Suhyb Salama | University of Twente, Faculty of Geoinformation Science and Earth Observation (ITC) (original) (raw)
Papers by Suhyb Salama
Proceedings of IAHS, May 6, 2015
Earth observations (EOs) following empirical and/or analytical approaches are a feasible alternat... more Earth observations (EOs) following empirical and/or analytical approaches are a feasible alternative to obtain spatial and temporal distribution of water quality variables. The limitations observed in the use of empirical approaches to estimate high concentrations of suspended particulate matter (SPM) in the estuarine water of Guadalquivir have led the authors to use a semi-analytical model, which relates the water constituents' concentration to the water leaving reflectance. In this work, the atmospheric correction has been carried out simultaneously and the aerosol reflectance and backscattering coefficients of SPM obtained. The results are validated using in situ SPM data series provided by a monitoring network in the study area. The results show that the model allows us to successfully estimate backscattering coefficients of SPM in the estuary, differentiating clear and turbid water and using two ε(4,5) .These considerations improve the value of R 2 from 0.68 (single ε(4,5)) to 0.86 (two ε(4,5)) on 18 May 2009. This method could be used as a preliminary approach to obtain SPM concentration in the Guadalquivir estuary with the limitations that the model shows for turbid waters.
VLIZ Special Publication, 2002
status: published, 2003
... Table 1: The operational mode of each sensor. Parameter CHRIS DAIS ROSIS ... 2000 [3]). This ... more ... Table 1: The operational mode of each sensor. Parameter CHRIS DAIS ROSIS ... 2000 [3]). This will reduce the induced errors due to roughened sea surface and bottom albedo. Saturation-of-reflectance occurs at high concentrations of SPM (Althuis and Shimwell 1995 [4]). ...
Frontiers in remote sensing, Feb 4, 2022
It is common in estuarine waters to place fixed monitoring stations, with the advantages of easy ... more It is common in estuarine waters to place fixed monitoring stations, with the advantages of easy maintenance and continuous measurements. These two features make fixed monitoring stations indispensable for understanding the optical complexity of estuarine waters and enable an improved quantification of uncertainties in satellite-derived water quality variables. However, comparing the point-scale measurements of stationary monitoring systems to time-snapshots of satellite pixels suffers from additional uncertainties related to temporal/spatial discrepancies. This research presents a method for validating satellite-derived water quality variables with the continuous measurements of a fixed monitoring station in the Ems Dollard estuary on the Dutch-German borders. The method has two steps; first, similar in-situ measurements are grouped. Second, satellite observations are upscaled to match these point measurements in time and spatial scales. The upscaling approach was based on harmonizing the probability distribution functions of satellite observations and in-situ measurements using the first and second moments. The fixed station provided a continuous record of data on suspended particulate matter (SPM) and chlorophyll-a (Chl-a) concentrations at 1 min intervals for 1 year (2016-2017). Satellite observations were provided by Sentinel-2 (MultiSpectral Instrument, S2-MSI) and Sentinel-3 (Ocean and Land Color Instrument, S3-OLCI) sensors for the same location and time of in-situ measurements. Compared to traditional validation procedures, the proposed method has improved the overall fit and produced valuable information on the ranges of goodness-of-fit measures (slope, intercept, correlation coefficient, and normalized root-mean-square deviation). The correlation coefficient between measured and derived SPM concentrations has improved from 0.16 to 0.52 for S2-MSI and 0.14 to 0.84 for S3-OLCI. For the Chl-a matchup, the improvement was from 0.26 to 0.82 and from 0.14 to 0.63 for S2-MSI and S3-OLCI, respectively. The uncertainty in the derived SPM and Chl-a concentrations was reduced by 30 and 23% for S2-SMI and by 28 and 16% for S3-OLCI. The high correlation and reduced uncertainty signify that the matchup pairs are observing the same fluctuations in the measured variable. These new goodness-of-fit measures correspond to the results of the performed sensitivity analysis, previous literature, and reflect the inherent accuracy of the applied derivation model.
