Extraction and replacement operators are also implemented. Functions for calculation of the position of the sun, times of sunrise and sunset, day length and night length are also provided. The package supports storage and manipulation of data for radiation quantities and for optical properties of objects. This package is the core of a suite of R packages for photobiological calculations described at the r4photobiology web site.
We use a measured solar spectrum and a measured filter transmission spectrum. Two articles introduce the basic ideas behind the design of the suite and describe its use: Aphalo P. A handbook written before the suite was developed contains useful information on the quantification and manipulation of ultraviolet and visible radiation: Aphalo, P. If you use this package to produce scientific or commercial publications, please cite according to:. Aphalo pedro. Released under the GPL, version 2 or greater. Silicon detectors are used across the spectrum.
Scientific instruments can therefore utilize this spectral range by operating in an oxygen-free atmosphere commonly pure nitrogen , without the need for costly vacuum chambers. Technology for VUV instrumentation was largely driven by solar astronomy for many decades. While optics can be used to remove unwanted visible light that contaminates the VUV, in general, detectors can be limited by their response to non-VUV radiation, and the development of "solar-blind" devices has been an important area of research. Wide-gap solid-state devices or vacuum devices with high-cutoff photocathodes can be attractive compared to silicon diodes.
EUV is strongly absorbed by most known materials, but it is possible to synthesize multilayer optics that reflect up to about 50 percent of EUV radiation at normal incidence. Some sources use the distinction of "hard UV" and "soft UV" - in the case of astrophysics the boundary may be at the Lyman limit i. Very hot objects emit UV radiation see black-body radiation. Extremely hot stars emit proportionally more UV radiation than the Sun. There is essentially no UVC.
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UV-B also plays a major role in plant development as it affects most of the plant hormones. The shorter bands of UVC, as well as even more-energetic UV radiation produced by the Sun, are absorbed by oxygen and generate the ozone in the ozone layer when single oxygen atoms produced by UV photolysis of dioxygen react with more dioxygen. The ozone layer is especially important in blocking most UVB and the remaining part of UVC not already blocked by ordinary oxygen in air. Ultraviolet absorbers are molecules used in organic materials polymers , paints , etc.
The absorbers can themselves degrade over time, so monitoring of absorber levels in weathered materials is necessary. Suspended nanoparticles in stained glass prevent UV rays from causing chemical reactions that change image colors. A set of stained glass color reference chips is planned to be used to calibrate the color cameras for the ESA Mars rover mission, since they will remain unfaded by the high level of UV present at the surface of Mars.
Common soda—lime glass is partially transparent to UVA but is opaque to shorter wavelengths, whereas fused quartz glass, depending on quality, can be transparent even to vacuum UV wavelengths. Wood's glass is a nickel-bearing form of glass with a deep blue-purple color that blocks most visible light and passes ultraviolet. A black light lamp emits long-wave UVA radiation and little visible light. Fluorescent black light lamps work similarly to other fluorescent lamps , but use a phosphor on the inner tube surface which emits UVA radiation instead of visible light. Some lamps use a deep-bluish-purple Wood's glass optical filter that blocks almost all visible light with wavelengths longer than nanometres.
Incandescent black lights are also produced, using a filter coating on the envelope of an incandescent bulb that absorbs visible light see section below. These are cheaper but very inefficient, emitting only a fraction of a percent of their power as UV. Black lights are used in applications in which extraneous visible light must be minimized; mainly to observe fluorescence , the colored glow that many substances give off when exposed to UV light.
Shortwave UV lamps are made using a fluorescent lamp tube with no phosphor coating, composed of fused quartz , since ordinary glass absorbs UVC. These lamps emit ultraviolet light with two peaks in the UVC band at Such tubes have two or three times the UVC power of a regular fluorescent lamp tube.
They also emit bluish-white visible light, due to mercury's other spectral lines. These "germicidal" lamps are used extensively for disinfection of surfaces in laboratories and food-processing industries, and for disinfecting water supplies. Due to its black-body spectrum a filament light bulb is a very inefficient ultraviolet source, emitting only a fraction of a percent of its energy as UV. Specialized UV gas-discharge lamps containing different gases produce UV radiation at particular spectral lines for scientific purposes.
Argon and deuterium arc lamps are often used as stable sources, either windowless or with various windows such as magnesium fluoride. Other UV sources with more continuous emission spectra include xenon arc lamps commonly used as sunlight simulators , deuterium arc lamps , mercury-xenon arc lamps , and metal-halide arc lamps. The excimer lamp , a UV source developed in the early s, is seeing increasing use in scientific fields. It has the advantages of high-intensity, high efficiency, and operation at a variety of wavelength bands into the vacuum ultraviolet.
Light-emitting diodes LEDs can be manufactured to emit radiation in the ultraviolet range. Such LEDs are increasingly used for UV curing applications, and are already successful in digital print applications and inert UV curing environments. UVC LEDs are beginning to be used in disinfection  and as line sources to replace deuterium lamps in liquid chromatography instruments.
