2,913 research outputs found

    Satellite estimates of wide-range suspended sediment concentrations in Changjiang (Yangtze) estuary using MERIS data

    Get PDF
    The Changjiang (Yangtze) estuarine and coastal waters are characterized by suspended sediments over a wide range of concentrations from 20 to 2,500 mg l-1. Suspended sediment plays important roles in the estuarine and coastal system and environment. Previous algorithms for satellite estimates of suspended sediment concentration (SSC) showed a great limitation in that only low to moderate concentrations (up to 50 mg l-1) could be reliably estimated. In this study, we developed a semi-empirical radiative transfer (SERT) model with physically based empirical coefficients to estimate SSC from MERIS data over turbid waters with a much wider range of SSC. The model was based on the Kubelkaโ€“Munk two-stream approximation of radiative transfer theory and calibrated using datasets from in situ measurements and outdoor controlled tank experiments. The results show that the sensitivity and saturation level of remote-sensing reflectance to SSC are dependent on wavelengths and SSC levels. Therefore, the SERT model, coupled with a multi-conditional algorithm scheme adapted to satellite retrieval of wide-range SSC, was proposed. Results suggest that this method is more effective and accurate in the estimation of SSC over turbid water

    Hyperspectral remote sensing of cyanobacterial pigments as indicators for cell populations and toxins in eutrophic lakes

    Get PDF
    The growth of mass populations of toxin-producing cyanobacteria is a serious concern for the ecological status of inland waterbodies and for human and animal health. In this study we examined the performance of four semi-analytical algorithms for the retrieval of chlorophyll a (Chl a) and phycocyanin (C-PC) from data acquired by the Compact Airborne Spectrographic Imager-2 (CASI-2) and the Airborne Imaging Spectrometer for Applications (AISA) Eagle sensor. The retrieval accuracies of the semi-analytical models were compared to those returned by optimally calibrated empirical band-ratio algorithms. The best-performing algorithm for the retrieval of Chl a was an empirical band-ratio model based on a quadratic function of the ratio of re!ectance at 710 and 670 nm (R2=0.832; RMSE=29.8%). However, this model only provided a marginally better retrieval than the best semi-analytical algorithm. The best-performing model for the retrieval of C-PC was a semi-analytical nested band-ratio model (R2=0.984; RMSE=3.98 mg mโˆ’3). The concentrations of C-PC retrieved using the semi-analytical model were correlated with cyanobacterial cell numbers (R2=0.380) and the particulate and total (particulate plus dissolved) pools of microcystins (R2=0.858 and 0.896 respectively). Importantly, both the empirical and semi-analytical algorithms were able to retrieve the concentration of C-PC at cyanobacterial cell concentrations below current warning thresholds for cyanobacteria in waterbodies. This demonstrates the potential of remote sensing to contribute to early-warning detection and monitoring of cyanobacterial blooms for human health protection at regional and global scales

    Remote sensing for Mapping TSM concentration in Mahakam Delta: an analytical approach

    Get PDF
    The Indonesian coastal zones have always been under heavy pressures, including those from fisheries, oil industries and sea transportation. The presence of these activities carry a large portion of risk in damaging the environment as well as in destroying the marine resources, leading to the need for an integrated management approach based on an environmental information system that is comprehensive and multi-disciplinary in nature. The Mahakam Delta has the same general problems as other coastal regions in Indonesia. The method is based on bio optical modeling. The forward water analysis comprised the laboratory measurements of water quality (TSM and Chl) and Inherent Optical Properties (IOPs) to derive Spesific Inherent Optical properties (SIOPs). SIOPs (of water, TSM, Chl and CDOM), coefficient f and B were used to developed R(0-) model. The inverse atmosphere analysis comprised the image preprocessing (i.e. geometric correction, atmospheric correction, air-water interface correction). The last step is inverse water analysis, which comprised the development of algorithm and image processing to develop TSM concentration maps. The spectrometer measurements collected in the field were used for obtaining the subsurface irradiance reflectance. The subsurface irradiance reflectance R(0-) is the ratio of upwelling (Ewu) and downwelling irradiance (Ewd) just beneath the water surface. There are some discrepancies from matching R(0-) model and R(0-) measured in the field, especially in the blue region and NIR region. The reason of the discrepancies could be due to the fact that the Q factor (the angular distribution factor of spectral radiance) is still not understood completely. This model is very susceptible to the decrease of the proportional factor f, and to the increase of the backscattering probability B. The results indicates that red band of satellite sensor is sensitive to detect higher TSM concentration. For Mahakam Delta, red band algorithm was used to derive TSM map, since higher TSM concentration occurred in the delta

