The polar regions are expected to be particularly sensitive to anthropogenic global change. Due to the difficulties in modeling high latitude climate and the logistical challenges with polar field work, satellite remote sensing will have an increasingly important role to play in polar climate research. For studies of atmospheric radiation and meteorology, accurate cloud detection and classification is crucial. Modern methods for polar cloud classification utilize both multispectral threshold and automated pattern recognition techniques. For monitoring sea ice concentration, passive microwave sensors offer an all-weather advantage over visible or infrared scanners, although over clear-sky scenes the latter can provide a much finer spatial resolution. The various algorithms for satellite retrieval and remote sensing in the polar regions are constantly being refined and improved.

A new Arctic stratospheric observatory (AStrO) has been established at Eureka (80 degree(s)N, 86 degree(s)W) in northern Canada. This observatory is one of the three designated components of the Arctic Primary Station of the Network for the Detection of Stratospheric Change (NDSC). Among the complement of sensors being installed at Eureka are two state-of-the-art lidar systems for monitoring stratospheric ozone and polar stratospheric clouds (PSC). The ozone Differential Absorption Lidar (DIAL) system utilizes a xenon chloride excimer laser transmitter operating at 308 nm as the absorbed `on' radiation. A hydrogen Raman shifter generates the `off' wavelength at 353 nm. The system provides an average output power of about 60 watts at 300 Hz. The receiver is a 1 meter Newtonian telescope provided with several special optical features to permit daylight operation. The second lidar utilizes a Nd:YAG laser source operating at 1064 and 532 nm with a 20 Hz prf. This paper describes the new lidar facilities at AStrO and presents a summary of the data obtained during the first months of operation.

The Discrete Ordinate Radiative Transfer (DISORT) model of Stamnes et al. (1988) has been used to investigate the role of cloud-surface interactions on the net surface solar flux in various atmospheric and surface conditions. To that effect, we have analyzed the sensitivity of the net (down minus up) solar flux at top-of-atmosphere (TOA) and the net surface solar flux with respect to water vapor amount in the atmosphere and cloud properties (specified through optical thickness) and types (specified through the equivalent radius - R_E) for two extreme (with respect to their reflecting properties) types of surface conditions: snow and ocean.

From May 20 to November 5, 1980 hourly temperature and daily moisture measurements were made in the L, F, H, and A1 horizons of a birch forest in Alaska. Laboratory measurements of respiration were made on the same forest floor horizons under varying conditions of temperature and moisture. From the respiration's responses to temperature and moisture variation we simulated mathematically how a natural forest floor emits CO₂ and how these emissions change with varying climate. The simulation accounted for 79 -90% of the sum of the squared differences of the mean for each moisture-temperature bin and the overall mean of such bin means. When the response model was applied to the field data of moisture and temperature to estimate a seasonal respiration of CO₂, the estimates were in excellent agreement with independent field measurements of the season's CO₂ respiration. The climate of the F, H, and A1 horizons was also simulated mathematically as determined by the climate of the L horizon. The two models were tandemed to provide a new estimate of the season's total CO₂ emission. Again, there was excellent agreement with the observed respiration.

A number of problems of aerosol/cloud and radiation/cloud interactions, as well as cloud chemistry, related to climate change study, which could be addressed with 3-D cloud structure models which incorporate a detailed `inventory' of physical processes. Also, cloud remote sensing problems can be sensitive to the 3-D structure of clouds. Those problems motivate us to develop a 3-D Large Eddy Simulation model with explicit description of cloud microphysical processes. The model output contains fields of aerosol and drop size distributions, among other output parameters. Some results of recent model runs are presented. In order to study a 3-D radiance response of the system we derive a `two-stream' approximation of radiative transfer for a 3-D inhomogeneous medium based on a 3-D delta- Eddington method. The basic equations of the method are derived and the solution method is outlined. Relevance of the model to investigation of arctic stratus layers is discussed.

