Bio-Optical Relationship of Case I Waters: The Difference between the Low- and Mid-Latitude Waters and the Southern Ocean

Both historic and currently operational chlorophyll algorithms of the satellite-borne ocean color sensors, such as SeaWiFS, were evaluated for in situ spectral radiation and chlorophyll data in some Case I waters, including the waters in the Indian Ocean sector of the Southern Ocean. Chlorophyll a concentration of the data set (n = 73) ranged from 0.04 to 1.01 mg m^–3. The algorithms had higher accuracy for the low- and mid-latitude waters (RMSE: 0.163–0.253), specifically the most recently developed algorithms of OCTS and Sea WiFS showed 0.163 and 0.170 of Root Mean Square Errors, respectively. However, these algorithms had large errors (0.422–0.621) for the Southern Ocean data set and underestimated the surface chlorophyll by more than a factor of 2.6. The absorption coefficients in the blue spectral region retrieved from remote sensing reflectance varied in a nonlinear manner with chlorophyll a concentration, and the value in the Southern Ocean was significantly lower than that in the low- and mid-latitude waters for each chlorophyll a concentration. The underestimation of chlorophyll a concentration in the Southern Ocean with these algorithms was caused by the lower specific absorption coefficient in the region compared with the low- and mid-latitude waters under the same chlorophyll a concentration.     

Validation of aerosol products derived from ocean colour in East African coastal waters

The aerosol products derived from the ocean colour missions SeaWiFS and MODIS (Aqua and Terra) were assessed with AERONET field measurements collected at sites in Mozambique (Inhaca) and Kenya (Malindi). The median of absolute relative differences between satellite and AERONET aerosol optical thickness τ_a at 443 nm varied between 12% and 22% for the different missions and sites. These differences tended to be higher at Malindi and for longer wavelengths. This analysis was supplemented by data collected offshore in the framework of the Maritime Aerosol Network. Results showed a general consistency between satellite missions and with global validation statistics. This suggests that the uncertainties associated with the atmospheric correction scheme and consequently with the distributions of ocean colour reflectance in the study area may be compared with those found in other regions. This result lends some confidence to the use of ocean colour data in the coastal waters of south-eastern Africa.     

eaWiFS产品格式及转换

为了使更多的用户尽快使用ＳｅａＷｉＦＳ资料,国家海洋局第二海洋研究所（以下简称海洋二所）将ＳｅａＷｉＦＳ产品从复杂的ＨＤＦ格式转换为简单的海洋二所（ＳＩＯ）格式。ＨＤＦ格式在记录结构、函数调用方式、参数存放次序三方面说明,海洋二所为实现格式转换花费大量时间和精力是非常必要的,为许多用户在ＳｅａＷｉＦＳ资料应用中节省了宝贵的时间,大大扩大了ＳｅａＷｉＦＳ资料的应用面和利用率。同时,对ＨＤＦ格式的深入了解,可以为我国的海洋卫星资料数据格式提供技术参考。     

利用SeaDAS从SeaWiFS卫星数据反演中国东海叶绿素浓度

卫星海洋遥感反演海中叶绿素浓度,对海洋初级生产力估算及赤潮预报均有重要意义.本文介绍了SeaWiFS卫星传感器业务化算法OC4,利用SeaDAS软件反演中国东海叶绿素浓度,并与东海同步现场数据进行验证.结果表明:利用SeaDAS方法计算的东海叶绿素含量与实测含量之间具有较好的相关性,但总体上计算值要高于实际测量值;东海叶绿素含量具有分带性,河口、近岸海域高,中陆架次之,外陆架最低,这种发育特点与该海域的陆源营养盐输入、海洋动力系统有着显著的关系.     

Are trends in SeaWiFS chlorophyll time-series unusual relative to historic variability

For selected locations in the Atlantic and Pacific Ocean, we compared surface ocean chlorophyll time series extracted from SeaWiFS imagery from 1997–2004 with the results of an ocean coupled circulation and biogeochemical model covering the period 1958–2004. During the 1997–2004 time period, linear trends in model and satellite time series were significantly correlated at most of the 44 sites we studied. Eleven sites were selected for further study, and we used the longer time series of the model to assess whether trends observed during the SeaWiFS period at these 11 sites were unusual in relation to those observed over the longer historical period covered by the model. The results show that the trends observed during the SeaWiFS period were not unusual and fell well within the range in magnitude of linear trends observed in other 8-year periods of model output. This result implies that the SeaWiFS satellite ocean color time series is not yet sufficiently long, on its own, to directly observe any long term changes in phytoplankton chlorophyll that may be occurring in the surface waters of the open ocean as a result of increased ocean stratification linked to global climate changed.     