    ์œ ๋ฅ˜์˜ค์—ผ ํƒ์ง€๋ฅผ ์œ„ํ•œ ํ•ด์–‘ํ‘œ๋ฉด ๋งˆ์ดํฌ๋กœํŒŒ ํ›„๋ฐฉ์‚ฐ๋ž€ ๋ถ„์„๊ธฐ๋ฐ˜์˜ ์ค€๊ฒฝํ—˜์  ์ž„๊ณ„๋ชจ๋ธ

    Get PDF
    ํ•™์œ„๋…ผ๋ฌธ(์„์‚ฌ) -- ์„œ์šธ๋Œ€ํ•™๊ต๋Œ€ํ•™์› : ์ž์—ฐ๊ณผํ•™๋Œ€ํ•™ ์ง€๊ตฌํ™˜๊ฒฝ๊ณผํ•™๋ถ€, 2023. 8. ๊น€๋•์ง„.In an automatic oil spill monitoring system that utilizes SAR satellites, the dark spot detection step, which is responsible for the segmentation of potential oil spills, is undeniably significant. As the initial stage of automatic oil spill detection, this process is typically the most time-consuming and substantially influences the system performance. Considering the vast expanses of ocean that require thorough surveillance, it is crucial to have an efficient method that accurately identifies oil spill candidates at this critical early stage. In this study, a semi-empirical model was carefully proposed, grounded in a comprehensive analysis of the physical characteristics governing the interaction between electromagnetic waves and the sea surface, as well as oil spill observation data from SAR. This model utilizes wind speed, relative wind direction, and incidence angle as independent variables to calculate the threshold radar backscatter coefficient, to differentiate oil spill candidates from the ocean. To determine the parameters of the proposed model, large oil spill observational data was collected from the Sentinel-1 satellite, and the corresponding wind field data was derived from the ECMWF ERA5 reanalysis data. When compared to widely used dark spot detection methods such as the Otsu, Bradley, and active contour methods, the proposed model demonstrated outstanding performance. The model achieved an average F1 score of 0.7948 on the evaluation dataset, while the aforementioned methods showed 0.3315, 0.6400, and 0.5191, respectively. The