Remote estimation of chlorophyll concentration in hyper-eutrophic aquatic systems: Model tuning and accuracy optimization

In this study, semi-analytical algorithms such as two-band and three-band models were used to estimate the chlorophyll-a (Chl-a) concentration in the turbid river using an airborne hyperspectral imagery. In order to select the optimal wavelength band to be used in the empirical equation, surface water was collected at the same time of acquisition of the aerial hyperspectral imagery. The spectral characteristic of the Chl-a, PC, CDOM, NAP, and phytoplankton were analyzed from by collected samples. The concentrations of PC and CDOM which affect the spectral characteristics to Chl-a were low and there was no change over time. So the range of wavelengths was able to broaden than the existing cases. As the result of widening the wavelength band, the two-band and three-band models were found to be higher R2 than the results obtained by using the existing formula. Because the three-band model is more statistical significance than the two-band model, it is more appropriate to estimate the chlorophyll-a concentration in the turbid river. However, the Chl-a concentration of this study was relatively low at 45 mg/m3, and the effect of PC and CDOM also was small. To estimate the correct Chl-a concentration, data such as airborne hyperspectral imagery and water sample need to be accumulated in different years and the correlation between optical properties and concentration should be thoroughly analyzed.

Accurate assessment of phytoplankton chlorophyll-a (chl-a) concentration in turbid waters by means of remote sensing is challenging because of the optical complexity of case 2 waters. We applied a bio-optical model of the form [R–1(λ1) – R–1(λ2)](λ3), where R(λi) is the remote-sensing reflectance at wavelength λi, to estimate chl-a concentration in coastal waters. The objectives of this article are (1) to validate the three-band bio-optical model using a data set collected in coastal waters, (2) to evaluate the extent to which the three-band bio-optical model could be applied to the spectral radiometer (SR) ISI921VF-512T data and the hyperspectral imager (HSI) data on board the Chinese HJ-1A satellite, (3) to evaluate the application prospects of HJ-1A HSI data in case 2 waters chl-a concentration mapping. The three-band model was calibrated using three SR spectral bands (λ1 = 664.9 nm, λ2 = 706.54 nm, and λ3 = 737.33 nm) and three HJ-1A HSI spectral bands (λ1 = 637.725 nm, λ2 = 711.495 nm, and λ3 = 753.750 nm). We assessed the accuracy of chl-a prediction with 21 in situ sample plots. Chl-a predicted by SR data was strongly correlated with observed chl-a (R2 = 0.93, root mean square error (RMSE) = 0.48 mg m–3, coefficient of variation (CV) (RMSE/mean(chl-amea)) = 3.72%). Chl-a predicted by HJ-1A HSI data was also closely correlated with observed chl-a (R2 = 0.78, RMSE = 0.45 mg m–3, CV (RMSE/mean(chl-amea)) = 7.51%). These findings demonstrate that the HJ-1A HSI data are promising for quantitative monitoring of chl-a in coastal case-2 waters.

The theory of phonon-assisted two-photon exeiton transitions is developed from third-order time-dependent perturbation theory. Three different band models are introduced:a) a four-band model corresponding to Loudon’s three-hand model in the case of direct twophoton transitions;b) a two-band model corresponding to that of Mahan for the two-photon transitions case;c) an intermediate (three-band) model which seems to be more convenient for this type of problem. Selection rules are different for the different models. For example, in modela) only δ-excitons are allowed, whilst in modelb)s andd excitons are permitted. In modelc) we find that the selection rules allowp-exciton states only. The symmetry of the phonons which contribute to the transitions for each model, and a group-theoretical analysis of the final exciton symmetry, are given for GaP, Ge and Si. We find that the threeband model is the most favourable for indirect two-photon processes. Numerical calculations, considering the different energy denominators which appear in the expression of the transition rates, show that the three-band model has the largest absorption coefficient, and the twoband model the smallest. This is due to the different matrix elements and energy denominators used for each model.