In situ soil moisture measurement networks are essential for developing, improving and validating... more In situ soil moisture measurement networks are essential for developing, improving and validating satellite soil moisture products. In the east of the Netherlands, an area susceptible to droughts, a monitoring network for soil moisture and – temperature has been operational since 2009. Spread across an area of 45 by 40 km, twenty profile monitoring stations observe moisture and temperature in the root zone. Four field campaigns were conducted in order to calibrate the sensors and to assess the spatial representativeness of the measurements.The network has proven to be of great value for validation of satellite products (e.g. for SMAP soil moisture). In addition, continuation of the measurements will increase its value for climate studies. Currently, the network is being redesigned to better suit operational water management in the region, while preserving the value of long time series for climatological research, and taking into account its potential value for future missions. Here, we present an overview of the network and the observations since its establishment, including the adjustments that are being made to the network and research opportunities.Van der Velde, R., Benninga, H.J.F., Retsios, B., Vermunt, P.C., Salama, M.S. (2022) - Twelve years profile soil moisture and temperature measurements in Twente, the Netherlands. Earth System Science Data Discussions, 1-44.Velde, dr. ir. R van der (University of Twente) (2022): Twelve years profile soil moisture and temperature measurements in Twente, the Netherlands. DANS. https://doi.org/10.17026/dans-znj-wyg5
Frontiers in Environmental Science, Mar 2, 2023
One of the major sources of pollution affecting inland and coastal waters is related to poorly tr... more One of the major sources of pollution affecting inland and coastal waters is related to poorly treated or untreated wastewater discharge, particularly in urbanized watersheds. The excess of nutrients, organic matter, and pathogens causes an overall deterioration of water quality and impairs valuable ecosystem services. The detection of wastewater pollution is essential for the sustainable management of inland and coastal waters, and remote sensing has the capability of monitoring wastewater contamination at extended spatial scales and repeated frequencies. This study employed satellite-derived water quality indicators and spatiotemporal analysis to assess the risk of wastewater contamination in Conceição Lagoon, a coastal lagoon in Southern Brazil. Using an analytical model, three water quality indicators were derived from Level 2A Sentinel-2 MSI images: the absorption coefficients of chlorophyll-a and detritus combined with coloured dissolved organic matter, and the backscattering coefficient of suspended solids. The temporal standardized anomalies were calculated for each water quality indicator for the period of 2019-2021, and their anomalies during a known outfall event were used to evaluate spatial variation modes. The spatial mode explaining most of the variability was used to estimate weights for the water quality indicators anomalies in a linear transformation that can indicate the risk of wastewater contamination. Results showed that the wastewater spatial mode for this region was characterized by positive anomalies of backscattering coefficient of particulate matter and absorption coefficient of detritus combined with coloured dissolved organic matter, each with a relative importance of 50%. The application of this spatiotemporal analysis was formulated as the Wastewater Contamination Index. With the aid of photographic records, and additional meteorological and water quality data, the results of the index were verified for wastewater outfall events in the study area. The methodology for constructing the proposed Wastewater Contamination Index applies to other locations and can be a valuable tool for operational monitoring of wastewater contamination.
Hydrology and Earth System Sciences, Jul 13, 2009
Remote sensing of water quality in inland waters requires reliable retrieval algorithms, accurate... more Remote sensing of water quality in inland waters requires reliable retrieval algorithms, accurate atmospheric correction and consistent method for uncertainty estimation. In this paper, the GSM semi-analytical inversion model is modified for inland waters to derive inherent optical properties (IOPs) and their spectral dependencies from air and space borne data. The modified model was validated using two data sets from the Veluwe and the Vecht Dutch lakes. For the Veluwe lakes, the model was able to derive a linear relationship between measured concentrations and estimated IOPs with R 2 values above 0.7 for chlorophyll-a (Chl-a) and up to 0.9 for suspended particulate matters (SPM). In the Vecht lakes, the modified model derived accurate values of IOPs. The R 2 values were 0.89 for Chl-a and up to 0.95 for SPM. The RMSE values were 0.93 mg m −3 and 0.56 g m −3 for Chl-a and SPM respectively. Finally, the IOPs of the Veluwe lakes are derived from multi-spectral, ocean color and hyperspectral airborne data. Inversion-uncertainties of the derived IOPs were also estimated using a standard nonlinear regression technique. The study shows that inversionuncertainties of remote sensing derived IOPs are proportional to water turbidity.
Remote Sensing, Dec 1, 2018
The seasonal variability of sea surface salinity anomalies (SSSAs) in the Indian Ocean is investi... more The seasonal variability of sea surface salinity anomalies (SSSAs) in the Indian Ocean is investigated for its role in the South Asian Summer Monsoon. We have observed an elongated spatial-feature of the positive SSSAs in the southwestern Indian Ocean before the onset of the South Asian Summer Monsoon (SASM) by using both the Aquarius satellite and the Argo float datasets. The maximum variable areas of SSSAs in the Indian Ocean are along (60 • E-80 • E) and symmetrical to the equator, divided into the southern and northern parts. Further, we have found that the annual variability of SSSAs changes earlier than that of sea surface temperature anomalies (SSTAs) in the corresponding areas, due to the change of wind stress and freshwater flux. The change of barrier layer thickness (BLT) anomalies is in phase with that of SSSAs in the southwestern Indian Ocean, which helps to sustain the warming water by prohibiting upwelling. Due to the time delay of SSSAs change between the northern and southern parts, SSSAs, therefore, take part in the seasonal process of the SASM via promoting the SSTAs gradient for the cross-equator currents.