Gas lasers , laser diodes and solid-state lasers can be manufactured to emit ultraviolet rays, and lasers are available which cover the entire UV range. The nitrogen gas laser uses electronic excitation of nitrogen molecules to emit a beam that is mostly UV. The strongest ultraviolet lines are at Another type of high power gas laser is the excimer laser. They are widely used lasers emitting in ultraviolet and vacuum ultraviolet wavelength ranges.
Ultraviolet lasers can also be made by applying frequency conversion to lower-frequency lasers. Ultraviolet lasers have applications in industry laser engraving , medicine dermatology , and keratectomy , chemistry MALDI , free air secure communications , computing optical storage and manufacture of integrated circuits. The generation is generally done in gasses e. By making one of the lasers tunable, the VUV can be tuned. If one of the lasers is resonant with a transition in the gas or vapor then the VUV production is intensified.
However, resonances also generate wavelength dispersion, and thus the phase matching can limit the tunable range of the 4 wave mixing. The EUV is not emitted by the laser, but rather by electron transitions in an extremely hot tin or xenon plasma, which is excited by an excimer laser. The impact of ultraviolet radiation on human health has implications for the risks and benefits of sun exposure and is also implicated in issues such as fluorescent lamps and health.
Getting too much sun exposure can be harmful, but in moderation, sun exposure is beneficial. There is no doubt that a little sunlight is good for you! But 5 to 15 minutes of casual sun exposure of hands, face and arms two to three times a week during the summer months is sufficient to keep your vitamin D levels high. The human body needs some UV radiation in order for one to maintain adequate vitamin D levels; however, excess exposure produces harmful effects that typically outweigh the benefits. Vitamin D promotes the creation of serotonin. The production of serotonin is in direct proportion to the degree of bright sunlight the body receives.
UV rays also treat certain skin conditions.
Modern phototherapy has been used to successfully treat psoriasis, eczema, jaundice, vitiligo, atopic dermatitis, and localized scleroderma. In humans, excessive exposure to UV radiation can result in acute and chronic harmful effects on the eye's dioptric system and retina. The risk is elevated at high altitudes and people living in high latitude countries where snow covers the ground right into early summer and sun positions even at zenith are low, are particularly at risk.
The differential effects of various wavelengths of light on the human cornea and skin are sometimes called the "erythemal action spectrum". At still shorter wavelengths of UV, damage continues to happen, but the overt effects are not as great with so little penetrating the atmosphere. The WHO-standard ultraviolet index is a widely publicized measurement of total strength of UV wavelengths that cause sunburn on human skin, by weighting UV exposure for action spectrum effects at a given time and location. Overexposure to UVB radiation not only can cause sunburn but also some forms of skin cancer.
However, the degree of redness and eye irritation which are largely not caused by UVA do not predict the long-term effects of UV, although they do mirror the direct damage of DNA by ultraviolet. All bands of UV radiation damage collagen fibers and accelerate aging of the skin. The most deadly form of skin cancer , malignant melanoma , is mostly caused by DNA damage independent from UVA radiation.
In the past, UVA was considered not harmful or less harmful than UVB, but today it is known to contribute to skin cancer via indirect DNA damage free radicals such as reactive oxygen species. UVA can generate highly reactive chemical intermediates, such as hydroxyl and oxygen radicals, which in turn can damage DNA. UVB radiation excites DNA molecules in skin cells, causing aberrant covalent bonds to form between adjacent pyrimidine bases, producing a dimer. Most UV-induced pyrimidine dimers in DNA are removed by the process known as nucleotide excision repair that employs about 30 different proteins.
As a defense against UV radiation, the amount of the brown pigment melanin in the skin increases when exposed to moderate depending on skin type levels of radiation; this is commonly known as a sun tan. The purpose of melanin is to absorb UV radiation and dissipate the energy as harmless heat, protecting the skin against both direct and indirect DNA damage from the UV. UVA gives a quick tan that lasts for days by oxidizing melanin that was already present and triggers the release of the melanin from melanocytes.
UVB yields a tan that takes roughly 2 days to develop because it stimulates the body to produce more melanin. Medical organizations recommend that patients protect themselves from UV radiation by using sunscreen. Five sunscreen ingredients have been shown to protect mice against skin tumors. However, some sunscreen chemicals produce potentially harmful substances if they are illuminated while in contact with living cells.
Several studies suggest that the absence of UVA filters may be the cause of the higher incidence of melanoma found in sunscreen users compared to non-users. The photochemical properties of melanin make it an excellent photoprotectant. However, sunscreen chemicals cannot dissipate the energy of the excited state as efficiently as melanin and therefore, if sunscreen ingredients penetrate into the lower layers of the skin, the amount of reactive oxygen species may be increased. In an experiment by Hanson et al. In the first 20 minutes, the film of sunscreen had a protective effect and the number of ROS species was smaller.