proposed model exhibited distinguished accuracy with a straightforward implementation process, balancing effectiveness with simplicity, which makes it particularly suitable for real-time oil spill detection where efficiency is paramount. A notable feature of the proposed model is its ability to compute threshold at the pixel-level, unlike conventional patch-level methods that require iterative processes to detect oil spill candidates of varying sizes. This allows the model to identify oil spills in a single operation regardless of their sizes. While the proposed model is flexible in using diverse wind input sources such as buoys, scatterometers, or geophysical model functions, it is crucial to note that its performance depends on the accuracy of the wind field information, specifically, how well it reflects the wind conditions at the exact SAR acquisition time. In conclusion, this study has thoroughly investigated the behavior of the radar backscatter coefficient under both slick-free and slick-covered sea surfaces, leading to the development of a semi-empirical model that can enhance the efficiency of oil spill monitoring systems. The practical implications of the model extend beyond improving system performance; it can be used to create balanced deep-learning datasets by selectively choosing patches with dark spots. Moreover, the physically-grounded nature of the model enables advanced future research, such as distinguishing types of oil or estimating slick thickness.SAR ์œ„์„ฑ์„ ํ™œ์šฉํ•œ ์ž๋™ ์œ ๋ฅ˜์˜ค์—ผ ๋ชจ๋‹ˆํ„ฐ๋ง ์‹œ์Šคํ…œ์—์„œ ์œ ๋ฅ˜์˜ค์—ผ ํ›„๋ณด๋ฅผ ํƒ์ง€ํ•˜๋Š” ๊ณผ์ •์ธ dark spot detection ๋‹จ๊ณ„๋Š”, ์‹œ์Šคํ…œ์˜ ์ฒซ ๋ฒˆ์งธ ๋‹จ๊ณ„๋กœ์„œ ์ผ๋ฐ˜์ ์œผ๋กœ ๊ฐ€์žฅ ๋งŽ์€ ์‹œ๊ฐ„์ด ์†Œ์š”๋˜๊ณ , ์ตœ์ข… ํƒ์ง€ ์„ฑ๋Šฅ์— ๊ฒฐ์ •์ ์ธ ์˜ํ–ฅ์„ ๋ฏธ์นœ๋‹ค. ๋„“์€ ํ•ด์ƒ ์˜์—ญ์„ ํšจ๊ณผ์ ์œผ๋กœ ๊ฐ์‹œํ•˜๊ธฐ ์œ„ํ•ด์„œ๋Š”, ์ด์™€ ๊ฐ™์ด ์ดˆ๊ธฐ ๋‹จ๊ณ„์—์„œ ์œ ๋ฅ˜์˜ค์—ผ ํ›„๋ณด๋ฅผ ์ •ํ™•ํ•˜๊ณ  ํšจ์œจ์ ์œผ๋กœ ์‹๋ณ„ํ•  ํ•„์š”์„ฑ์ด ๊ฐ•์กฐ๋œ๋‹ค. ๋ณธ ๋…ผ๋ฌธ์—์„œ๋Š” ์ „์ž๊ธฐํŒŒ์™€ ์œ ๋ฅ˜๋ง‰์œผ๋กœ ๋ฎ์ธ ํ•ด์–‘ ํ‘œ๋ฉด ๊ฐ„์˜ ์ƒํ˜ธ์ž‘์šฉ์— ๋Œ€ํ•œ ๊ด‘๋ฒ”์œ„ํ•œ ๋ถ„์„๊ณผ ์œ ๋ฅ˜์˜ค์—ผ ์œ„์„ฑ ๊ด€์ธก๊ฐ’์„ ๊ธฐ๋ฐ˜์œผ๋กœ ์ค€๊ฒฝํ—˜์  ๋ชจ๋ธ์„ ์ œ์‹œํ•˜์˜€๋‹ค. ์ œ์•ˆ๋œ ๋ชจ๋ธ์€ ํ’์†, ์ƒ๋Œ€ ํ’ํ–ฅ, ์ž…์‚ฌ๊ฐ์„ ๋…๋ฆฝ๋ณ€์ˆ˜๋กœ ๊ฐ€์ง€๋ฉฐ ๋ฐ”๋‹ค์™€ ์œ ๋ฅ˜์˜ค์—ผ ํ›„๋ณด๋ฅผ ํšจ๊ณผ์ ์œผ๋กœ ๊ตฌ๋ถ„ํ•˜๋Š” ๋ ˆ์ด๋” ํ›„๋ฐฉ์‚ฐ๋ž€ ๊ณ„์ˆ˜์˜ ์ž„๊ณ„๊ฐ’์„ ์‚ฐ์ถœํ•œ๋‹ค. ๋ชจ๋ธ์˜ ๋งค๊ฐœ๋ณ€์ˆ˜๋ฅผ ๊ฒฐ์ •ํ•˜๊ธฐ ์œ„ํ•ด, Sentinel-1 ์œ„์„ฑ์—์„œ ๋Œ€๋Ÿ‰์˜ ์œ ๋ฅ˜์˜ค์—ผ ๊ด€์ธก ๋ฐ์ดํ„ฐ๋ฅผ ์ˆ˜์ง‘ํ•˜์˜€๊ณ , ์ด์— ํ•ด๋‹นํ•˜๋Š” ๋ฐ”๋žŒ์žฅ ๋ฐ์ดํ„ฐ๋ฅผ ECMWF ERA5 ์žฌ๋ถ„์„ ๋ฐ์ดํ„ฐ๋กœ๋ถ€ํ„ฐ ์ถ”์ถœํ•˜์—ฌ ์‚ฌ์šฉํ•˜์˜€๋‹ค. ๋ณธ ์—ฐ๊ตฌ์—์„œ ์ œ์•ˆํ•œ ๋ชจ๋ธ์˜ segmentation ์„ฑ๋Šฅ ํ‰๊ฐ€ ๊ฒฐ๊ณผ, ํ‰๊ท  F1 ์ ์ˆ˜๋Š” 0.7948๋กœ ๋‚˜ํƒ€๋‚ฌ์œผ๋ฉฐ, ๊ธฐ์กด์˜ ๋Œ€ํ‘œ์ ์ธ ์ ‘๊ทผ๋ฐฉ๋ฒ•์ธ Otsu, Bradley, active contour model์˜ ์„ฑ๋Šฅ์ด ๊ฐ๊ฐ 0.3315, 0.6400, 0.5191์ธ ๊ฒƒ๊ณผ ๋น„๊ตํ•˜์—ฌ ์šฐ์ˆ˜ํ•œ ํƒ์ง€ ์„ฑ๋Šฅ์„ ๋ณด์˜€๋‹ค. ํ•ด๋‹น ๋ชจ๋ธ์€ ๋ฌผ๋ฆฌ์  ํŠน์„ฑ์„ ๊ณ ๋ คํ•œ ์ง๊ด€์ ์ธ ์•Œ๊ณ ๋ฆฌ์ฆ˜๊ณผ ๋†’์€ segmentation ์ •ํ™•๋„๋กœ, ํŠนํžˆ ํšจ์œจ์„ฑ์ด ๊ฐ•์กฐ๋˜๋Š” ์‹ค์‹œ๊ฐ„ ์œ ๋ฅ˜์˜ค์—ผ ๋ชจ๋‹ˆํ„ฐ๋ง์— ๋งค์šฐ ์ ํ•ฉํ•˜๋‹ค. ๋˜ํ•œ ์ œ์•ˆ๋œ ๋ชจ๋ธ์€ ํ”ฝ์…€ ๋‹จ๊ณ„์˜ ์ž„๊ณ„๊ฐ’ ๊ณ„์‚ฐ์ด ๊ฐ€๋Šฅํ•˜์—ฌ, ๋‹ค๋ฅธ patch ๋‹จ์œ„๋กœ ๋™์ž‘ํ•˜๋Š” ํƒ์ง€ ๋ชจ๋ธ๋“ค๊ณผ ๋‹ฌ๋ฆฌ, ๋‹ค์–‘ํ•œ ํฌ๊ธฐ์˜ ์œ ๋ฅ˜์˜ค์—ผ์„ ํƒ์ง€ํ•˜๊ธฐ ์œ„ํ•ด ์—ฌ๋Ÿฌ ํฌ๊ธฐ์˜ ์œˆ๋„์šฐ๋ฅผ ๋ฐ˜๋ณต์ ์œผ๋กœ ์‚ฌ์šฉํ•˜์—ฌ ํƒ์ง€ํ•  ํ•„์š”๊ฐ€ ์—†๋‹ค. ํ•ด๋‹น ๋ชจ๋ธ์€ ํ•ด์ƒ ๋ถ€์ด, ์‚ฐ๋ž€๊ณ„์™€ ๊ฐ™์€ ๋‹ค์–‘ํ•œ ๋ฐ”๋žŒ์žฅ ์ •๋ณด๋ฅผ ์ž…๋ ฅ๊ฐ’์œผ๋กœ ์‚ฌ์šฉํ•  ์ˆ˜ ์žˆ์œผ๋‚˜, ๋ชจ๋ธ์˜ ์„ฑ๋Šฅ์€ ํ•ด๋‹น ๋ฐ์ดํ„ฐ์˜ ์ •ํ™•๋„์— ํฌ๊ฒŒ ์˜์กดํ•˜๋ฉฐ, ํŠนํžˆ SAR ์ด๋ฏธ์ง€ ์ทจ๋“ ์‹œ์ ์˜ ๋ฐ”๋žŒ ์ƒํƒœ๋ฅผ ์–ผ๋งˆ๋‚˜ ์ •ํ™•ํžˆ ๋ฐ˜์˜ํ•˜๋Š”์ง€์— ๋”ฐ๋ผ ๋‹ฌ๋ผ์ง„๋‹ค๋Š” ํŠน์ง•์„ ๊ฐ€์ง„๋‹ค. ๊ฒฐ๋ก ์ ์œผ๋กœ, ๋ณธ ๋…ผ๋ฌธ์—์„œ๋Š” ์œ ๋ฅ˜์˜ค์—ผ์ด ์—†๋Š” ๋ฐ”๋‹ค ํ‘œ๋ฉด๊ณผ ์žˆ๋Š” ํ‘œ๋ฉด์—์„œ์˜ ๋ ˆ์ด๋” ํ›„๋ฐฉ์‚ฐ๋ž€ ๊ณ„์ˆ˜์˜ ๋ณ€ํ™”๋ฅผ ์„ธ๋ฐ€ํ•˜๊ฒŒ ๋ถ„์„ํ•˜์—ฌ, ์œ ๋ฅ˜์˜ค์—ผ ๋ชจ๋‹ˆํ„ฐ๋ง ์‹œ์Šคํ…œ์˜ ํšจ์œจ์„ฑ์„ ๊ฐ•ํ™”ํ•  ์ˆ˜ ์žˆ๋Š” ์ค€๊ฒฝํ—˜์  ์œ ๋ฅ˜์˜ค์—ผ ํ›„๋ณด ์ถ”์ถœ ์ž„๊ณ„๊ฐ’ ๋ชจ๋ธ์„ ๊ฐœ๋ฐœํ•˜์˜€๋‹ค. ์ œ์•ˆ๋œ ๋ชจ๋ธ์€ ๋ชจ๋‹ˆํ„ฐ๋ง ์‹œ์Šคํ…œ์˜ ์„ฑ๋Šฅ์„ ํ–ฅ์ƒ์‹œํ‚ฌ ์ˆ˜ ์žˆ์„ ๋ฟ๋งŒ ์•„๋‹ˆ๋ผ, dark spot์ด ์žˆ๋Š” patch๋ฅผ ์„ ๋ณ„ํ•˜์—ฌ ๊ท ํ˜•์žกํžŒ ๋”ฅ๋Ÿฌ๋‹ ๋ฐ์ดํ„ฐ์…‹์„ ์ƒ์„ฑํ•˜๋Š” ๋ฐ์—๋„ ํ™œ์šฉ๋  ์ˆ˜ ์žˆ๋‹ค. ๋˜ํ•œ, ๋ณธ ๋ชจ๋ธ์€ ์œ ๋ฅ˜์˜ค์—ผ๊ณผ ํ•ด์–‘์˜ ๋ฌผ๋ฆฌ์  ํŠน์„ฑ์— ๊ทผ๊ฑฐํ•˜๋ฏ€๋กœ, ์œ ์ข… ์‹๋ณ„ ๋˜๋Š” ์œ ๋ฅ˜ ๋‘๊ป˜์ถ”์ •๊ณผ ๊ฐ™์€ ํ›„์† ์—ฐ๊ตฌ์˜ ๊ฐ€๋Šฅ์„ฑ์„ ์ œ์‹œํ•œ๋‹ค.Chapter 1. Introduction 1 1.1 Research Background 1 1.2 Literature Review 4 1.3 Research Objective 9 Chapter 2. Microwave Backscattering Properties from the Sea Surface 11 2.1 Microwave backscattering from the Slick-Free Ocean Surface 11 2.1.1 Radar Scattering Model 11 2.1.2 Geophysical Model Function 13 2.2 Microwave backscattering from the Slick-Covered Ocean Surface 18 2.2.1 The Action Balance Equation 18 2.2.2 The Damping Ratio 27 Chapter 3. Development and Validation of the Semi-Empirical Model 29 3.1 Formulation of the Theoretical Framework for the Semi-Empirical Model 29 3.2 Data Acquisition 34 3.2.1 Acquisition of SAR Image Data 34 3.2.2 Acquisition of Wind Field Data 40 3.3 Parameter Determination of the Semi-Empirical Model 44 Chapter 4. Performance Evaluation of the Semi-Empirical Model 47 4.1 Experimental Design 47 4.2 Performance Evaluation with Other Methods 51 4.3 Performance Evaluation for Different Wind Conditions and Regions 60 Chapter 5. Application of the Semi-Empirical Model 69 Chapter 6. Conclusion 72 Bibliography 75 Abstract in Korean 82์„