Remote Sensing of Environment, Mar 1, 2016
The 2SeaColor model (Salama and Verhoef, 2015) was proposed to analytically retrieve the diffuse ... more The 2SeaColor model (Salama and Verhoef, 2015) was proposed to analytically retrieve the diffuse attenuation coefficient (K d) from remote sensing reflectance (R rs), but its parameterization was based on approximations and subjected to large uncertainties. In this study, we present an improvement on the parametrization equations in the inverse scheme of the 2Seacolor model. The improved model is then validated with three in-situ datasets and compared with the Zhang model (Zhang and Fell, 2007) and the Lee model (Lee et al., 2005a). Validation with radiometric data shows that the 2SeaColor model provides the best estimates of K d for the full range of observations, with the largest determination coefficient (R 2 = 0.935) and the smallest root mean squared error (RMSE = 0.078 m-1). For clear waters, where K d (490) < 0.2, the Zhang model provides the most accurate K d estimations, but results from the Lee model and the 2SeaColor are rather comparable. For turbid waters, where K d (490) > 0.2 m-1 , the 2SeaColor model is found to be
During the Eagle 2006 campaign intensive in-situ and air/space borne measurements were carried ou... more During the Eagle 2006 campaign intensive in-situ and air/space borne measurements were carried out over the Wolderwijd and Veluwemeer natural waters in the Netherlands. In this paper, we modify the GSM semi-analytical inversion model for these lakes to derive inherent optical properties (IOPs) and their spectral dependencies from air and space borne data. Uncertainties of the derived IOPs are estimated using a nonlinear regression technique. The modified model succeeded in deriving accurate estimates of IOPs with R 2 higher than 0.9 and RMSE values equal to 0.12 and 0.05 for absorption and scattering coefficients, respectively. Finally, we show that the uncertainty of derived absorption coefficients is slightly independent of absorption's magnitude. While the uncertainty of all derived IOPs increases with water turbidity.
Earth System Science Data, Apr 27, 2023
Spread across Twente and its neighbouring regions in the east of the Netherlands, a network of 20... more Spread across Twente and its neighbouring regions in the east of the Netherlands, a network of 20 profile soil moisture and temperature (5, 10, 20, 40, and 80 cm depths) monitoring stations was established in 2009. Field campaigns have been conducted covering the growing seasons of 2009, 2015, 2016, and 2017, during which soil sampling rings and handheld probes were used to measure the top 5 cm volumetric soil moisture content (VSM) of 28 fields near 12 monitoring stations. In this paper, we describe the design of the monitoring network and the field campaigns, adopted instrumentation, experimental setup, field sampling strategies, and the development of sensor calibration functions. Maintenance and quality control procedures and issues specific to the Twente network are discussed. Moreover, we provide an overview of open third-party datasets (i.e. land cover/use, soil information, elevation, groundwater, and meteorological observations) that can support the use and analysis of the Twente soil moisture and temperature datasets beyond the scope of this contribution. An indication for the spatial representativeness of the permanent monitoring stations is provided through comparisons of the 5 cm station measurements with the top 5 cm field-averaged VSM derived from the field campaign measurements. The results reveal in general reasonable agreements and root mean squared errors that are dominated by underestimations of the field-averaged VSM, which is particularly apparent for the grass fields and is strong after heavy rain. Further, we discuss the prospects the datasets offer to investigate (i) the reliability of soil moisture references that serve the development and validation of soil moisture products, and (ii) the water and energy exchanges across the groundwater-vadose-zone-atmosphere continuum within a lowland environment in a changing climate. The datasets discussed are publicly available at https://doi.org/10.17026/dans-znj-wyg5 (Van der Velde et al., 2022).
Frontiers in Marine Science, Jul 17, 2023
Turbid coastal plumes carry sediments, nutrients, and pollutants. Satellite remote sensing is an ... more Turbid coastal plumes carry sediments, nutrients, and pollutants. Satellite remote sensing is an effective tool for studying water quality parameters in these turbid plumes while covering a wide range of hydrological and meteorological conditions. However, determining boundaries of turbid coastal plumes poses a challenge. Traditionally, thresholds are the approach of choice for plume detection as they are simple to implement and offer fast processing (especially important for large datasets). However, thresholds are site-specific and need to be readjusted for different datasets or when meteorological and hydrodynamical conditions differ. This study compares state-of-the-art threshold approaches with a novel algorithm (PLUMES) for detecting turbid coastal plumes from satellite remote sensing, tested for Patos Lagoon, Brazil. PLUMES is a semi-supervised, and spatially explicit algorithm, and does not assume a unique plume boundary. Results show that the thresholds and PLUMES approach each provide advantages and limitations. Compared with thresholds, the PLUMES algorithm can differentiate both low or high turbidity plumes from the ambient background waters and limits detection of coastal resuspension while automatically retrieving metrics of detected plumes (e.g., area, mean intensity, core location). The study highlights the potential of the PLUMES algorithm for detecting turbid coastal plumes from satellite remote sensing products, which can have significantly positive implications for coastal management. However, PLUMES, despite its demonstrated effectiveness in this study, has not yet been applied to other study sites.
