Proceedings Volume 7105

Remote Sensing of the Ocean, Sea Ice, and Large Water Regions 2008

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Proceedings Volume 7105

Remote Sensing of the Ocean, Sea Ice, and Large Water Regions 2008

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Volume Details

Date Published: 2 October 2008
Contents: 6 Sessions, 29 Papers, 0 Presentations
Conference: SPIE Remote Sensing 2008
Volume Number: 7105

Table of Contents

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Table of Contents

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  • Front Matter: Volume 7105
  • Ocean and Water Color
  • Infrared and Visible Imagery and Spectral Assessments
  • Hyperspectral Imagery and In-situ Data
  • Microwave and Altimetry Measurements and Image-Related Assessments
  • Poster Session
Front Matter: Volume 7105
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Front Matter: Volume 7105
This PDF file contains the front matter associated with SPIE Proceedings Volume 7105, including the Title Page, Copyright information, Table of Contents, Introduction (if any), and the Conference Committee listing.
Ocean and Water Color
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An optical model for the interpretation of remotely sensed multispectral images of oil spill
F. Carnesecchi, V. Byfield, P. Cipollini, et al.
This work is focused on the interpretation of multispectral images of oil spills, by introducing an optical model of spectral signature for oil-covered sea surface. Oil spill detection and oil type identification can potentially be achieved using data from multispectral optical sensors. However, multispectral images interpretation is challenging, because the spectral signature depends not only on oil optical properties and film thickness, but also on the optical properties of the water column, the incident light distribution and the instrument viewing geometry. In this work a simulator has been developed, starting from an optical model for both clean and polluted surfaces, which makes it possible to analyze variability in the optical signal from an oil-covered water surface. Several simulations have been performed varying the water optical properties within a range typical of Case I waters, and considering different crude and refined oils. Incident light distributions and viewing configurations have been chosen according to a typical viewing geometry of the MERIS sensor over a particularly interesting Mediterranean area: the marine ecosystem of the Tuscan Archipelago. The results, shown in terms of both upwelling radiance and oil-water optical contrast, provide some general rules that may aid interpretation of MERIS data. In particular, the detectability of an oil slick has been shown to depend on oil type and film thickness: very thin oil films (sheens) are more easily detected at viewing directions near the sun-glint zone, while very thick films are more likely to be detected at viewing angles away from the sun. For films of intermediate thickness the detectability depends mainly on the oil's specific optical properties.
Colored dissolved organic matter in the northern Gulf of Mexico using ocean color: seasonal trends in 2005
Eurico J. D'Sa, Mitsuko Korobkin
The optical properties of colored dissolved organic matter (CDOM) were studied for the northern Gulf of Mexico coastal and oceanic waters influenced by the Mississippi-Atchafalaya river system. CDOM absorption determined from field measurements in March, May, July and August of 2005 at a station off the Atchafalaya river indicated influences related to river discharge while the CDOM spectral slope S indicated effects of CDOM photooxidation in a sample acquired in late summer. A previously derived CDOM algorithm using the reflectance band ratios of Rrs(510)/Rrs(555) were used to derive estimates of surface CDOM absorption distribution at 412 nm from the Sea-viewing Wide Field-of-view Sensor (SeaWiFS) imagery. Spatial and temporal CDOM absorption distributions from satellite for the northern Gulf of Mexico in the year 2005 indicated strong seasonal influence associated with discharge from the Mississippi-Atchafalaya river system. A seasonal increase in storms and hurricanes allowed an assessment of the effects of hurricane Rita in September 2005. SeaWiFS estimates of CDOM revealed a decrease in nearshore CDOM absorption due to the transport of low CDOM offshore waters towards the coast following hurricane Rita. Using conservative CDOM-salinity relationship for the region, SeaWiFS surface salinity derived from CDOM absorption also indicated an increase in nearshore salinity east of the hurricane track. However, an increase in CDOM and a decrease in salinity were observed in coastal waters near the location of hurricane landfall likely associated with coastal runoff following extensive coastal flooding.
Red tide detection simulation for integrated ray tracing model in-orbit performance verification with GOCI
Sun Jeong Ham, Sug-Whan Kim, Hyung Sik Yun, et al.
The Geostationary Ocean Colour Instrument (GOCI) is a satellite ocean colour instrument on board the Communication-Ocean-Meteorology Satellite (COMS) scheduled to be launched into a geostationary orbit sometime after late 2009. GOCI primary science objectives are i) to monitor the marine environments around Korean peninsula, ii) to produce the fishery information such as chlorophyll concentration and iii) to monitor the long-term and short-term changes in marine ecosystem. We report a new end-to-end optical model for GOCI in-orbit radiometric and imaging performance verification. The model includes the source (i.e. the sun), target (i.e. a 2500 km x 2500 km region of the Earth's surface) and the payload (i.e. GOCI optical system) incorporated in the single optical ray tracing environment. It was then applied for the measurement simulation for red tide infection commonly observed in the Korean coastal water environment. The simulation results show that the estimated water leaving radiance (WLR) of 14 red tide-infected case-I water target scenes exhibits a close proximity to those obtained from the COART model, and satisfies the red tide detection criteria reported elsewhere. The simulated WLR results were also used to check the validity of 14 chlorophyll algorithms commonly used in the ocean science field. This demonstrates the practical usefulness of the model, as an important mission-support and analysis tool. It is also envisaged that the model deployment can bring a significant improvement, in the process throughput, to the GOCI pre-flight and in-flight performance verification phases. The model concept, simulation results and implications are described in detail.
Infrared and Visible Imagery and Spectral Assessments
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Multiresolution optical properties for infrared sea surface modeling
Karine Caillault, Sandrine Fauqueux, Pierre Simoneau
An analytical sea surface optical properties model in the infrared band is described. It allows the introduction of multiresolution in the simulated field-of-view answering the need in computed images including any observational configurations. It is valid for fully-developed seas, includes shadowing and hiding functions but not breaking and foam nor multiple reflections. For the model validation purposes, the MIRAMER field campaign took place in the Mediterranean sea during May 2008, both ground-based and on board an oceanographic ship. Radiometric datasets along with the associated environmental measurements have been collected in various environmental and observation conditions. First campaign results are presented in this paper.
Untangling the make-up of the NIR reflectance peak in coastal waters and its impact on remote sensing retrievals of [Chl] and fluorescence height algorithms
Recent studies show that the contribution of the chlorophyll fluorescence component to the NIR reflectance is significant only for relatively low concentrations of minerals; furthermore, Fluorescence Line Height (FLH) algorithms do not work properly for [Chl] > 5-10 mg/m3 because of the deviation of elastic reflectance from the baseline. But even for relatively low chlorophyll concentration [Chl] values the relationship between FLH and [Chl] is affected by several factors which should be taken into account. The sensitivity of this relationship to atmospheric correction schemes, incident and viewing angles and chlorophyll retrieval algorithms are analyzed, and a special correlation procedure is developed to minimize these effects. Effective fluorescence quantum yield distributions retrieved from field measurements and satellite imagery are also compared with the previously indirectly estimated values based on the analysis of the shift of the observed NIR reflectance peak from the fluorescence peak at 685 nm.
Characterization of multi-angular hyperspectral polarized reflectance from coastal waters
A. Gilerson, A. Tonizzo, J. Zhou, et al.
Since scattering by molecules, particles, aerosols, hydrosols and reflection at the sea surface introduce and modify the polarization state of light, the polarized underwater light field contains embedded information about the intrinsic nature of various water constituents (biogenic, nonalgal and inorganic particles, dissolved matter), and can be used in retrieval algorithms for the separation of organic and inorganic particulates, in improving underwater visibility and in other active techniques and applications. To study underwater polarization characteristics a new instrument has been developed by the Optical Remote Sensing Laboratory at CCNY. The instrument consists of three Satlantic Hyperspectral radiance sensors mounted on a scanning system controlled by an underwater electric stepper motor. The motor rotates the sensors in a vertical plane in a specific angular range. This can be adjusted according to the solar altitude angle in order to cover the full 0-180° scattering angle range. Linear polarizers are attached in front of the sensors; the polarizers are oriented at 0° (vertical), 90 °(horizontal) and 45°. By rotating the sensors relative to the nadir direction, the instrument scans the angular features of the underwater polarized light field in a vertical plane defined by its azimuth angle relative to the sun. Angular variations of the degree of polarization are found to be consistent with theory. Maximum values of the degree of polarization do not exceed 0.5 while the position of the maximum is shifted from 90° towards higher scattering angles. The results presented here will need to be corroborated with additional measurements in varying water conditions.