Remote detection of cyanobacteria through phycocyanin for water supply source using three-band model

Intensity of two-photon excitonic absorption in two-band and three-band models

As the invasion of alien species intensifies, the native salt marsh vegetation, especially the ecosystem of Suaeda salsa (S. salsa), in Chinese coastal wetlands has been severely disrupted, significantly impeding its functionality within coastal wetland ecosystems. Chlorophyll content (Cab) is an important parameter for monitoring the growth and health status of vegetation. However, the remote sensing mechanism of Cab for different phenotypes of green and red vegetation influenced by betacyanin under different water and salt conditions is not clear. Therefore, to further clarify the remote sensing mechanism of S. salsa and improve the generality of Cab prediction for different phenotypes under different water and salt conditions, we designed a growth experiment under different groundwater levels and salt concentrations. This experiment was used to simulate the growth of S. salsa in different habitats in nature and investigate the relationship between their physicochemical parameters, spectra, and environmental stress. We propose using the specific absorption coefficient of betacyanin (Beta) to adjust PROSAIL-D to better fit the spectral characteristics of S. salsa. The relationship between Beta and Cab was utilized to further optimize the simulation accuracy of the PROSAIL-D model in different environments. Feature extraction algorithms, including differential enhancement of two-dimensional correlation spectroscopy (FD-2DCOS) and three-band models, were introduced to construct multiple spectral features for establishing a Cab prediction model for S. salsa. The research results showed that: (1) S. salsa had the best response of Cab and spectra to salinity under a higher groundwater level and showed a gradual reddening trend. (2) The spectral curves simulated by the adjusted PROSAIL-D model were more consistent with the spectral characteristics of S. salsa under different water-salt environments, and the simulation effect could be further optimized by using the relationship between Beta and Cab. (3) The FD-2DCOS analysis method we proposed could highlight the useful spectral information related to Cab better than the original 2DCOS algorithm. The final eight spectral features of (1/R701–1/R540)R540, Mean(D590–600), Mean(D660–670), Mean(D677–685), FDVI_NRG, FDVI_NIR, Skewness (D677–750) and Position(D677–750) had the best response to Cab of S. salsa, and had the least influence on LAI and soil background. (4) The particle swarm optimization random forest regression (PSO-RFR) model based on eight spectral features and adding 70% measured spectral data performed the best in predicting the actual Cab of S. salsa, with an RMSE of 2.326 μg·cm−2. Although further optimization and calibration of the adjusted PROSAIL-D model and Cab prediction model of S. salsa are needed in the future, this study extended its application to S. salsa, a special local salt marsh vegetation, and promoted the development of Cab monitoring of salt marsh vegetation in coastal wetlands.

We present here results that demonstrate the potential of the recently launched Ocean and Land Colour Instrument (OLCI) onboard the satellite Sentinel-3A to deliver accurate estimates of chlorophyll-a (chl-a) concentration in coastal waters using reflectances in the red and near-infrared (NIR) spectral regions. Two-band and three-band NIR-red models that were previously used for data from the MEdium Resolution Imaging Spectrometer (MERIS) were applied to OLCI data from the Sea of Azov and the Taganrog Bay, Russia. Atmospherically corrected reflectance data from OLCI were compared to in situ reflectance data collected concurrently with a field spectrometer. Results show that the default atmospheric correction procedure currently applied to OLCI data performs well in preserving the spectral shape of chl-a-specific reflectance features in the red and NIR regions. Similar to what was achieved with MERIS data, the NIR-red models yield accurate estimates of chl-a concentration, with accuracies on the order of 90%, though the parameters of the NIR-red algorithms based on OLCI data are slightly different from what was obtained with MERIS data. More data, from various geographical locations, need to be analyzed to establish robust NIR-red algorithms for OLCI data.

Physico-Chemical Surveillance Data Obtained for Lake Ontario, 1974 and Their Relationship to Chlorophyll a

