The Effects of Time Compositing on Obtaining Clear-Sky Coverage for Infrared Temperature and Moisture Profiling from Geosynchronous Orbit

Abstract

The impact of time compositing on infrared profiling from geosynchronous orbit was evaluated for two convective outbreak cases. Time compositing is the accumulation of the data from several successive images taken at short intervals to provide a single field of measurements with the temporal resolution equal to the time to take all of the images. This is especially effective when the variability of the measurement is slow compared to the image interval. Time compositing should be able to reduce the interference of clouds for infrared measurements since clouds move and change. The convective outbreak cases were on 4 and 21 May 1990 over the eastern Midwest and southeastern United States, respectively. Geostationary Operational Environmental Satellite imagery was used to outline clear areas at hourly intervals by two independent analysts. Time compositing was done every 3 h (1330?1530 UTC; 1630?1830 UTC) and over the full 5-h period. For both cases, a significant increase in coverage was measured with each 3-h compositing (about a factor of 2) and a further increase over the full period (approximately a factor of 3). The increase was especially useful in areas of broken cloud cover where large gaps between potential profiting areas on each image were reduced. To provide information an measurement variability over local areas, the regions where the clear-area analyses were done were subdivided into 0.5° latitude-longitude boxes, and if some portion of each box was clear. It was assumed that at least one profile could he obtained within the box. In the largest clear areas, at least some portion was clear every hour. Even in the cloudier regions, multiple clear looks were possible during the entire period.