Solar radiation having been absorbed by the atmosphere and underlying surface and then being transformed into other forms of energy regulates all the dynamic processes occurring in the Earth's climate system. The clouds covering a considerable portion of the globe represent the major modulator of radiation energetics of the climatic system. Cloud cover as being subjected to strong variations in its forms and in the space is the major contributor to the dynamics of the radiation regime and brightness fields of the system. In this connection, one of the most important problems in the theory of radiative transfer lies in the study of the effects associated with the extreme spatial variability of clouds as well as in the construction of adequate parameterization schemes of radiation balance of the system `atmosphere-underlying surface' in the numerical models of weather forecast and climate. On the basis of the theory of radiative transfer in the statistically homogeneous cloud fields with stochastic geometry and deterministic optical parameters inside the individual clouds (broken clouds) we intended to evaluate the sensitivity of the mean spectral fluxes of visible solar radiation to the variations in such characteristics as (1) cloud drop size distribution function; and (2) optical parameters of atmospheric aerosol being contained both inside the clouds (as condensation nuclei) and outside them.

In recent years there has been an increasing awareness of the importance of including the radiative effects of clouds and aerosols in atmospheric radiative applications, e.g., chemical dynamical radiative transfer models and UV-dose calculations. In this work we review radiative transfer theory and present some new results of how clouds and aerosols affect UV- doses, photochemistry, and dynamics. We start by deriving the equation pertinent to radiation transport in cloudy and aerosol loaded atmospheres. A discrete ordinate solution of the radiative transfer equation is outlined. Further, a brief summary is given of how UV-doses and radiative quantities relevant for photochemistry and dynamics may be efficiently and accurately calculated. The presence of clouds and aerosols affect stratospheric and tropospheric photodissociation and warming/cooling rates, and UV-doses at the ground. We give examples of how large the radiative effects of clouds and aerosols may be on these quantities. The importance of the radiative coupling between the troposphere and the stratosphere is demonstrated. Implications for ozone chemistry and stratospheric dynamics are mentioned. Finally some interesting areas for future research are highlighted.

Radiative perturbation theory is a technique for calculating the influence of selected atmospheric variations on certain radiative effects, such as fluxes, heating rates, exiting radiances, etc. This technique has already demonstrated its utility by its ability to handle the wide variability of aerosol optical properties. To date, all applications have been to azimuth- averaged effects, such as fluxes and heating rates. In the present study, we have looked at exiting radiances, and how these may be affected by perturbations to the aerosol phase function. Radiative perturbation theory is the ideal tool for such a study, as it is able to show explicitly the sensitivity of exiting radiances to selected parameters in the Legendre series expansion of the phase function.

The U.S. Department of Energy (DOE) initiated the ARM Program in 1990 to provide an experimental testbed for the study of cloud and radiative processes with the ultimate goal of improving the performance of general circulation models for global and regional prediction of climate change. The concept of the program is to acquire high-quality, long-term data at sites representing important climatological regimes, to conduct long-term and campaign experiments and to establish strong coordination among the U.S. National Laboratories, the non-DOE scientific community, and national and international research programs. During the past three years, several key experiment locales have been identified, a science team has been selected, a few short term experiments have been conducted, and the first permanent surface site has been established in Lamont, Oklahoma, U.S.A.

The North Slope of Alaska and the adjacent Arctic Ocean has been chosen as the primary high-latitude ARM site. This is a region of the globe where, on average, the planet loses more energy to space than it receives from the sun. Global climate models appear to be particularly sensitive to climate perturbations at high Northern latitudes. It is therefore important to pay careful attention to these heat sink regions and incorporate high-latitude climate processes correctly. Once we get high latitude processes `right,' we can use the polar regions as a diagnostic for global climate change. The Arctic is characterized by extreme seasonal variation in insolation, surface properties, and exchange of water vapor between the surface and the atmosphere. This extreme variation leads to important climate feedback mechanisms involving the interaction between surface temperature and water vapor, cloud cover, and surface albedo. The challenge for the North Slope of Alaska ARM site is to capture these high-latitude feedback processes for inclusion in global climate models.