Quantitatively relating 13 C/12 C, 2 H/1 H and 18 O/16 O ratios of plant α-cellulose and 2 H/1 H of n-alkanes to environmental conditions and metabolic status should ideally be based on the leaf, the plant organ most sensitive to environmental change. The fact that leaf organic matter is composed of isotopically different heterotrophic and autotrophic components means that it is imperative that one be able to disentangle the relative heterotrophic and autotrophic contributions to leaf organic matter. We tackled this issue by two-dimensional sampling of leaf water and α-cellulose, and specific n-alkanes from greenhouse-grown immature and mature and field-grown mature banana leaves, taking advantage of their large areas and thick waxy layers. Leaf water, α-cellulose and n-alkane isotope ratios were then characterized using elemental analysis isotope ratio mass spectrometry (IRMS) or gas chromatography IRMS. A three-member (heterotrophy, autotrophy and photoheterotrophy) conceptual linear mixing model was then proposed for disentangling the relative contributions of the three trophic modes. We discovered distinct spatial leaf water, α-cellulose and n-alkane isotope ratio patterns that varied with leaf developmental stages. We inferred from the conceptual model that, averaged over the leaf blade, only 20% of α-cellulose in banana leaf is autotrophically laid down in both greenhouse-grown and field-grown banana leaves, while approximately 60% and 100% of n-alkanes are produced autotrophically in greenhouse-grown and field-grown banana leaves, respectively. There exist distinct lateral (edge to midrib) gradients in autotrophic contributions of α-cellulose and n-alkanes. Efforts to establish quantitative isotope-environment relationships should take into account the fact that the evaporative leaf water 18 O and 2 H enrichment signal recorded in autotrophically laid down α-cellulose is significantly diluted by the heterotrophically formed α-cellulose. The δ2 H value of field-grown mature banana leaf n-alkanes is much more sensitive than α-cellulose as a recorder of the growth environment. Quantitative isotope-environment relationship based on greenhouse-grown n-alkane δ2 H values may not be reliable.

Chlorophyll and polyphenols are chemical compound related to parameter quality of green tea. We studied the variation of chlorophyll and polyphenol in the development stage of tea leaves (bud, 1st, 2nd, 3rd, and 4th). Five clones of tea (Camelia sinensis var. sinensis) from Indonesia and a clone from Japan were used in this study. The results showed that total chlorophyll and total polyphenol content in bud between 1.59-2.15 mg/g (db) and 12.24-14.59% respectively. The concentration of chlorophyll increased significantly with developments stage of leaf while total polyphenol tended to decrease with leaf maturity. Pearson Correlation analysis showed that chlorophyll content was negatively correlated (r = -0.83; p = 0.05) with total polyphenol during developmental stage of tea leaves. Results suggests that five clones of tea from Indonesia have similar quality with tea clone from Japan in chlorophyll and polyphenol content. The present study also provides guidelines on application plucking standard to produce high quality of green tea.

Effect of Nile River water quality on algal distribution at Cairo, Egypt

Spatio–temporal variation in Chlorophyll, Nutrients and Primary Productivity of some selected sampling stations in Lagos lagoon were investigated using conventional method from November 2019 to July 2020, in order to compare the result with data from satellite image using MODIS Aqua. Global Positioning Receiver was used to capture the geographic coordinates of the sampling stations. Water sampling was carried out monthly using standard methods during wet and dry seasons. The observed data were subjected to statistical analysis using Microsoft Excel and SPSS version 20. In wet season, the highest mean value for Chlorophyll a (1.15±0.02 µg/L) was recorded in Ofin while the lowest values (0.06±0.01 µg/L) was observed in Okobaba. During the dry season, the highest mean value (0.75±0.10 µg/L) was in Ofin while the lowest mean value (0.27±0.0.08 µg/L) was recorded in Ibeshe. The MODIS satellite variation in chlorophyll-a showed that the highest value of highest recorded value (1.37±0.00 µg/L) was in wet season (Ijede) while the lowest value (0.12±0.01 µg/L) was observed in dry season (Okobaba). The highest transparency value (0.97±0.01 mg/L) was recorded in dry season (Ofin) while the lowest value (0.35±0.25 mg/L) was recorded in wet season (Oworonsoki). The highest mean value of Surface Sea temperature was recorded in the dry season of Apapa (30.28±1.15oC) while the lowest mean value (26.41±1.15oC) was observed in Okobaba in the wet season. The chlorophyll-a concentration analyzed using standard method and MODIS satellite, in both dry and wet seasons in the sampled stations differ greatly from one another in terms of the mean concentration. The primary productivity of Lagos Lagoon was relatively low, with no significant spatial variations between sampling stations. The results of sea surface temperature, transparency and chlorophyll ‘a’ estimation from the MODIS revealed that the values were positively correlated with laboratory result with r2-value of 0.67, 0.80 and 0.77. This indicates that MODIS data and laboratory results generated for Lagos Lagoon were positively related.

