Vol.27, NO.1, 2016

Display Method:
Verification and Diagnostics for Data Assimilation System of Global GRAPES
Liu Yan, Xue Jishan, Zhang Lin, Lu Huijuan
2016, 27(1): 1-15. DOI: 10.11898/1001-7313.20160101
Numerical Weather Prediction Center of China Meteorological Administration has upgraded the global GRAPES (Global/Regional Assimilation and PrEdiction System) variation data assimilation system. The new data assimilation system employs the same coordinate, grids and atmospheric state variables as those of the GRAPES model. It can reduce analysis errors due to the interpolation and variable transformations, and also provide basics for developing GRAPES four-dimension variation assimilation system. Some key characteristics of the new global GRAPES data assimilation system are discussed, and then the performance is evaluated in detail, by comparing with observations, analysis or reanalysis data from advanced operational numerical weather prediction centers, and the medium-range forecast from background and analysis fields and different forecast models. Some guidelines for further optimizing the system is also given based on diagnosis and quantitatively estimating the impact of observations. Results show that the GRAPES data assimilation system assimilates conventional observations, satellite radiances and radio occultation observations effectively, making analyses closer to the real atmosphere and improving the forecast skill. The analysis of GRAPES are similar to those of European Centre for Medium-Range Weather Forecasts and National Center for Environmental Prediction at the large-scale circulation fields. However, some differences still remains, which actually expose issues of GRAPES. These differences are related to overlarge contributions from radiosonde, surface, ships, aircraft and radio occultation observations, and the relatively weaker influence of satellite radiance observations.There is broad consensus among the global numerical weather prediction centers that these types of observations tend to be the highest-ranked contributors to forecast skill: Microwave temperature sounder, hyper-spectral infrared sounder, radiosondes, aircraft observations, radio occultation and atmospheric motion vectors, although not necessarily uniformly in this order. However, contributions of the microwave temperature sounder and hyper-spectral infrared sounder in GRAPES are not dominant, because GRAPES still uses less radiance data, and on the other hand, the bias correction effect is not so good.Contributions of wind and humidity observation are less in GRAPES. Additionally, biases in regions of the Tibet Plateau, upper levels of the model and the tropics are relatively larger compared to observations and the reanalysis, which are related to the treatment method of topography and upper boundary of model. To gain better analysis and forecast skill, there is a requirement to place more emphasis on the above issues.
3D Spatial-temporal Characteristics of Initial Breakdown Process in Lightning Observed by Broadband Interferometer
Liu Hengyi, Dong Wansheng, Xu Liangtao, Zhang Yijun
2016, 27(1): 16-24. DOI: 10.11898/1001-7313.20160102
The location from where lightning initiate and the initial breakdown process of lightning are both important issues in research of lightning. In the summer of 2010, a series of 3D location data of lightning initial breakdown process are observed by two VHF broadband interferometers, which can provide the image of the development of lightning discharge with a time resolution of 5 μs and a space resolution better than 1 km. The initiation height distribution and 3D time-space characteristic of initial breakdown process in lightning are given by some statistical analysis on 80 intra-cloud lightning records and 61 negative cloud to ground lightning records. Results show that there are two obvious peak values, 5.0 km and 8.8 km above the ground, in the distribution of lightning initiation height. This two-peak feature can meet the picture described by the tripole gross charge structure of thunderstorms very well. The average velocities of 23 intra-cloud lightnings and 22 cloud-to-ground lightnings during the first 15 ms of initial breakdown process is calculated every 5 ms. The calculation indicates that the average velocities during the first 15 ms of initial breakdown process are in 104-105 order of magnitude both in intra-cloud flash and cloud to ground flash. Most intra-cloud flash and cloud to ground flash decelerated during the first 10-15 ms of the initial discharge. This result is a little different from a previous study in which all of the 24 intra-cloud flash records present a deceleration phase in the first 10-15 ms. It also demonstrates a possibility that runaway breakdown mechanism is not the only effective lightning initiation mechanism. Proportions of the intra-cloud flash which decelerated during the first 10 ms and 15 ms are both higher than those of cloud to ground flash in this observation. This may indicate that there is some difference between initiation processes of intra-cloud flash and cloud to ground flash. At last, it is found that the initial stage of intra-cloud lightning and cloud to ground lightning both have three possible development tendencies: Upward, downward and horizontal in vertical direction. The development direction of lighting initial stage is related to the environment electric field, and that can be used to give information about the direction of the electric field at the initiation location of lightning.