Measurements of surface radiation fluxes and radiosonde sounding data under overcast cloud situations during spring-summer 1988 at Barrow (Alaska) are analyzed. These data were combined with calculations from simple radiation models to estimate the surface radiation budget as well as reflectance, transmittance, and absorptance of the earth-atmosphere system on an hourly basis. Warming/cooling rates of the whole atmosphere were computed. These parameters for clear sky conditions are also presented.

Recently, Smith and collaborators from University of Wisconsin-Madison have clearly established the possibilities of sounding tropospheric temperature and water vapor profiles with a ground-based uplooking interferometer. With the same perspective but for somewhat different applications, the Defence Research Establishment Valcartier (DREV) has initiated a project with the aim of exploring the many possible avenues of similar approaches. DREV, in collaboration with BOMEM (Quebec, Canada), has developed an instrument referred to as the Double Beam Interferometer Sounder (DBIS). This sounder has been conceived to match the needs encountered in many remote sensing scenarios: slant path capability, small field of view, very wide spectral coverage, and high spectral resolution. Preliminary tests with the DBIS have shown sufficient accuracy for remote sensing applications. In a series of field measurements, jointly organized by the Geophysics Directorate/PL, Hanscom AFB, and DREV, the instrument has been run in a wide variety of sky conditions. Several atmospheric emission spectra recorded with the sounder have been compared to calculations with FASCODE and MODTRAN models. The quality of measurement-model comparisons has prompted the development of an inversion algorithm based on these codes. The purpose of this paper is to report the recent progress achieved in this research. First, the design and operation of the instrument are reviewed. Second, recent field measurements of atmospheric emission spectra are analyzed and compared to models predictions. Finally, the simultaneous retrieval approach selected for the inversion of DBIS spectra to obtain temperature and water vapor profiles is described and preliminary results are presented.

Ideally measurements of spectral ultraviolet irradiances require a perfect adaption of the entrance optics to the cosine of the incidence angle. Other requirements of the entrance optics are: No ageing, high throughput at all wavelengths, weatherproofness, and no fluorescence of their material. In practice, however, available entrance optics differ by more than 10% from the ideal cosine response for incident angles greater than 60 degree(s). Without a correction this introduces a great uncertainty in the absolute measurement of irradiances, especially when the sun is low. A measurement of the angular dependence of the entrance optics and a knowledge of the ratio of the direct to the diffuse component of the global irradiance can be used to correct this cosine error. The correction is dependent on wavelength and sun elevation. For our cosine diffuser the corrections vary between 3% and 18%. The accuracy of the corrections is limited by the accuracy of the measurement of the angular dependence of the cosine diffuser, by the knowledge of the ratio of the direct to the diffuse radiation and by the knowledge of the angular dependence of the radiance of the diffuse component. We assume that our method reduces the overall cosine uncertainty from about +/- 10% to about +/- 3%.

A UV-B meter having sharply increasing sensitivity with decreasing wavelength can be shown to well represent a large number of known biological action spectra. The accuracy of the meter, which is temperature stabilized, and its long term stability enable accurate UV and UV trend information to be obtained. The meter is readily calibrated in the laboratory or in the field since it has cosine law agreement. Spectral responses between meters are negligibly different. The meter requires very little maintenance. An on-board computer stores months of data and can be remotely interrogated. The initial cost is low making an extensive network possible. The redundancy of a network enables long term UV trend determinations to be made with even greater confidence than that from a single meter.

Solar calibrations and laboratory tests were performed for erythemally weighted Robertson- Berger type UV radiometers. The test instruments included four Solar Light Model 500 and two Model 501 meters. The solar calibrations were performed at different elevation angles with relatively clear skies. The absolutely calibrated Optronic 742 spectroradiometer was used as a reference instrument and the measurement results were normalized to the temperature of 25 degree(s)C. The uncertainty of the spectroradiometric measurements is estimated to be +/- 8%. The absolute average calibration factors obtained varied from 1.05 to 1.16 for Model 500 meters and from 0.93 to 0.98 for two Model 501 meters. The spectral responsivity and cosine responses were found to be satisfactory for both meter types. To obtain better knowledge of the thermal properties of the Solar Light Model 500 meters a temperature sensor was installed at the underside of the green filter located just below the phosphor layer. The obtained temperature coefficient based on the green filter temperature measurements was 0.80%/ degree(s)C. The overall uncertainty of Solar Light Model 501 measurements is estimated to be +/- 11% and according to the phosphor temperature corrected SL 500 measurements +/- 14%. Without temperature correction the uncertainty of Model 500 measurements increases up to +/- 19%.

