Global atmospheric trends in ozone column amount have focused attention on the environmental risk of exposure to ultraviolet (UV) radiation. Monitoring UV irradiance in diverse and remote locations is necessary to understand the variability of exposure, dose rates, and resultant vulnerability of ecological systems. The U.S. Department of Agriculture (USDA) UV-B Monitoring Program maintains a wide network for ground-based continuous measurement of solar radiation in several wavelengths of interest for photosynthesis, plant growth, UV exposure to humans, and photochemistry. This network provides data for analysis of UV climatology and trends at those sites. A satellite-based method to produce mesoscale-resolution mapped distributions of UV spectral irradiance has been developed that utilizes this network data for verification. The methodology combines radiative transfer modeling, multispectral image pixel classification, cloud optical depth retrievals, and auxiliary remote sensing data. Retrieved parameters are compared with ground-based measurements from the USDA network instrumentation at two sites [Poker Flat Research Range, Alaska; 65.12 deg N, 147.43 deg W, 550 m mean sea level (MSL); and Storm Peak Laboratory, Colorado, 40.45 deg N, 106.73 deg W, 3220 m MSL]. The results are used to evaluate the effects of cloud distribution and surface albedo in determining mesoscale variability of UV exposure and photolysis rates in high-latitude and high-altitude environments.
Global atmospheric trends in ozone column amount has focused attention on the environmental risk of exposure to ultraviolet (UV) radiation. Monitoring UV irradiance in diverse and remote locations is necessary to understand the variability of exposure, dose rates and resultant vulnerability of ecological systems. The USDA UV-B Monitoring Program maintains a wide network for ground-based continuous measurement of solar radiation in several wavelengths of interest for photosynthesis, plant growth and UV exposure to humans. This network provides data for analysis of UV climatology and trends at those sites. A satellite-based technique for producing mesoscale-resolution mapped distributions of UV spectral irradiance has been developed for extending this information into a region surrouding the network sites. The methodology combines radiative transfer modeling, multispectral image pixel classification, cloud optical depth retrievals and auxiliary remote sensing data. The results of the method are compared with ground-based measurements and utilized to examine the role of cloud distribution and surface albedo in determining mesoscale variability of UV exposure in high-latitude and high-altitude environments.
Airborne hyperspectral radiometers provide the opportunity to obtain calibrated remote sensing data for simulation of the exact spatial and spectral resolutions of current and future satellite systems. This paper describes the use of the NASA advanced visible and infrared imaging spectrometer (AVIRIS) instrument, flown on an ER-2 jet in the lower stratosphere, to simulate shortwave radiances from the future AVHRR-K sensors on the NOAA polar-orbiting satellites. The high spatial resolution (20 m) and discrete 10 nm spectral channels of AVIRIS allow the spectral signatures of individual pixel types to be intercompared. Observations of multiple cloud types have been obtained using the AVIRIS instrument and were used in deriving estimates of cloud optical depth and particle size using visible and near-infrared spectral reflectances. These retrievals were then compared with similar retrievals from simulated AVHRR-K radiances, using spectral weighting and spatial averaging. Coincident cloud physical measurements provided verification of the cloud parameters. The analysis results are used to evaluate the impact of AVHRR pixel resolution and bandwidth on cloud retrievals.
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