Impacts of Raindrop Velocity Measurement Error on Raindrop Size Distribution Estimation from PARSIVEL Disdrometer
Li Tao, Ruan Zheng, Ge Runsheng, Jin Long
2016, 27(1): 25-34. DOI: 10.11898/1001-7313.20160103
The error of raindrop size distribution estimation using PARSIVEL disdrometer is carefully studied, and an error correction method is proposed. Raindrop distribution data of two kind of precipitation by PARSIVEL disdrometer at Yangjiang in 2014 are analyzed. Results show that, the measured raindrop size distribution data are in good consistency with the empirical curve from Atlas, but the velocity measurement error is large when the particle size is below 1 mm or above 3 mm. The error analysis indicates that velocity measurement error of big particle is caused by deformation, while the error of small particle is caused by the instrument itself, and the vertical air motion near the disdrometer is influential for both situations.According to the detective principle of PARSIVEL disdrometor and the relationship between the deformation particle, a corrected Atlas-Ulbrich curve is given. The detective data of stratiform cloud precipitation are stable. An correction error curve of small particles is given by calculating the vertical air velocity of no less than 1 mm in diameter data from the stable precipitation, excluding the air motion in the diameter less than 1 mm. Small particle data are corrected, and the corrected raindrop distribution data are in good consistency with corrected Atlas-Ulbrich curve. The droplet concentration increases significantly and large drops concentration reduce slightly after correction. The intercept, slope and shape parameters of Gamma distribution of two kinds of precipitations are calculated before and after the correction, and the comparison shows that the corrected intercept parameter and slope parameter increase obviously, while the shape parameter barely changes.
Meteorological Conditions and Impact Factors of a Heavy Air Pollution Process at Xi'an in December 2013
Zhang Yabin, Lin Lin, Wu Qizhong, Wang Wenyan, Fan Chao, Zhao Rong, Liu Bo, Yao Dongsheng
2016, 27(1): 35-46. DOI: 10.11898/1001-7313.20160104
As one of the most famous historical and cultural cities, Xi'an is located at the central part of the Guanzhong Basin, its northern and southern areas are the Loess Plateau and the Qinling Mountains, respectively. Increasing trend of air pollution weather disturbs Xi'an in recent years. Based on high resolution observations from air quality monitor, laser radar and automatic weather stations, meteorological conditions and impact factors of heavy air pollution process from 18 Dec to 25 Dec in 2013 are analyzed. Results show that during heavy air pollution process, the circulation at 500 hPa is meridional circulation pattern including a trough and a ridge in high latitude area. Shaanxi Province is located at the front of warm ridge with weak wind, and south to the Mongolia cold high on ground. When air quality improves, the front and wind at 500 hPa increase, and ground cold front move southeast quickly. Laser radar monitoring indicates the aerosol conglomerations below 0.5 km are uplift and the boundary layer height increases significantly. Heavy air pollution process leads to severe haze and its daily average visibility is less than 1.5 km. The boundary layer height is less than 0.7 km and its peak appears at about 1500 BT. Temperature and humidity conditions are conducive to strengthen pollution, significantly different from common periods. An inversion of temperature exists at 2~3.2 km or 0.7~1.5 km height and relative vertical humidity distribution is wet-dry-wet below 3.5 km. Severe haze is mainly wet haze and its daily average duration in suburban is 5 hours longer than urban. Concentration of fine particle PM2.5 is much higher than that of coarse particulate defined by PM10 minus PM2.5 during heavy air pollution process. The former has obvious increasing trend and the latter doesn't change obviously with time. Concentrations of PM10 and PM2.5 reach peaks at 1300 BT and 2200 BT, and maintain low values from 0500 BT to 1000 BT every day. Pollutant concentration rises fast from 1000 BT to 1300 BT. Unlike typical process with a downward trend after noontime, there is an average concentration peak of pollutants in Xi'an during the heavy air pollution process. This phenomenon is probably caused by factors including very low boundary layer height, the Guanzhong Basin terrain and diurnal variation of local ground wind.
