The Visible and Infrared Scanner VIRS) is one of the primary instruments on board the Tropical Rainfall Measuring Mission (TRMM) launched in November, 1997. VIRS is one of the three instruments in the rain-measuring package will serve as a very indirect indicator of rainfall. It will also tie in TRMM measurements with other measurements that are made routinely using the meteorological Polar Orbiting Environmental Satellites POES) and those that are made using the Geostationary Operational Environmental Satellites (GOES) operated by the United States.

VIRS, as its name implies, senses radiation coming up from the Earth in five spectral regions, ranging from visible to infrared, or 0.63 to 12 micrometers. VIRS is included in the primary instrument package for two reasons. First is its ability to deliniate rainfall. The second, and even more important reason, is to serve as a transfer standard to other measurements that are made routinely using POES and GOES satellites. The intensity of the radiation in the various spectral regions (or bands) can be used to determine the brightness (visible and near infrared) or temperature (infrared) of the source.

If the sky is clear, the temperature will correspond to that of the surface of the Earth, and if there are clouds, the temperature will tend to be that of the cloud tops. Colder temperatures will produce greater intensities in the shorter wavelength bands, and warmer temperatures will produce greater intensities in the longer wavelength bands. Since colder clouds occur at higher altitudes the measured temperatures are useful as indicators of cloud heights, and the highest clouds can be associated with the presence of rain.

Instrument

The VIRS is a 5-channel cross-track scanning radiometer that measures radiance in five bandwidths from the visible through the infrared spectral regions: 0.63, 1.6, 3.75, 10.80, and 12.0 µm at 2km resolution. Although the VIRS instrument is designed primarily to study clouds and precipitation, it is capable of spotting active fires as well as evidence of burn scars. The TRMM VIRS 4km² Fire Product shows the number of 4.4 km² pixels in each half-degree grid cell (each cell is 2500 square kilometers at the equator) that are hot enough to contain a large fire. These data, summarized for each month, are currently being used to monitor natural and man-made fires in the Tropical and Sub-tropical zones (+/- 40 degrees from the equator). The TRMM orbit causes the local overpass time to drift over the entire 24 hours of a day approximately once each month, enabling observation of regional diurnal burning cycles.

Data Access

All TRMM products are archived and distributed by the Goddard Distributed Active Archive Center (>DAAC) and its subcenter under TRMM data access page. For further information concerning TSDIS operations go to ths TSDIS homepage.

The TRMM Mission, its Objectives and the role of VIRS

TRMM is NASA's first mission dedicated to observing and understanding the tropical rainfall and how this rainfall affects the global climate. The joint mission with the National Space Development Agency of Japan was launched on Nov. 27, 1997, from the Japanese Space Center, Tanegashima, Japan, and has produced continuous data since Dec. 8, 1997. The primary rainfall instruments on TRMM are the TRMM Microwave Imager (TMI), the precipitation radar (PR), and the Visible and Infrared Radiometer System (VIRS). Additionally, TRMM carries the Lightning Imaging Sensor (LIS) and the Clouds and the Earth's Radiant Energy System Instrument (CERES). These instruments can all function individually or in combination with one another. TRMM is part of NASA's Mission to Planet Earth, a long-term, coordinated research effort to study the Earth as a global system.

VIRS on TRMM adds cloud-top temperatures and structures to complement the description of the two microwave sensors. While direct precipitation information from VIRS is less reliable than that obtained by the microwave sensors, VIRS serves an important role as a bridge between the high quality but infrequent observations from TMI and PR with the more available data and longer time series data available from the geostationary VIS/IR satellite platforms.

Links

• Visit Earth Observatory to built your own animation by given datasets.
• Official Tropical Rainfall Measuring Mission

Contact

If you would like to have more information about the VIRS data, please contact wdc@dlr.de.