SCIAMACHY, the scanning imaging absorption spectrometer for atmospheric cartography on Envisat-1 (1998) measures global distributions of ozone and greenhouse tracegases by employing DOAS and SBUV techniques. As an aid in the development of instrument hardware and data-processing algorithms, an instrument simulator has been developed predicting signal to noise performance. Calculated performance is substantiated by early test results on the optical unit and shows that instrument requirement specifications can be met in most instances.

Changes in atmospheric ozone have been identified from long-term, ground-based, and satellite observations of column ozone amount over much of the earth's surface, yet there is little data available on the resultant ground level ultraviolet (UV) radiation about which there is so much concern. This is explained in part by the difficulties of making UV measurements in the environment, and the lack of any standard instruments or protocols for such work. Instruments designed for spectral solar UV measurement have been compared under laboratory and field conditions. Results indicate that it is possible to consider different instruments contributing to a single network of UV monitoring sites provided careful attention is given to calibration and operation procedures and to understanding each aspect of the instruments' performance.

Spectral measurements of solar ultraviolet irradiance carried out near Thessaloniki, Greece, are analyzed with respect to very strong variations of aerosol optical depth while the other influencing parameters are about constant. When aerosol optical depth is increased about twofold, global UV irradiance (from sun and sky) decreases less than 10%. In contrast, direct irradiance (from sun only) is reduced about twofold. If spectral measurements of global irradiance only are made, it is not possible to distinguish between situations with highly different aerosol contents. Measurements of both, global and direct irradiance, appreciate additional information to adapt radiation transfer models to actual atmospheric aerosol conditions.

Two methods have been investigated to map UV surface irradiance over Antarctica and the adjacent oceans using satellite remote sensing and ground truth radiometer measurements. Both methods are based on radiance observations from the Advanced Very High Resolution Radiometer (AVHRR) and from the Total Ozone Mapping Spectrometer (TOMS). Surface albedo and cloud optical depth are estimated from visible and infrared AVHRR data, and ozone concentration is derived from TOMS data. Radiative transfer models are applied to retrieve geophysical parameters from satellite data but also to compute the surface UV irradiance. The two methods differ in: (1) the derivation of cloud optical depth, and (2) the type of radiative transfer model used. Preliminary results from both methods are presented and compared with ground measurements made at Palmer Station, Antarctica.

Exceptionally low total ozone up to 40% below the normal level has been measured over Northern Europe during winter and spring in 1992 and 1993. The increase in the UV exposure of the Finnish population associated with the combined effects of ozone depletion and snow reflection was examined in this study with the aid of broadband measurements and theoretical calculations. The theoretical calculations were verified with spectral and broadband measurements. The calculations show that the annual horizontal doses in Helsinki (60.2 degree(s)N, 25 degree(s)E) are about 30% higher than in Saariselka (68.4 degree(s)N, 27.5 degree(s)E), but the difference is only 12% for vertical doses owing to the stronger contribution to vertical (facial) surfaces of the reflection of UV from snow. In Saariselka, the maximum vertical irradiance at the end of April approaches the midsummer values. The ozone depletions had no significant effect on the biologically effective UV in 1992 since the total ozone returned to normal at the end of March before the UV increased to biologically significant level. In contrast, in 1993 low ozone levels were measured still at least up to mid May resulting in an average theoretical increase of 8% during a period from 14 April until 22 May in biologically effective UV.

Quantitative spectral, solar UV measurements are introduced together with lunar spectral measurements in arbitrary units. Meteorological factors have a more pronounced effect on the UV irradiance than the ozone layer, and the ozone layer has an increasing attenuation effect towards higher latitudes. Coordinated biological and spectral lunar observations are outlined.