After 60 minutes, however, the amount of absorbed sunscreen was so high that the amount of ROS was higher in the sunscreen-treated skin than in the untreated skin. Radiation of this wavelength is almost absent from sunlight but is found in welder's arc lights and other artificial sources. Exposure to these can cause "welder's flash" or "arc eye" photokeratitis and can lead to cataracts , pterygium and pinguecula formation. Protective eyewear is beneficial to those exposed to ultraviolet radiation. Since light can reach the eyes from the sides, full-coverage eye protection is usually warranted if there is an increased risk of exposure, as in high-altitude mountaineering.
Mountaineers are exposed to higher-than-ordinary levels of UV radiation, both because there is less atmospheric filtering and because of reflection from snow and ice. Most plastic lenses give more protection than glass lenses, because, as noted above, glass is transparent to UVA and the common acrylic plastic used for lenses is less so. Some plastic lens materials, such as polycarbonate , inherently block most UV. UV degradation is one form of polymer degradation that affects plastics exposed to sunlight. The problem appears as discoloration or fading, cracking, loss of strength or disintegration.
The effects of attack increase with exposure time and sunlight intensity. The addition of UV absorbers inhibits the effect. Sensitive polymers include thermoplastics and speciality fibers like aramids. UV absorption leads to chain degradation and loss of strength at sensitive points in the chain structure. Aramid rope must be shielded with a sheath of thermoplastic if it is to retain its strength.
Many pigments and dyes absorb UV and change colour, so paintings and textiles may need extra protection both from sunlight and fluorescent bulbs, two common sources of UV radiation. Window glass absorbs some harmful UV, but valuable artifacts need extra shielding.
Many museums place black curtains over watercolour paintings and ancient textiles, for example. Since watercolours can have very low pigment levels, they need extra protection from UV. Various forms of picture framing glass , including acrylics plexiglass , laminates, and coatings, offer different degrees of UV and visible light protection.
Because of its ability to cause chemical reactions and excite fluorescence in materials, ultraviolet radiation has a number of applications. The following table  gives some uses of specific wavelength bands in the UV spectrum. Slightly yellow UV-blocking filters are often used for outdoor photography to prevent unwanted bluing and overexposure by UV rays. For photography in the near UV, special filters may be used. Digital cameras sensors may have internal filters that block UV to improve color rendition accuracy. Sometimes these internal filters can be removed, or they may be absent, and an external visible-light filter prepares the camera for near-UV photography.
A few cameras are designed for use in the UV. Photography by reflected ultraviolet radiation is useful for medical, scientific, and forensic investigations, in applications as widespread as detecting bruising of skin, alterations of documents, or restoration work on paintings.
Photography of the fluorescence produced by ultraviolet illumination uses visible wavelengths of light. In ultraviolet astronomy , measurements are used to discern the chemical composition of the interstellar medium, and the temperature and composition of stars. Because the ozone layer blocks many UV frequencies from reaching telescopes on the surface of the Earth, most UV observations are made from space. Corona discharge on electrical apparatus can be detected by its ultraviolet emissions. Corona causes degradation of electrical insulation and emission of ozone and nitrogen oxide.
These modules have a transparent quartz window on the top of the chip that allows the UV radiation in. Colorless fluorescent dyes that emit blue light under UV are added as optical brighteners to paper and fabrics. The blue light emitted by these agents counteracts yellow tints that may be present and causes the colors and whites to appear whiter or more brightly colored.
UV fluorescent dyes that glow in the primary colors are used in paints, papers, and textiles either to enhance color under daylight illumination or to provide special effects when lit with UV lamps. Blacklight paints that contain dyes that glow under UV are used in a number of art and aesthetic applications. Amusement parks often use UV lighting to fluoresce ride artwork and backdrops. This often has the side effect of causing rider's white clothing to glow light-purple. To help prevent counterfeiting of currency, or forgery of important documents such as driver's licenses and passports , the paper may include a UV watermark or fluorescent multicolor fibers that are visible under ultraviolet light.
Postage stamps are tagged with a phosphor that glows under UV rays to permit automatic detection of the stamp and facing of the letter. UV fluorescent dyes are used in many applications for example, biochemistry and forensics. Some brands of pepper spray will leave an invisible chemical UV dye that is not easily washed off on a pepper-sprayed attacker, which would help police identify the attacker later.
In some types of nondestructive testing UV stimulates fluorescent dyes to highlight defects in a broad range of materials. These dyes may be carried into surface-breaking defects by capillary action liquid penetrant inspection or they may be bound to ferrite particles caught in magnetic leakage fields in ferrous materials magnetic particle inspection. UV is an investigative tool at the crime scene helpful in locating and identifying bodily fluids such as semen, blood, and saliva. Other applications include the authentication of various collectibles and art, and detecting counterfeit currency.
Even materials not specially marked with UV sensitive dyes may have distinctive fluorescence under UV exposure or may fluoresce differently under short-wave versus long-wave ultraviolet.
Using multi-spectral imaging it is possible to read illegible papyrus , such as the burned papyri of the Villa of the Papyri or of Oxyrhynchus , or the Archimedes palimpsest. The technique involves taking pictures of the illegible document using different filters in the infrared or ultraviolet range, finely tuned to capture certain wavelengths of light. FACE free air carbon-dioxide enhancement. FEL a certain type of W incandescent lamp.
FWHM full-width half-maximum. H exposure, frequently called dose by biologists kJ m2 d1. H BE biologically effective energy exposure kJ m2 d1. HpBE biologically effective photon exposure mol m2 d1. HPS high pressure sodium, a type of discharge lamp. HSD honestly signifcant difference. L radiance W sr1 m2. LAI leaf area index, the ratio of projected leaf area to the ground area. LED light emitting diode. LME linear mixed effects type of statistical model.
LSD least significant difference. N total number of experimental units in an experiment. NA Avogadro constant also called Avogadros number. NLME non-linear mixed effects statistical model. OTC open-top chamber. PAR photosynthetically active radiation, nm. PC polycarbonate, a plastic. PG UV action spectrum for plant growth. PID proportional-integral-derivative control algorithm. PMMA polymethylmethacrylate. PTFE polytetrafluoroethylene. PVC polyvinylchloride.
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Q photon irradiance mol m2 s1. Q spectral photon irradiance mol m2 s1 nm1. RAF radiation amplification factor nondimensional. SDK software development kit. SR spectroradiometer. T temperature. TUV tropospheric UV. U electric potential difference or voltage e. VIS radiation visible to the human eye nm. VPD water vapour pressure deficit Pa. In this handbook we discuss methods relevant to research account.
In contrast, water and impurities like dissolved on the responses of plants to ultraviolet UV radiation. Basic concepts of of UV radiation, and the design of UV experiments. We photobiology, radiation physics and UV in the natural give guidelines and practical recommendations for ob- environment of plants are discussed in chapter 1. We Varied approaches are used in the study of the effects cover research both on terrestrial and aquatic plants sea- of UV radition on plants. The main dichotomy is whether weeds, marine angiosperms and freshwater higher plants 1 UV radiation is added by means of special lamps to are included, but microalgae are excluded from the scope either sunlight or to visible light from other lamps, or of this work.
We consider experimentation on ecological, 2 UV radiation in sunlight is excluded or attenuated eco-physiological and physiological questions. Both approaches are extensively The handbook will be most useful to early stage re- discussed in chapter 2. However, more experienced researchers For any experimental approach used in UV research we will also find information of interest. The guidelines need to quantify UV radiation and express it as mean- themselves, we hope, will ensure a high and uniform ingful physical quantities that allow comparison among standard of quality for UV research within our COST ac- experiments and to natural conditions.
When comparing tion, and the whole UV research community. We have UV irradiance from sources differing in spectral compos- written this text so that it is useful both for reading from ition, the comparison requires the calculation of biolo- cover to cover and for reference. It will also be useful as gically effective doses. The appendices present in detail Physiological and eco-physiological experiments can the calculations needed when measuring action spec- attempt to respond to different objective questions: 1 tra, and for calculating biologically effective UV doses will a future increase in UV radiation affect growth and both with Excel and R.
An R package which facilitates morphology of plants? This is petition? Finally with plants using an enclosing structure such as open- applied research related to agricultural and horticultural top chambers OTC , greenhouses or aquaria. These and production and produce is based on questions like: 1 many other considerations about the cultivation of plants can manipulations of UV radiation be used to manage are discussed in chapter 4. The point of view, allow valid conclusions to be reached.
In approach suitable for a given experiment will depend on addition a valid statistical analysis of the data, consistent its objectives. Well designed ex- medium surrounding the stems and leaves is air. At periments are also efficient in the use of resources both short path lengths air has little influence on UV irradi- time and money. The design of UV experiments and the ance and only when considering the whole depth of the analysis of the data obtained are discussed in chapter 5.
As the same. In the PDF file all links and crossreferences are live: amazon. They are marked by coloured boxes in the viewer but these boxes Helsinki, Pedro J. Aphalo are not printed. Matthew Robson book, please, send feedback directly to the lead ed- Copenhagen, Eva Rosenqvist itor at mailto:pedro. October The writing and publication of this book was made pos- Devices Ltd. We thank Prof. Donat Hder for supplying the realise that a book on UV research methods was needed. We thank Dr. Ulf Riebesell two and a half days of intense writing and discussions and Jens Christian Nejstgaard for photographs.
We thank Profs. Aphalo ac- for reading the whole manuscript and giving numerous knowledges the support of the Academy of Finland de- suggestions for improvement. Andy Mlaga April, Corrections of errors, sug- McLeod acknowledges the support of a Royal Society gestions for improvement and complains about difficult Leverhulme Trust Senior Research Fellowship and re- to understand passages from participants are acknow- search awards from the Natural Environment Research ledged.
Council U. Phototropins are well known for their role in ultraviolet radiation plant movements such as stomatal opening in blue light and the movement of chloroplasts see Christie, ; Mglich et al. The amount and quality of UV radiation they are exposed to depends on the time of the year, the The balance between the different wavebands, UV-B, latitude, the elevation, position in the canopy, clouds UV-A and PAR photosynthetically active radiation, and aerosols, and for aquatic plants the depth, solutes nm , has a big influence on the effect of UV-B radi- and particles contained in the water see sections 1.