Characteristics of Persistent Activity and Strength of Cold Vortex During May and June in Northeast China
Liu Gang, Wang Ning, Qin Yulin, Cao Ling, Chu Qucheng, Yao Yao
2016, 27(1): 47-55. DOI: 10.11898/1001-7313.20160105
Using the NCEP/NCAR daily reanalysis data from 1960 to 2012, processes of the northeast cold vortex (NECV) are identified objectively. Combined with the characteristic of precipitation, a process standard of NECV persistent activities is proposed, and quantitative analysis is done using the NECV intensity index which has great significance on its persistence. If the NECV is stronger, the activity of the blocking situation over the Ural Mountains and the Lake Baikal in May, and blocking situation over the Okhotsk Sea in June is more frequent. The composition of high and low index year circulation is calculated including the geopotential height, temperature and wind between 1000 hPa and 200 hPa, and two features in the identification zone of NECV are revealed. First, the NECV converge in middle to upper troposphere (from 500 hPa to 200 hPa), having a deep and cold structure. The low pressure system exists form lower troposphere (1000 hPa) to upper troposphere (200 hPa) and a strong baroclinic component exists in geopotential height field. There is cold center in upper troposphere and thermal trough in lower troposphere. In middle to upper troposphere, westerlies have obvious shunt and confluent, and the blocking situation between them shows higher in northeast and lower in southwest. Second, the NECV converge in middle to lower troposphere (from 850 hPa to 1000 hPa), the cold center is shallow and the structure is not obvious. It is straight in the westerlies in middle to upper troposphere (from 500 hPa to 200 hPa) and the blocking situation has vanished. The weak cold center only exists in upper level, and the lower troposphere is controlled by low pressure and warm ridge. This definition of cold vortex persistent activities provides basis and reference for further study on its climate effect and short-term climate prediction.
Observational Analysis of Mesoscale Rain Cluster During Typical Torrential Rain Processes in Inner Mongolia
Chang Yu
2016, 27(1): 56-66. DOI: 10.11898/1001-7313.20160106
Inner Mongolia Autonomous Region is located in the northern frontier of China, where characteristics of torrential rain are local and convective, and the strong precipitation duration is short. High temporal and spatial data such as the satellite cloud, lighting data and automatic weather station data are very effective tools for discovering and monitoring mesoscale convective sgstem (MCS) continuously. But these approaches are not often carried out in Inner Mongolia. In view of this, using black body temperature (TBB) data of FY-2E, lightning data, automatic weather station data and hourly precipitation data, characteristics of mesoscale rain cluster (RC) of seven typical torrential rain cases are studied in Inner Mongolia from June to August during 2009-2013. Results show that in Inner Mongolia, hourly rain intensity of torrential rain processes can reach torrential rain or heavy torrential rain in 1 h or 3 h, and 80% RC activity is caused by MCS. The strong precipitation is closely related with the terrain, and the highest value occurs in the southward mountain facing warm moist airflow, which are favorable for the development of MCS. The highest peak of strong precipitation occurs in the afternoon, and the secondary peak occurs in the midnight and early morning. It has important presage function with regard to intensity and development of RC that the TBB no more than-52℃ cold-cloud shield centroid of MCS and high value center of cloud-to-ground lightning flashes density (CGD). RC in MCS of cold front cloud system gives expression to generation and extinction in the same region, the TBB no more than-52℃ cold-cloud shield centroid is small and last for 2-8 h, CGD increases slowly and has lower frequency. RC occurs jumpily in cold cloud area or the side cold air flowing into in MCS of the vortex clouds system, the TBB no more than-62℃ cold-cloud shield centroid emerge and last for 24 h, CGD increases rapidly and occur with higher frequency. RC is located in right side of coldest cloud of forward MCS where the cold air flows into. But the region where MCS shifts out exist RC caused by stratiform clouds. Approximately 60% RC of seven cases is associated with cloud-to-ground lightning flashes activities. RC appears around the highest value of CGD. The moment of maximum CGD value indicates maximum precipitation and the maturity stage of MCS in the future of 1-3 h. When CGD decrease or increase is not obvious, the rainfall intensity of RC weakens, and MCS is in the dissipation phase. Mesoscale convergence line on the dense surface wind field is prior to the MCS and RC, and the local convergence caused by mesoscale convergence line can be used as starting mechanism of MCS development.