Solar irradiance in the spectral region 280 to 400 (800) nm was measured with a double monochromator at two Arctic locations, Tromso (70 degree(s)N) and Longyearbyen (78 degree(s)N). During the observational (midnight sun) period in Longyearbyen, the maximum UVB irradiance recorded was less than 0.3 W/m², and no radiation was detected for wavelengths below 300 nm. Such low levels are believed to be a consequence of the low solar elevation angle and the high ozone content of the Arctic ozone layer, which absorbs the incident UV light. With ozone levels between 280 and 350 DU over the period of study, Tromso and Longyearbyen recorded only one-ninth of the calculated UVB radiation at the equator. Malignant melanoma of the skin is three times higher in Oslo than in the northernmost parts of Norway and the rate of skin cancer is 7-8 times higher in the white population of equatorial countries than in Arctic regions. The low UVB radiation combined with a high protective ozone shield in the Arctic means people are at little risk from sun induced skin damage and development of skin cancer in this region.

A radiative transfer model is developed for the calculation of ultraviolet (UV) fluxes in the atmosphere-ocean system. The radiative transfer equation for the atmosphere is solved by the modified discrete ordinate method. Obtained angular distribution of radiance at the ocean surface serves as a boundary condition for radiative transfer equation in the ocean. The latter is solved by the quasi-single approximation. The comprehensive models are used for the spectral dependencies of optical properties of the atmosphere and the ocean. Calculations of spectral irradiance within the 290 - 400 nm region have been carried out for different solar zenith angles and total amount of ozone inherent to high latitude regions. By convolution of irradiance spectra for the ocean with the phytoplankton action spectrum the UV dose rates have been obtained for different depths.

The model of the infrared glow in the upper polar atmosphere has been developed. An influence of intense auroral disturbances has been investigated. It is shown that infrared emissions play an important role in the thermal state of the upper polar thermosphere. The calculations result in a temperature overestimate about 200 degree(s)K at the altitude 120 km if they were made without infrared cooling. The roles of the major and minor atmospheric components in the thermospheric infrared glow have been studied. It was found that O, NO, CO₂, NO⁺ components are the principal thermospheric infrared radiators. The 63 (mu) , 5.3 (mu) , 15 (mu) and 4.3 (mu) - emissions of these compounds determine the thermospheric thermal state during an aurora. Model calculations of the infrared emission intensities have been compared with rocket measurements in the aurora. A good agreement between model calculations and experimental data has been obtained.

Global spectral UV-B measurements performed at Reykjavik (64 degree(s)N), Iceland since November 1991 are used in this work to study the influence of changes in total ozone on the UV-B solar radiation reaching the earth's surface at high latitudes, under variable weather conditions. The measured UV-B levels during the winter-spring season of 1992 are compared with those of the same season in 1993, during which significantly low ozone values were observed. This comparison shows increases in solar UV-B fluxes at ground level of as high as 40%. Also, the UV-B variability during summer time, when prolonged daylight exists, is studied. The broad range of total ozone levels measured during the period of study allows the calculation of the UV-B amplification factor due to changes in total ozone at different solar zenith angles which were found to range between about 2 and 4.

Increases in ultraviolet radiation (UV) caused by ozone depletion in the stratosphere are expected to have physiological effects on plants and animals. Biologists require high wavelength resolution UV data to adequately assess these effects. Numerical simulations of scattering and absorption in the atmosphere provide a useful way of predicting the global UV irradiance reaching the ground. Results from radiative transfer calculations are presented here. Two different methods are used to calculate diffuse irradiances, either the Discrete-Ordinate (D-O) method or the Delta-Eddington (D-E) approximation. Surface UV irradiances obtained with the D-O scheme are compared to those using the D-E approximation for a wide variety of atmospheric conditions, to assess how changes in tropospheric aerosol and cloud affect the accuracy of the D-E approximation. Stratospheric aerosol has been shown to be capable of increasing the UV irradiances at the ground. The magnitude of these increases is shown to depend strongly on the absorption of multiple scattered photons by ozone. The prediction of this increase by numerical models provides a good test of the accuracy of any radiative transfer approximations used. It is shown that the Delta-Eddington approximation appears to be deficient for high wavelength resolution surface irradiance prediction, in certain circumstances.

