Ocean optics

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The properties of particles, such as this single particle of detritus, determine how they absorb and scatter light. PARTICLE OF DETRITUS PHOTOGRAPHED AT THE ATLANTIC MARINE FISHERIES LABORATORY AT SANDY HOOK, NEW JERSEY. HEAVY METALS... - NARA - 555838.jpg
The properties of particles, such as this single particle of detritus, determine how they absorb and scatter light.

Ocean optics is the study of how light interacts with water and the materials in water. Although research often focuses on the sea, the field broadly includes rivers, lakes, inland waters, coastal waters, and large ocean basins. How light acts in water is critical to how ecosystems function underwater. Knowledge of ocean optics is needed in aquatic remote sensing research in order to understand what information can be extracted from the color of the water as it appears from satellite sensors in space. The color of the water as seen by satellites is known as ocean color. While ocean color is a key theme of ocean optics, optics is a broader term that also includes the development of underwater sensors using optical methods to study much more than just color, including ocean chemistry, particle size, imaging of microscopic plants and animals, and more.

Contents

Key terminology

Optically deep

Where waters are “optically deep,” the bottom does not reflect incoming sunlight, and the seafloor cannot be seen by humans or satellites. [1] The vast majority of the world's oceans by area are optically deep. Optically deep water can still be relatively shallow water in terms of total physical depth, as long as the water is very turbid, such as in estuaries.

MODIS-Aqua satellite image of the Black Sea captured on June 20, 2006. All the water that we can see at the scale of this image is optically deep, because the seafloor is not visible to the satellite sensor. 2006 satellite image of Phytoplankton Blooms in the Black Sea.jpg
MODIS-Aqua satellite image of the Black Sea captured on June 20, 2006. All the water that we can see at the scale of this image is optically deep, because the seafloor is not visible to the satellite sensor.
Many oceanographic buoys and weather buoys at sea are located in optically deep waters, like the one being recovered in this photo 60 nautical miles north of Oahu, Hawaii. PMNM - Buoy Recovery (27225663874).jpg
Many oceanographic buoys and weather buoys at sea are located in optically deep waters, like the one being recovered in this photo 60 nautical miles north of Oahu, Hawaii.

Optically shallow

Where waters are “optically shallow,” the bottom reflects light and often can be seen by humans and satellites. [2] Here, ocean optics can also be used to study what is under the water. Based on what color they appear to sensors, researchers can map habitat types, including macroalgae, corals, seagrass beds, and more. Mapping shallow-water environments requires knowledge of ocean optics because the color of the water must be accounted for when looking at the color of the seabed environment below.

Where light reaches the bottom, the water is known as optically shallow, such as in this pool. The pattern of light on the bottom is caused by light refraction at the surface when ripples and small waves bend the water surface. Woman-freediver-underwater-caustics-copyright-jayhempix-com.jpg
Where light reaches the bottom, the water is known as optically shallow, such as in this pool. The pattern of light on the bottom is caused by light refraction at the surface when ripples and small waves bend the water surface.
The water at many tropical beaches, such as this beach on the Kure Atoll, is optically shallow. Light reflects off white-colored sand, creating a turquoise color. PMNM - monkseal lays on beach (26634440364).jpg
The water at many tropical beaches, such as this beach on the Kure Atoll, is optically shallow. Light reflects off white-colored sand, creating a turquoise color.

Inherent optical properties (IOPs)

Sentinel-2 satellite image of the confluence of the Rio Negro and the Solimoes River in Brazil. The dark colored water of the Rio Negro is rich in dissolved substances (high absorption), while the brighter brown colored water of the Solimoes River is rich in sediments (high scattering). The properties of these two water types can be studied with methods central to the field of ocean optics. Negro-Amazon confluence and Manaus (Brazil) from space (cropped).jpg
Sentinel-2 satellite image of the confluence of the Rio Negro and the Solimões River in Brazil. The dark colored water of the Rio Negro is rich in dissolved substances (high absorption), while the brighter brown colored water of the Solimões River is rich in sediments (high scattering). The properties of these two water types can be studied with methods central to the field of ocean optics.