Remote Sensing, Jan 23, 2023
This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY
EAGLE2006-an intensive field campaign for the advances in land surface hydrometeorological proces... more EAGLE2006-an intensive field campaign for the advances in land surface hydrometeorological processes-was carried out in the Netherlands from 8 to 18 June 2006, involving 16 institutions with in total 67 people from 16 different countries. In addition to the acquisition of multi-angle and multi-sensor satellite data, several airborne instruments-an optical imaging sensor, an imaging microwave radiometer, and a flux airplane-were deployed and extensive ground measurements were conducted over one grassland site at Cabauw and two forest sites at Loobos and Speulderbos in the central part of the Netherlands. The generated data set is both unique and urgently needed for the development and validation of models and inversion algorithms for quantitative land surface parameter estimation and land surface hydrometeorological process studies. EAGLE2006 was led by the Department of Water Resources of the International Institute for Geo-Information Science and Earth Observation (ITC) and originated from the combination of a number of initiatives supported by different funding agencies. The objectives of the EAGLE2006 campaign were closely related to the HESSD
IOP Conference Series: Earth and Environmental Science
Water in coastal and estuary areas needs to be investigated as human activities is allegedly decr... more Water in coastal and estuary areas needs to be investigated as human activities is allegedly decrease their quality. This has led to optical remote sensing for mapping optical water quality using empirical and semi-analytical approaches. Therefore, this study aims to estimate the Total Suspended Matter (TSM) concentration from Medium Resolution Imaging Spectrometer (MERIS) data using a spectral unmixing approach combined with a radiative transfer model. This approach was implemented in the equatorial tropical coastal water, the Berau estuary, Indonesia, by generating a look-up table (LUT) of top-of-atmosphere radiance spectra through the coupled forward models, and the endmembers were selected from the LUT. The spectral unmixing algorithm was employed to the MERIS data for decomposing the image into haze and sediment components. The data were then transformed into images of a constant haze level corresponding to 50 km visibility, and the atmospheric correction was applied. Furthermo...
EGU General Assembly Conference Abstracts, Apr 1, 2019
This paper investigates the performance of MERIS reduced resolution data to monitor water quality... more This paper investigates the performance of MERIS reduced resolution data to monitor water quality parameters in the Berau estuary waters, Indonesia. Total Suspended Matter (TSM) and Chlorophyll-a (Chl-a) concentration were derived from MERIS data using three different algorithms for coastal waters: standard global processor (MERIS L2), C2R and FUB. The outcomes were compared to in situ measurements collected in 2007. MERIS data processed with C2R gave the best retrieval of Chl-a, while MERIS L2 performed *the best for TSM retrieval, but large deviations from in situ data were observed, pointing at inversion problems over these tropical waters for all standard processors. Nevertheless, MERIS can be of use for monitoring equatorial coastal waters like the Berau estuary and reef system.
IGARSS 2018 - 2018 IEEE International Geoscience and Remote Sensing Symposium, 2018
In this study, the effect of tide on the variation of concentrations of Chlorophyll-a (Chla) and ... more In this study, the effect of tide on the variation of concentrations of Chlorophyll-a (Chla) and Suspended Particulate Matters (SPM), retrieved from a complete dataset of diurnal close-range hyperspectral observations recorded at the NIOZ jetty station (NJS) located at the Marsdiep inlet in the Dutch part of the Wadden Sea, was evaluated. The two-stream radiative transfer model 2SeaColor was inverted to retrieve Chla and SPM concentrations per each hyperspectral observation of the quality-controlled dataset. Concurrently with these diurnal observations, tidal information was obtained from the Den Helder station located at 3.7 km from the NJS. From the performed analysis and evaluation of this study, we concluded that the tide has little observable effects on the diurnal changes of SPM concentration at the NJS located in the Dutch part of the Wadden Sea. The results of this evaluation and the favorable location of the NJS, which is not influenced by the tidal phase, will contribute t...
Proceedings of IAHS, May 6, 2015
Earth observations (EOs) following empirical and/or analytical approaches are a feasible alternat... more Earth observations (EOs) following empirical and/or analytical approaches are a feasible alternative to obtain spatial and temporal distribution of water quality variables. The limitations observed in the use of empirical approaches to estimate high concentrations of suspended particulate matter (SPM) in the estuarine water of Guadalquivir have led the authors to use a semi-analytical model, which relates the water constituents' concentration to the water leaving reflectance. In this work, the atmospheric correction has been carried out simultaneously and the aerosol reflectance and backscattering coefficients of SPM obtained. The results are validated using in situ SPM data series provided by a monitoring network in the study area. The results show that the model allows us to successfully estimate backscattering coefficients of SPM in the estuary, differentiating clear and turbid water and using two ε(4,5) .These considerations improve the value of R 2 from 0.68 (single ε(4,5)) to 0.86 (two ε(4,5)) on 18 May 2009. This method could be used as a preliminary approach to obtain SPM concentration in the Guadalquivir estuary with the limitations that the model shows for turbid waters.