Water quality mapping using remote sensing technique in Penang Straits, Malaysia
H. S. Lim, M. Z. MatJafri, K. Abdullah, et al.
The application of remote sensing to assess water quality for coastal and open ocean has escalated recently due to its capability of scanning wide water bodies within a short time period. In this paper, we examined the spatial variability of chlorophyll within Penang straits, Malaysia. Coastal and estuarine ecosystems typically exhibit high temporal and spatial variability in phytoplankton biomass that is often too difficult to characterize with a limited set of in situ shipboard measurements. In this study, we used ALOS satellite imagery acquired on 24 April 2007. An algorithm for retrieval of chlorophyll level was developed for ALOS data. Chlorophyll samples were collected using a small boat simultaneously with the acquisition of the satellite image. The water locations were determined using a handheld Global Positioning System (GPS). And then the digital numbers for each band corresponding to the sea-truth locations were extracted and then converted into radiance values and reflectance values. The reflectance values were used for calibration of the chlorophyll algorithm. For the regression model, the correlation coefficient (R) and the root-mean-square deviation (RMS) were noted. The proposed algorithm is considered superior based on the values of the correlation coefficient and root-mean-square The water quality image was generated using the multispectral data set and the proposed calibrated TSS algorithm. This study demonstrates that remote sensing can play an important role in water quality assessment by using high resolution satellite image of ALOS data.
China offshore wind energy resources assessment with the QuikSCAT data
Jingwei Xu, Yong Luo, Xiuzhi Zhang, et al.
With the data, which were obtained from the SeaWinds scatterometer on board the National Aeronautics and Space Administration (NASA) QuikSCAT satellite (12.5km*12.5km available from 1999 to current daily orbit swath), the China offshore region were studied (105-135° E 15-45° N). Because swath location is not fixed, interpolation was applied to get a fixed grid with 0.1° resolution. We calculate and analysis China offshore wind resources effective density of wind energy (EDWE) at 10 meters high above the sea level. And find that EDWE is rich in offshore area. The highest EDWE is in Taiwan Strait and North and South of the strait, with the EDWE 600-800W/m2, the next highest is East China Sea and South China Sea. The lowest EDWE is Yellow Sea and Bohai bay, less than 400W/m2. And several other wind energy resource-rich areas are: 1)the north of Bohai Bay, with wind power density more than 800 w/m2 decline to the south, 2)the East China Sea area the power density above 400 w/m2 increase to the southward. Guangdong coastal waters are rich in wind resources energy.
Hyperspectral Imagery and In-situ Data
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An update on SeaBED: a TesBED for validating subsurface aquatic hyperspectral remote sensing algorithms
James A. Goodman, Miguel Vélez-Reyes, Samuel Rosario-Torres
SeaBED is an integrated data set and testing infrastructure for researchers to validate subsurface aquatic remote sensing algorithms. The purpose behind developing SeaBED is to collect multiple levels of image, field, and laboratory data with which to validate physical models, inversion algorithms, feature extraction tools and classification methods for subsurface aquatic sensing using hyperspectral imaging. The focus of this testbed facility is a field site located on Enrique Reef in southwestern Puerto Rico. This field site, which includes a heterogeneous mixture of both coral reef and seagrass habitats, offers a well defined system for evaluating analysis techniques under natural environmental conditions. Data produced from the field site currently includes airborne, satellite, and field-level hyperspectral and multispectral images, in situ spectral signatures, and water bio-optical properties. This data provides a valuable combination of sensing imagery and fully characterized ground truth information for developing and validating remote sensing algorithms. A major accomplishment for SeaBED was the collection of high-resolution hyperspectral imagery and associated ground truth of the near shore reefs and coastal ecosystems in southwestern Puerto Rico in 2007. The mission included 1740 km2 of imagery acquired at 4 m spatial resolution, with 110 km2 enhanced coverage of four science areas at 1, 2, 4 and 8 m spatial resolutions to facilitate investigation of spatial scaling issues and the testing of subsurface unmixing algorithms. We present an overview of SeaBED and also describe particulars of the 2007 data collection campaign, including both image acquisition and field data collection efforts.