Inherent optical properties (IOPs) depend on what is in the water. These properties stay the same no matter what the incoming light is doing (daytime or nighttime, low sun angle or high sun angle). [3]

Absorption

Water with large amounts of dissolved substances, such as lakes with large amounts of colored dissolved organic matter (CDOM), experience high light absorption. Phytoplankton and other particles also absorb light. [4]

Scattering involves how light is bounced into many directions by objects such as very small particles in the ocean. Measuring light scattering involved measuring light coming from different angles. Haze-Reflection-2.png
Scattering involves how light is bounced into many directions by objects such as very small particles in the ocean. Measuring light scattering involved measuring light coming from different angles.

Scattering

Areas with sea ice, estuaries with large amounts of suspended sediments, and lakes with large amounts of glacial flour are examples of water bodies with high light scattering. All particles scatter light to some extent, including plankton, minerals, and detritus. Particle size effects how much scattering happens at different colors; for example, very small particles scatter light exponentially more in the blue colors than other colors, which is why the ocean and the sky are generally blue (called Rayleigh scattering). Without scattering, light would not “go” anywhere (outside of a direct beam from the sun or other source) and we would not be able to see the world around us. [5]

Attenuation

Attenuation in water, also called beam attenuation or the beam attenuation coefficient, is the sum of all absorption and scattering. Attenuation of a light beam in one specific direction can be measured with an instrument called a transmissometer. [6]

Apparent optical properties (AOPs)

Apparent optical properties (AOPs) depend on what is in the water (IOPs) and what is going on with the incoming light from the Sun. AOPs depend most strongly on IOPs and only depend somewhat on incoming light aka the “light field.” Characteristics of the light field that can affect AOP measurements include the angle at which light hits the water surface (high in the sky vs. low in the sky, and from which compass direction) and the weather and sky conditions (clouds, atmospheric haze, fog, or sea state aka roughness of the surface of the water). [7]

Remote sensing reflectance (Rrs)

Remote sensing reflectance (Rrs) is a measure of light radiating out from beneath the ocean surface at all colors, normalized by incoming sunlight at all colors. Because Rrs is a ratio, it is slightly less sensitive to what is going on with the light field (such as the angle of the sun or atmospheric haziness). [8]

Rrs is measured using two paired spectroradiometers that simultaneously measure light coming in from the sky and light coming up from the water below at many wavelengths. Since it is a measurement of a light-to-light ratio, the energy units cancel out, and Rrs has the units of per steradian (sr-1) due to the angular nature of the measurement (upwelling light is measured at a specific angle, and incoming light is measured on a flat plane from a half-hemispherical area above the water surface). [9]

Light attenuation coefficient (Kd)

Kd is the diffuse (or downwelling) coefficient of light attenuation (Kd), also called simply light attenuation, the vertical extinction coefficient, or the extinction coefficient. [10] Kd describes the rate of decrease of light with depth in water, in units of per meter (m−1). The “d” stands for downwelling light, which is light coming from above the sensor in a half-hemispherical shape (aka half of a basketball). Scientists sometimes use Kd to describe the decrease in the total visible light available for plants in terms of photosynthetically active radiation (PAR) – called “Kd(PAR).” In other cases, Kd can describe the decrease in light with depth over a spectrum of colors or wavelengths, usually written as “Kd(λ).” At one color (one wavelength) Kd can describe the decrease in light with depth of one color, such as the decrease in blue light at the wavelength 490 nm, written as “Kd(490).”

In general, Kd is calculated using Beer's Law and a series of light measurements collected from just under the water surface down through the water at many depths. [11] [12]

A scientist measures Kd(PAR) from a boat in the Chesapeake Bay. This is a measure of downwelling light attenuation using a flat-topped light sensor (small brown metal cylinder at left), called a cosine collector, to measure the light coming down onto a flat surface from above. (EPA Science Chesapeake Bay 2) 412-DSP-2-2012-08-29 MDNR SusquehannaFlats 015.jpg - DPLA - 8a697e8c61e6c57300120a90fbfacd4f.jpg
A scientist measures Kd(PAR) from a boat in the Chesapeake Bay. This is a measure of downwelling light attenuation using a flat-topped light sensor (small brown metal cylinder at left), called a cosine collector, to measure the light coming down onto a flat surface from above.
Divers set up an equipment package including a sensor to measure PAR at the seafloor. This is a measure of scalar light using a round shaped light sensor (white lightbulb-like object at left), called a spherical quanta sensor, to measure light coming from all directions spherically. May, 2012 Monitoring water conditions on the ocean floor (7160593215).jpg
Divers set up an equipment package including a sensor to measure PAR at the seafloor. This is a measure of scalar light using a round shaped light sensor (white lightbulb-like object at left), called a spherical quanta sensor, to measure light coming from all directions spherically.

