Wiwin Ambarwulan

Universiteit Twente, Enschede, Overijssel, Netherlands

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Publications (5)3.92 Total impact

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    ABSTRACT: This study presents the application of a semi-empirical approach, based on the Kubelka–Munk (K-M) model, to retrieve the total suspended matter (TSM) concentration of water bodies from ocean colour remote sensing. This approach is validated with in situ data sets compiled from the tropical waters of Berau estuary, Indonesia. Compared to a purely empirical approach, the K-M model provides better results in the retrieval of TSM concentration on both data sets (in situ and Medium Resolution Imaging Spectrometer (MERIS)). In this study, the K-M model was calibrated with in situ measurements of remote-sensing reflectance (Rrs) and TSM concentration. Next, the inverse K-M model was successfully applied to images taken by the MERIS instrument by generating regional maps of TSM concentration. MERIS top-of-atmosphere radiances were atmospherically corrected using the Moderate Spectral Resolution Atmospheric Transmittance (MODTRAN) radiative transfer model. The best correlation between Rrs measured in situ and Rrs MERIS was found to be at a wavelength of 620 nm. The TSM concentrations retrieved using the K-M model showed a lower root mean square error (RMSE), a higher coefficient of determination and a smaller relative error than those retrieved by the purely empirical approach.
    International Journal of Remote Sensing 08/2012; 33(16):4919-4936. · 1.36 Impact Factor
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    ABSTRACT: Specific inherent optical properties (SIOP) of the Berau coastal waters were derived from in situ measurements and inversion of an ocean color model. Field measurements of water-leaving reflectance, total suspended matter (TSM), and chlorophyll a (Chl a) concentrations were carried out during the 2007 dry season. The highest values for SIOP were found in the turbid waters, decreasing in value when moving toward offshore waters. The specific backscattering coefficient of TSM varied by an order of magnitude and ranged from 0.003m2g−1, for clear open ocean waters, to 0.020m2g−1, for turbid waters. On the other hand, the specific absorption coefficient of Chl a was relatively constant over the whole study area and ranged from 0.022m2mg−1, for the turbid shallow estuary waters, to 0.027m2mg−1, for deeper shelf edge ocean waters. The spectral slope of colored dissolved organic matter light absorption was also derived with values ranging from 0.015 to 0.011nm−1. These original derived values of SIOP in the Berau estuary form a corner stone for future estimation of TSM and Chl a concentration from remote sensing data in tropical equatorial waters. KeywordsSubsurface irradiance reflectance-Total suspended matter-Chlorophyll a-Ocean optics-Bio-optical model-Tropical waters
    Hydrobiologia 01/2011; 658(1):197-211. · 1.99 Impact Factor
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    ABSTRACT: This article investigates the performance of MERIS reduced resolution data to monitor water quality parameters in the Berau estuary waters, Indonesia. Total suspended matter (TSM), Chlorophyll-a (Chl-a) concentration and diffuse attenuation coefficient (Kd ) 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. Applying a Kd (490) local algorithm to the MERIS RR data over the study area showed a sufficient good correlation to the in situ measurements (R 2 = 0.77).
    Geocarto International 11/2010; 25(7):525-541. · 0.58 Impact Factor
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    Idham Khalil, C.Mannaerts, W.Ambarwulan
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    ABSTRACT: Regular monitoring of near-shore and open-water parameters for marine management in East Kalimantan waters, Indonesia is still limited. The objective of this research is to determine and interpret the seasonal and spatial variability of sea surface temperature (SST) and Chlorophyll-a concentration (Chl-a) in East Kalimantan waters. A standard MODIS SST split-window algorithm and empirical Chlorophyll-a 0C-3M algorithm were used to generate the Level 2 MODIS SST and Chl-a images. MODIS or Moderate Resolution Imaging Spectroradiometer is a key instrument aboard the Terra and Aqua satellites. From March 2005 to August 2006, the SST and Chl-a were retrieved from the sensor data in East Kalimantan coastal and open-sea waters. In situ measurements from near-shore waters were used to validate the MODIS Level 2 data. A comparison of MODIS with in situ values for SST and Chl-a shows: RMSE=1.21°C, Bias=-3.42, n=121 and RMSE=1.01mg.m-3, Bias=+2.45, n=75, although some anomalies were observed in the retrievals in both datasets. The analysis of seasonal variations indicates that there was low SST variability between wet and dry season. There was also low variability between SST values in near-shore and open-sea waters. However, for both seasons, open-sea SST was paradoxically found to be warmer than the near-shore waters. The Chl-a maps revealed low Chl-a variability between wet and dry season. Different value ranges in Chl-a were found between near-shore waters (1.00-56.00 mg.n-3) and open waters (1.00-4.00 mg.n-3). The Chl-a values retrieved from MODIS for both seasons were higher in near-shore water. The SST and Chl-a in near-shore waters have a low positive interrelationship in wet season. During dry season, the relationship between these two variables varies from positive to negative. This study demonstrated that MODIS Level 2 data from Malaysia Ground Receiving Station (MGRS) can successfully be used to obtain SST and Chl-a in Southeast Asian coastal and open waters.
    Journal of Sustainability Science and Management 01/2009;
  • Wiwin Ambarwulan