Laser remote sensing of underwater objects
J. Wojtanowski, Z. Mierczyk, M. Zygmunt
Theoretical and practical aspects of laser application in the field of underwater remote sensing have been presented. A multi-level analysis and computational results dealing with 0.532 μm laser wavelength were performed to determine the expected capabilities of underwater laser penetration with regard to the Lidar system developed in Optoelectronics Institute of Military University of Technology in Warsaw. Since the device is to perform underwater measurements from above the water level, the influence of the water-atmosphere interface had to be included in the analysis. Sea water characteristics concerning electromagnetic radiation propagation have been widely considered covering the mechanisms of absorption, scattering and the effective attenuation typical for representative types of sea waters. Software application developed in Mathcad environment enabled to model the impact of both absorption and scattering coefficients of different types of sea water on geometrical and energetic parameters of laser beam propagating in the underwater environment. The impact of reflectance properties of the remotely sensed underwater object on the reflected signal level has been investigated as well. Analytical approach covered both "echo" signal reflected from an underwater object and background noise signal level generated mainly by the sunlight and diffuse atmospheric illumination.
Background and study concerning water wave effects on airborne imagery
This paper describes ongoing research and initial results regarding collection of airborne imagery for detection of submerged features in optically shallow water types. The approach is to utilize land surface, water surface and submerged or in-situ line targets of various types during the airborne flights or fixed platforms. The imagery collected by the airborne sensing systems is processed in concept to correct for the presence of the water surface wave effects and water column effects. The correction approach is based upon calculation of a residual image between either (a) the observed submerged target image and the non-submerged image or (2) the observed submerged target within a scene and a synthetic image of the same scene. The residual image thus contains the distortion and blurring effects due to the presence of water waves and the water column. The residual image contains the information needed to scientifically explain in order to improve our scientific understanding of submerged feature recognition. The approach is described can be applied to airborne, fixed platforms, modeled hyperspectral signatures as well as hyperspectral synthetic reflectance imagery of environmental media, features and objects within such media. When applied to hyperspectral airborne imagery of water, the techniques an be used to identify and optimize the bands and channels that can also be utilized in creating filters to be used in traditional, but high spatial resolution mapping cameras for mapping aquatic and coastal environments. Results presented of submerged target imagery demonstrate the ease to detect submerged features on the order of 3 cm2 using airborne digital data as well as traditional scanned film cameras. The results suggest that gravity wave effects may be removed from low altitude and high spatial and spectral resolution airborne imagery by careful calibration of airborne sensors, especially focal plane focusing calibration and related sensor settings.
Microwave and Altimetry Measurements and Image-Related Assessments
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An alternative procedure for the estimation of the altimeter bias for the Jason-1 satellite using the dedicated calibration site at Gavdos
Stelios P. Mertikas, Ath. Papadopoulos, Erricos C. Pavlis
The dedicated calibration site for satellite radar altimeters in Gavdos has been operational since 2004. The small island of Gavdos is located along a repeating ground track of Jason satellites (crossover point No.109 ascending and No.18 descending pass and adjacent to Envisat), and additionally where the altimeter and radiometer footprints do not experience significant land intrusion. The purpose of such permanent Cal/Val facility is to calibrate the sea-surface height and ancillary measurements made by the satellite as it passes overhead, by using observations from tide gauges, GPS, DORIS and other sensors directly placed under the satellite ground tracks. Up to now, altimeter calibration at Gavdos has been performed by averaging gridded sea-level anomalies as produced by the satellite altimeter measurements and then comparing the result with the tide gauge observations. The absolute altimeter bias has thus been previously estimated to be +121 mm ±10 mm for Jason-1 satellite. In this work, the absolute altimeter bias of Jason-1 has been determined using (1) approximately one year of sea-surface height observations; (2) the GDR-B altimeter record and the seasonal effects of sea level; and (3) an alternative approach for calibration by interpolating each individual altimetric correction given by the satellite at its point of closest approach over the corresponding value of the tide gauge observation.