Closure

“Closure” refers to how optical oceanographers measure the consistency of models and measurements. Models refer to anything that is not explicitly measured in the water, including satellite-derived variables that are estimated using empirical relationships (for example, satellite-derived chlorophyll-a concentration is estimated from the ratios between green and blue remote sensing reflectance using an empirical relationship). Closure includes measurement closure, model closure, model-data closure, and scale closure. Where model-data closure experiments show misalignment between data and models, the cause of the misalignment may be due to measurement error, issues with the model, both, or some other external factor. [13] [14]

Focus areas

Ocean optics has been applied to study topics like primary production, phytoplankton, zooplankton, [15] [16] shallow-water habitats like seagrass beds and coral reefs, [17] [18] marine biogeochemistry, [19] heating of the upper ocean, [20] and carbon export to deep waters by way of the ocean biological pump. [21] The portion of the electromagnetic spectrum usually involved in ocean optics is ultraviolet through infrared, about 300 nm to less than 2000 nm wavelengths. [22]

Common optical sensors used in oceanography

A conductivity-temperature-depth rosette (CTD-rosette) sampler instrument package ready for deployment. PAR sensors are often attached to the top circular rung of the equipment package. Optical sensors like fluorometers and transmissometers are often attached to the bottom section of the equipment package, below the Niskin bottles, on the same level as the CTD sensor (light green cylinder just visible at the bottom of this image). CTDondeck.jpg
A conductivity-temperature-depth rosette (CTD-rosette) sampler instrument package ready for deployment. PAR sensors are often attached to the top circular rung of the equipment package. Optical sensors like fluorometers and transmissometers are often attached to the bottom section of the equipment package, below the Niskin bottles, on the same level as the CTD sensor (light green cylinder just visible at the bottom of this image).

The most widely used optical oceanographic sensors are PAR sensors, chlorophyll-a fluorescence sensors (fluorometers), and transmissometers. These three instruments are frequently mounted on CTD(conductivity-temperature-depth)-rosette samplers. These instruments have been used for many years on CTD-rosettes in global repeat oceanographic surveys like the CLIVAR GO-SHIP campaign. [23] [24]

Particle size in the ocean

Optical instruments are often used to measure the size spectrum of particles in the ocean. For example, phytoplankton organisms can range in size from a few microns (micrometers, μm) to hundreds of microns. The size of particles is often measured to estimate how quickly particles will sink, and therefore how efficiently plants can sequester carbon in the ocean's biological pump.

Ocean optics studies dissolved and particulate substances in the water, spanning a wide range of sizes. Many of these things are very small in size, from less than 0.1 nm to organisms at the centimeter scale. A single human hair is ~100 microns in width, for reference. Size and classification of marine particles.png
Ocean optics studies dissolved and particulate substances in the water, spanning a wide range of sizes. Many of these things are very small in size, from less than 0.1 nm to organisms at the centimeter scale. A single human hair is ~100 microns in width, for reference.
Particle size in the ocean follows a logarithmic pattern with concentration: there are exponentially more small particles than large particles. This plot shows concentration (number of particles per volume of water) on the y axis vs. particle size on the x axis. Natural particle size distributions in the ocean.webp
Particle size in the ocean follows a logarithmic pattern with concentration: there are exponentially more small particles than large particles. This plot shows concentration (number of particles per volume of water) on the y axis vs. particle size on the x axis.

Imaging of ocean particles and organisms

Researchers prepare an Imaging FlowCytoBot (IFCB) for water sampling. Prepping the Imaging Flow Cytobot.jpg
Researchers prepare an Imaging FlowCytoBot (IFCB) for water sampling.
Scientists stand next to an Imaging FlowCytoBot (IFCB). Ready for a View of Tiny Things.jpg
Scientists stand next to an Imaging FlowCytoBot (IFCB).