VLIZ Special Publication, 2002
status: published, 2003
... Table 1: The operational mode of each sensor. Parameter CHRIS DAIS ROSIS ... 2000 [3]). This ... more ... Table 1: The operational mode of each sensor. Parameter CHRIS DAIS ROSIS ... 2000 [3]). This will reduce the induced errors due to roughened sea surface and bottom albedo. Saturation-of-reflectance occurs at high concentrations of SPM (Althuis and Shimwell 1995 [4]). ...
Frontiers in remote sensing, Feb 4, 2022
It is common in estuarine waters to place fixed monitoring stations, with the advantages of easy ... more It is common in estuarine waters to place fixed monitoring stations, with the advantages of easy maintenance and continuous measurements. These two features make fixed monitoring stations indispensable for understanding the optical complexity of estuarine waters and enable an improved quantification of uncertainties in satellite-derived water quality variables. However, comparing the point-scale measurements of stationary monitoring systems to time-snapshots of satellite pixels suffers from additional uncertainties related to temporal/spatial discrepancies. This research presents a method for validating satellite-derived water quality variables with the continuous measurements of a fixed monitoring station in the Ems Dollard estuary on the Dutch-German borders. The method has two steps; first, similar in-situ measurements are grouped. Second, satellite observations are upscaled to match these point measurements in time and spatial scales. The upscaling approach was based on harmonizing the probability distribution functions of satellite observations and in-situ measurements using the first and second moments. The fixed station provided a continuous record of data on suspended particulate matter (SPM) and chlorophyll-a (Chl-a) concentrations at 1 min intervals for 1 year (2016-2017). Satellite observations were provided by Sentinel-2 (MultiSpectral Instrument, S2-MSI) and Sentinel-3 (Ocean and Land Color Instrument, S3-OLCI) sensors for the same location and time of in-situ measurements. Compared to traditional validation procedures, the proposed method has improved the overall fit and produced valuable information on the ranges of goodness-of-fit measures (slope, intercept, correlation coefficient, and normalized root-mean-square deviation). The correlation coefficient between measured and derived SPM concentrations has improved from 0.16 to 0.52 for S2-MSI and 0.14 to 0.84 for S3-OLCI. For the Chl-a matchup, the improvement was from 0.26 to 0.82 and from 0.14 to 0.63 for S2-MSI and S3-OLCI, respectively. The uncertainty in the derived SPM and Chl-a concentrations was reduced by 30 and 23% for S2-SMI and by 28 and 16% for S3-OLCI. The high correlation and reduced uncertainty signify that the matchup pairs are observing the same fluctuations in the measured variable. These new goodness-of-fit measures correspond to the results of the performed sensitivity analysis, previous literature, and reflect the inherent accuracy of the applied derivation model.
In situ soil moisture measurement networks are essential for developing, improving and validating... more In situ soil moisture measurement networks are essential for developing, improving and validating satellite soil moisture products. In the east of the Netherlands, an area susceptible to droughts, a monitoring network for soil moisture and – temperature has been operational since 2009. Spread across an area of 45 by 40 km, twenty profile monitoring stations observe moisture and temperature in the root zone. Four field campaigns were conducted in order to calibrate the sensors and to assess the spatial representativeness of the measurements.The network has proven to be of great value for validation of satellite products (e.g. for SMAP soil moisture). In addition, continuation of the measurements will increase its value for climate studies. Currently, the network is being redesigned to better suit operational water management in the region, while preserving the value of long time series for climatological research, and taking into account its potential value for future missions. Here, we present an overview of the network and the observations since its establishment, including the adjustments that are being made to the network and research opportunities.Van der Velde, R., Benninga, H.J.F., Retsios, B., Vermunt, P.C., Salama, M.S. (2022) - Twelve years profile soil moisture and temperature measurements in Twente, the Netherlands. Earth System Science Data Discussions, 1-44.Velde, dr. ir. R van der (University of Twente) (2022): Twelve years profile soil moisture and temperature measurements in Twente, the Netherlands. DANS. https://doi.org/10.17026/dans-znj-wyg5
Frontiers in Environmental Science, Mar 2, 2023
One of the major sources of pollution affecting inland and coastal waters is related to poorly tr... more One of the major sources of pollution affecting inland and coastal waters is related to poorly treated or untreated wastewater discharge, particularly in urbanized watersheds. The excess of nutrients, organic matter, and pathogens causes an overall deterioration of water quality and impairs valuable ecosystem services. The detection of wastewater pollution is essential for the sustainable management of inland and coastal waters, and remote sensing has the capability of monitoring wastewater contamination at extended spatial scales and repeated frequencies. This study employed satellite-derived water quality indicators and spatiotemporal analysis to assess the risk of wastewater contamination in Conceição Lagoon, a coastal lagoon in Southern Brazil. Using an analytical model, three water quality indicators were derived from Level 2A Sentinel-2 MSI images: the absorption coefficients of chlorophyll-a and detritus combined with coloured dissolved organic matter, and the backscattering coefficient of suspended solids. The temporal standardized anomalies were calculated for each water quality indicator for the period of 2019-2021, and their anomalies during a known outfall event were used to evaluate spatial variation modes. The spatial mode explaining most of the variability was used to estimate weights for the water quality indicators anomalies in a linear transformation that can indicate the risk of wastewater contamination. Results showed that the wastewater spatial mode for this region was characterized by positive anomalies of backscattering coefficient of particulate matter and absorption coefficient of detritus combined with coloured dissolved organic matter, each with a relative importance of 50%. The application of this spatiotemporal analysis was formulated as the Wastewater Contamination Index. With the aid of photographic records, and additional meteorological and water quality data, the results of the index were verified for wastewater outfall events in the study area. The methodology for constructing the proposed Wastewater Contamination Index applies to other locations and can be a valuable tool for operational monitoring of wastewater contamination.