Poster Session
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COASTALT: improving radar altimetry products in the oceanic coastal area
Jesús Gómez-Enri, Paolo Cipollini, Christine Gommenginger, et al.
Fifteen years of global altimetry data over the coastal ocean lie, largely unexploited, in the data archives, simply because intrinsic difficulties in the corrections and issues of land contamination in the footprint. These data would be invaluable for studies of coastal circulation, sea level change and impact on the coastline. Amongst some initiatives, we describe here the COASTALT Project, funded by ESA. The main objective of the COASTALT Project is to contribute towards making the status of pulse-limited coastal altimetry operational. In this paper we will first illustrate the first project phase, based on the assessment of user requirements, and summarize those requirements. Then we will describe the COASTALT methodology and objectives. Finally, we will illustrate and discuss the various options for coastal waveform retracking, and present a plan for the validation of the retracked data. The first results in the radar altimeter waveform analysis show the complexity of the coastal signals due to land contamination and calm/rough waters.
Derive the backscattering coefficients of particles from in-situ measurements
The ocean color satellite sensors measure the water-leaving radiance from ocean, which is used to deduce the global chlorophyll-a concentration distribution and other information. The water-leaving radiance is mainly caused by the backscatter of particles in the water. Spectral backscattering coefficients of particles play an important role in determining the remote sensing reflectance and a model is developed to study the spectral characteristics of the particle backscattering coefficients. The backscattering model of particles is established based on the measured data at two wavelengths of 470nm and 700nm and the backscattering coefficients of phytoplankton are also deduced from the total particles. The parameter n in the model is deduced from chlorophyll-a instead of using a constant value and the backscattering coefficient of particles at 700nm is retrieved from chlorophyll-a using a power function. To deduce the backscattering model of phytoplankton, the ratio of phytoplankton absorption to the total absorption of particles is used to separate the phytoplankton part from total backscattering values. The backscattering model of phytoplankton is established with a high correlation coefficient of 0.80 and the parameter values of the model are very close to those of Sathyendranath. The range of phytoplankton backscattering coefficients is from 0.0018 to 0.016m-1, almost half of that scattered by total particles. The backscattering properties of phytoplankton also agree with the normalized diffuse attenuation coefficients of seawater, which can be used in the bio-optical models in the coastal ocean.
Method to correct both foam and rain effects on dual frequency altimeter Jason1 wind measurements in typhoon Shanshan
Altimetry data under extreme weather events such as tropical cyclones, typhoons and hurricanes are valuable although the measurements are affected by various factors associated with high sea states, such as big winds, high waves, especially atmospheric rains and ocean surface foams. Both rains and foams can strongly affect the propagation and reflection of microwave signal, but the effects of sea foam on altimeter measurements have not been adequately addressed. Although the sea foam only appears when the wind speed is high and ocean wave is breaking, the attenuation effect of foam in typhoons should not be neglected. The major challenge is the effects of rain and foam on altimeter received backscatter are similar and are hard to be separated. In this paper, we proposed a iterative method to correct both rain and sea foam effects using a simplified stratified foam model and the liquid water content measurements from nadir viewing Jason1 Microwave Radiometer. Finally a case study to maintain accurate wave height, wind speed, and rain rate measurements and to retrieve the additional results of foam coverage considering both the effects of rain and sea foam in the typhoon Shanshan is presented.
Chinese progress toward marine applications of synthetic aperture radar
This paper presents the progress toward marine applications of synthetic aperture radar (SAR) data and a review of the SAR satellite program in China. The technique development includes the development of algorithms and of methodology for extracting oceanographic parameters from SAR data. Marine applications range from environmental monitoring to oceanographic research. Two series of SAR satellites have been planned. The first SAR satellite of the Environmental and Disaster Monitoring Satellite series (HJ series) will be launched in 2009 while the first SAR satellite of the Ocean SAR Satellite series (HY-3 series) is in planning phase. A description is given of the instruments and their plateforms.