SUMMARY. 1. Temporal coherence between pairs of lakes over 7 years was measured for thirty‐seven limnological variables in seven lakes at the North Temperate Lakes Long Term Ecological Research site in Northern Wisconsin. This analysis tested. First, whether lakes more similar in exposure to the atmosphere were more temporally coherent than lakes which differed more in exposure and, second, whether temporal coherence in lakes progressively decreased from variables more directly influenced by climatic factors such as thermal and hydrologic properties, to those chemical and biological properties which may be less directly influenced by climatic factors.2. The lakes were a heterogeneous set in respect to exposure to climatic factors as estimated by the ratio of‘lake area/mean depth’and by other morphometric features, and they also differed in their position in the landscape, fertility and fish assemblages. Limnological variables formed a progression from those expected to respond directly to climatic factors to those which would not. They ranged from water level and temperatures to chemical variables such as pH, calcium concentrations and total dissolved phosphorus to biological variables such as chlorophyll concentrations, invertebrate and fish abundances.3. Coherence was estimated by the correlation between lake pairs for each of the different variables. The mean correlation and the percentage of strong correlations were calculated for each lake pair across all variables, and for each variable across all lake pairs, and both measures of coherence gave similar answers to the questions posed above.4. Temporal coherence between takes was higher for lakes similar in their exposure to climatic factors; mean correlation (r̄) being +0.3 to +0.7 for these lakes and <+0.3 for lakes not similar in exposure. None of the lake pairs had high coherence across all variables.5. Temporal coherence between lakes was greater for limnological variables directly influenced by climatic factors than for variables either indirectly affected by climate or complexly influenced by other types of factors. Water‐level variables had a coherence near 1, r̄=0.9. All biological variables had low coherence, some near r̄=0.0. Chemical variables more likely to be influenced directly by climatic factors appeared to be more coherent than those more influenced by hydrology or biology. Most silica and phosphorus variables had coherences less than r̄=0.15.6. Coherence was not as strongly related to similarity in landscape position as it was to similarity in exposure to climatic factors, and was not jelated to the proximity of the lake pairs or to their similarity in fertility.7. A conceptual model was presented to explain how climatic signals are filtered by the lake's exposure to climatic factors and by terrestrially mediated and in‐lakc processes to reduce the coherence of lake pairs owing to time lags, frequency shifts and complex interference pattems.8. Coherence is an important property to evaluate because it influences how broadly we can extrapolate results from a lake or set of lakes (for example, to a lake district) and because manipulative whole lake experiments often use adjacent lakes as reference lakes to evaluate treatment effects. The low coherence in this set of lakes in general and of individual variables such as chlorophyll concentrations and yellow perch year‐class strength are discussed.9. We found no studies that explicitly addressed interlake coherence; one long‐term study of forest production made it clear that coherence among sites in a landscape will be a function of scale.

High Variability of Phytoplankton Photosynthesis in Response to Environmental Forcing in Oligotrophic Lake Malawi/Nyasa

Advances in remote sensing technologies, especially the increasing application of hyperspectral datasets, provide new opportunities to develop reliable, robust indicators of canopy health for Australian eucalypt forests. Leaf reflectance in the visible and near-infrared wavelengths measured using a hand-held spectroradiometer were compared with foliar damage, leaf morphology, chlorophyll fluorescence and chlorophyll content sampled from eucalypt leaves exhibiting symptoms of canopy dieback. Compact Airborne Spectrographic Imager (CASI-2) imagery was also collected over the crowns and spectral signatures extracted from the 80 cm spatial resolution imagery. Results indicate that a number of spectroradiometer derived indices were significantly correlated with leaf variables. These indices were predominantly those that incorporated the spectral red-edge such as changes in slope, the slope of the lower red-edge, the maximum slope, the inflection wavelength and newly proposed red/green indices which specifically target anthocyanins. Mean leaf chlorophyll content, leaf chlorophyll fluorescence, leaf length to width ratio, and estimated percent leaf with red discoloration were all highly significantly correlated to several CASI-2 derived indices. Overall the research has demonstrated strong relationships between eucalypt leaf spectra and leaf damage and morphometry variables.