Unrealistically low levels of UV-A radi- 1. Caldwell information about the environment of plants. However, et al. One reason for this is that UV-A radiation is when exposed to enhanced doses of UV radiation or UV required for photoreactivation, the repair of DNA damage radiation of short wavelengths, plants can be damaged.
When exposed to small doses of UV-B radiation plants From the s until the s the main interest in respond by a mechanism involving the perception of the research on the effects of UV-B on plants and other or- radiation through a photoreceptor called UVR8 Christie ganisms was generated by the increase in ambient UV-B et al. Wu et al. This e. Caldwell, ; Caldwell and Flint, b; Caldwell et protein behaves as a pigment at the top of a transduction al. This led to many studies on the ef- chain that regulates gene expression.
Several genes have fects of increased UV-B radiation, both outdoors, in green- been identified as regulated by UV-B radiation perceived houses and in controlled environments. Frequently the through UVR8. Some are related to the metabolism of results obtained in outdoor experiments differed from phenolic compounds and are involved in the accumula- those obtained indoors. This lead to the realization that it tion of these metabolites.
Genes related to hormone respect to UV-B radiation and its ratio compared to other metabolism are also affected, and this could be one of the bands of the solar spectrum. Interactions of responses mechanisms for photomorphogenesis by UV-B radiation, to UV-B radiation with other environmental factors like for example an increase in leaf thickness or reduction in availability of mineral nutrients, water and temperature, height of plants.
Morphological effects of UV-B mediated were also uncovered. Effects on terrestrial and aquatic by UVR8 have been described Wargent et al. These reports include that absorb both UV-A radiation and blue light. The best chapters on terrestrial ecosystems Ballar et al. Cryptochromes are involved in many pho- From the s onwards, the interest in the study of tomorphogenic responses, including the accumulation of the effects of normal i.
Other phenolics may behave as antioxidants Julkunen-Tiitto et al. Aphalo, ; Jansen and Bornman, ; visible radiation Paul, This was in part due to the realization that even low UV exposures elicit plant responses, and that In a physical sense, ultraviolet UV and visible VIS ra- these are important for the acclimation of plants to their diation i. Furthermore, as these ef- described by the Maxwells equations. The long wavelengths of solar ture e. Paul et al. A further subject of current interest is the enhanced The colour ranges indicated in Table 1. The electromagnetic spectrum is continuous mass caused by action of UV radiation on pectins e.
Another long- next. Especially in the IR region the subdivision is some- standing subject of research are the direct and indirect what arbitrary and the boundaries used in the literature effects of solar UV radiation on litter decomposition e. Radiation can also be thought of as composed of Austin and Ballar, ; Newsham et al. The energy of a quantum To be able to obtain reliable results from experiments of radiation in a vacuum, q, depends on the wavelength, on the effects of UV radiation on plants, there are many , or frequency3 , , different problems that need to be addressed.
When dealing 1. Thus, the energy of one mole of photons, q0 , is which the human eye, as well as the photosynthetic apparatus, is sensitive to nm. Example 1: shorter wavelengths than visible light and infra-red red light at nm has about kJ mol1 , therefore, longer wavelengths. Both particle and wave attributes 1 mol photons has 0. Example 2: UV-B radiation of radiation are needed for a complete description of its at nm has about kJ mol1 , therefore, 1 mol behaviour.
Light particles or quanta are called photons. Equations 1. The geometry is illustrated in Figure Stark-Einstein law Each absorbed quantum activates 1. The radiation only one molecule. The relation between dA and d in spherical adequate for an electron to jump to another possible coordinates is geometrically explained in Figure 1.
The consequence of The solid angle is calculated from the zenith angle this is that substances have colours, i. See Nobel and radiation beam Bjrn for detailed descriptions of the interactions between light and matter. Table 1. Figure 1. The angle denoted by is the azimuth angle and is the zenith angle. The area of the receiving surface is calculated by a com- is for example the Monte Carlo method. The parameters bination of the solid angle of the beam, the distance r of the light field can be simulated by modelling the paths from the radiation source and the angle of the tilt: of photons.
For an infinite number of photons the light field parameters reach their exact values asymptotically. In this case, the result is not exact, but it has the The unit of the solid angle is a steradian sr. The solid advantage of fast computing and the analytical equations angle of an entire sphere is calculated by integration of can be inverted just as fast.
This leads to the idealised equation 1. Then, equation 1. For example, the sun or moon seen from the Earths can be integrated easily and yields surface appear to have a diameter of about 0. The processes responsible for the variation of the ra- The boundary value L z0 is presumed known. This res- diance L , , as the radiation beam travels through ult is known as Beers law or Lamberts law, Bouguers any kind of material, are primarily absorption a and scat- law, Beer-Lambert law , denotes any instance of expo- tering b, which are called inherent optical properties, nential attenuation of light and is exact only for purely because they depend only on the characteristics of the absorbing mediai.
Ra- It is of direct application in analytical chemistry, as it diance is added to the directly transmitted beam, coming describes the direct proportionality of absorbance A to from different directions, due to elastic scattering, by the concentration of a coloured solute in a transparent which a photon changes direction but not wavelength solvent.