SAR measurements of the Taiwan Shoal in China
The submarine sand waves of the Taiwan Shoal in the coastal area of China have been observed with ERS-1 SAR images. A numerical model for shallow water bathymetric survey by SAR has been used to derive the heights and the slopes of the submarine sand waves while a feature tracking method has been applied to measure the movement of the submarine sand waves with sequential images. The results show that the submarine sand waves align parallel to the east direction with a height scale of 2-6m and a slope scale of 2°-14°. The lengths and widths of the submarine sand waves are about 500-5000m and 200 to 2000m respectively. The submarine sand waves move towards the south and the southeast. The displacement of the submarine sand waves varies between 20 to 450m with an average value of about 146m.
On the use of polarization phase information for ship detection
Weigen Huang, Juan Wang, Jingsong Yang, et al.
Fully polarimetric synthetic aperture radar (SAR) data has been found to have many potential marine applications. This paper investigates in the polarization phase information for ship detection using Space-borne Imaging Radar-C/X-band SAR (SIR-C/X-SAR) data. It is shown that there exits large difference in polarization phase between ships and sea surface. The HH-VV polarization phase difference has largest ship-sea contrast among all polarization phase differences. An algorithm for ship detection has been proposed based on the ship-sea contrast in polarization phase information. The results have indicated that the polarization phase difference information can be used to detect ships with high accuracy.
A moving ship detection method with time sequential shipborne radar imagery
One of the main problems in ship detection is the presence of sea clutter inherent to radar imagery. A moving ship detection method with time sequential shipborne radar imagery has been developed based on the radar backscattering properties of ships. The method consists of the coherence image computation, ship detection threshold estimation and false alarm removal. It has been tested with the X-band shipborne radar imagery. The results show that the method works well.
Seasonal variation of absorption spectral characteristics of CDOM and de-pigmented particles in East China Sea
The Colored Dissolved Organic Materials (CDOM) and the de-pigmented particles are the main components affecting the ocean colors in China coastal waters (which are commonly considered as the Case II waters). Understanding of their spectral characteristics is very important to develop the regional bio-optical algorithms for ocean color remote sensing. The coastal water in East China Sea (ECS) is influenced by the terrestrial materials especially the Yangtze River outflow, which has high dissolved organic and suspended materials concentration and complex particles composition. In this paper, we analyze the in situ datasets collected in four seasons between 2006 and 2007 in ECS, and get the spectral absorption models of CDOM and de-pigmented particles. The distributions of absorption coefficients of CDOM ( ) and de-pigmented particles ( ) show a decreasing trend from coastal water to the off-shore waters, which is influenced mainly by the Yangtze River outflow and coastal currents with remarkable seasonal variation in ESC. The maxima of adp CDOM a dp a dp is very high and even up to 90 m-1 level in estuary waters that it will apparently influence the retrieval of CDOM. The frequency of slops of the exponential spectrum of de-pigmented particles obeys the Gaussian distribution and it has good relationships with the absorption coefficient especially in the near-shore areas. The optical characteristics in ECS will give feasible reference to the further development of regional bio-optical algorithms.
Remote sensing estimation of chlorophyll-a concentration in east coastal water in China based on MAMS data
Remote sensing (RS) data can be used to estimate the chlorophyll-a concentration of water body, which has become a key issue of water quality monitoring. Processed and analyzed the MAMS on August 2005, we estimated chlorophyll-a concentration using ratio and differential coefficient method in East coastal water. But these two models' applicability confined in single area and single phase. In this paper we used mixing spectral analysis model for extracting chlorophyll-a concentration and mapping the distribution of chlorophyll-a concentration. The result shows that the new style of remote sensing data MAMS can be used for monitoring chlorophyll-a concentration, and that mixing spectral analysis is an optimal method for estimating water chlorophyll-a concentration.
