Browsing by Author "Pahlevan, Nima"

Now showing 1 - 5 of 5
  • Thumbnail Image
    Item
    Advancing cyanobacteria biomass estimation from hyperspectral observations: Demonstrations with HICO and PRISMA imagery
    (Elsevier, 2021-12) O'Shea, Ryan E.; Pahlevan, Nima; Smith, Brandon; Bresciani, Mariano; Egerton, Todd; Giardino, Claudia; Li, Lin; Moore, Tim; Ruiz-Verdu, Antonio; Ruberg, Steve; Simis, Stefan G. H.; Stumpf, Richard; Vaičiūtė, Diana; Earth Sciences, School of Science
    Retrieval of the phycocyanin concentration (PC), a characteristic pigment of, and proxy for, cyanobacteria biomass, from hyperspectral satellite remote sensing measurements is challenging due to uncertainties in the remote sensing reflectance (∆Rrs) resulting from atmospheric correction and instrument radiometric noise. Although several individual algorithms have been proven to capture local variations in cyanobacteria biomass in specific regions, their performance has not been assessed on hyperspectral images from satellite sensors. Our work leverages a machine-learning model, Mixture Density Networks (MDNs), trained on a large (N = 939) dataset of collocated in situ chlorophyll-a concentrations (Chla), PCs, and remote sensing reflectance (Rrs) measurements to estimate PC from all relevant spectral bands. The performance of the developed model is demonstrated via PC maps produced from select images of the Hyperspectral Imager for the Coastal Ocean (HICO) and Italian Space Agency's PRecursore IperSpettrale della Missione Applicativa (PRISMA) using a matchup dataset. As input to the MDN, we incorporate a combination of widely used band ratios (BRs) and line heights (LHs) taken from existing multispectral algorithms, that have been proven for both Chla and PC estimation, as well as novel BRs and LHs to increase the overall cyanobacteria biomass estimation accuracy and reduce the sensitivity to ∆Rrs. When trained on a random half of the dataset, the MDN achieves uncertainties of 44.3%, which is less than half of the uncertainties of all viable optimized multispectral PC algorithms. The MDN is notably better than multispectral algorithms at preventing overestimation on low (<10 mg m−3) PC. Visibly, HICO and PRISMA PC maps show the wider dynamic range that can be represented by the MDN. The available in situ and satellite-derived Rrs matchups and measured in situ PC demonstrate the robustness of the MDN for estimating low (<10 mg m−3) PC and the reduced impact of ∆Rrs on medium-to-high in situ PC (>10 mg m−3). According to our extensive assessments, the developed model is anticipated to enable practical PC products from PRISMA and HICO, therefore the model is promising for planned hyperspectral missions, such as the Plankton Aerosol and Cloud Ecosystem (PACE). This advancement will enhance the complementary roles of hyperspectral radiometry from satellite and low-altitude platforms for quantifying and monitoring cyanobacteria harmful algal blooms at both large and local spatial scales.
  • Thumbnail Image
    Item
    Errata to “Impact of Spectral Resolution on Quantifying Cyanobacteria in Lakes and Reservoirs: A Machine-Learning Assessment”
    (IEEE, 2023-08) Zolfaghari, Kiana; Pahlevan, Nima; Binding, Caren; Gurlin, Daniela; Simis, Stefan G. H.; Verdú, Antonio Ruiz; Li, Lin; Crawford, Christopher J.; VanderWoude, Andrea; Errera, Reagan; Zastepa, Arthur; Duguay, Claude R.; Earth and Environmental Sciences, School of Science
    In the above article [1], the references in the following paragraph should be corrected as shown below. This excerpt appears in the first column on page 4 of the above article.
  • Thumbnail Image
    Item
    GLORIA - A globally representative hyperspectral in situ dataset for optical sensing of water quality
    (Nature, 2023-02) Lehmann, Moritz K.; Gurlin, Daniela; Pahlevan, Nima; Alikas, Krista; Conroy, Ted; Anstee, Janet; Balasubramanian, Sundarabalan V.; Barbosa, Cláudio C. F.; Binding, Caren; Bracher, Astrid; Bresciani, Mariano; Burtner, Ashley; Cao, Zhigang; Dekker, Arnold G.; Di Vittorio, Courtney; Drayson, Nathan; Errera, Reagan M.; Fernandez, Virginia; Ficek, Dariusz; Fichot, Cédric G.; Gege, Peter; Giardino, Claudia; Gitelson, Anatoly A.; Greb, Steven R.; Henderson, Hayden; Higa, Hiroto; Rahaghi, Abolfazl Irani; Jamet, Cédric; Jiang, Dalin; Jordan, Thomas; Kangro, Kersti; Kravitz, Jeremy A.; Kristoffersen, Arne S.; Kudela, Raphael; Li, Lin; Ligi, Martin; Loisel, Hubert; Lohrenz, Steven; Ma, Ronghua; Maciel, Daniel A.; Malthus, Tim J.; Matsushita, Bunkei; Matthews, Mark; Minaudo, Camille; Mishra, Deepak R.; Mishra, Sachidananda; Moore, Tim; Moses, Wesley J.; Nguyễn, Hà; Novo, Evlyn M. L. M.; Novoa, Stéfani; Odermatt, Daniel; O'Donnell, David M.; Olmanson, Leif G.; Ondrusek, Michael; Oppelt, Natascha; Ouillon, Sylvain; Filho, Waterloo Pereira; Plattner, Stefan; Ruiz Verdú, Antonio; Salem, Salem I.; Schalles, John F.; Simis, Stefan G. H.; Siswanto, Eko; Smith , Brandon; Somlai-Schweiger, Ian; Soppa, Mariana A.; Spyrakos, Evangelos; Tessin, Elinor; van der Woerd, Hendrik J.; Vander Woude, Andrea; Vandermeulen, Ryan A.; Vantrepotte, Vincent; Wernand, Marcel R.; Werther, Mortimer; Young, Kyana; Yue, Linwei; Earth and Environmental Sciences, School of Science
    The development of algorithms for remote sensing of water quality (RSWQ) requires a large amount of in situ data to account for the bio-geo-optical diversity of inland and coastal waters. The GLObal Reflectance community dataset for Imaging and optical sensing of Aquatic environments (GLORIA) includes 7,572 curated hyperspectral remote sensing reflectance measurements at 1 nm intervals within the 350 to 900 nm wavelength range. In addition, at least one co-located water quality measurement of chlorophyll a, total suspended solids, absorption by dissolved substances, and Secchi depth, is provided. The data were contributed by researchers affiliated with 59 institutions worldwide and come from 450 different water bodies, making GLORIA the de-facto state of knowledge of in situ coastal and inland aquatic optical diversity. Each measurement is documented with comprehensive methodological details, allowing users to evaluate fitness-for-purpose, and providing a reference for practitioners planning similar measurements. We provide open and free access to this dataset with the goal of enabling scientific and technological advancement towards operational regional and global RSWQ monitoring.
