Deriving inherent optical properties from classical water color measurements: Forel-Ule index and Secchi disk depth

Wang, Shenglei; Lee, Zhongping; Shang, Shuo; Li, Junsheng; Zhang, Fangfang; Gong, Lin

doi:10.1364/oe.27.007642

Cited by 26 publications

(16 citation statements)

References 55 publications

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“…Turn on the cleaning glass pump 4 Stop motor 3 Operate pump for 15 seconds 5 Turn off the cleaning glass pump 6 Stop the instrument for 5 minutes 7 Turn on the motor to lower the tube 8 Stop motor 10 Turn on the LED 11 Measure light intensity by sensor 12 Turn off the LED 13 Calculate the water clarity based on light intensity algorithm 14 Send data to server 15 Turn on the motor for elevating the tube 2…”

Section: Working Principlementioning

confidence: 99%

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Development of a Solar-Powered IoT-Based Instrument for Automatic Measurement of Water Clarity

Pham

Nguyen

et al. 2020

Sensors

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Water clarity is the most common indicator of water quality. The purpose of the study was to develop an instrument which can automatically measure water clarity in place of manual measurement by Secchi disk. The instrument is suspended by buoys at the water surface and uses solar energy to measure the light intensity of LED bulbs after passing through a water column; the result is then converted to Secchi depth by using a regression function. Measurement data are stored in a cloud server so that mobile users can access via an Internet connection. Three experiments were conducted to examine the instrument performance: (i) to ensure light intensity of the LED bulbs is strong enough to pass through the water column; (ii) to determine the regression relationship between the measured light intensity of the instrument and Secchi depth; and (iii) to evaluate the coefficient of variation (CV) of the measured water clarity when using our instrument and a conventional Secchi disk. Experiment results show that the measured values of light intensity are stable with the average CV = 5.25%. Moreover, although there are slight differences between the Secchi depth measured by our instrument and those measured by Secchi disk, the measurements by our instrument can efficiently replace the measurements by conventional Secchi disk, which can be affected by weather conditions as well as by human subjectivity.

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Section: Working Principlementioning

confidence: 99%

“…There are several methods to measure water clarity. The simplest and most popular method is using Secchi disk [7,8]. The Secchi disk, created in 1865 by Angelo Secchi, is a plain white, circular disk 30 cm in diameter used to measure water clarity in bodies of water.…”

Section: Introductionmentioning

confidence: 99%

Development of a Solar-Powered IoT-Based Instrument for Automatic Measurement of Water Clarity

Pham

Nguyen

et al. 2020

Sensors

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“…These data are available online: http://www.agroambient.gva.es/es/ (accessed on 6 October 2019). SDD was measured with a 30 cm diameter black-and-white disk, which was submerged in the water until it was no longer visible to an observer on the surface [25,26]. Secchi disk depth is inversely proportional to the amount of dissolved and/or particulate matter present in the water column; thus, is a turbidity indicator.…”

Section: Secchi Disk and Suspended Mattermentioning

confidence: 99%

Sentinel 2 Analysis of Turbidity Patterns in a Coastal Lagoon

et al. 2019

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Coastal lagoons are transitional ecosystems with complex spatial and temporal variability. Remote sensing tools are essential for monitoring and unveiling their variability. Turbidity is a water quality parameter used for studying eutrophication and sediment transport. The objective of this research is to analyze the monthly turbidity pattern in a shallow coastal lagoon along two years with different precipitation regimes. The selected study area is the Albufera de Valencia lagoon (Spain). For this purpose, we used Sentinel 2 images and in situ data from the monitoring program of the Environment General Subdivision of the regional government. We obtained Sentinel 2A and 2B images for years 2017 and 2018 and processed them with SNAP software. The results of the correlation analysis between satellite and in situ data, corroborate that the reflectance of band 5 (705 nm) is suitable for the analysis of turbidity patterns in shallow lagoons (average depth 1 m), such as the Albufera lagoon, even in eutrophic conditions. Turbidity patterns in the Albufera lagoon show a similar trend in wet and dry years, which is mainly linked to the irrigation practice of rice paddies. High turbidity periods are linked to higher water residence time and closed floodgates. However, precipitation and wind also play an important role in the spatial distribution of turbidity. During storm events, phytoplankton and sediments are discharged to the sea, if the floodgates remain open. Fortunately, the rice harvesting season, when the floodgates are open, coincides with the beginning of the rainy period. Nevertheless, this is a lucky coincidence. It is important to develop conscious management of floodgates, because having them closed during rain events can have several negative effects both for the lagoon and for the receiving coastal waters and ecosystem. Non-discharged solids may accumulate in the lagoon worsening the clogging problems, and the beaches next to the receiving coastal waters will not receive an important load of solids to nourish them.

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“…Some studies have analysed the distribution of sediment in suspension allowing the construction of a synoptic description of turbidity patterns [4]. MODIS images have been used to determine the spatio-temporal variability of turbidity from their reflectance; this variability has been related to the Secchi disk depth in ocean and coastal waters [5]- [8] and to a lesser extent in rivers [9]. Also, Landsat reflectance images have been used (in a turbid estuary [10]), and their signal penetration at different depths [11], [12].…”

Section: Introductionmentioning

confidence: 99%

“…In addition to remote sensors, a simple and low-cost way of observing changes in suspended matter is the Secchi disk depth. It is a measure of water transparency, measured by lowering a white (in marine waters) or black-and-white (in continental waters) disk with a diameter of about 30 cm in the water until it is no longer visible to an observer on the surface [8], [17].…”

Section: Introductionmentioning

confidence: 99%

Turbidity Patterns in the Albufera Lake, Spain, and Their Relation to Irrigation Cycles

Sebastiá-Frasquet

Aguilar-Maldonado

Santamaría-del-Ángel

et al. 2019

WIT Transactions on Ecology and the Environment

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The Albufera Natural Park (Valencia, Spain) is one of the most representative coastal wetlands in the Mediterranean basin. It holds several protection designations at national and international level, such as Spanish Natural Park, Special Protection Areas (SPAs) for birds, Sites of Community Importance (SCIs) and Ramsar Site. Both the park and its main lake, Albufera's lake, face several environmental problems. One of them is reduced transparency and lake clogging. The lake is highly dependent on the rice cycle and on irrigation returns, mainly from the Acequia Real. In this study, we analyse the monthly transparency and turbidity patterns during year 2018, and we relate them to irrigation cycles. We used Sentinel 2A satellite images from the European Space Agency, which have an atmospheric correction. Remote sensing results were compared with in situ data from the monitoring program of the Environment General Subdivision of the regional government. This monitoring program samples five points on a monthly basis, and analyses Secchi disk depth, suspended solids and chlorophyll a. Our results show the temporal and spatial pattern of turbidity in the Albufera lake which offers relevant information for water resources management.

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Deriving inherent optical properties from classical water color measurements: Forel-Ule index and Secchi disk depth

Cited by 26 publications

References 55 publications

Development of a Solar-Powered IoT-Based Instrument for Automatic Measurement of Water Clarity

Development of a Solar-Powered IoT-Based Instrument for Automatic Measurement of Water Clarity

Sentinel 2 Analysis of Turbidity Patterns in a Coastal Lagoon

Turbidity Patterns in the Albufera Lake, Spain, and Their Relation to Irrigation Cycles

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