Irradiance Meter Research Articles

Underwater radiant energy absorbed by phytoplankton, detritus, dissolved organic matter, and pure water

The spectral irradiance distribution at five stations on lakes and at sea was measured with a portable underwater spectral irradiance meter. Chlorophyll a concentration and the absorption coefficient of the water were concurrently measured. From measured spectral irradiance distributions, radiant energy absorbed per unit volume was computed. At these stations, the effect of upward irradiance on total quanta absorbed by the water was negligibly small for all layers. The relative contributions of phytoplankton, detritus, dissolved organic matter, and pure water to the total absorbed quanta were also computed by taking into consideration the spectral dependency of each component: the contribution of quanta absorbed by phytoplankton was about 3–10% in clear water and about 30–40% in the plankton‐rich water.

Zooplankton sound scattering layers in north Norwegian fjords: Specifications and functioning of the acoustical, data- and net-sampling systems

The specifications and functioning of the acoustic, data and environmental monitoring systems used in the ‘Zooplankton Sound Scattering Layers Project’ of the University of Tromso are described. The instrumentation onboard RV ‘Johan Ruud’ for studying sound scattering layers includes 38 and 120 kHz echosounders, a digital echointegrator, a computer (for data storage, retrieval, and analyses — including echointegration, and conductivity, temperature, oxygen, and depth-sonde analyses), fluorometer, irradiance meters, pelagic and prawn trawls, a Longhurst-Hardy Plankton Recorder, and a Tucker trawl. Various advantages and limitations as well as possible future development of the systems are discussed with respect to zoo-plankton-orientated research on sound scattering layers.

Measurement of near-UV irradiance taking into consideration reciprocity law failure for irradiated materials.

A method of evaluating effective irradiance is discussed for photoresist with the reciprocity law failure property irradiated by fluctuating radiation. The resultant formula for evaluating effective irradiance suggests that both reciprocity law failure and time response for the photochemical reaction should be considered when evaluating effective irradiance. This method is used in an irradiance meter which measures the distribution of near ultraviolet effective irradiance. This irradiance meter is applied to the photoresist exposure process in color TV picture tube fabrication. This meter automatically measures relative irradiance over 51 points on the phosphor screen of a color TV picture tube, in about 1 min. Reproducibility and accuracy for measured values are estimated to be about 0.2% and 1%, respectively. Absolute irradiance is measured at the center of the screen, with an accuracy of about 3%.

A design for a simple underwater irradiance meter

A description is given of the assembly, calibration and performance of an irradiance meter intended for underwater measurements in a single wave-band. The meter features high sensitivity by utilizing CdS photoconductors and a FET-type ohm meter, giving a linear response from 10−1–10−6 W m−2. Instrument performance is discussed in relation to angular light response, immersion effect, response time, temperature dependence and filter bandwidth error.

SOME FURTHER CONSIDERATIONS ON THE USE OF REPAIR‐DEFECTIVE ORGANISMS AS BIOLOGICAL DOSIMETERS FOR BROAD‐BAND ULTRAVIOLET RADIATION SOURCES

Abstract— The extreme variation in biological effectiveness of the various components of solar ultraviolet radiation (solar UV) which reaches the earth's surface, especially photons of wavelengths between 295 and 330 nm, makes the dosimetry of solar UV a complex and, as yet, unresolved problem. A proper weighting of the various components of solar UV would permit expression of expsoure as a single parameter (dose). Weighting could compensate for the variations in composition of solar UV which might occur during exposure or the differences in sources of UV radiations; weighting would permit comparison of exposures at various locations on the earth and extrapolation of laboratory observations to field situations where wavelength composition might be rather different. Various radiation‐sensitive microorganisms have been proposed as biological dosimeters. Biological dosimeters automatically weight the subcomponents of solar UV differently than a purely physical irradiance meter. We have examined the available evidence regarding the weighting which repair‐defective mutants provide in comparison with response of a number of wild‐type organisms and would caution investigators that, for broad‐band UV sources, especially those with significant biological actions through the range of 300–330 nm, repair‐sensitive mutants may improperly weight the components, leading to errors of dosimetry and thus to possible errors of interpretation of results of solar UV exposure of wild‐type organisms

Irradiance Measurements in the Upper Ocean

Abstract Observations were made of downward solar radiation as a function of depth during an experiment in the North Pacific (35°N, 155°W). The irradiance meter employed was sensitive to solar radiation of wavelength 400–1000 nm arriving from above at a horizontal surface. Because of selective absorption of the short and long wavelengths, the irradiance decreases much faster than exponential in the upper few meters, falling to one-third of the incident value between 2 and 3 m depth. Below 10 m the decrease was exponential at a rate characteristic of moderately clear water of Type IA. Neglecting one case having low sun altitude, the observations are well represented by the expression I/I0=Rez/ζ1+(1−R)ezζ2, where I is the irradiance at depth −z, I0 is the irradiance at the surface less reflected solar radiation, R=0.62, ζ1 and ζ2 are attenuation lengths equal to 1.5 and 20 m, respectively, and z is the vertical space coordinate, positive upward with the origin at mean sea level. The depth at which the irrad...