Hydrology and Earth System Sciences, Jul 13, 2009
Remote sensing of water quality in inland waters requires reliable retrieval algorithms, accurate... more Remote sensing of water quality in inland waters requires reliable retrieval algorithms, accurate atmospheric correction and consistent method for uncertainty estimation. In this paper, the GSM semi-analytical inversion model is modified for inland waters to derive inherent optical properties (IOPs) and their spectral dependencies from air and space borne data. The modified model was validated using two data sets from the Veluwe and the Vecht Dutch lakes. For the Veluwe lakes, the model was able to derive a linear relationship between measured concentrations and estimated IOPs with R 2 values above 0.7 for chlorophyll-a (Chl-a) and up to 0.9 for suspended particulate matters (SPM). In the Vecht lakes, the modified model derived accurate values of IOPs. The R 2 values were 0.89 for Chl-a and up to 0.95 for SPM. The RMSE values were 0.93 mg m −3 and 0.56 g m −3 for Chl-a and SPM respectively. Finally, the IOPs of the Veluwe lakes are derived from multi-spectral, ocean color and hyperspectral airborne data. Inversion-uncertainties of the derived IOPs were also estimated using a standard nonlinear regression technique. The study shows that inversionuncertainties of remote sensing derived IOPs are proportional to water turbidity.
Remote Sensing, Dec 1, 2018
The seasonal variability of sea surface salinity anomalies (SSSAs) in the Indian Ocean is investi... more The seasonal variability of sea surface salinity anomalies (SSSAs) in the Indian Ocean is investigated for its role in the South Asian Summer Monsoon. We have observed an elongated spatial-feature of the positive SSSAs in the southwestern Indian Ocean before the onset of the South Asian Summer Monsoon (SASM) by using both the Aquarius satellite and the Argo float datasets. The maximum variable areas of SSSAs in the Indian Ocean are along (60 • E-80 • E) and symmetrical to the equator, divided into the southern and northern parts. Further, we have found that the annual variability of SSSAs changes earlier than that of sea surface temperature anomalies (SSTAs) in the corresponding areas, due to the change of wind stress and freshwater flux. The change of barrier layer thickness (BLT) anomalies is in phase with that of SSSAs in the southwestern Indian Ocean, which helps to sustain the warming water by prohibiting upwelling. Due to the time delay of SSSAs change between the northern and southern parts, SSSAs, therefore, take part in the seasonal process of the SASM via promoting the SSTAs gradient for the cross-equator currents.
Remote Sensing of Environment, Mar 1, 2016
The 2SeaColor model (Salama and Verhoef, 2015) was proposed to analytically retrieve the diffuse ... more The 2SeaColor model (Salama and Verhoef, 2015) was proposed to analytically retrieve the diffuse attenuation coefficient (K d) from remote sensing reflectance (R rs), but its parameterization was based on approximations and subjected to large uncertainties. In this study, we present an improvement on the parametrization equations in the inverse scheme of the 2Seacolor model. The improved model is then validated with three in-situ datasets and compared with the Zhang model (Zhang and Fell, 2007) and the Lee model (Lee et al., 2005a). Validation with radiometric data shows that the 2SeaColor model provides the best estimates of K d for the full range of observations, with the largest determination coefficient (R 2 = 0.935) and the smallest root mean squared error (RMSE = 0.078 m-1). For clear waters, where K d (490) < 0.2, the Zhang model provides the most accurate K d estimations, but results from the Lee model and the 2SeaColor are rather comparable. For turbid waters, where K d (490) > 0.2 m-1 , the 2SeaColor model is found to be
During the Eagle 2006 campaign intensive in-situ and air/space borne measurements were carried ou... more During the Eagle 2006 campaign intensive in-situ and air/space borne measurements were carried out over the Wolderwijd and Veluwemeer natural waters in the Netherlands. In this paper, we modify the GSM semi-analytical inversion model for these lakes to derive inherent optical properties (IOPs) and their spectral dependencies from air and space borne data. Uncertainties of the derived IOPs are estimated using a nonlinear regression technique. The modified model succeeded in deriving accurate estimates of IOPs with R 2 higher than 0.9 and RMSE values equal to 0.12 and 0.05 for absorption and scattering coefficients, respectively. Finally, we show that the uncertainty of derived absorption coefficients is slightly independent of absorption's magnitude. While the uncertainty of all derived IOPs increases with water turbidity.