Scientists study individual tiny objects such as plankton and detritus particles using flow cytometry and in situ camera systems. Flow cytometers measure sizes and take photographs of individual particles flowing through a tube system; one such instrument is the Imaging FlowCytoBot (IFCB). [26] In situ camera systems are deployed over the side of a research vessel, alone or attached to other equipment, and they capture photographs of the water itself to image the particles present in the water; one such instrument is the Underwater Vision Profiler (UVP). [27] Other imaging technologies used in the ocean include holography [28] and particle imaging velocimetry (PIV), which uses 3D video footage to track the movement of underwater particles. [29]

Research in support of satellite remote sensing

Ocean color remote sensing involves learning about the ocean based on its color as viewed by satellite sensors. The light reaching the satellite sensor starts as incoming light from the Sun, then gets scattered and absorbed by Earth's atmosphere and surface, including water on the surface. Accurate ocean color measurements depend on accurate measurements of the optical properties of the water. The path covered by light from the sun through the water body to the remote sensing sensor.jpg
Ocean color remote sensing involves learning about the ocean based on its color as viewed by satellite sensors. The light reaching the satellite sensor starts as incoming light from the Sun, then gets scattered and absorbed by Earth's atmosphere and surface, including water on the surface. Accurate ocean color measurements depend on accurate measurements of the optical properties of the water.

Ocean optics research done “in situ” (from research vessels, small boats, or on docks and piers) supports research that uses satellite data. In situ optical measurements provide a way to: 1) calibrate satellite sensors when they are just beginning to collect data, 2) develop algorithms to derive products or variables like chlorophyll-a concentration, and 3) validate data products derived from satellites. Using satellite data, researchers estimate things like particle size, carbon, water quality, water clarity, and bottom type based on the color profile as seen by satellite; all of these estimations (aka models) must be validated by comparing them to optical measurements made in situ. [30] In situ data are often available from publicly accessible data libraries like the SeaBASS data archive.

A researcher prepares a filtration rig aboard a research vessel. Some optical properties of water, like absorption by particles, are measured by filtering water and measuring the color signature of the material on the filter. Preparing to Gather Water Samples.jpg
A researcher prepares a filtration rig aboard a research vessel. Some optical properties of water, like absorption by particles, are measured by filtering water and measuring the color signature of the material on the filter.
Visualization of satellite-derived global plant life, both oceanic (mg m chlorophyll-a) and terrestrial (normalized difference land vegetation index), provided by the SeaWiFS Project, NASA Goddard Space Flight Center. The field of ocean optics includes methods that help researchers estimate ocean chlorophyll-a concentrations. Seawifs global biosphere 2002.png
Visualization of satellite-derived global plant life, both oceanic (mg m chlorophyll-a) and terrestrial (normalized difference land vegetation index), provided by the SeaWiFS Project, NASA Goddard Space Flight Center. The field of ocean optics includes methods that help researchers estimate ocean chlorophyll-a concentrations.
Schematic of processes that need to be measured to fully understand ocean productivity and carbon sequestration. Many of these topics involve optical measurements. Monitoring processes in the ocean from remote sensing.jpg
Schematic of processes that need to be measured to fully understand ocean productivity and carbon sequestration. Many of these topics involve optical measurements.

Major contributing scientists

Oceanographers, physicists, and other scientists who have made major contributions to the field of ocean optics include (incomplete list):

David Antoine, Marcel Babin, Paula Bontempi, Emmanuel Boss, Annick Bricaud, Kendall Carder, Ivona Cetinic, Edward Fry, Heidi Dierssen, David Doxaran, Gene Carl Feldman, Howard Gordon, Chuanmin Hu, Nils Gunnar Jerlov, George Kattawar, John Kirk, ZhongPing Lee, Hubert Loisel, Stephane Maritorena, Michael Mishchenko, Curtis Mobley, Bruce Monger, Andre Morel, Michael Morris, Norm Nelson, Mary Jane Perry, Rudolph Preisendorfer, Louis Prieur, Chandrasekhara Raman, Collin Roesler, Rüdiger Röttgers, David Siegel, Raymond Smith, Heidi Sosik, Dariusz Stramski, Michael Twardowski, Talbot Waterman, Jeremy Werdell, Ken Voss, Charles Yentsch, and Ronald Zaneveld.