The analysis of the aerosol optical thickness at visible wavelengths for the marine aerosol is presented. Several methods preparatory for atmospheric correction (in cases where the only known optical parameter is one of the following: irradiance, visibility, relative humidity, or size distribution for aerosols) are compared. Experimental data measured in the years 1987 - 1989 and 1991 - 1992 in the region of the Norwegian Sea and the Arctic Sea are used in order to verify the theoretical models.

The spectral albedo of snow surface and the radiant flux density inside the snow are investigated by a multiple scattering model for the atmosphere-snow system. When the snow is composed of two layers with different grain sizes, albedos at the wavelengths shorter and longer than 1.4 micrometers are close to the albedos of the lower and upper layer, respectively. On the other hand, the spectral distribution of the radiant flux density inside the snow changes with the optical depth. When the optical depth of snow increases, the blue light at the wavelength from 0.45 to 0.50 micrometers becomes relatively stronger than other wavelengths. This effect is remarkable for the snow with large grain size.

Spectrally resolved radiometric measurements of middle infrared atmospheric emission can be used in conjunction with detailed radiative transfer calculations to retrieve cloud emissivity, and to estimate cloud liquid water path (LWP), optical depth, and equivalent radius of the droplet size distribution. Using a discrete-ordinates radiative transfer formulation, an algorithm has been developed to retrieve these cloud properties from FTIR data. The algorithm has been successfully applied to a four month Antarctic data set provided by the CalSpace FTIR Spectroradiometer. Radiative transfer calculations were performed to estimate spectral cloud emissivity for a range of cloud optical depth, liquid water content, and equivalent radius, sufficient to bracket values expected in the field. These calculations made use of bi-modal droplet size distributions actually observed in Antarctic clouds. Using a least- squares algorithm, a theoretical cloud emission spectrum is chosen which best reproduces a given measured brightness temperature spectrum. The results show marked differences in cloud emissivity between high and low overcast layers, and between clouds with and without precipitation. The results also suggest that the emissivity of a maritime Antarctic cloud deck should be smaller for a given LWP than the parameterization frequently used in general circulation models.

The spectral Earth's albedo in the 0.25 - 0.34 micrometers range for the solar zenith angles O degree(s) - 85 degree(s) has been obtained from the analysis of experiment BUFS on the spaceship `Meteor' and the theoretical albedo calculations carried out for various atmospheric conditions taking into account the ozone radiation absorption in the Hartley and Huggins bands and Rayleigh radiation scattering. The obtained results are compared with those of the SBUV `Nimbus' and SME data.

Spectral ultraviolet measurements in the wavelength range 290 to 325 nm made at Sodankyla (67.4 degree(s)N, 26.6 degree(s)E) in 1990 - 1992 were used to study the effects of surface albedo, atmospheric total ozone, and atmospheric aerosol content on UV irradiance on the surface of the Earth. Clear sky observations with optical air masses 1.4 and 2.0 were used in the analysis. The annual course of surface albedo between 0.1 and 0.8 was found to be responsible for a change of 10% in irradiance at 325 nm, but no effect was seen at lower wavelengths or in CIE-weighted integrated values.

An automatic spectroradiometer has been developed. Spectral measurements of the direct solar irradiation and of the angular dependence of the diffuse radiation are performed. The spectral range is 400 - 2300 nm with a resolution varying from 8 to 80 nm. The direction is selected by a scanning mirror/collimator system. Grating monochromators are used with Si and PbS photon detectors. The whole system is built into a caravan and intended for continuous operation. Based on long term time series from this instrument, detailed statistical models of the radiation are developed.