Earth System Science Data, Apr 27, 2023
Spread across Twente and its neighbouring regions in the east of the Netherlands, a network of 20... more Spread across Twente and its neighbouring regions in the east of the Netherlands, a network of 20 profile soil moisture and temperature (5, 10, 20, 40, and 80 cm depths) monitoring stations was established in 2009. Field campaigns have been conducted covering the growing seasons of 2009, 2015, 2016, and 2017, during which soil sampling rings and handheld probes were used to measure the top 5 cm volumetric soil moisture content (VSM) of 28 fields near 12 monitoring stations. In this paper, we describe the design of the monitoring network and the field campaigns, adopted instrumentation, experimental setup, field sampling strategies, and the development of sensor calibration functions. Maintenance and quality control procedures and issues specific to the Twente network are discussed. Moreover, we provide an overview of open third-party datasets (i.e. land cover/use, soil information, elevation, groundwater, and meteorological observations) that can support the use and analysis of the Twente soil moisture and temperature datasets beyond the scope of this contribution. An indication for the spatial representativeness of the permanent monitoring stations is provided through comparisons of the 5 cm station measurements with the top 5 cm field-averaged VSM derived from the field campaign measurements. The results reveal in general reasonable agreements and root mean squared errors that are dominated by underestimations of the field-averaged VSM, which is particularly apparent for the grass fields and is strong after heavy rain. Further, we discuss the prospects the datasets offer to investigate (i) the reliability of soil moisture references that serve the development and validation of soil moisture products, and (ii) the water and energy exchanges across the groundwater-vadose-zone-atmosphere continuum within a lowland environment in a changing climate. The datasets discussed are publicly available at https://doi.org/10.17026/dans-znj-wyg5 (Van der Velde et al., 2022).
Frontiers in Marine Science, Jul 17, 2023
Turbid coastal plumes carry sediments, nutrients, and pollutants. Satellite remote sensing is an ... more Turbid coastal plumes carry sediments, nutrients, and pollutants. Satellite remote sensing is an effective tool for studying water quality parameters in these turbid plumes while covering a wide range of hydrological and meteorological conditions. However, determining boundaries of turbid coastal plumes poses a challenge. Traditionally, thresholds are the approach of choice for plume detection as they are simple to implement and offer fast processing (especially important for large datasets). However, thresholds are site-specific and need to be readjusted for different datasets or when meteorological and hydrodynamical conditions differ. This study compares state-of-the-art threshold approaches with a novel algorithm (PLUMES) for detecting turbid coastal plumes from satellite remote sensing, tested for Patos Lagoon, Brazil. PLUMES is a semi-supervised, and spatially explicit algorithm, and does not assume a unique plume boundary. Results show that the thresholds and PLUMES approach each provide advantages and limitations. Compared with thresholds, the PLUMES algorithm can differentiate both low or high turbidity plumes from the ambient background waters and limits detection of coastal resuspension while automatically retrieving metrics of detected plumes (e.g., area, mean intensity, core location). The study highlights the potential of the PLUMES algorithm for detecting turbid coastal plumes from satellite remote sensing products, which can have significantly positive implications for coastal management. However, PLUMES, despite its demonstrated effectiveness in this study, has not yet been applied to other study sites.