Education

While ocean optics is an interdisciplinary field of study applies to a wide range of topics, it is not often taught as a course in graduate programs for marine science and oceanography. Two summer-term courses have been developed for graduate students from many different institutions. First, there is a summer lecture series operated by the International Ocean Colour Coordinating Group (IOCCG) which usually takes place in France. [31] Second, there is an ongoing course in the United States called the “Optical Oceanography Class” or “Ocean Optics Class” in Washington State and later in Maine, which has been running continuously since 1985. [32]

For independent learning, Curt Mobley, Collin Roesler, and Emmanuel Boss wrote the Ocean Optics Web Book as an open-access online guide.

See also

Related fields and topics:

Inherent and apparent optical properties and in-water methods:

Remote sensing and radiometric methods:

Related Research Articles

In physics, attenuation is the gradual loss of flux intensity through a medium. For instance, dark glasses attenuate sunlight, lead attenuates X-rays, and water and air attenuate both light and sound at variable attenuation rates.

<span class="mw-page-title-main">Backscatter</span> Reflection which reverses the direction of a wave, particle, or signal

In physics, backscatter is the reflection of waves, particles, or signals back to the direction from which they came. It is usually a diffuse reflection due to scattering, as opposed to specular reflection as from a mirror, although specular backscattering can occur at normal incidence with a surface. Backscattering has important applications in astronomy, photography, and medical ultrasonography. The opposite effect is forward scatter, e.g. when a translucent material like a cloud diffuses sunlight, giving soft light.

SeaWiFS was a satellite-borne sensor designed to collect global ocean biological data. Active from September 1997 to December 2010, its primary mission was to quantify chlorophyll produced by marine phytoplankton.

A scatterometer or diffusionmeter is a scientific instrument to measure the return of a beam of light or radar waves scattered by diffusion in a medium such as air. Diffusionmeters using visible light are found in airports or along roads to measure horizontal visibility. Radar scatterometers use radio or microwaves to determine the normalized radar cross section of a surface. They are often mounted on weather satellites to find wind speed and direction, and are used in industries to analyze the roughness of surfaces.

<span class="mw-page-title-main">MERIS</span>

MEdium Resolution Imaging Spectrometer (MERIS) was one of the main instruments on board the European Space Agency (ESA)'s Envisat platform. The sensor was in orbit from 2002 to 2012. ESA formally announced the end of Envisat's mission on 9 May 2012.

<span class="mw-page-title-main">Optical fiber</span> Light-conducting fiber

An optical fiber, or optical fibre, is a flexible glass or plastic fiber that can transmit light from one end to the other. Such fibers find wide usage in fiber-optic communications, where they permit transmission over longer distances and at higher bandwidths than electrical cables. Fibers are used instead of metal wires because signals travel along them with less loss and are immune to electromagnetic interference. Fibers are also used for illumination and imaging, and are often wrapped in bundles so they may be used to carry light into, or images out of confined spaces, as in the case of a fiberscope. Specially designed fibers are also used for a variety of other applications, such as fiber optic sensors and fiber lasers.

<span class="mw-page-title-main">Fluorometer</span> Device used to identify the presence and the amount of specific molecules in a medium

A fluorometer, fluorimeter or fluormeter is a device used to measure parameters of visible spectrum fluorescence: its intensity and wavelength distribution of emission spectrum after excitation by a certain spectrum of light. These parameters are used to identify the presence and the amount of specific molecules in a medium. Modern fluorometers are capable of detecting fluorescent molecule concentrations as low as 1 part per trillion.

<span class="mw-page-title-main">Ocean color</span> Explanation of the color of oceans and ocean color remote sensing

Ocean color is the branch of ocean optics that specifically studies the color of the water and information that can be gained from looking at variations in color. The color of the ocean, while mainly blue, actually varies from blue to green or even yellow, brown or red in some cases. This field of study developed alongside water remote sensing, so it is focused mainly on how color is measured by instruments.

<span class="mw-page-title-main">Transmissometer</span> Meteorological instrumentation

A transmissometer or transmissiometer is an instrument for measuring the extinction coefficient of the atmosphere and sea water, and for the determination of visual range. It operates by sending a narrow, collimated beam of energy through the propagation medium. A narrow field of view receiver at the designated measurement distance determines how much energy is arriving at the detector, and determines the path transmission and/or extinction coefficient. In a transmissometer the extinction coefficient is determined by measuring direct light transmissivity, and the extinction coefficient is then used to calculate visibility range.

