Assessment of Polymer Atmospheric Correction Algorithm for Hyperspectral Remote Sensing Imagery over Coastal Waters

Spaceborne imaging spectroscopy, also called hyperspectral remote sensing, has shown huge potential to improve current water colour retrievals and, thereby, the monitoring of inland and coastal water ecosystems. However, the quality of water colour retrievals strongly depends on successful removal of the atmospheric/surface contributions to the radiance measured by satellite sensors. Atmospheric correction (AC) algorithms are specially designed to handle these effects, but are challenged by the hundreds of narrow spectral bands obtained by hyperspectral sensors. In this paper, we investigate the performance of Polymer AC for hyperspectral remote sensing over coastal waters. Polymer is, in nature, a hyperspectral algorithm that has been mostly applied to multispectral satellite data to date. Polymer was applied to data from the Hyperspectral Imager for the Coastal Ocean (HICO), validated against in situ multispectral (AERONET-OC) and hyperspectral radiometric measurements, and its performance was compared against that of the hyperspectral version of NASA’s standard AC algorithm, L2gen. The match-up analysis demonstrated very good performance of Polymer in the green spectral region. The mean absolute percentage difference across all the visible bands varied between 16% (green spectral region) and 66% (red spectral region). Compared with L2gen, Polymer remote sensing reflectances presented lower uncertainties, greater data coverage, and higher spectral similarity to in situ measurements. These results demonstrate the potential of Polymer to perform AC on hyperspectral satellite data over coastal waters, thus supporting its application in current and future hyperspectral satellite missions.

Citizen Scientists Contribute to Real-Time Monitoring of Lake Water Quality Using 3D Printed Mini Secchi Disks

Citizen science aims to mobilise the general public, motivated by curiosity, to collect scientific data and contribute to the advancement of scientific knowledge. In this article, we describe a citizen science network that has been developed to assess the water quality in a 100 km long tropical lake-estuarine system (Vembanad Lake), which directly or indirectly influences the livelihood of around 1.6 million people. Deterioration of water quality in the lake has resulted in frequent outbreaks of water-associated diseases, leading to morbidity and occasionally, to mortality. Water colour and clarity are easily measurable and can be used to study water quality. Continuous observations on relevant spatial and temporal scales can be used to generate maps of water colour and clarity for identifying areas that are turbid or eutrophic. A network of citizen scientists was established with the support of students from 16 colleges affiliated with three universities of Kerala (India) and research institutions, and stakeholders such as houseboat owners, non-government organisations (NGOs), regular commuters, inland fishermen, and others residing in the vicinity of Vembanad Lake and keen to contribute. Mini Secchi disks, with Forel-Ule colour scale stickers, were used to measure the colour and clarity of the water. A mobile application, named “TurbAqua,” was developed for easy transmission of data in near-real time. In-situ data from scientists were used to check the quality of a subset of the citizen observations. We highlight the major economic benefits from the citizen network, with stakeholders voluntarily monitoring water quality in the lake at low cost, and the increased potential for sustainable monitoring in the long term. The data can be used to validate satellite products of water quality and can provide scientific information on natural or anthropogenic events impacting the lake. Citizens provided with scientific tools can make their own judgement on the quality of water that they use, helping toward Sustainable Development Goal 6 of clean water. The study highlights potential for world-wide application of similar citizen-science initiatives, using simple tools for generating long-term time series data sets, which may also help monitor climate change.

Remote Sensing-Based Analysis of Spatial and Temporal Water Colour Variations in Baiyangdian Lake after the Establishment of the Xiong’an New Area

The Forel-Ule Index (FUI) is an important parameter that can be calculated from optical remote sensing data to assess water quality based on water colour. Using Sentinel-2 images from April to November within the 2016–2020 period coupled with the Google Earth Engine Platform, we calculated FUI to analyse the spatial distribution, seasonal variations, and inter-annual variations of water colour in Baiyangdian Lake in the Xiong’an New Area established on 1 April 2017. The lake was divided into seven sub-regions, A–G; subsequently, high and low FUI values were observed in the south and north, respectively. Additionally, the mean FUI values of G and F zones in the south were 11.9 and 12.7, respectively, whereas those for the A, B, C, D, and E zones in the north were 10.5, 9.8, 10.4, 11.1, 11.2, respectively. The seasonal variations in the Baiyangdian Lake and seven sub-regions were consistent, with turbid water in spring and autumn, and clear water in summer. Inter-annual variations analyses for 2016–2020 indicated that the zone of A became progressively turbid, whereas the B, C, D, E, F, and G zones exhibited slow and gradually decreasing trends. Our findings suggest that the overall water quality of Baiyangdian Lake may be better, which may be related to the governance policies of the region.

