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 ...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.展开更多
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-bas...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.展开更多
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（Septembe...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.展开更多
We developed a dual-satellite stereoscopic cloud top height(CTH)retrieval algorithm based on the visible band(0.65µm)data of Fengyun-4A(FY-4A)and FY-4B.This algorithm offers an extensive longitude coverage from 5...We developed a dual-satellite stereoscopic cloud top height(CTH)retrieval algorithm based on the visible band(0.65µm)data of Fengyun-4A(FY-4A)and FY-4B.This algorithm offers an extensive longitude coverage from 55°E to 177°W.The analysis of system error based on error theory shows that the CTH we retrieved has an accuracy of 0.20–0.88 km and an uncertainty of 0.24–1.08 km over the entire area.The space resolution of the CTH we retrieved reached less than 0.005°.We conducted a CTH retrieval experiment and proceeded to compare our results with FY-4B’s CTH product and the Cloud–Aerosol Lidar and Infrared Pathfinder Satellite Observations(CALIPSO).Compared to CALIPSO,the CTH we retrieved has a bias of−2.4 km and the correlation coefficient is 0.80.In general,two next-generation geostationary satellites were used simultaneously to retrieve the CTH in our study,demonstrating the ability of this satellite combination to obtain better-quality CTH products by stereoscopic retrieval.展开更多
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, C...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.展开更多
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 com...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.展开更多
为了解FY-4A卫星云顶高度(cloud top height,CTH)产品对陕南暖季降水云的反映状况,以陕南地区2020年暖季(5-10月)降水过程为例,对比分析FY-4A卫星CTH产品与汉中天气雷达回波顶高(echo top height,ET)产品对该地区降水云的探测资料。结...为了解FY-4A卫星云顶高度(cloud top height,CTH)产品对陕南暖季降水云的反映状况,以陕南地区2020年暖季(5-10月)降水过程为例,对比分析FY-4A卫星CTH产品与汉中天气雷达回波顶高(echo top height,ET)产品对该地区降水云的探测资料。结果表明:(1)在暖季21次降水过程中,卫星产品的云顶高度揭示了陕南地区降水云的空间变化,尤其在大巴山峡口附近,CTH值显著偏高的区域与陕南强降水的多发区相吻合。(2)以2020年暖季一次强降水过程为例,云顶高度探测表明卫星CTH的高值区通常与雷达ET的高值区相对应,说明卫星能够揭示陕南山区降水云体的时空变化,但在雷达ET高值区卫星CTH存在以填充值代替的现象,说明复杂地形区CTH填充值可能是潜在强降水区。(3)对比两种探测在降水云体发展中差异,结果显示在降水云初生和消亡阶段,两者绝对差值小于2 km的格点数与总格点数的占比都超过50%,说明CTH产品能有效捕捉降水云的初生和消亡变化。在降水云成熟阶段,两者平均差值超过4 km,卫星探测云体不确定性增加,较难反映降水云体特征。展开更多
基金supported by the National Basic Research Program of China (973 Program, Grant No. 2009CB421202)the National Natural Science Foundation of China (Grant No. 40706061)the National High Technology Research and Development Program of China (863 Program, Grant Nos. 2007AA12Z137 and 2008AA09Z104)
文摘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.
基金funded by the National Natural Science Found-ation of China(Grant Nos.41775032 and 41275040).
文摘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.
基金supported by the principal project, “Development and application of technology for weather forecasting (NIMR-2012-B-1)” of the National Institute of Meteorological Sciences of the Korea Meteorological Administration
文摘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.
基金Supported by the National Natural Science Foundation of China(42105068)Innovation Group Project of Southern Marine Science and Engineering Guangdong Laboratory(Zhuhai)(311022006).
文摘We developed a dual-satellite stereoscopic cloud top height(CTH)retrieval algorithm based on the visible band(0.65µm)data of Fengyun-4A(FY-4A)and FY-4B.This algorithm offers an extensive longitude coverage from 55°E to 177°W.The analysis of system error based on error theory shows that the CTH we retrieved has an accuracy of 0.20–0.88 km and an uncertainty of 0.24–1.08 km over the entire area.The space resolution of the CTH we retrieved reached less than 0.005°.We conducted a CTH retrieval experiment and proceeded to compare our results with FY-4B’s CTH product and the Cloud–Aerosol Lidar and Infrared Pathfinder Satellite Observations(CALIPSO).Compared to CALIPSO,the CTH we retrieved has a bias of−2.4 km and the correlation coefficient is 0.80.In general,two next-generation geostationary satellites were used simultaneously to retrieve the CTH in our study,demonstrating the ability of this satellite combination to obtain better-quality CTH products by stereoscopic retrieval.
基金Supported by the National Natural Science Foundation of China(41705007 and 41575028)
文摘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.
基金supported by the National Natural Science Foundation of China (Grant Nos. 41590874 and 41590875)the Ministry of Science and Technology of China (Grant No. 2014CB953703)
文摘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.
文摘为了解FY-4A卫星云顶高度(cloud top height,CTH)产品对陕南暖季降水云的反映状况,以陕南地区2020年暖季(5-10月)降水过程为例,对比分析FY-4A卫星CTH产品与汉中天气雷达回波顶高(echo top height,ET)产品对该地区降水云的探测资料。结果表明:(1)在暖季21次降水过程中,卫星产品的云顶高度揭示了陕南地区降水云的空间变化,尤其在大巴山峡口附近,CTH值显著偏高的区域与陕南强降水的多发区相吻合。(2)以2020年暖季一次强降水过程为例,云顶高度探测表明卫星CTH的高值区通常与雷达ET的高值区相对应,说明卫星能够揭示陕南山区降水云体的时空变化,但在雷达ET高值区卫星CTH存在以填充值代替的现象,说明复杂地形区CTH填充值可能是潜在强降水区。(3)对比两种探测在降水云体发展中差异,结果显示在降水云初生和消亡阶段,两者绝对差值小于2 km的格点数与总格点数的占比都超过50%,说明CTH产品能有效捕捉降水云的初生和消亡变化。在降水云成熟阶段,两者平均差值超过4 km,卫星探测云体不确定性增加,较难反映降水云体特征。