The marine optical buoy (MOBY) measures light at and very near the sea surface in a specific location over a long period of time, serving as part of an ocean color observation system. Satellites are another component of the system, providing global coverage through remote sensing; however, satellites measure light above the Earth's atmosphere, becoming subject to interference from the atmosphere itself and other light sources. The Marine Optical Buoy helps alleviate that interference and thus improve the quality of the overall ocean color observation system.

A closure experiment in atmospheric science is a combination of different measurement techniques to describe the current state of the investigated system as fully as possible, and to find inaccuracies in one or some of the methods involved. The comparison of different types of measurement often involves model calculations, which may also be tested in this process.

Geostationary Ocean Color Imager, is the world's first geostationary orbit satellite image sensor in order to observe or monitor an ocean-color around the Korean Peninsula [1][2]. The spatial resolution of GOCI is about 500m and the range of target area is about 2,500 km×2,500 km centered on Korean Peninsula. GOCI was loaded on Communication, Ocean, and Meteorological Satellite (COMS) of South Korea which was launched in June, 2010. It will be operated by Korea Ocean Satellite Center (KOSC) at Korea Institute of Ocean Science & Technology (KIOST), and capture the images of ocean-color around the Korean Peninsula 8 times a day for 7.7 years.

<span class="mw-page-title-main">Water remote sensing</span> System to measure the color of water by observing the spectrum of radiation leaving the water.

Water Remote Sensing is the observation of water bodies such as lakes, oceans, and rivers from a distance in order to describe their color, state of ecosystem health, and productivity. Water remote sensing studies the color of water through the observation of the spectrum of water leaving radiance. From the spectrum of color coming from the water, the concentration of optically active components of the upper layer of the water body can be estimated via specific algorithms. Water quality monitoring by remote sensing and close-range instruments has obtained considerable attention since the founding of EU Water Framework Directive.

<span class="mw-page-title-main">Haiyang (satellite)</span> Chinese ocean observation satellite

Haiyang is a series of marine remote sensing satellites developed and operated by the People's Republic of China since 2002. The name "Haiyang" translates to "ocean" in English. As of October 2022, eight satellites have been launched with ten more planned. Built by the state-owned aerospace contractor China Academy of Space Technology (CAST), Haiyang satellites carry a variety of ocean-imaging sensor payloads and are operated by the National Satellite Ocean Application Service (NSOAS), a subordinate agency of the State Oceanic Administration (SOA). Haiyang satellites are launched from Taiyuan Satellite Launch Center (TSLC) into Sun-synchronous orbit (SSO) aboard Long March-series rockets.

<span class="mw-page-title-main">Plankton, Aerosol, Cloud, ocean Ecosystem</span> NASA Earth-observing satellite

Plankton, Aerosol, Cloud, ocean Ecosystem (PACE) is a 2020s NASA Earth-observing satellite mission to observe global ocean color, biogeochemistry, and ecology, as well as the carbon cycle, aerosols and clouds. PACE is intended to be used to identify the extent and duration of phytoplankton blooms and improve understanding of air quality. These and other uses of PACE data are expected to benefit the economy and society according to NASA, especially sectors that rely on water quality, fisheries and food security.

<span class="mw-page-title-main">North Atlantic Aerosols and Marine Ecosystems Study</span>

The North Atlantic Aerosols and Marine Ecosystems Study (NAAMES) was a five-year scientific research program that investigated aspects of phytoplankton dynamics in ocean ecosystems, and how such dynamics influence atmospheric aerosols, clouds, and climate. The study focused on the sub-arctic region of the North Atlantic Ocean, which is the site of one of Earth's largest recurring phytoplankton blooms. The long history of research in this location, as well as relative ease of accessibility, made the North Atlantic an ideal location to test prevailing scientific hypotheses in an effort to better understand the role of phytoplankton aerosol emissions on Earth's energy budget.