    Theoretical modeling of dual-frequency scatterometer response: improving ocean wind and rainfall effects

    Get PDF
    Ocean surface wind is a key parameter of the Earthโ€™s climate system. Occurring at the interface between the ocean and the atmosphere, ocean winds modulate fluxes of heat, moisture and gas exchanges. They reflect the lower branch of the atmospheric circulation and represent a major driver of the ocean circulation. Studying the long-term trends and variability of the ocean surface winds is of key importance in our effort to understand the Earthโ€™s climate system and the causes of its changes. More than three decades of surface wind data are available from spaceborne scatterometer/radiometer missions and there is an ongoing effort to inter-calibrate all these measurements with the aim of building a complete and continuous picture of the ocean wind variability. Currently, spaceborne scatterometer wind retrievals are obtained by inversion algorithms of empirical Geophysical Model Functions (GMFs), which represent the relationship between ocean surface backscattering coefficient and the wind parameters. However, by being measurement-dependent, the GMFs are sensor-specific and, in addition, they may be not properly defined in all weather conditions. This may reduce the accuracy of the wind retrievals in presence of rain and it may also lead to inconsistencies amongst winds retrieved by different sensors. Theoretical models of ocean backscatter have the big potential of providing a more general and understandable relation between the measured microwave backscatter and the surface wind field than empirical models. Therefore, the goal of our research is to understand and address the limitations of the theoretical modeling, in order to propose a new strategy towards the definition of a unified theoretical model able to account for the effects of both wind and rain. In this work, it is described our approach to improve the theoretical modeling of the ocean response, starting from the Ku-band (13.4 GHz) frequency and then broadening the analysis at C-band (5.3 GHz) frequency. This research has revealed the need for new understanding of the frequency-dependent modeling of the surface backscatter in response to the wind-forced surface wave spectrum. Moreover, our ocean wave spectrum modification introduced to include the influences of the surface rain, allows the interpretation/investigation of the scatterometer observations in terms not only of the surface winds but also of the surface rain, defining an additional step needed to improve the wind retrievals algorithms as well as the possibility to jointly estimate wind and rain from scatterometer observations