Citizen Science Tools Reveal Changes in Estuarine Water Quality Following Demolition of Buildings

Turbidity and water colour are two easily measurable properties used to monitor pollution. Here, we highlight the utility of a low-cost device—3D printed, hand-held Mini Secchi disk (3DMSD) with Forel-Ule (FU) colour scale sticker on its outer casing—in combination with a mobile phone application (‘TurbAqua’) that was provided to laymen for assessing the water quality of a shallow lake region after demolition of four high-rise buildings on the shores of the lake. The demolition of the buildings in January 2020 on the banks of a tropical estuary—Vembanad Lake (a Ramsar site) in southern India—for violation of Indian Coastal Regulation Zone norms created public uproar, owing to the consequences of subsequent air and water pollution. Measurements of Secchi depth and water colour using the 3DMSD along with measurements of other important water quality variables such as temperature, salinity, pH, and dissolved oxygen (DO) using portable instruments were taken for a duration of five weeks after the demolition to assess the changes in water quality. Paired t-test analyses of variations in water quality variables between the second week of demolition and consecutive weeks up to the fifth week showed that there were significant increases in pH, dissolved oxygen, and Secchi depth over time, i.e., the impact of demolition waste on the Vembanad Lake water quality was found to be relatively short-lived, with water clarity, colour, and DO returning to levels typical of that period of year within 4–5 weeks. With increasing duration after demolition, there was a general decrease in the FU colour index to 17 at most stations, but it did not drop to 15 or below, i.e., towards green or blue colour indicating clearer waters, during the sampling period. There was no significant change in salinity from the second week to the fifth week after demolition, suggesting little influence of other factors (e.g., precipitation or changes in tidal currents) on the inferred impact of demolition waste. Comparison with pre-demolition conditions in the previous year (2019) showed that the relative changes in DO, Secchi depth, and pH were very high in 2020, clearly depicting the impact of demolition waste on the water quality of the lake. Match-ups of the turbidity of the water column immediately before and after the demolition using Sentinel 2 data were in good agreement with the in situ data collected. Our study highlights the power of citizen science tools in monitoring lakes and managing water resources and articulates how these activities provide support to Sustainable Development Goal (SDG) targets on Health (Goal 3), Water quality (Goal 6), and Life under the water (Goal 14).

A dataset of remote-sensed Forel-Ule Index for global inland waters during 2000–2018

Water colour is the result of its constituents and their interactions with solar irradiance; this forms the basis for water quality monitoring using optical remote sensing data. The Forel-Ule Index (FUI) is a useful comprehensive indicator to show the water colour variability and water quality change in both inland waters and oceans. In recent decades, lakes around the world have experienced dramatic changes in water quality under pressure from both climate change and anthropogenic activities. However, acquiring consistent water colour products for global lakes has been a challenge. In this paper we present the first time series FUI dataset for large global lakes from 2000–2018 based on MODIS observations. This dataset provides significant information on spatial and temporal changes of water colour for global large lakes during the past 19 years. It will be valuable to studies in search of the drivers of global and regional lake colour change, and the interaction mechanisms between water colour, hydrological factors, climate change, and anthropogenic activities.

Testing of pilot 2 m3 exposure chamber for formation of brochantite based patina on copper and copper alloys – objects of practical dimensions

Formation of natural patina on copper and copper alloys objects takes tens of years. There are solutions for patination, which are used in restorers’ practice. However, these artificial patinas are usually based on nitrates, carbonates or chlorides. Patina based on brochantite is the most stable phase under atmospheric conditions. This type of patina was successfully formed in laboratory in a small exposure chamber with higher content of SO2. This work is next step of the experiment to make this method become more practicable. It started with construction 2 m3 exposure chamber and simulation of ideal conditions for patination process. The length of drying phase, homogeneity of conditions, pH of feeding water, colour of patina, placement of samples and final appearance were observed. The chamber construction allows to achieve ideal pH value of feeding water, samples surface became dry during the ventilation and temperature during condensation was stable at 40 °C. These conditions are ideal for patination process.