Remote sensing research on the influence on the ocean color environment of the East and South China Sea from snowstorm in cold winter this year
At the beginning of 2008, the south area of China suffered a rare heavy snow and low temperature weather, which brought enormous economic lose and broke the environment. The abnormal weather also influenced the ocean color environment. Through analysis of MODIS remote sensing 3A data during 2 months before and after the snowstorm and low temperature weather, the author finds that, on the one hand,compared with same period of last year, the sea surface temperature (SST) from the East China Sea to the South China Sea (18°N-32°N 108°E-126°E descended 2.57°C; the average chlorophyll-a concentration(CHL-a)rose from 1.198 mg. m-3 to 1.75 mg. m-3 in the snowstorm and low temperature weather period from January 11 to 31 of 2008 which was 1.46 times more than that of the same period of last year. On the other hand, compared with the period before snowstorm,the SST decreased from 22.42°C to 18.34°C but the CHL-a rose from 1.32 mg. m-3 to 1.60 mg. m-3 after the snowstorm. In addition,the sea water transparency(SDD) had a certain increase in the open sea of South China Sea, but the suspended sediment concentration(SSC) increased significantly near the seashore, the Yangtse River Estuary and the Pearl River Estuary, which increased 200% compared with the period before the snowstorm 2008. Through researching and indicating, the main reason of increase of the CHL-a in the near seashore area(the I water) was more probably due to the increase of the SSC, and the CHL-a by remote sensing has greater error, which rising from the high SSC led to the increase of CHL-a; but in the open sea the increase of CHL-a is that the SDD improved and then the euphotic increased. As a result,this could promote the growth of primary productivity. Therefore, it faces the better applied foreground to monitor the influence on the ocean ecosystem environment caused by the snowstorm and low temperature weather through remote sensing.
Wind analysis on the observations of sand wave SAR images in Taiwan Shoal
Kaiguo Fan, Weigen Huang, Mingxia He, et al.
This paper discusses the relationship between the observations of submarine sand wave SAR images in Taiwan shoal and sea surface wind. A total of 43 SAR images over 11 years are collected and 496 profiles of sand wave SAR images are used, the wind are estimated from blended wind data and current direction is from mode. Results show submarine sand waves are observed by SAR under wind speed of 10 m/s, only littlie are imaged above 10 m/s. The number of observed sand waves reaches its maximum under the adverse wind direction, while the crosswind has its minimum. These support that low and middle wind speed and adverse wind direction are favorable for SAR imaging submarine sand waves, high wind speed and crosswind are unfavorable. The comparison between monthly mean wind speed and sand waves observed by SAR also shows a strong correlation between both, which is lower wind speeds, the higher probability of sand waves observed by SAR. This may indicate that the higher observation of the sand waves by SAR is partly due to wind speed.
Wind retrievals in typhoons from QuikSCAT considering rain effect
By analyzing several collocated QuikSCAT measurements and Special Sensor Microwave Imager (SSM/I) rain rate in typhoons, the evidence of rain influence to wind retrieval is presented. The results show that the present of heavy rain in typhoons will cause large bias in both wind speed and wind direction for QuikSCAT wind retrieval. So that the Holland's model is applied in the ambiguity clear process to correct the errors in wind direction induced by rain. Also, a radiate transfer function (RTF) and collocated SSM/I rain rate is employed to correct the attenuation and scattering effects of rain. The performance of RTF method is limited due to lack of information of the collocated rain rate and the un-precise of the RTF. As an alternative way to RTF, an interpolation method which just uses the data from QuikSCAT itself is introduced to correct the attenuation and scattering effects of rain. This method is applied to retrieve the wind vector in typhoon Ioke, the result shows that the bias in the wind direction and wind speed induced by rain has both been well corrected, indicating that our correction to the impacts of rain on QuikSCAT wind retrieval in typhoons is effective.
The remote sensing algorithm of spectral diffuse attenuation coefficient of ocean
Diffuse attenuation coefficient is an apparent optical property (AOP) which directly links to the inherent optical properties in ocean color remote sensing. So far, the study on the satellite retrieve algorithm of water diffuse attenuation coefficient has not been deeply-going, which is mainly discussed using the bands-ratio methods based on the in situ data. Only a few scientists apply the remote sensing data (such as SeaWiFS and MODIS) to retrieve the diffuse attenuation coefficient based on the model developed by Mueller (2002). In this paper, a quasi-analytical algorithm of spectral diffuse attenuation coefficients were developed based on the QAA algorithm of the inherent optical properties (IOPs) developed by Lee (2002). The model could retrieve multi-bands of the diffuse attenuation coefficients at 412 nm, 443 nm, 490 nm, 510 nm and 555nm wavelength. The in-situ optical dataset of South China Sea in 1999 was used to validate the model, and the results showed that the model had a good performance in the case I water in South China Sea, and the relative errors were 15.4%, 12.6%, 13.3%, 10.2%, 11.9%, 9.8% and 10.3% for the 412 nm, 443 nm, 490 nm, 510 nm, 520 nm, 555nm and 565 nm bands respectively. For the complex case II water, the model should be further localized and tested.