This paper presents field measurements taken during last winter with a Barnes transmissometer. Transmission data in four infrared bands were recorded; a description of the instrument is presented along with the measured transmissions. The atmospheric transmission over a 200 m path has been calculated on a PC with FASCOD2 using `winmaker:' substitution of maker by an interactive editor under windows.

A high-precision absolute electrical substitution radiometer with a thermally stabilized cavity as a receiving element was designed at VNIIOFI and used to derive the Russian Special Standard of the solar irradiance. This nonselective radiometer is used in the measuring range from 50 to 2000 W/m² with uncertainty of 0.1% and from 1 to 50 W/m² with uncertainty not more than 0.5%. Measurement and data processing in the radiometer are completely automated. The method using this absolute radiometer was realized for calibration of solar cells and other selective detectors. For example we have calibrated different detectors based on photodiodes with filters used for measuring the solar irradiance in spectral regions: 0.29 - 0.34 micrometers , 0.34 - 0.39 micrometers , 0.38 - 1.10 micrometers . This method includes the relative measurements of spectral sensitivity of photodetectors, filters transmittance, spectral irradiance of sources of radiation, and absolute calibration of photodetectors using the absolute radiometer.

A UV spectrometer system is developed consisting of a highly accurate scanning double monochromator for especially the biologically relevant UV-B region and a multichannel detection system for UV-A radiation measurements. Integrated global irradiance is monitored continuously using a pyranometer. The operation of the combined system is fully automatic. The system is mounted in a light-tight and temperature-stabilized mobile container. The advantage of the combination of the two spectrometers is a reduction of the duration of a measurement cycle and the possibility to study systematic measurement errors. An additional advantage is that differences in global irradiances can be detected by a series of multichannel measurements during the scan of the shorter wavelengths.

The Robertson-Berger sunburn meter, model 500, has no temperature compensation, and the effect of temperature on the instrument response has been investigated and discussed in several reports. It is recommended to control the temperature of the detector or at least measure it. The temperature sensor is recommended to be positioned within the detector unit. We have measured the temperature at three different positions in the detector: At the edge of the green filter where the phosphor layer is placed; at the glass tube covering the cathode; and, finally, the air temperature inside the instrument. These measurements have been performed outdoors since July 1991, with corresponding measurements of the global and direct solar radiation. There was no difference between the temperature of the glasstube covering the cathode and the air inside the instrument, at any radiation level. However, there was a difference between the green filter and the two others. The difference is linearly dependent on the amount of global radiation. The temperature difference, (Delta) T (temperature between the green filter and the air inside the sensor), increased 0.8 degree(s)C when the global irradiation increased by 100 W/m². At maximum global radiation in Trondheim (latitude 63.4 degree(s)N) (Delta) T was approximately 5 - 6 K when the global radiation was about 700 W/m². This was valid for temperatures between 7 degree(s)C and 30 degree(s)C. Only clear days were evaluated.

Because of the very steep decrease of ozone absorption in the wavelength-range between 290 nm and 350 nm it is important to achieve a very high wavelength accuracy for high-resolution spectral measurements of solar UV-radiation. A wavelength error of 0.1 nm may result in an intensity error up to 10%. Therefore, a method is needed for determining the wavelength shift of measured solar UV-spectra in relation to a reference spectrum. By a comparison of the Fraunhofer structures of the measured spectrum and the extraterrestrial solar radiation, a wavelength correction with an accuracy of about 0.02 nm is possible.

Abstract not available.

In this work we considered a possibility to register harmful technical gases NO₂, Cl₂, SO₂ which are contained at the atmospheric layer closest to the Earth from the outer space as well as from the Earth for their limit concentrations. We defined the technical parameters of radiometric facilities which allow us to record the spatial distribution of those gases.

A possible effect of the atmospheric transparency decrease, caused by solar cosmic rays, is investigated. The data of transparency measurements on the high and mid-latitude stations: Murmansk, Archangelsk, Leningrad have shown that the effect really took place in a number of events with great intensity of solar protons. Two to four times the number of density increase of the big aerosol particles was observed in all these cases. So the obvious cause of the transparency decrease is an attenuation by the aerosols generated by the energetic solar particles.