶高反演结果进行定量对比验证,结果表明:CloudSat、掩星和探空仪检测到高云的比例差异较大,掩星和探空仪云检测效率相近,但云检测质量掩星优于探空仪,云层沿高度的发生概率同样掩星与CloudSat具有更好的一致性;陆地与海洋地区掩星和探空仪云底高反演精度大于云顶高,且反演精度与云层高度有关,二者对不同类型云的边界高度具有不同的反演优势,云底高发生概率掩星和探空仪与CloudSat都有很好的一致性,但云顶高概率掩星与CloudSat的吻合程度更好;CloudSat云边界高度随纬度升高而减小,其与掩星和探空仪的反演偏差同样是低纬大于中高纬,且具有不同的季节分布特点.此外,三者检测的底层云中低云所占比例从冬季到夏季逐渐减小,顶层云中云顶高于10km的比例从冬季到夏季却逐渐增加.

基于A-Train综合资料的云顶高度反演研究

提出一种适用性较强的云顶高度反演方法。利用2007年低纬地区(15°S^15°N)的A-Train综合资料反演云顶高度。首先以M0DIS通道31和通道32的亮温值为特征参数,基于SVM分类法,将云分为不透明云、半透明云和透明云三类,分类准确率达到90.6%。然后对三类云分别用核回归法反演云顶高度,将其与CloudSat的2B-GEOPROF-LIDAR产品对比,均方根误差分别为0.95、1.17和1.27 km。与未分类的核回归法结果相比,分类后三种云的反演误差都有所减小。最后分析了三个典型个例。该方法可推广至其他含有红外分裂窗通道的卫星上,发挥更多卫星资源的效用。

双星立体观测云顶高度几何反演方法

通过双星立体观测中卫星-球心-投影云-真云的平面和球面三角几何关系推导出真云云顶高度计算公式,利用云顶高度变化和图像匹配的方法,对模拟得到的双星"立体观测图像对"进行云顶高度反演实验。通过对具有台风和冷锋形态分布的卫星红外云图模拟资料进行实验,得出平均垂直高度误差不超过500m的云顶高度,并对图像对比中1个像素偏移导致的云顶高度误差进行了误差分析。

静止卫星云图的云位置偏差及其几何校正

利用静止气象卫星云图红外亮温数据和大气的温度层结曲线计算云顶高度。根据几何关系推导出观测云与真云位置偏差的计算公式,得到中国大陆地区对流云的观测偏差一般为5-20 km的结论。通过观测云经纬度和云顶高度计算真云经纬度,在此基础上进行了卫星云图几何校正实验,得到误差不超过2 km的云图校正结果。通过校正前后云图与雷达图的对比,验证了校正方法的有效性。最后,分析了云顶高度估算误差所造成的云图校正误差。

三线阵云立体探测技术

根据三线阵立体测绘原理,给出了探测云顶高的三线阵卫星影像模拟方法.提出了改进的SIFT匹配算法,并利用该算法结合前方交会法,获得云顶高度信息.通过实验验证了三线阵卫星影像模拟的正确性,探索了一种获取夜间低照度条件下云顶高参数的新途径.最后,针对测高误差来源,详细分析了三线阵立体探测云顶高的测高误差,并针对云移动给出了一种误差纠正方法.