Remote sensing in oceanography is a widely used observational technique which enables researchers to acquire data of a location without physically measuring at that location. Remote sensing in oceanography mostly refers to measuring properties of the ocean surface with sensors on satellites or planes, which compose an image of captured electromagnetic radiation. A remote sensing instrument can either receive radiation from the Earth’s surface (passive), whether reflected from the Sun or emitted, or send out radiation to the surface and catch the reflection (active). All remote sensing instruments carry a sensor to capture the intensity of the radiation at specific wavelength windows, to retrieve a spectral signature for every location. The physical and chemical state of the surface determines the emissivity and reflectance for all bands in the electromagnetic spectrum, linking the measurements to physical properties of the surface. Unlike passive instruments, active remote sensing instruments also measure the two-way travel time of the signal; which is used to calculate the distance between the sensor and the imaged surface. Remote sensing satellites often carry other instruments which keep track of their location and measure atmospheric conditions.

<span class="mw-page-title-main">SeaBASS (data archive)</span> Data archive of in situ oceanographic data

The SeaWiFS Bio-optical Archive and Storage System (SeaBASS) is a data archive of in situ oceanographic data used to support satellite remote sensing research of ocean color. SeaBASS is used for developing algorithms for satellite-derived variables and for validating or “ground-truthing” satellite-derived data products. The acronym begins with “S” for SeaWiFS, because the data repository began in the 1990s around the time of the launch of the SeaWiFS satellite sensor, and the same data archive has been used ever since. Oceanography projects funded by the NASA Earth Science program are required to upload data collected on research campaigns to the SeaBASS data repository to increase the volume of open-access data available to the public. As of 2021 the data archive contained information from thousands of field campaigns uploaded by over 100 principal investigators.

Nils Gunnar Jerlov (1909–1990) was a Swedish oceanographer, physicist, scientist, and researcher who studied how light interacts with water. He was a pioneering scientist in the field of ocean optics, and his water types are used to define the color and characteristics of natural water bodies.

<span class="mw-page-title-main">Water clarity</span> How deeply visible light penetrates through water

Water clarity is a descriptive term for how deeply visible light penetrates through water. In addition to light penetration, the term water clarity is also often used to describe underwater visibility. Water clarity is one way that humans measure water quality, along with oxygen concentration and the presence or absence of pollutants and algal blooms.

