Stereographic Observations from Geosynchronous Satellites: An Important New Tool for the Atmospheric Sciences

Abstract

The capability of making stereographic observations of clouds and their temporal changes from two simultaneously scanning geosynchronous satellites is a new basic meteorological analysis tool with a broad spectrum of applications. Stereo height measurements, because of their higher horizontal resolution and dependence on only straightforward geometric relationships, represent a big improvement over previously used infrared-based techniques. Verification using high altitude mountain lakes indicates that stereo cloud height accuracies of ± 0.1–0.2 km are possible near reference points of known elevation. The smallest cloud features observed by the present operational geosynchronous satellites (GOES), which have spatial and temporal resolution of 1.0 km and 3 min, can be measured with height accuracies of ± 0.5 km. Absolute stereo height accuracy, far from landmarks, is also about ± 0.5 km if accurate navigation solutions are available for both satellites. Computer remapping of digital image pairs allows the display and height measurement on time sequences of stereo images using an interactive information processing system. Rapid time sequencing of the series of stereo image pairs gives an effective 4-dimensional representation of cloud dynamics. Several interactive techniques have been developed for point measurements of cloud height and cloud height contouring. The stereo observations have been applied to meteorological problems, including: cloud top height contours of intense convective clouds in hurricanes and severe thunderstorms; cloud top and cloud base height estimates for satellite cloud-wind altitude assignment; atmospheric temperature profiles from the combination of stereo heights and infrared cloud top temperatures; determination of cloud emissivity; and finally, comparisons are made between stereo-observed, tropopause-penetrating thunderstorm tops with altitudes up to 17 km and severe weather observations from radar and surface reports. Present stereo coverage using the operational GOES satellites for research demonstrations includes large areas of North and South America and the surrounding oceans. Recommendations are given for operational stereo observations with greater coverage and improved performance employing a third GOES satellite at 105°W.