利用Sea WiFS资料反演我国海域气溶胶粒子密度分布

在卫星数据反演气溶胶光学厚度产品的基础上,讨论了二次反演大气柱中气溶胶粒子密度的问题.通过理论分析,利用多波段气溶胶光学厚度提取大气柱中气溶胶粒子密度是可行的,并指出能否准确确定多波段气溶胶光学厚度会直接影响粒子密度的反演结果.定义并分析了气溶胶粒子消光体积权重系数随粒子半径的变化,表明从气溶胶光学厚度中反演大气柱中气溶胶积聚模态和粗模态粒子密度的结果是可信的.利用SeaWiFS气溶胶光学厚度产品,运用蒙特卡罗法反演了2002年我国海域上空大气柱中积聚模态和粗模态气溶胶粒子密度,结果表明,积聚模态粒子密度比粗模态的高2~3个量级,它们的空间分布趋势一致;我国近岸海域大气柱中气溶胶粒子密度高于离岸海域的;春季气溶胶粒子密度高于其他季节的,特别在黄海、东海海区是如此.     

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.     

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.     

An optical model for the remote sensing of coloured dissolved organic matter in coastal/ocean waters

An optical model is developed for the remote sensing of coloured dissolved organic matter (CDOM) in a wide range of waters within coastal and open ocean environments. The absorption of CDOM (denoted as a_g) is generally considered as an exponential form model, which has two important parameters – the slope S and absorption of CDOM at a reference wavelength a_g(λ₀). The empirical relationships for deriving these two parameters are established using in-situ bio-optical datasets. These relationships use the spectral remote sensing reflectance (R_rs) ratio at two wavelengths R_rs(670)/R_rs(490), which avoids the known atmospheric correction problems and is sensitive to CDOM absorption and chlorophyll in coastal/ocean waters. This ratio has tight relationships with a_g(412) and a_g(443) yielding correlation coefficients between 0.77 and 0.78. The new model, with the above parameterization applied to independent datasets (NOMAD SeaWiFS match-ups and Carder datasets), shows good retrievals of the a_g(λ) with regression slopes close to unity, little bias and low mean relative and root mean square errors. These statistical estimates improve significantly over other inversion models (e.g., Linear Matrix-LM and Garver-Siegel-Maritorena-GSM semi-analytical models) when applied to the same datasets. These results demonstrate a good performance of the proposed model in both coastal and open ocean waters, which has the potential to improve our knowledge of the biogeochemical cycles and processes in these domains.     

Comparative Analysis of Chlorophyll-a Distribution from SeaWiFS,MODIS-Aqua,MODIS-Terra and MERIS in the Arabian Sea

The variability of Chlorophyll-a (Chl-a) distribution derived from MODIS (on Aqua and Terra platforms) and MERIS sensors have been compared with SeaWiFS data in the Arabian Sea. MODIS Aqua has overestimated the SeaWiFS Chl-a within 25–32% in the coastal turbid (eutrophic) waters and underestimated in open ocean waters with error within 20%. However, there is no significant bias (?0.1 on log-scale) observed as the slope is well within 0.97-1.1 (log transformed). MODIS-Terra has underestimated the Chl-a concentration in open ocean waters by about 29–31%, which is higher than MODIS-Aqua. MODIS-Terra is observed to be more accurate than MODIS-Aqua in the coastal waters. MERIS is overestimating the SeaWiFS Chl-a with log RMS error of ～0.15 and log bias of ～0.13–0.2. The differences in the Chl-a estimates between each sensor are possibly due to differences in the sensor design, bio-optical algorithms and also due to the time differences between the satellites over passes. We have examined that the MERIS is performing similar to SeaWiFS and the MODIS-Aqua (Terra) data are reliable in open ocean (coastal) waters. However, Chl-a retrieval algorithms need to be improved especially for coastal turbid waters to continue with SeaWiFS data for long-term studies.     

Dolphin noises recorded by echo‐sounder

The ultrasonic signals of dolphins show as “interference noise” on an echo‐sounder record. Some records obtained from Delphinus delphis in Hauraki Gulf, New Zealand, suggest that these emissions were being used for echo‐ranging, a phenomenon well established by previous work. Possible uses of such records in studying dolphin behaviour are explained.     

Assessment of chlorophyll variability along the Louisiana coast using multi-satellite data

Variability in surface chlorophyll (Chl) concentrations derived from the Sea-Viewing Wide Field-of-View Sensor (SeaWiFS) were examined in conjunction with river discharge, QuikSCAT satellite-derived winds, and sea surface height (SSH) anomaly data along the Louisiana coast, USA. Surface Chl distributions exhibited rapid response to strong northerly winds following a frontal passage. A comparison of time series (1998–2010) river discharge and monthly Chl data indicated Chl variability to be well correlated to seasonal river discharge only for locations near the two river deltas, while offshore, enhancements in Chl during fall–winter was likely due to cross-shelf transport or mixing associated with strong northerly wind stress. Variance in Chl examined using wavelet analysis applied to nearly 10 years (1998–2007) of SeaWiFS data indicated patterns of significant Chl variability due to combined enhanced wind and river discharge, offshore flows associated with Ekman transport and coastal wind convergence, and the effect of Hurricane Rita in 2005. Instances of significant Chl variance were also observed to occur during years of large hypoxic zone size suggesting potential linkages to hypoxia. SSH anomaly imagery indicated the presence of warm-core eddies that were responsible for the offshore dispersal of elevated Chl observed in the monthly SeaWiFS imagery. Overall, the use of multi-satellite data better described the forcing and patterns of Chl distributions along the river-dominated Louisiana coast and shelf.     

Discerning resuspended chlorophyll concentrations from ocean color satellite imagery

Ocean color satellite imagery has been used to detect blooms of phytoplankton for decades. A bloom in this sense is defined as a rapid increase in chlorophyll-a concentration from newly synthesized sources (primary production) within the photic zone. Chlorophyll also has the potential to enter the water column from benthic sources as a result of resuspension events. Currently available bio-optical ocean color algorithms estimate the near-surface chlorophyll concentration in the water column but cannot characterize the source. By estimating resuspension, one can isolate the proportion of the total chlorophyll present in the water column that originated from benthic sources. The increase in remote sensing reflectance (Rrs) at 670nm as measured by SeaWiFS appears as a result of an increase in suspended materials, therefore, providing an estimate of resuspension. After examining imagery in locations of variable resuspension along the Texas coast, a strong positive correlation between the Rrs(670) produced by resuspension and the ratio of resuspended chlorophyll to total water column chlorophyll was observed.     

The Hillarys Transect (3): Optical and chlorophyll relationships across the continental shelf off Perth

An interdisciplinary study of the waters across the continental shelf off Perth, Western Australia, has provided the first detailed climatology of the physical, chemical, optical, and biological processes across the shelf. In support of this work, remote-sensing data were utilised to provide a broad view of the spatial and temporal chlorophyll concentration dynamics, to support in situ observations, and to help “fill the gaps” inherent in in situ point sampling.