Use of a quanta meter to measure attenuation and underwater reflectance of photosynthetically active radiation in some inland and coastal south-eastern Australian waters

The attenuation of total photosynthetically active radiation (PAR) in natural waters and its characterization by means of a vertical attenuation coefficient are briefly discussed. The factors determining underwater reflectance (ratio of upward to downward irradiance at a given depth) are considered, and a simple mathematical treatment is presented which leads to the conclusion that within that part of the water body where the asymptotic radiance distribution exists, if reflection from the bottom is negligible then the reflectance is equal to the asymptotic backscattering coefficient (defined in the text) divided by 2K, where K is the (natural logarithm) vertical attenuation coefficient. Data collected using a commercially available quantum irradiance meter over a 2-year period for various inland and coastal waters in south-eastern Australia are presented together with measure- ments of levels of yellow substance and phytoplankton. In the turbid inland waters attenuation of PAR closely follows an exponential law. In the much clearer coastal waters, by contrast, attenuation of PAR is approximately biphasic, the vertical attenuation coefficient in the upper few metres being noticeably higher than that at greater depths. Within any one water body the vertical attenuation coefficient was observed to vary up to four-fold during the 2-year period: nevertheless there were indications that the average attenuation of PAR tended to differ characteristically from one water body to another. In one of the inland waters, measurements at different times of day showed that the vertical attenuation coefficient was not strongly dependent on solar altitude. Underwater reflectance values in the inland waters were surprisingly high (0.04-0.21) compared to values in the literature: this is probably a consequence of the high turbidity of these waters. Calculated values of the asymptotic backscattering coefficient for the inland lakes are presented. It is suggested that measurements of yellow substance and phytoplankton, together with some estimate of light scattering, in parallel with measurements of attenuation of PAR would facilitate an understanding of the factors responsible for that attenuation.

A self-contained instrument for logarithmic recording of submarine quantum irradiance

The construction of a recording quantum irradiance meter is described. A commercially available filtered silicon diode sensor provides signals which are amplified logarithmically and recorded on a strip-chart recorder. Recording range is 1 to 1000 μE m-2sec-1 on three-decade chart paper. The unit will function unattended for periods of up to 7 days in 20 m of water.

A remote operating submarine irradiance meter

The near-surface submarine irradiance measured by a meter suspended from a ship may be reduced by up to 50% by the shading effect of the ship under certain conditions, such as an overcast sky. To avoid this, an irradiance meter has been constructed that operates remotely at a large distance from the ship. A continuous record of submarine irradiance is obtained as the meter free-falls through the water.

Comparison of Ground Based Measurements of Solar UV Index with Satellite Estimation at Four Sites of Nepal

The main objective of this study is to compare the ground based measurements and satellite estimation of solar UV index in four sites namely, Kathmandu, Pokhara, Biratnagar and Lukla. Kathmandu (27.72°N, 85.32°E), Pokhara (28.22°N, 83.32°E) Biratnagar (26.45°N, 87.27° E) and Lukla ( 27.69°N, 86.73°E) and are located at an elevation of 1350m, 800m, 72m and 2850m respectively from the sea level. The ground based measurements and satellite estimation were performed by NILUUV irradiance meter and EOS Aura OMI satellite. The NILUUV irradiance meter is a six channel radiometer designed to measure hemispherical irradiances on a flat surface. The Ozone Monitoring Instrument (OMI) on board, the NASA EOS Aura space craft is a nadir viewing spectrometer that measures solar reflected and back scattered light in ultraviolet and visible spectrum. The study shows that OMI overestimate the ground based data before monsoon by 71.28%, 47.29%, 27.92% and 35.83% respectively at Kathmandu, Pokhara, Biratnagar and Lukla. However during the monsoon period the same comes down to 8.55%, 15.63%, 10.74%, and 11.33% respectively. The main reason behind these discrepancies might be due to the spatial resolution of the satellite which estimates the UV Index on the basis of 13×24 km2 in nadir where as the ground measurement is for a single point. The correlation between satellite derived and ground measured ozone column was found to be 91 % and 89% for Kathmandu and Lukla respectively. DOI: http://dx.doi.org/10.3126/jie.v8i3.5932 JIE 2011; 8(3): 58-71

The evolution of the instrumental technique in underwater optics

Thanks to the use of the photovoltaic cell significant pioneer work in underwater optics was made in the 1930's. Among the principal instruments designed at that time, the beam transmittance meter and the scatterance meter were introduced in oceanographic studies by Hans Pettersson. The development of a technique with photomultiplier tubes provided a new impetus in optical research particularly in the study of scattering problems. A distinct advantage with photomultiplier tubes is that their high sensitivity makes possible the use of interference filters by which almost monochromatic measurements are obtained and the treacherous “band width error” occurring with broad filters is avoided.An equipment of in situ instruments fit for routine observations is described, namely an irradiance meter, a beam transmittance meter and a scatterance meter which measure the spectral energy distribution, the total attenuation coefficient and the total scattering coefficient respectively. The meters are provided with simple depth sensing units and records are obtained with an x−y recorder.It is emphasized that the optical parameters contribute greatly to the description and characterization of water masses.

Self-contained integrating irradiance meter for use underwater

A self-contained instrument is described which will record the total light energy, within known spectral limits, received at a point during a period of time such as one day. It has a linear response to light intensity and makes its recording in digital form. It was designed to be used at sea. The integrator is basically electronic, not mechanical, so that it is not affected by the accelerations to which bodies floating near the surface of the sea are subjected.