Mechanisms controlling the intra-annual mesoscale variability of SST and SPM in the southern North Sea

Thermal and optical remote sensing data were used to investigate the spatial and temporal distribution of sea surface temperature (SST) and of suspended particulate matter (SPM) in the southern North Sea. Monthly SST composites showed pronounced seasonal warming of the southern North Sea and delineated the English coastal and continental coastal waters. The East-Anglia Plume is the dominant feature of the English coastal waters in the winter and autumn SPM composites, and the Rhine region of freshwater influence (ROFI), including the Flemish Banks, is the dominant feature of the continental waters. These mesoscale spatial structures are also influenced by the evolution of fronts, such as the seasonal front separating well-mixed water in the southern Bight, from the seasonally stratified central North Sea waters. A harmonic analysis of the SST and SPM images showed pronounced seasonal variability, as well as spring-neap variations in the level of tidal mixing in the East Anglia Plume, the Rhine ROFI and central North Sea. The harmonic analysis indicates the important role played by the local meteorology and tides in governing the SST and near-surface SPM concentrations in the southern North Sea. In the summer, thermal stratification affects the visibility of SPM to satellite sensors in the waters to the north of the Flamborough and Frisian Fronts. Haline stratification plays an important role in the visibility of SPM in the Rhine ROFI throughout the year. When stratified, both regions typically exhibit low surface SPM values. A numerical model study, together with the harmonic analysis, highlights the importance of tides and waves in controlling the stratification in the southern North Sea and hence the visibility of SPM.     

Satellite-derived variability of the Aegean Sea ecohydrodynamics

Eight years of AVHRR-derived sea surface temperature (SST) and SeaWiFS-derived surface chlorophyll (Chl) data (1998–2005) are used to investigate key processes affecting the spatial and temporal variability of the two parameters in the Aegean Sea. Seasonal mean SST and Chl maps are constructed using daily data to study seasonal dynamics whereas empirical orthogonal function (EOF) and correlational analysis is applied to the 8-day composite SST and Chl anomaly time-series in order to study the variability and co-variability of the two parameters from subseasonal to interannual time-scales. The seasonal mean fields show that Black Sea cold and chlorophyll-rich waters enter through the Dardanelles Strait and they are accumulated in the north-eastern part of the Aegean Sea, steered by the Samothraki anticyclone. Large chlorophyll concentrations are encountered in the hydrological front off the Dardanelles Strait as well as in coastal areas affected by large riverine/anthropogenic nutrient loads. The SST seasonal mean patterns reveal strong cooling that is associated with upwelling along the eastern boundary of the basin during summer due to strong northerly winds, a process which is not present in the surface chlorophyll climatology. The Chl dataset presents much stronger sub-seasonal variability than SST, with large variations in the phase and strength of the phytoplankton seasonal cycles. EOF analysis of the anomaly time-series shows that SST non-seasonal variability is controlled by synoptic weather variations and anomalies in the north–south wind-stress component regulating the summer coastal upwelling regime. Mean SST and Chl patterns, and their associated variations, are not closely linked implying that Black Sea and riverine inputs mainly control the intra-annual and interannual variability of the surface chlorophyll in the Aegean Sea rather than mixing and/or upwelling processes.     

东亚沙尘源地、沙尘输送路径的遥感研究

东亚沙尘灾害严重影响东亚各国的生态环境 ,在源地大量侵蚀表层土壤 ,在输送过程中严重污染大气环境质量。此外 ,作为气溶胶 ,对区域辐射平衡和天气系统产生重大影响。本文利用 Sea Wi FS遥感数据分析了东亚沙尘灾害的源地、沙尘输送路径 ,结果显示 :东亚沙尘的三个主要源地是蒙古的戈壁、内蒙古中西部的沙漠戈壁和塔克拉玛干沙漠。沙尘输送路径有北路、中路和南路三条 ,北路主要影响中国的东北地区 ,中路主要影响中国的华北地区 ,南路主要影响中国的华中、华东地区。通过遥感确定沙尘源地和沙尘输送路径对于东亚沙尘灾害的治理有指导意义 ,也是对沙尘大气模式的一种检验。     

Estimation of colored dissolved organic matter and salinity fields in case 2 waters using SeaWiFS: Examples from Florida Bay and Florida Shelf

Estimates of water quality variables such as chlorophylla concentration (Chl), colored dissolved organic matter (CDOM), or salinity from satellite sensors are of great interest to resource managers monitoring coastal regions such as the Florida Bay and the Florida Shelf. However, accurate estimates of these variables using standard ocean color algorithms have been difficult due to the complex nature of the light field in these environments. In this study, we process SeaWiFS satellite data using two recently developed algorithms; one for atmospheric correction and the other a semianalytic bio-optical algorithm and compare the results with standard SeaWiFS algorithms. Overall, the two algorithms produced more realistic estimates of Chl and CDOM distributions in Florida Shelf and Bay waters. Estimates of surface salinity were obtained from the CDOM absorption field assuming a conservative mixing behavior of these waters. A comparison of SeaWiFS-derived Chl and CDOM absorption with field measurements in the Florida Bay indicated that although well correlated, CDOM was underestimated, while Chl was overestimated. Bottom reflectance appeared to affect these estimates at the shallow central Bay stations during the winter. These results demonstrate the need for new bio-optical algorithms or tuning of the parameters used in the bio-optical algorithm for local conditions encountered in the Bay.     

遥感图像数据重采样的一种快速算法

从原始遥感图像几何畸变特征出发，建立了SeaStarStarSeaWiFS和NOAA AVHRR遥感图像数据重采样的一种快速算法，并提出了邻点权重重采样方式。该种快速长法能有效地提高遥感图像几何校正的速度，并适用于连续对地观测系统遥感数据的重采样过程。邻点权重重采样方式可用以替代通常的最近邻点和双线性插值采样方式。