Remote Sensing, Jan 23, 2023
This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY
EAGLE2006-an intensive field campaign for the advances in land surface hydrometeorological proces... more EAGLE2006-an intensive field campaign for the advances in land surface hydrometeorological processes-was carried out in the Netherlands from 8 to 18 June 2006, involving 16 institutions with in total 67 people from 16 different countries. In addition to the acquisition of multi-angle and multi-sensor satellite data, several airborne instruments-an optical imaging sensor, an imaging microwave radiometer, and a flux airplane-were deployed and extensive ground measurements were conducted over one grassland site at Cabauw and two forest sites at Loobos and Speulderbos in the central part of the Netherlands. The generated data set is both unique and urgently needed for the development and validation of models and inversion algorithms for quantitative land surface parameter estimation and land surface hydrometeorological process studies. EAGLE2006 was led by the Department of Water Resources of the International Institute for Geo-Information Science and Earth Observation (ITC) and originated from the combination of a number of initiatives supported by different funding agencies. The objectives of the EAGLE2006 campaign were closely related to the HESSD
IOP Conference Series: Earth and Environmental Science
Water in coastal and estuary areas needs to be investigated as human activities is allegedly decr... more Water in coastal and estuary areas needs to be investigated as human activities is allegedly decrease their quality. This has led to optical remote sensing for mapping optical water quality using empirical and semi-analytical approaches. Therefore, this study aims to estimate the Total Suspended Matter (TSM) concentration from Medium Resolution Imaging Spectrometer (MERIS) data using a spectral unmixing approach combined with a radiative transfer model. This approach was implemented in the equatorial tropical coastal water, the Berau estuary, Indonesia, by generating a look-up table (LUT) of top-of-atmosphere radiance spectra through the coupled forward models, and the endmembers were selected from the LUT. The spectral unmixing algorithm was employed to the MERIS data for decomposing the image into haze and sediment components. The data were then transformed into images of a constant haze level corresponding to 50 km visibility, and the atmospheric correction was applied. Furthermo...
EGU General Assembly Conference Abstracts, Apr 1, 2019
This paper investigates the performance of MERIS reduced resolution data to monitor water quality... more This paper investigates the performance of MERIS reduced resolution data to monitor water quality parameters in the Berau estuary waters, Indonesia. Total Suspended Matter (TSM) and Chlorophyll-a (Chl-a) concentration were derived from MERIS data using three different algorithms for coastal waters: standard global processor (MERIS L2), C2R and FUB. The outcomes were compared to in situ measurements collected in 2007. MERIS data processed with C2R gave the best retrieval of Chl-a, while MERIS L2 performed *the best for TSM retrieval, but large deviations from in situ data were observed, pointing at inversion problems over these tropical waters for all standard processors. Nevertheless, MERIS can be of use for monitoring equatorial coastal waters like the Berau estuary and reef system.
IGARSS 2018 - 2018 IEEE International Geoscience and Remote Sensing Symposium, 2018
In this study, the effect of tide on the variation of concentrations of Chlorophyll-a (Chla) and ... more In this study, the effect of tide on the variation of concentrations of Chlorophyll-a (Chla) and Suspended Particulate Matters (SPM), retrieved from a complete dataset of diurnal close-range hyperspectral observations recorded at the NIOZ jetty station (NJS) located at the Marsdiep inlet in the Dutch part of the Wadden Sea, was evaluated. The two-stream radiative transfer model 2SeaColor was inverted to retrieve Chla and SPM concentrations per each hyperspectral observation of the quality-controlled dataset. Concurrently with these diurnal observations, tidal information was obtained from the Den Helder station located at 3.7 km from the NJS. From the performed analysis and evaluation of this study, we concluded that the tide has little observable effects on the diurnal changes of SPM concentration at the NJS located in the Dutch part of the Wadden Sea. The results of this evaluation and the favorable location of the NJS, which is not influenced by the tidal phase, will contribute t...
In book: Scientific Research, New Technologies and Applications Vol. 1Publisher: BP International, 2024
Smartphones, although not empowered as water quality sensing devices, can be used to obtain spect... more Smartphones, although not empowered as water quality sensing devices, can be used to obtain spectral information about our water quality through their enhanced capability to capture images and process using applications (APPs) developed to work within given colour spaces. As the focus of this study, models were developed through two colour spaces used by existing smartphone APPs; RGB colour space by HydroColor and XYZ colour space by Citclops (now called EyeOnWater). For each colour space, a single band semi-analytical model and a logarithmic model were developed and evaluated to estimate turbidity and the concentration of suspended particulate materials (SPM) using smartphone images and validated with laboratory measurements. Although the two-colour spaces used in this research are different, they can be converted from one colour space to another. The models developed from the RGB colour space was suitable for a wider range of water bodies compared to the original models used by HydroColor APP. The XYZ colour space on conversion were also used to estimate turbidity and SPM compared to its original Citclops APP that estimated colour. Comparatively, the logarithmic models did well in the estimation of turbidity and SPM through the RGB and XYZ colour space with R2 ranging from 0.63 to 0.90 and RMSE from 5.86 to 20.18, to the semi-analytical model with R2 from 0.45 to 0.78 and RMSE from 0.83 to 27.25. In the broader context of water quality monitoring, these findings underscore the viability of smartphones in democratizing environmental data collection. The user-friendly XYZ colour space, requiring only water surface images, positions smartphone APPs as powerful tools for citizen engagement in water quality monitoring initiatives. This research contributes to advancing accessible and efficient methods for environmental monitoring, fostering a more citizen participatory approach towards safeguarding water resources, and addressing a novel approach to real-time water quality monitoring and mapping using widely accessible technology-smartphones.