Summer Precipitation in the Huaihe River Basins and Relevant Climate Indices
Wang Yue, Zhang Qiang, Gu Xihui, Kong Dongdong
2016, 27(1): 67-74. DOI: 10.11898/1001-7313.20160107
ENSO having significant impacts on global climate changes. Evident relations are found between ENSO and precipitation anomaly changes across the Huaihe River Basins. Besides, impacts on precipitation changes in the Huaihe River Basins can also be expected from PDO, NAO and other climate indices. These influences and related stability of the influence are investigated, and combined effects of these climate indices on seasonal precipitation changes in the Huaihe River Basins are studied. In this case, objectives of this paper are to investigate influences of ENSO, NAO, IOD and PDO on the summer precipitation regimes across the Huaihe River Basins, and related stability of the influence; explore whether ENSO, NAO, IOD and PDO are the dominant influencing factors behind occurrences or intensities of precipitation events across the Huaihe River Basins; and understand how climate indices influence seasonal precipitation changes across the Huaihe River Basins, especially from the viewpoint of water vapor transportation. The result may provide valuable information for improving the long-term forecasting of precipitation using its relationship with ENSO, NAO, IOD and PDO, and will provide important theoretical basis for water resources management and disaster prevention.Based on rotated empirical orthogonal decomposition method (REOF), the relationship between the summer precipitation in the Huaihe River Basins and the El Niño/Southern Oscillation (ENSO), the North Atlantic Oscillation (NAO), the Indian Ocean Dipole (IOD), the Pacific Decadal Oscillation (PDO) is analyzed. Influences of individual climatic factor or combined influences of climate factors on summer precipitation in the Huaihe River Basins are discussed.Results indicate that PDO and IOD are the key factors influencing summer precipitation in the Huaihe River Basins, where the PDO is in negative significant correlation with summer precipitation. Strong correlation is found between the REOF time coefficients for the summer precipitation anomaly and the climatic factors, and correlations are persistent and steady. Warm and cool periods of ENSO, NAO, IOD, PDO have different impacts on summer precipitation. Cold periods of IOD, NAO and PDO can trigger significantly increasing trend of summer precipitation in the northern Huaihe River Basins. PDO combined with ENSO, NAO and IOD heavily affects summer precipitation and this influence modifies spatial patterns of summer precipitation under influences of individual climate factor. Combined PDO, ENSO, NAO and IOD have evident impacts on summer precipitation, and evident impacts of these climatic factors are also found on precipitation in the northern Huaihe River Basins, also the upper Huaihe River Basins.
Effects of Atmospheric Low-frequency Variation on Typical Persistent Heavy Rains During Pre-flood Season in Fujian
Chen Caizhu, Gao Jianyun, Huang Lina, You Lijun, Lin Xin, Chen Lin
2016, 27(1): 75-84. DOI: 10.11898/1001-7313.20160108
The daily precipitation data of 66 stations in Fujian and NCEP reanalysis data during 1961-2010 are used to analyze the atmospheric low-frequency (LF) variability responsible for 27 typical persistent heavy rain processes (TPHRP) in Fujian during pre-flood season. Using Butterworth band-pass filtering method, low frequency band signals of 30-60 d intraseasonal oscillation (ISO) are extracted from filtered air circulation time series grid data. A physical conceptual model about the atmospheric LF disturbances during TPHRP is suggested as follows.In the upper troposphere, LF between the Korean Peninsula and the Bohai Gulf is low and weak high system dominates in the west of the Tibet Plateau, together with the subtropical westerly jet (SWJ) core located between the Yangtze River estuary and the East China Sea, leading to the LF divergence over Fujian. These low-frequency systems are relative to the Northeast cold vortex, South Asia high and the subtropical westerly jet core, respectively, which provide high-level divergence dynamic conditions and driving dynamic conditions of vertical circulation for persistent heavy rains.In the middle troposphere, when LF disturbance pattern as double block high enhanced type, the Ural block high enhanced type, the Lake Baikal block high enhanced type, or the Okhotsk Sea block high enhanced type, LF low may maintain over Fujian showing on the weather map as two troughs and one ridge type, two ridges and one trough type, one trough and one ridge type, one ridge and one ridge type, respectively. The cold air from the middle and east influences Fujian, providing continuous cold air for persistent heavy rain processes.In the lower troposphere, there is a LF cyclone over Fujian with its center located in South China Sea (SCS) or south of the Yangtze River. The current of air from subtropical high provide continuous moisture conditions, low level convergence dynamic conditions, instability stratification conditions and maintain low-level vertical circulation dynamic conditions for persistent heavy rain processes.In vapor flux fields, whenever one of the LF disturbance strengthens in the vapor passageways as Somali to the Bay of Bengal, the western flank of the Western Pacific Subtropical High (WPSH) or the westerly transport, the water vapor flux convergence over Fujian will be enhanced, providing continuous water vapor transport. TPHRPs are finally triggered by the abnormal LF circulation configuration from lower to upper troposphere as above with favorable synoptic systems for heavy persisted rains. Because of the LF system with continuous and periodicity, the physical conceptual model provides scientific basis for the extension of the TPHRP forecast in Fujian during pre-flood season.
