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Introduction

The UV-B Monitoring and Research Program operates a national network of solar irradiance monitoring stations equipped with instruments that provide measurements to meet the needs of both agricultural and atmospheric researchers. All instruments have on-board data logging capability. Measurements are provided as 3-minute averages, aggregated from 15/20 second readings of each instruments' raw output voltage. Our instruments and support equipment typically receive annual on-site servicing and maintenance. Mission critical sensors are calibrated annually. Measurements are scrutinized both automatically and manually by program staff daily. Trained on-site technicians service and maintain field instruments weekly, and are available to respond quickly to requests for problem resolution. These measures result in the collection of high quality data with very good capture rates. Data and data products are available for download in numeric or graphic format from the menus at the right. To access any of the data and products click on the item at the right. Our data is selected by a location and a time. Simply fill out the form and click on the button. For time periods over two months, you can download a file. For periods of two months or less, plots of the data are available.

The Spectral Irradiance section, contains data that is in situ calibrated as well as using a calibration factor. Our Data Processing Procedures link gives detailed information on our calibration methods.

Using in situ calibrations - Refers to application of the Langley calibration method to measured UV or visible MFRSR cosine corrected voltages. In situ responsivities are obtained after various filtering techniques have been applied to sequences of recently derived Langley voltage offsets after instrument deployment.

Using MLO calibrations - Irradiances derived using MLO calibrations are values produced by applying Langley derived responsivities to the UV or visible MFRSR cosine corrected voltages. The MLO calibrations are Langley calibrations from carefully selected periods of deployment at NOAA’s Mauna Loa Observation site.

Historical Lamp calibrations - Irradiances derived using historical lamp calibrations are values produced by applying lamp derived responsivities to the UV or visible MFRSR cosine corrected voltages. The lamp calibrations, were obtained from NOAA's CUCF mainly before 2008.

The Weigthed Irradiance section, contains both Erythemal Radiation and Photosynthetically Active Radiation.

Erythemal - Erythemal Radiation is the irradiance in Watts per square meter measured over the 300 through 400 nanometer range and weighted with the McKinlay and Diffey, (1987) action spectrum.

PAR - Photosynthetically Active Radiation (PAR) irradiance is an irradiance in Watts per square meter over the 400 to 700 nanometer spectral range. It is measured with a separate PAR pyranometer sensor.

The Derived Products section uses the measured irradiance to provide the products listed below:

Daily Sums - Daily sum values represent an integration over time. Basically by summing the readings over the number of seconds in the measurement period, the units of radiant power are converted to radiant energy and are useful for studying daily effects related to daily exposure. Contour Maps can be generated from Daily, Monthly or Annual Sums.

UV Index - UV Index is a measure of exposure to erythemally weighted irradiance. Basically, the erythemal irradiance in milliwatts per square meter is divided by 25 in order to provide a convenient index useful to the public. The number 25 is chosen because a typical clear sky, mid-day erythemal irradiance is about 250 milliwatts per square meter which results in a UV index of 10, which is simple to relate to potential for skin damage.

Synthetic Spectra - Synthetic Spectra is an estimation of the continuous spectrum of UV spectral irradiance incident at the surface. It is derived using an algorithm that can be best described as a physically consistent curve fitting algorithm, in which the UV-MFRSR measurements are used to determine a continuous transmittance curve for UV radiation. The transmittance is multiplied by the extra-terrestrial radiation to produce total, diffuse and direct spectral irradiances. For further information see Min and Harrison(1998).

Column Ozone - Column Ozone is an inference of the total ozone in a vertical atmospheric column above the measurement site. The ozone values are inferred from UV-MFRSR measurements using a double wavelength pair technique that separates out the Rayleigh and aerosol optical depth from the total optical depth leaving the ozone optical depth as the only significant component. The ozone optical depth is expressed in Dobson units. For a more complete presentation see Gao et al. (2001).

Optical Depths - Optical Depths are provided as instantaneous or average values. Instantaneous optical depths total or (aerosol + cloud) are given at 3-minute intervals. Total optical depths are calculated using the standard Beer's Law approach, (ln(V0) - ln(V))/airmass. Rayleigh and ozone optical depths are subtracted from total optical depths to give aerosol optical depths. V0 for each wavelength and requested date is determined from a time series of Langley-generated voltage intercepts for morning periods. The Langley method is described in Harrison and Michalsky (1994). Average optical depths are total optical depths from Langley analyses for each morning and/or afternoon on which a successful analysis was obtained. Each value is the slope of a regression of ln(voltage) on airmass, as described in Harrison and Michalsky (1994). Time periods included in the analyses are limited to specific airmass ranges which vary by wavelength: 1.5-3.0 for 332 and 368nm; 2.0-6.0 for 415-870nm.

The Instrument Characterisitics section, shows deployment history by location or serial number as well as the calibration information.

Filter Function - Filter Function represent the relative response of the individual channels as a function of wavelength. For the UV-MFRSR these response functions have a nominal 2 nm bandwidth at half max whereas for the vis-MFRSR the filter functions allow a broader 10 nm nominal bandpass at half max.

Angular Cosine Corrections - These plots define the normalized ratio or error of the measured angular response to ideal(cosine) response for each channel for each shadowband instrument. This radiometric characterization is made along two orthogonal planes (-90 to +90 south-north and -90 to +90 west-east) of the diffuser. The UV-MFRSR fore optic is designed for near-perfect angular response, and the Lambertian response of these instruments has been described by Harrison et al. (1994) and Michalsky et al. (1995). These angular corrections are applied to the direct-beam measurement, and also to the diffuse measurement assuming isotropic sky irradiance, then these corrected direct and diffuse values are added to get a revised total horizontal value.

Langley Voltage Intercepts - Langley Voltage Intercept or V0 represents a hypothetical voltage reading that the detector - amplifier system would have if it were making its measurement at the top of the atmosphere where the optical depth is zero. This instrument characteristic is used to derive a responsivity of the respective channels assuming the extraterrestrial solar spectral irradiance is known and constant.

Serial Number Deployment History - The Serial Number Deployment History page displays the deployment history of UV-MFRSR, Vis-MFRSR, the PAR sensor and the UVB-1 broadband instruments. After selecting an instrument type and serial number, the dates that the instrument was located at all sites during its history of deployment are displayed.

Site Location Gap History - The Site Location Gap History lists the periods for which no data is available for the UV-MFRSR or vis-MFRSR for the selected site.

Our Anciliary Measurement section allows access to various other measurements logged.

Internal Head Temperature - The internal head temperature (C° ) is given for selectable UV and vis-MFRSR instruments.

Air Temp., Humidity, Barometer and Reflective Solar Irradiance - These are supporting meteorological measurements for selectable sites. The Reflective Solar Irradiance(albedo) is the upwelling visible irradiance measured by a downward looking pyranometer and is used primarily to indicate the presence of snow.

Electronic Offset(Bias) - The Electronic Offset or Bias is a voltage which is measured around local midnight. This voltage is subtracted from the measured instrument voltages before calibration coefficients are applied.

UVA (uncalibrated) - The UVA (uncalibrated) data present the millivolt output signal of the UVA sensor. This is a special use signal that indicates the relative change in the UVA signal.