The Phenotyping Dilemma—The Challenges of a Diversified Phenotyping Community
An example of this is Raleigh scattering Different physical quantities are used to describe the in very small particles, which causes the scattering of amount of radiation and their definitions and abbrevi- light in a rainbow. A further gain of radiance into the ations are listed in Table 1.
Taking into account Equa- direct path is due to inelastic processes like fluorescence, tion 1. Internal sources of radiances, LS , like bioluminescence The irradiance decreases by the square of the distance of biological organisms or cells contribute also to the to the source and depends on the tilt of the detecting detected radiance. The path of the radiance through a surface area.
This is valid only for point sources. For artificial light sources simple LEDs Putting all this together, the radiative transfer equation light-emitting diodes without optics on top are also is effectively point sources. No exact analytical solution to the radiative of irradiance proportional to the square of the distance transfer equation exists, hence it is necessary either to from the light source. The layer is separated from other layers of different characteristics by boundary lines at height z0 and z1.
In plant research this is called usually dose H , while in Physics dose refers to absorbed radi- ation. Therefore, radiation is weighted by a luminosity function or visual sensitivity function describing the wavelength dependent response of the human eye. Due to the physiology of the eye, having rods and cones as light receptors, different sensitivity functions exist for the day photopic vision and night scotopic vision , V and V 0 , respectively. Both response functions normalised to their maximum are shown in the figure below as established by the Commission Internationale de lclairage CIE, International Commission on Illumination, Vienna, Austria in for photopic vision and for scotopic vision Schwiegerling, Until now, V is the basis of all photometric measurements.
Relative spectral intensity of human colour sensation during day solid line and night dashed line , V and V 0 respectively. Corresponding to the physical quantities of radiation summarized in the table 1. The dark-adapted sensitivity of the eye scotopic vision has its maximum at nm with lm W1. The base unit of luminous intensity is candela cd. The luminous flux of a normal candle is around 12 lm 12 lm. Photometric quantities of light.
Box 1. When we are interested in photochemical reactions, the most relevant radiation quantities are those expressed in photons. The reason for this is that, as discussed in section 1. The surplus energy decays by non-photochemical processes. When studying photosynthesis, where many photons of different wavelengths are simultaneously important, we normally use photon irradiance to describe amount of PAR. When dealing with energy balance of an object instead of photochemistry, we use energy irradiance.
In meteorology both UV and visible radiation, are quantified using energy-based quantities. According to the physical energetic quantities in the table 1. Photon quantities of light. To determine a quantity in terms of photons, an energetic quantity has to be weighted by the number of photons, i. This yields for example. For integrated values of UV-B or UV-A radiation the calculation is done analogously by integrating from to nm or to nm, respectively.
If we have measured energy irradiance, and want to convert this value to photon irradiance, the exact conversion will be possible only if we have information about the spectral composition of the measured radiation. Conversion factors at different wavelengths are given in the table below. For PAR, 1 W m2 of average daylight is approxim- ately 4. This is exact only if the radiation is equal from to nm, because the factor is the value at the central wavelength at nm.
Further details are discussed in section 3. Conversion factors of photon and energy quantities at different wavelengths. The human eye as a detector led to these photometric solar radiation, which can be estimated from the known units, and they are commonly used by lamp manufactur- activity of the sun productivity of photons , that can ers to describe their artificial light sources. See Box 1. The spectral irradiance of the sun Es can be estimated assuming a homogeneous flux and using the Depending on the shape of a detector which may be correlation of intensity I and radiance L from their defin- either planar or spherical the irradiance is called plane itions in table 1.
The intensity of the sun Is is given irradiance E or fluence rate also called scalar irradiance by the radiance Ls multiplied by the apparent sun E0. To on the incident angle and a spherical sensor detects all calculate the decreased solar irradiance at the moment photons equally weighted for all directions. See section of reaching the Earths atmosphere, the distance of the 3. In photobiology there are good equation 1.
Thus, the extraterrestrial solar irradiance reasons to quantify radiation based on photons. See Box is r2 1. The azimuth angle extraterrestrial solar radiation Wehrli, 5 and the is measured clockwise from the North on a horizontal spectrum calculated by equation 1. The position on the vertical plane is measured of equation 1. W m2 at top of the atmosphere Kopp and Lean, See Figure 1. In former times, a diagram. In contrast to Figure 1. For example, the irradiance at the the origin of the system of coordinates, when describing top of the atmosphere the integrated value changes by the position of the sun as in Figure 1.
A detailed analysis of light in vacuum : is given by Frhlich and Lean Sun Zenith. The azimuth angle is , the elevation angle is h and the zenith angle is. These angles are measured on two perpendicular planes, one horizontal and one vertical. For an isotropic- diation travelling directly from the sun, while diffuse ally emitting source Lambertian emitter , this means radiation is that scattered by the atmosphere. The contribution of W m2 K4. From this value, we can obtain presence of clouds Figures 1. The spectral 1. Using some of the colours introduced ozone column.