Effects of Urbanization on Temperatures over the Qinling Mountains in the Past 50 Years
Wang Zhao, Luo Hui, Li Yali, Li Hongmei
2016, 27(1): 85-94. DOI: 10.11898/1001-7313.20160109
Based on the normalized temperature datasets of China Meteorological Administration from 1961 to 2012, inter-annual and seasonal varying characteristics of maximum, minimum and mean temperatures over the Qinling Mountains are analyzed.The result shows that average increment of annual average temperature, annual maximum and minimum temperatures in the northern regions are greater than those in southern regions of the Qinling Mountains. The seasonal variation of temperature is different, for average temperature, there is an increase in spring and winter, while the maximum temperature increases obviously in summer, and minimum temperature increases remarkably in winter. There is an obvious increase of diurnal temperature range in spring and autumn while there is a decrease in summer and winter. Mean and maximum temperatures declines remarkably while minimum temperature increasing in summer are the direct cause of summer diurnal temperature range reducing. In order to understand the factor of temperature variation, the DMSP (defense meteorological satellite program)/OLS (operational linescan system) data are used to calculate effects of urbanization and their contributions on air temperature for 5 typical zones. The increase of minimum temperature and average temperature of urban station is found remarkably higher than that of rural station, while the increase of maximum temperature is almost the same. This result shows that effects of urbanization are significant on the increasing of average temperature and minimum temperature. While the variation of maximum temperature is mainly caused by climate change itself. Urbanization development is not at the same pace, the northern part of the Qinling Mountains develops much faster than the southern part. The process of urbanization enhances the warming trend of average and minimum temperature in northern part of the Qinling Mountains, especially in spring and winter. And for the maximum temperature, the process of urbanization weakens the increasing trend in southern part but enhances the warming trend in the northern part. That means the impact of urbanization on temperature may show different characteristics at different climatic zones. The difference of the development of urbanization over the Qinling Mountains enhanced the inhomogeneity of temperature changes.
