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During snowmelt net radiation above a snow surface was measured simultaneously at forty-four locations to permit comparison of measurements in a black spruce forest with those in the open. / Data, obtained during cloudy daylight and at night were used to produce meaningful surface radiation maps of the experimental site. For all periods of observation the range in values recorded between any two sensors was greatest between those positioned in the forest. Spatially, net radiation varied most within the forest. The location of high and low net radiation values recorded during the day are the reverse at night. The spruce canopy reduces net radiation at the snow surface on cloudy days by obstructing a portion of the incident diffuse sky radiation. Conversely, the canopy is shown to exert considerable effect as a source of longwave radiation. Surface net longwave radiation increases sharply with proximity to trees. The effect of local and snow surface topography is greatest on clear days when irradiance is highly directional. On clear nights the forest edge is distinguished by a steep gradient of net radiation. On cloudy nights the variability and range in surface net radiation are greatly reduced.

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