Retrieval of shallow water topography surface currents from SAR image
A new method for retrieving shallow water topography surface currents from SAR image is introduced based on the shallow water topography SAR imaging mechanism. M4S was applied to forward simulate radar signatures of the oceanic features over the ocean surface. The first guessed surface currents can be estimated from the normalized radar cross section (NRCS) of the shallow water topography profile in the SAR image according to the AH linear theory, the NRCS induced by the varying shallow water topography surface currents could be simulated by the forward simulating model. The wind speed and shallow water topography surface currents gradients are modified using the iterative method for the simulated radar signals close to the NRCS calculated from SAR image. Finally, the wind speed and the surface currents can be retrieved. This method is tested on an ERS-2 SAR image in the Taiwan Shoal. The result shows that the simulated shallow water topography radar signal is consistent with the NRCS measured from SAR image, and their correlation coefficient is up to 90%, which means that this method is convergent and applicable.
Remote sensing algorithm of particle attenuation coefficient in East China Sea
China coastal sea is characteristic of the high concentration of suspended matter which has complex components of mineral particles, organic detritus and phytoplankton, etc. The similarity of spectrum characters of mineral particles and organic particles in backscattering coefficient, and the organic detritus and color dissolve organic matters (CDOM) in absorption coefficient makes the information inverse of coastal ocean color become a very difficult work. In this paper, based on the in situ data of optical investigation in East China Sea in the spring of 2003, including the absorption coefficients of CDOM and de-pigment particles from laboratory spectrophotometer measurement, and the field measurement with ac-9 (WET labs, Inc.), the optical properties of suspended particles were studied. And then, a semi-analysis algorithm of particle attenuation coefficient (Cp) in ECS was developed. There are two key steps in this algorithm, one is the estimation of the ratio of particle backscattering coefficient to the total scattering coefficient; and the other is the retrieval of absorption coefficient of CDOM. With this inversion algorithm of Cp and the input of remote sensing reflectance obtained from the underwater profiler radiometer (Satlantic. Inc.), the particle attenuation coefficient was inversed, which was consistent well with the in situ data of Cp . In the high turbid water, the scattering signal is dominant in the Cp values, so the modeled-Cp was less than the in situ data due to the underestimation of backscattering coefficient in IOPs semi-analysis algorithms. The modeled -Cp at 660nm wavelength has the R2 of 0.84 and RMSE=0.22 compared with the attenuation coefficient at 650nm measured by the ac-9, in which the absorption coefficient of CDOM is neglect. The semi-analysis algorithms of Cp developed in this paper showed a good potential to estimate the biogeochemical parameters, like POC, but the further study should be focused on the distinguish of the sub-division materials with more in situ data set.
Using satellite remote sensing to monitor the total suspended solids (TSS) over Penang Island, Malaysia
H. S. Lim, M. Z. MatJafri, K. Abdullah, et al.
Total suspended solid (TSS) is a major factor affecting water quality in aquatic ecosystem. An investigation has been conducted to test the feasibility of using SPOT 5 data for estimating TSS in the coastal waters of Penang Island, Malaysia. Atmospheric correction of the satellite measurements is critical for aquatic remote sensing. Atmospheric correction of the remotely sensed image was performed using the ENVI FLAASH. Water samples were collected simultaneously with the satellite image acquisition and later analyzed in the laboratory. The digital numbers for each band corresponding to the sea-truth locations were extracted and then converted into reflectance values. The variables of the reflectance were used for calibration of the water quality algorithm. Regression technique was employed to calibrate the algorithm using the SPOT multispectral signals. An algorithm was developed based on the reflectance model, which is a function of the inherent optical properties of water that can be related to the concentration of its constituents. Spatial distribution map of the water quality parameter was produced using the calibrated algorithm. The efficiency of the present algorithm, in comparison to other forms of algorithm, was also investigated. Finally, the TSS map was generated using the proposed algorithm.