Assessment of Autumn Drought Risk of Sugarcane in Guangxi
Li Li, Kuang Zhaomin, Mo Jianfei, Liu Fang, Huang Xiaohan
2016, 27(1): 95-101. DOI: 10.11898/1001-7313.20160110
Guangxi is one of the annual precipitation-rich regions of the country. However, seasonal drought occurs in high frequency because of spatiotemporal nonuniform distribution of rainfall. Seasonal drought has rather large influences on the agricultural production, especially on the sucrose industry, which is one of the most important economic pillar industries in Guangxi. Autumn is the critical elongation and sugar accumulation stage for sugarcane. Severe autumn drought will cause a decline in production, or which at sugar accumulation stage, will decrease sugar content, increase pectin weight, reduce sugar yield and recovery rate, and cause a decline in commodity quality. Therefore, it will affect the sugar market and the whole industry chain, as well as sugarcane farmers and the local agricultural economy. In order to strengthen the risk assessment and emergency management capability of the autumn drought disasters of sugarcane, according to the concept of risk triangle, the autumn drought risk assessment indicator system is established. Indicators of system are determined according to drought risk, possibility of disaster, vulnerability of disaster bearing body, by use of meteorological data, vegetation, basic geographic information and socio-economic data from the database. The database is constructed for risk assessment of drought disasters of sugarcane, including disaster-causing factors (such as rainfall), disaster-forming environment (such as topography, hydrographic net, vegetative cover, etc.), disaster bearing body (such as sugarcane planting area, economy, etc.), and disaster prevention and mitigation capability (such as reservoir and other water conservancy facilities). Then factor weights are obtained by analytic hierarchy process (AHP), and the comprehensive assessment model is established and calculated to get the disaster risk index, which are regionalized by geographic information system (GIS). The distribution indicates that the highest and higher risk areas include the part of Laibin and Chongzuo, which are the largest main sugarcane-producing regions, at the top of the planting area list, the medium risk area consists the most part of Chongzuo, the east and west of Laibin, the south-central of Liuzhou, the west of Nanning, and the lowest risk areas include the southeast of Guangxi.Validating results show that the distribution of autumn drought disaster risk of sugarcane is basically consistent with the spatial distribution of drought disaster losses. The analysis also shows that regional differences of drought risk of sugarcane is reflected, because of different effects of hazard, formative, damage and disaster relief, by choosing the right and feasibility evaluation metrics appropriately. Above all, the autumn drought risk assessment method is feasible by introducing risk triangle theory and taking advantage of AHP and GIS, and the evaluation is more reasonable with higher verification accuracy.
Performance Improvement for FY-2E Convection Monitoring Using a Spatial-response Matched Filter Method
Wang Xin, Guo Qiang, Chen Yiyu
2016, 27(1): 102-111. DOI: 10.11898/1001-7313.20160111
In China, severe convective weather system often causes sudden disasters, and its occurrence time and falling area is difficult to be forecasted. The improvement of convection monitoring and forecasting closely depends on the advance of the monitoring capability. Geostationary satellites can provide a large range, full day cloud information, so they may be the most practical tools for monitoring the convection. In these years, the convective cloud identification method is mainly based on infrared channels of satellites using brightness temperature threshold. The accuracy of the brightness temperature is crucial for convective cloud identification, which depends on not only the satellite calibration, but also the satellite instruments sensitivity, especially for the mesoscale and small-scale targets. Based on the observation performance and principle of FY-2E meteorological satellite, a spatial-response matched filter (SRMF) method for FY-2E is set up and applied for convection observations in the thermal infrared band, the MTSAT/JAMI is used as the reference standard of the revised method, and the spatial-response of VISSR and JAMI is matched with the same infrared band. Accordingly, the infrared channel brightness temperature is corrected. Furthermore, some typical convection examples are selected during summer of 2013 and 2014 for statistics, the SRMF performance is evaluated focusing on convection spatial distribution, development process and convective cloud inner structure.Results indicate recovered images after SRMF processing show more sensitivity of convective cloud identification. For small-scale convective core in the mesoscale cloud and very short time convection, it has significant improvement for reducing effect from the high temperature background smoothing, and also it enhances the ability to reveal the mesoscale and finer scales cloud. Besides, after SRMF processing, the convection distribution statistical error is reduced, improving the missing problem for the short time and small scope convective cloud. The SRMF method also enhances the characterization ability for the convection development potential. These results all indicate that the SRMF is more suitable for convection nowcasting, such a progress is believed to be beneficial to convection monitoring and forecasting. In the future, monitoring operational work on the convective weather, for small-scale and mesoscale clouds, this SRMF technique could be applied to reduce the overall observation error, and then improve the spatial resolution for the deep convective cloud top identification. The method can also be extended to the detail inner structure of tropical cyclones.