    A semi-analytical model for estimating total suspended matter in highly turbid waters

    Get PDF
    Total suspended matter (TSM) is related to water quality. High TSM concentrations limit underwater light availability, thus affecting the primary productivity of aquatic ecosystems. Accurate estimation of TSM concentrations in various waters with remote sensing technology is particularly challenging, as the concentrations and optical properties vary greatly among different waters. In this research, a semi-analytical model was established for Hangzhou Bay and Lake Taihu for estimating TSM concentration. The model construction proceeded in two steps. 1) Two indices of the model were calculated by deriving absorption and backscattering coefficients of suspended matter (ap(λ) and bbp(λ)) from the reflectance signal using a semi-analytical method. 2) The two indices were then weighted to derive TSM. The performance of the proposed model was tested using in situ reflectance and Geostationary Ocean Color Imager (GOCI) data. The derived TSM based on in situ reflectance and GOCI images both corresponded well with the in situ TSM with low mean relative error (32%, 41%), root mean square error (20.1 mg/L, 43.1 mg/L), and normalized root mean square error (33%, 55%). The model was further used for the slightly turbid Xin’anjiang Reservoir to demonstrate its applicability to derive ap(λ) and bbp(λ) in other water types. The results indicated that the form Rrs −1(λ1) − Rrs −1(λ2) could minimize the effect of CDOM absorption in deriving ap(λ) from the total absorption. The model exploited the different relationships between TSM concentration and multiband reflectance, thus improving the performance and application range in deriving TSM

    A review of protocols for fiducial reference measurements of water-leaving radiance for validation of satellite remote-sensing data over water

    Get PDF
    ยฉ 2019 by the authors. This paper reviews the state of the art of protocols for measurement of water-leaving radiance in the context of fiducial reference measurements (FRM) of water reflectance for satellite validation. Measurement of water reflectance requires the measurement of water-leaving radiance and downwelling irradiance just above water. For the former there are four generic families of method, based on: (1) underwater radiometry at fixed depths; or (2) underwater radiometry with vertical profiling; or (3) above-water radiometry with skyglint correction; or (4) on-water radiometry with skylight blocked. Each method is described generically in the FRM context with reference to the measurement equation, documented implementations and the intra-method diversity of deployment platform and practice. Ideal measurement conditions are stated, practical recommendations are provided on best practice and guidelines for estimating the measurement uncertainty are provided for each protocol-related component of the measurement uncertainty budget. The state of the art for measurement of water-leaving radiance is summarized, future perspectives are outlined, and the question of which method is best adapted to various circumstances (water type, wavelength) is discussed. This review is based on practice and papers of the aquatic optics community for the validation of water reflectance estimated from satellite data but can be relevant also for other applications such as the development or validation of algorithms for remote-sensing estimation of water constituents including chlorophyll a concentration, inherent optical properties and related products

    Chlorophyll-a Algorithms for Oligotrophic Oceans: A Novel Approach Based on Three-Band Reflectance Difference

    Get PDF
    A new empirical algorithm is proposed to estimate surface chlorophyll-a concentrations (Chl) in the global ocean for Chl less than or equal to 0.25 milligrams per cubic meters (approximately 77% of the global ocean area). The algorithm is based on a color index (CI), defined as the difference between remote sensing reflectance (R(sub rs), sr(sup -1) in the green and a reference formed linearly between R(sub rs) in the blue and red. For low Chl waters, in situ data showed a tighter (and therefore better) relationship between CI and Chl than between traditional band-ratios and Chl, which was further validated using global data collected concurrently by ship-borne and SeaWiFS satellite instruments. Model simulations showed that for low Chl waters, compared with the band-ratio algorithm, the CI-based algorithm (CIA) was more tolerant to changes in chlorophyll-specific backscattering coefficient, and performed similarly for different relative contributions of non-phytoplankton absorption. Simulations using existing atmospheric correction approaches further demonstrated that the CIA was much less sensitive than band-ratio algorithms to various errors induced by instrument noise and imperfect atmospheric correction (including sun glint and whitecap corrections). Image and time-series analyses of SeaWiFS and MODIS/Aqua data also showed improved performance in terms of reduced image noise, more coherent spatial and temporal patterns, and consistency between the two sensors. The reduction in noise and other errors is particularly useful to improve the detection of various ocean features such as eddies. Preliminary tests over MERIS and CZCS data indicate that the new approach should be generally applicable to all existing and future ocean color instruments
    • โ€ฆ
    corecore