  • Thumbnail Image
    Item
    Hyperspectral retrievals of phytoplankton absorption and chlorophyll-a in inland and nearshore coastal waters
    (Elsevier, 2021-02) Pahlevan, Nima; Smith, Brandon; Binding, Caren; Gurlin, Daniela; Li, Lin; Bresciani, Mariano; Giardino, Claudia; Earth Sciences, School of Science
    Following more than two decades of research and developments made possible through various proof-of-concept hyperspectral remote sensing missions, it has been anticipated that hyperspectral imaging would enhance the accuracy of remotely sensed in-water products. This study investigates such expected improvements and demonstrates the utility of hyperspectral radiometric measurements for the retrieval of near-surface phytoplankton properties1, i.e., phytoplankton absorption spectra (aph) and biomass evaluated through examining the concentration of chlorophyll-a (Chla). Using hyperspectral data (409–800 nm at ~5 nm resolution) and a class of neural networks known as Mixture Density Networks (MDN) (Pahlevan et al., 2020), we show that the median error in aph retrievals is reduced two-to-three times (N = 722) compared to that from heritage ocean color algorithms. The median error associated with our aph retrieval across all the visible bands varies between 20 and 30%. Similarly, Chla retrievals exhibit significant improvements (i.e., more than two times; N = 1902), with respect to existing algorithms that rely on select spectral bands. Using an independent matchup dataset acquired near-concurrently with the acquisition of the Hyperspectral Imager for the Coastal Ocean (HICO) images, the models are found to perform well, but at reduced levels due to uncertainties in the atmospheric correction. The mapped spatial distribution of Chla maps and aph spectra for selected HICO swaths further solidify MDNs as promising machine-learning models that have the potential to generate highly accurate aquatic remote sensing products in inland and coastal waters. For aph retrieval to improve further, two immediate research avenues are recommended: a) the network architecture requires additional optimization to enable a simultaneous retrieval of multiple in-water parameters (e.g., aph, Chla, absorption by colored dissolved organic matter), and b) the training dataset should be extended to enhance model generalizability. This feasibility analysis using MDNs provides strong evidence that high-quality, global hyperspectral data will open new pathways toward a better understanding of biodiversity in aquatic ecosystems.
  • Thumbnail Image
    Item
    Impact of Spectral Resolution on Quantifying Cyanobacteria in Lakes and Reservoirs: A Machine-Learning Assessment
    (IEEE, 2022-10) Zolfaghari, Kiana; Pahlevan, Nima; Binding, Caren; Gurlin, Daniela; Simis, Stefan G. H.; Ruiz Verdú, Antonio; Li, Lin; Crawford, Christopher J.; VanderWoude, Andrea; Errera, Reagan; Zastepa, Arthur; Duguay, Claude R.; Earth Sciences, School of Science
    Cyanobacterial harmful algal blooms are an increasing threat to coastal and inland waters. These blooms can be detected using optical radiometers due to the presence of phycocyanin (PC) pigments. The spectral resolution of best-available multispectral sensors limits their ability to diagnostically detect PC in the presence of other photosynthetic pigments. To assess the role of spectral resolution in the determination of PC, a large ( N=905 ) database of colocated in situ radiometric spectra and PC are employed. We first examine the performance of selected widely used machine-learning (ML) models against that of benchmark algorithms for hyperspectral remote sensing reflectance ( Rrs ) spectra resampled to the spectral configuration of the Hyperspectral Imager for the Coastal Ocean (HICO) with a full-width at half-maximum (FWHM) of < 6 nm. Results show that the multilayer perceptron (MLP) neural network applied to HICO spectral configurations (median errors < 65%) outperforms other ML models. This model is subsequently applied to Rrs spectra resampled to the band configuration of existing satellite instruments and of the one proposed for the next Landsat sensor. These results confirm that employing MLP models to estimate PC from hyperspectral data delivers tangible improvements compared with retrievals from multispectral data and benchmark algorithms (with median errors between ∼73 % and 126%) and shows promise for developing a globally applicable cyanobacteria measurement approach.