Visible Images

Visible satellite images record visible light from the sun reflected back to the satellite by cloud tops, land surfaces and ocean surfaces. These black-and-white images show what your eye would see from space (if you were color blind) and hence represent nothing fancier than ordinary black-and-white photographs of the earth from space. The brightness of any feature on a visible satellite images depends on (1) how directly light from the sun strikes it, and (2) how reflective the feature is. Cloud tops and snow and ice surfaces tend to reflect visible light best, so they tend to be the brightest (i.e., whitest) features on a visible satellite image. Ocean surfaces tend to reflect the least visible light, so they tend to be the darkest features. Visible images are unavailable during the night when the sun is down.

Infrared Images

Infrared satellite images record invisible infrared radiation emitted directly by cloud tops, land surfaces or ocean surfaces. The warmer an object is, the more intensely it emits radiation, so the intensity with which a feature on earth emits infrared radiation tells us about that feature's temperature. Infrared images are available during the night when the sun is down.

Using a computer, we can take the intensities of infrared radiation recorded by a weather satellite and translate them arbitrarily into different shades of gray and/or different colors, constructing images that humans can see.

On the color-enhanced infrared images colors other than gray are assigned to some of the coldest temperatures. Far from the polar regions, the coldest features invariably comprise the tops of clouds in the upper troposphere or lower stratosphere and are often associated with thunderstorms, hurricanes or midlatitude cyclones. Hence, color-enhanced infrared images help highlight storms of various types.

NEXRAD WEATHER RADAR IMAGES

In July of 1996 the last US Next Generation Weather Radar (NEXRAD) WSR-88D Doppler radar system was built in Santa Ana Mountains. The system was accepted by the NWS in February 1997. This local NEXRAD system provides storm intensity monitoring over Orange County and the Upper Santa Ana River Watershed. The addition of the local system to the existing NEXRAD systems located in Santa Barbara (Vandenberg AFB), Ventura (Sulfur Mountain), and San Diego Counties provide coverage for metropolitan Southern California. The color images can be displayed, printed and saved to disk. Storm rainfall intensity and movement is monitored by running sequences of mosaic images. Mosaic images consist of imaging data from multiple radar sites overlaid on a regional map. The storm maps and images are displayed in multiple colors representing radar reflectivity from water droplets in the atmosphere.