Modelling Water Colour Characteristics in an Optically Complex Nearshore Environment in the Baltic Sea; Quantitative Interpretation of the Forel-Ule Scale and Algorithms for the Remote Estimation of Seawater Composition

The paper presents the modelling results of selected characteristics of water-leaving light in an optically complex nearshore marine environment. The modelled quantities include the spectra of the remote-sensing reflectance Rrs(λ) and the hue angle α, which quantitatively describes the colour of water visible to the unaided human eye. Based on the latter value, it is also possible to match water-leaving light spectra to classes on the traditional Forel-Ule water colour scale. We applied a simple model that assumes that seawater is made up of chemically pure water and three types of additional optically significant components: particulate organic matter (POM) (which includes living phytoplankton), particulate inorganic matter (PIM), and chromophoric dissolved organic matter (CDOM). We also utilised the specific inherent optical properties (SIOPs) of these components, determined from measurements made at a nearshore location on the Gulf of Gdańsk. To a first approximation, the simple model assumes that the Rrs spectrum can be described by a simple function of the ratio of the light backscattering coefficient to the sum of the light absorption and backscattering coefficients (u = bb/(a + bb)). The model calculations illustrate the complexity of possible relationships between the seawater composition and the optical characteristics of an environment in which the concentrations of individual optically significant components may be mutually uncorrelated. The calculations permit a quantitative interpretation of the Forel-Ule scale. The following parameters were determined for the several classes on this scale: typical spectral shapes of the u ratio, possible ranges of the total light absorption coefficient in the blue band (a(440)), as well as upper limits for concentrations of total and organic and inorganic fractions of suspended particles (SPM, POM and PIM concentrations). The paper gives examples of practical algorithms that, based on a given Rrs spectrum or some of its features, and using lookup tables containing the modelling results, enable to estimate the approximate composition of seawater.

Cztery wczesne wizerunki Chrystusa Miłosiernego: rysunek S. Kreduszyńskiego, fresk Felicjana Szczęsnego Kowarskiego w Hołubli, obrazy Henryka Uziembły w Lądzie i Jana Wałacha w Czerwińsku