When the whole spectrum Es of different wavelength intervals. In addition, on a log scale, and other components of the atmosphere, cause corres- it is clear that the relative effect of ozone depletion on ponding valleys to appear in the solar spectrum at ground the spectral irradiance at a given wavelength increases level. For example, estimates from measurements of the with decreasing wavelength. In addition to the regular seasonal variation, above nm. In relation to plant research, only the there is random variation as a result of changes in clouds coarse structure of peaks and valleys is relevant, because Figure 1.
Normal seasonal and spatial variation in absorption spectra of pigments in vivo have broad peaks UV can be sensed by plants, and could play a role in and valleys. This radiation has two components, direct radiation and has been hypothesized to be a factor in the determination scattered or diffuse radiation. Direct radiation is ra- of the tree line6 in these mountains Flenley, Spectral irradiance mW m2 nm1 An increase in the UV-B irradiance is caused by de- later updates. However, as CFCs have a long half life in pletion of the ozone layer in the stratosphere, mainly the atmosphere, of the order of years, their effect as a consequence of the release of chlorofluorocarbons on the ozone layer will persist for many years, even after CFCs , used in cooling devices such as refrigerators and their use has been drastically reduced.
Model-based air conditioners, and in some spray cans see Graedel predictions of changes in atmospheric circulation due to and Crutzen, The most dramatic manifestation global climate change have been used to derive future of this has been the seasonal formation of an ozone trends in UV index and ozone column thickness Hegglin hole over Antarctica.
It is controversial whether a true and Shepherd, In addition, increased cloudiness ozone hole has already formed in the Arctic, but strong and pollution, could lead to decreased UV and PAR, some- depletion has occurred in year Manney et al. Stanhill and Cohen, and atmospheric conditions needed for the formation of It should be noted that, through reflection, broken a deep ozone hole are not very different from those clouds can locally increase UV irradiance to values above prevalent in recent years.
Not so dramatic, but consistent, those under clear-sky conditions S. Daz et al. CFCs and some other halocarbons have been phased out following the Montreal agreement and. They show that in the UV-A band the diffuse component is proportionally larger than it is at longer wavelengths. This can be seen as reduced contrast.
Photographs taken by L. Radiation ex- The attenuation of visible and UV radiation by canopies tinction in canopies has yet to be studied in detail with is difficult to describe mathematically because it is a com- respect to UV radiation, mainly because of difficulties in plex phenomenon. The spatial distribution of leaves is in the measurement of UV radiation compared to PAR, a most cases not uniform, the display angle of the leaves spectral region which has been extensively studied.
Here we give faces, although cuticular waxes and pubescence on leaves only a description of the simplest approach, the use of an can sometimes increase UV reflectance. The diffuse com- approximation based on Beers law as modified by Monsi ponent of UV radiation is larger than that of visible light and Saeki , reviewed by Hirose Beers law Figure 1.
In sunlit patches in forest gaps the dif- Equation 1. However, a canopy is hetero- because direct radiation is not attenuated but part of the genous, with discrete light absorbing objects the leaves sky is occluded by the surrounding forest. Attenuation and stems distributed in a transparent medium air. The equation does not explicitly account for clover canopies with planophyle leaves. Allen et al. Parisi and Wong ation. Consequently, the empirical extinction coefficient measured UV-B doses within model plant canop- K obtained may vary depending on these factors.
K is ies using dosimeters. The position of leaves affects UV-B not only a function of plant species through leaf optical exposure, and it has been observed that heliotropism can properties, and how leaves are displayed , but also of moderate exposure and could be a factor contributing time-of-day, and season-of-yearas a consequence of to differences in tolerance among crop cultivars Grant, solar zenith angleand degree of scattering of the incid- , a,b, As the degree of scattering depends on Detailed accounts of different models describing the.
Fraction diffuse 0. Spectral irradiance of total downwelling radiation lower panel, solid line , diffuse downwelling radiation lower panel, long dashes , and ratio of diffuse downwelling to total downwelling spectral irradiance upper panel, dashed line are shown. Data from TUV model version 4. Simulations of global radiation direct plus diffuse radiation spectral irradi- ance on a horizontal surface at ground level for a hypothetical 21 May with cloudless sky at Jokioinen 60 49N, 23 30E , under normal ozone column conditions.
Effect of depletion is so small on the solar spectrum as a whole, that it would not visible in this figure. See Kotilainen et al. Spectral irradiance W m2 nm1 See fig. The effect of ozone depletion on global direct plus diffuse radiation. A logarithmic scale is used for spectral irradiance.
Irradiance at noon rel. Diffuse percent 60 0. In cloudy conditions the percentage of diffuse radiation increases. Day of year not specified. Redrawn from Flint and Caldwell Irradiance expressed relative to annual maximum of each waveband. Adapted from Brown et al. Ply ngen sruhe Pis. Erl Karl. Abi l. If the and Norman and Monteith and Unsworth The bottom reflectance is greatly influenced by 1. Albert and Mobley, ; Maritorena et al. The penetration of UV radiation through wa- ter bodies can vary from only few centimetres in highly humic lakes Huovinen et al.