Water Quality Satellite Remote Sensing Monitoring Model of Fujian Coastland Based on Fuzzy Evaluation
Zhang Chungui, Zeng Yindong, Ma Zhiguo
2016, 27(1): 112-122. DOI: 10.11898/1001-7313.20160112
As the development of satellite remote sensing technology of the high resolution and multi-survey spectrum channel, it brings an obvious advantage for ocean monitoring of water quality situation for continuous, real-time, large scale. With the observed samples of 12 marine water quality monitoring sites in the marine sector in Fujian coastal water, the remote sensing satellite standard algorithm and semi-analysis algorithm model is adopted, and marine ecological parameters are retrieved such as chlorophyll-a, particulate organic carbon, yellow substance and transparency. Evaluation factors of sea water closely related to the marine pollution degree in Fujian coastland are selected as dissolved oxygen, chemical oxygen demand, inorganic nitrogen and active phosphate, the statistical relationship model is established between marine ecology parameters and the evaluation factor of marine water quality. The evaluation of sea water quality is conducted by the fuzzy comprehensive evaluation method, and finally a set of marine water quality monitoring model is finished based on the satellite remote sensing and fuzzy evaluation model. The inversion precision of the model is verified by the synchronization acquisition field measurement of the marine water quality of Fujian coastal water in 2009-2013. Results show that, for the computed yellow substance by semi-analytical algorithm, the average relative error is 34%, the root mean square error is 0.179; for the computed transparency the average relative error is 26%, the root mean square error is 0.332, so the inversion result is ideal. For dissolved oxygen, the average relative error of the statistical model is the minimum, while the active phosphate model is the maximum, all four models have good agreement with measured values, and the correlation coefficient of the regression equation is more than 0.58. Results of the satellite remote sensing monitoring show that in most of the harbor and rivers into the sea along the coast of Fujian, the water quality barely meets class Ⅳ standard, the ocean water quality gradually improves with the offshore distance, and the harbor pollution trend is greater inside bay than that of the outside. From 304 samples of marine water quality monitoring, the satellite monitoring results of 245 samples are consistent with the ground observations, and the accurate rate of monitoring is 81%. The use of the monitoring model is feasible for the satellite remote sensing monitoring of sea water quality in Fujian coastland, so the prospect of business application is better. Because the accurate rate of the model is obviously higher to the marine water quality monitoring of Ⅳ than that of Ⅱ and Ⅲ , the marine water quality monitoring model is more suitable for the offshore sea area in Fujian.
Super Resolution Image Reconstruction for FY-3 MWRI 10.6 GHz Band
Chen Boyang, Gu Songyan, Chen Fansheng
2016, 27(1): 123-128. DOI: 10.11898/1001-7313.20160113
To improve the spatial resolution of FY-3 MWRI, super-resolution reconstruction algorithm is used for the first time. Analysis on the working model of FY-3 MWRI indicates that the 10.6 GHz channel data are over-sampled, and the information included in the over-sample data is the key factor for improving the spatial resolution by super-resolution reconstruction algorithm. Based on the super-resolution reconstruction theory, the orbit, attitude and characteristics of MWRI are all used as the physics restriction, the speed of the satellite and the antenna pattern are both used to calculate the over-sample rate along the orbit, the ground sample distance dividing the flying distance in the integral time of one pixel is over-sample rate along the orbit, the speed of scanning mirror and antenna pattern are both used to calculate the over-sample rate across the orbit, and the field of view dividing the scanning angel in the integral time is over-sample rate across the orbit. Based on the over-sample rates of two directions, the super-resolution imaging matrix is estimated, the scale of the matrix is over-sample rate value along the orbit times the over-sample rate value across the orbit, and parameters of the matrix are calculated out from the metrical value of the antenna pattern by integral. The 10.6 GHz image reconstruction is conducted with POCS reconstruction algorithm. Firstly, a high-resolution image is estimated from the low-resolution image by interpolation algorithm, the new observing image is estimated by the high-resolution times the super-resolution imaging matrix, and then the process is repeated over and over based on the error, through which the high-resolution image becomes closer and closer to the factual scene. In the experiment, a real 10.6 GHz image of FY-3 MWRI is processed, the spatial resolution of the high-resolution image is estimated by artificial observation and mathematic statistic. The average grads of one pixel advances from 11.72 to 14.82, the sum of the power spectral increases 5.7%, and reconstruction image is of a higher spatial resolution. The typhoon temperature analysis shows that more details can be found in the reconstruction image, and details are similar as that in the image of 37 GHz, proving the reconstruction is effective and right. The super-resolution reconstruction is useful for FY-3 MWRI image of 10.6 GHz, which can offer more images with higher spatial resolution, accelerating the application of FY-3 MWRI.