References

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  4. ↑ Roesler, Collin (6 April 2021). "Absorption Overview. Ocean Optics Web Book" . Retrieved 24 August 2021.
  5. ↑ Mobley, Curtis; Boss, Emmanuel (18 May 2021). "Scattering Overview. Ocean Optics Web Book" . Retrieved 24 August 2021.
  6. ↑ Mobley, Curtis (19 May 2021). "Measuring IOPs. Ocean Optics Web Book" . Retrieved 24 August 2021.
  7. ↑ Mobley, Curtis (27 October 2020). "Apparent Optical Properties. Ocean Optics Web Book" . Retrieved 24 August 2021.
  8. ↑ "Remote Sensing Reflectance (Rrs)". NASA Ocean Color. Retrieved 24 August 2021.
  9. ↑ Mobley, Curtis (28 October 2020). "Reflectances. Ocean Optics Web Book" . Retrieved 24 August 2021.
  10. ↑ "Light". Understanding: Lake Ecology Primer. Water on the Web. 31 January 2011. Retrieved 24 August 2021.
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  14. ↑ Chang, Grace C.; Dickey, Tommy D.; Mobley, Curtis D.; Boss, Emmanuel; Pegau, W. Scott (2003). "Toward closure of upwelling radiance in coastal waters". Applied Optics. 42 (9): 1574–1582. Bibcode:2003ApOpt..42.1574C. doi:10.1364/AO.42.001574. PMID   12665088.
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  17. ↑ Zimmerman, R. C.; Dekker, A. G. (2007). Aquatic Optics: Basic Concepts for Understanding How Light Affects Seagrasses and Makes them Measurable from Space. In: Seagrasses: Biology, Ecology and Conservation. Dordrecht: Springer. doi:10.1007/978-1-4020-2983-7_12.
  18. ↑ Hochberg, E. J.; Atkinson, M. J. (2000). "Spectral discrimination of coral reef benthic communities". Coral Reefs. 19 (2): 164–171. doi:10.1007/s003380000087. S2CID   34304562.
  19. ↑ Organelli, Emanuele; et al. (2017). "Two databases derived from BGC-Argo float measurements for marine biogeochemical and bio-optical applications". Earth System Science Data. 9 (2): 861–880. Bibcode:2017ESSD....9..861O. doi: 10.5194/essd-9-861-2017 . S2CID   21668439.
  20. ↑ Oschlies, Andreas (2004). "Feedbacks of biotically induced radiative heating on upper-ocean heat budget, circulation, and biological production in a coupled ecosystem-circulation model" (PDF). Journal of Geophysical Research: Oceans. 109 (C12). Bibcode:2004JGRC..10912031O. doi:10.1029/2004JC002430.
  21. ↑ Stemmann, L.; Boss, Emmanuel (2012). "Plankton and Particle Size and Packaging: From Determining Optical Properties to Driving the Biological Pump". Annual Review of Marine Science. 4: 263–290. Bibcode:2012ARMS....4..263S. doi:10.1146/annurev-marine-120710-100853. PMID   22457976.
  22. ↑ Mobley, Curtis (2021). "Ocean Color. Ocean Optics Web Book" . Retrieved 21 August 2021.
  23. ↑ Dickey, Tommy D. (1991). "The emergence of concurrent high-resolution physical and bio-optical measurements in the upper ocean and their applications". Reviews of Geophysics. 29 (3): 383–413. Bibcode:1991RvGeo..29..383D. doi:10.1029/91rg00578.
  24. ↑ Boss, Emmanuel; et al. (2015). "Optical techniques for remote and in-situ characterization of particles pertinent to GEOTRACES". Progress in Oceanography. 133: 43–54. Bibcode:2015PrOce.133...43B. doi:10.1016/j.pocean.2014.09.007. S2CID   51780423.
  25. ↑ Davies, Emlyn J.; Basedow, Sunnje L.; McKee, David (2021). "The hidden influence of large particles on ocean colour". Scientific Reports. 11 (1): 3999. Bibcode:2021NatSR..11.3999D. doi:10.1038/s41598-021-83610-5. hdl: 10037/21472 . PMC   7889869 . PMID   33597642.
  26. ↑ Olson, Robert J.; Sosik, Heidi M. (2007). "A submersible imaging-in-flow instrument to analyze nano-and microplankton: Imaging FlowCytobot". Limnology and Oceanography: Methods. 5 (6): 195–203. doi:10.4319/lom.2007.5.195. S2CID   83979355.
  27. ↑ Picheral, Marc; Guidi, Lionel; Stemmann, Lars; Karl, David M.; Iddaoud, Ghizlaine; Gorsky, Gabriel (2010). "The Underwater Vision Profiler 5: An advanced instrument for high spatial resolution studies of particle size spectra and zooplankton". Limnology and Oceanography: Methods. 8 (9): 462–473. doi: 10.4319/lom.2010.8.462 . S2CID   13671970.
  28. ↑ Nayak, Aditya R.; et al. (2021). "A Review of Holography in the Aquatic Sciences: In situ Characterization of Particles, Plankton, and Small Scale Biophysical Interactions". Frontiers in Marine Science. 7. doi: 10.3389/fmars.2020.572147 .
  29. ↑ "Deep particle image velocimetry". Monterey Bay Aquarium Research Institute (MBARI). 2017. Retrieved 24 August 2021.
  30. ↑ Mascarenhas, Veloisa; Keck, Therese (2018). Jungblut, S.; Liebich, V.; Bode, M. (eds.). "Marine Optics and Ocean Color Remote Sensing (Conference paper)". YOUMARES 8 – Oceans Across Boundaries: Learning from Each Other: 41–54. doi: 10.1007/978-3-319-93284-2_4 .
  31. ↑ "2022 IOCCG Summer Lecture Series". Frontiers in Ocean Optics and Ocean Colour Science. 2021. Retrieved 24 August 2021.
  32. ↑ Perry, Mary Jane (2016). "SIDEBAR. The Optical Oceanography Class Turned 30 in Summer 2015". Oceanography. 29 (1): 32–33. doi: 10.5670/oceanog.2016.07 .

Further reading

  1. ↑ Kirk, John T. O. (1994). Light and Photosynthesis in Aquatic Ecosystems (3rd ed.). Cambridge University Press. ISBN   0521459664.
  2. ↑ Preisendorfer, Rudolph W. (1976). Hydrologic Optics (6 Volumes) (PDF). U.S. Department of Commerce, National Oceanic and Atmospheric Administration, Environmental Research Laboratories, Pacific Marine Environmental Laboratory.
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