Some irradiance is reflected at the water water surface can be determined by Snells law, which surface, but the extent to which wavelengths in the UV describes the angular refraction of the incident beam. Seston is the sum of index n2. If the incoming direction of the radiation is living organic material mainly phytoplankton and non- given by the angle 1 , the beam is refracted to the angle living material tripton.
Non-living particles are further 2. Snells law is distinguished between organic material detritus and inorganic suspended matter. Theoretically, nW is not constant but depends on tem- This reflectance is described by a bidirectional reflectance perature, wavelength and salinity, as described by Quan. In principle, the shorter the wavelength, and 3 absorption and scattering by dead organic and the higher the refractive index of water, but in practice inorganic particles.
The influence of each constituent on the wavelength-dependent difference in refraction is un- the scattering process depends on wavelength, particle important. For example comparing the values at and size, concentration, and refractive index. Theoretical nm for 20 C and no salinity produces a difference details are explained in, for example, Hulst If the wind speed is high, the slope of surface CDOM mainly refers to coloured dissolved humic ma- waves also has to be taken into account.
A rough sur- terials and consists of humic and fulvic acids, originating face reflects and transmits the incoming radiation beam from decomposed plant material suspended in the water in more directions and makes the radiation field more or entering from the surrounding catchment area. The diffuse than a smooth surface. Kalle recognised that CDOM absorption decreases exponentially with increas- Water itself absorbs and scatters radiation. The optical ing wavelength in the visible part of the spectra.
Follow- properties of the water in the visible and ultraviolet UV ing the study of Morel and Prieur , Bricaud et al. Therefore, it is ne- CDOM absorption aY can be determined by cessary to rely on laboratory measurements to approxim- ate the values of these parameters. Buiteveld et al. The absorp- Bricaud et al. The amount of CDOM in water is de- effect increases with increasing wavelength; so, for ex- termined by filtration using membrane filters of 0.
The filtrate is collected into a quartz cuvette change in the absolute value of aW at nm. The absorption Einstein This approach is based on statistical coefficient at nm has been used as an indication thermodynamics and is called the theory of fluctuation. Experiments show with increasing size indicated by smaller ratios Haan, a slight deviation from the model, giving a better cor- , ; Haan et al. To determine aY from relation with 4.
Phytoplankton can contribute to the attenuation of The wavelength dependency of the absorption and scat- PAR through absorption by their photosynthetic pig- tering coefficients of pure water are shown in Figure 1. Water mainly contrib- also cause scattering. The absorption by phytoplank- utes to the attenuation of PAR and IR wavelengths, since ton aP is the sum of absorption by each pigment mul- absorption by pure water increases from around nm tiplied each by their concentrations.
Due to the fact towards longer wavelengths. This has been done by Absorption and scattering by water constituents is the Gege for freshwater Lake Constance in Germany sum of 1 absorption by CDOM, sometimes also called and by Prieur and Sathyendranath for an oceanic yellow or humic substances, gilvin or gelbstoff, 2 absorp- environment. Besides these examples, there are other tion and scattering by living material like phytoplankton, models for oceanic waters that use the specific in vivo.
Spectral absorption or scattering m1 Shown in logarithmic scale. For water containing a low concentra- a, achl and Cchl , respectively. Gordon and Morel developed an em- the best estimate of the absorption coefficient for his pirical model, which directly correlates scattering with data set.
Cchl is the concentration of chlorophyll-a in the pigment concentration of chlorophyll-a Cchl in units units of g l1. The scattering coefficient of phytoplankton bP chlorophyll absorption coefficient from Morel nor- in units of m1 is given by malized to maximum absorption at nm. The equation 1. The empirical 0. Gordon and Morel found that model of Bricaud et al. Higher values cific absorption coefficient from Cchl.
This model draws are used for other aquatic environments, for example on extensive studies of more than spectra to give turbid coastal waters. The proportionality factor depends on cells and the effect of the varying pigment composition the concentration of chlorophyll-a in the same manner on absorption. Dekker investigated the contribution to scattering of each The particulate structure of phytoplankton cells causes water constituent in inland waters9. He found that the scattering. Data available at the PhotochemCAD data. The in lakes. For lakes Dekker reported that the specific scattering In summary, after considering all the components that coefficient of phytoplankton ranges from 0.
The specific scat- waters blue-green wavelengths in the PAR spectrum dom- tering coefficients can be obtained by integrating the inate, whereas in highly-coloured, humic inland waters scattering phase function of the observed matter, here, blue wavelengths are rapidly attenuated. In humic lakes, phytoplankton. Huovinen et ments were done by Petzold Other functions can al.
The organic constituents are con- phytoplankton to UV attenuation can be significant Som- tained in phytoplankton cells or are fragments of dead maruga and Psenner, If very turbid water contains plankton and faecal pellets of zooplankton. These parts a large amount of inorganic particles, CDOM is bonded are often called detritus. Inorganic particles include sus- by calcium carbonate contained in the particles, and con- pended mineral coming from inflows or resuspension sequently the colour of the water returns to blue.