Wizerunek Chrystusa Miłosiernego jest dzisiaj znany i propagowany w dwóch wersjach malarskich. Pierwsza, to obraz namalowany w Wilnie w 1934 przez Eugeniusza Kazimirowskiego pod kierunkiem św. Faustyny Kowalskiej, która udzielała malarzowi szczegółowych wskazówek odnośnie do wyglądu powstającego wizerunku Chrystusa. Druga, bardziej znana wersja, to obraz Jezusa Miłosiernego Adolfa Hyły, namalowany w 1944 r. do kaplicy Zgromadzenia Matki Bożej Miłosierdzia w Krakowie-Łagiewnikach. Procesowi kształtowania się kultu Miłosierdzia Bożego, zwłaszcza w jego początkach podczas II wojny światowej i bezpośrednio po niej, towarzyszyło wiele przedstawień Chrystusa Miłosiernego. Przedstawienia te bardzo często odbiegały od wzorcowego wizerunku opisanego przez św. siostrę Faustynę Kowalską i obrazu namalowanego według jej wskazówek przez Kazimirowskiego. W tym opracowaniu zostały zaprezentowane cztery wczesne przykłady ilustracji wizerunku Chrystusa Miłosiernego, związane z rodzącym się kultem Miłosierdzia Bożego i dokumentujące proces kształtowania się ikonografii tematu. Rysunek S. Kreduszyńskiego (il. 1) i akwarela Aleksandra Maja (il. 2) dokumentują kult wizerunku Jezusa Miłosiernego podczas II wojny światowej, a zwłaszcza w czasie Powstania Warszawskiego. Świadectwem popularności wizerunku Jezusa Miłosiernego w czasie wojny jest też fresk Felicjana Szczęsnego-Kowarskiego w kościele parafialnym w Hołubli z 1943 r. (il. 4, 5). Obraz krakowskiego malarza Henryka Uziembły z 1942 r., obecnie w kościele parafialnym w Lądzie (il. 6), jest pierwszym przedstawieniem Chrystusa Miłosiernego na tle pejzażu, wyraźnie odbiegającym od wizji siostry Faustyny zilustrowanej w obrazie Kazimirowskiego. Na obrazie Uziembły wzorował się Adolf Hyła malując w 1944 r. obraz dla sióstr w Krakowie-Łagiewnikach (il. 7). W 1952 r. malarz dokonał korekty obrazu, zamalowując pejzażowe tło. Obraz Jana Wałacha, namalowany w 1952 r. do kaplicy salezjańskiego nowicjatu w Czerwińsku, ukazuje Chrystusa Miłosiernego unoszącego się nad światem (il. 8). W takiej postaci obraz nawiązuje do wizji jaką św. siostra Faustyna otrzymała w 1935 r. podczas nabożeństwa przy Ostrej Bramie w Wilnie, gdy po raz pierwszy został publicznie ukazany obraz Chrystusa Miłosiernego. Four Early Effigies of Merciful Jesus: drawing by S. Kreduszyński, fresco by Felicjan Szczęsny Kowarski in Hołubla, painting by Henryk Uziembło in Ląd, and that by Jan Wałach in Czerwińsk. The effigy of Merciful Jesus, epitomizing Divine Mercy, is today known and promoted in two painterly versions. The first was that executed in Vilnius in 1934 by Eugeniusz Kazimirowski under the guidance of St Faustina Kowalska, who gave the painter detailed information on the appearance of the effigy while it was being created. The second, a more popular version, is the painting of Merciful Jesus by Adolf Hyła executed in 1944 for the chapel of the Congregation of the Sisters of Our Lady of Mercy at Cracow-Łagiewniki. The process of the formation of the cult of Divine Mercy, particularly at its early stage, during WW II and immediately afterwards, was accompanied by numerous effigies of Merciful Jesus, some of them often distanced from the model described by St Sister Faustina Kowalska and the work painted under her guidance by Kazimirowski. The study presents four early examples of the effigy of Merciful Jesus related to the emerging cult of Divine Mercy and documenting the process of the topic’s iconography formation. Kreduszyński’s drawing (Fig.1) and Maj’s water-colour (Fig. 2) are records of the cult of Divine Mercy during WW II, and particularly during the Warsaw Uprising. The popularity of the effigy of Merciful Jesus during the war is testified by Felicjan Szczęsny-Kowarski’s 1943 fresco in the Parish Church at Hołubla (Figs. 4,5). The 1942 work of the Cracow painter Henryk Uziembło, currently in the Ląd Parish Church (Fig. 6), is the first effigy of Merciful Jesus against landscape, clearly distant from the vision of Sister Faustina illustrated in Kazimirowski’s painting. It was Uziembło’s work that served as the model for Adolf Hyła who executed the effigy for the Cracow-Łagiewniki Sisters in 1944 (Fig. 7). Painting over the landscaped background, the artist corrected his work in 1952. In turn, Jan Wałach’s 1952 painting for the Salesian novitiate chapel in Czerwińsk shows Merciful Jesus rising above the world (Fig. 8). In this form, it echoes the vision St Sister Faustina had in 1935 during the Mass at the Vilnius Gate of Dawn when the effigy of Merciful Jesus was first presented to the public.

Long term brownification process at the Lammi LTER area in Finland

<p>Browning of surface waters due to increased terrestrial loading of organic carbon is observed in boreal regions. It is explained by large scale changes in ecosystems, including decrease in sulphur deposition that affects soil organic matter solubility, increase in temperature that stimulates export of dissolved organic carbon (DOC) from organic soils, and increase in precipitation and thus runoff. Land use changes and forestry measures are also observed to be one reason for increased transport of DOC. The effects of brownification extend to ecosystem services like water purification, but also freshwater productivity through limiting light penetration and creating more stable thermal stratification. The research question at the Lammi LTER area (Southern Boreal Aquatic and Terrestrial Long-Term Ecological Research Area) was brownification of the lake Pääjärvi. We studied both past trends of organic carbon loading from catchments and water colour in the lake based on observations since early 1990’s. We also made simulations of loading for future climate by the physical Persist and INCA models. DOC concentration in the lake was simulated by the physical MyLake model. Simulated DOC concentration was transformed to water colour and light climate of the lake by empirical equations to study the influence on macrophytes (as an indicator of the ecosystem state). In future growing depths might decrease from 2 m to 1.2 m corresponding to observed shift from reference lakes to impacted lakes. Brownification was driven mainly by the change in climate and decay of organic matter in soil, with smaller impact of land use change on organic soil types. Decrease in sulphur deposition had only minor effect on brownification.</p>