TRMM: Tropical Rainfall Measuring Mission

Fig. 1. The TRMM satellite

Image courtesy of Goddard Space Flight Center, NASA

The Tropical Rainfall Measuring Mission (TRMM) satellite is a joint project between the United States (under the leadership of NASA's Goddard Space Flight Center) and Japan (under the leadership of the National Space Development Agency, or NASDA). The first spacecraft designed to monitor rain over the tropics, was successfully launched from Tanegashima, Japan, on November 27, 1997, at 13:27pm Los Angeles (California) time. TRMM travels between ± 35 degrees latitude in a low earth and low inclination orbit. TRMM is the first mission to measure precipitation quantitatively from space. It includes the first precipitation radar (PR) to be flown in space, along with a 9-channel SSM/I-like passive microwave imager (TMI), an AVHRR-like visible-infrared radiometer (VIRS), a lightning sensor and a cloud sensor. The PR, TMI , and the VIRS are designed to obtain rainfall and other relevant information (e.g. rain type, height of the bright band, cloud type, cloud top height) individually.

Visible Infrared Scanner (VIRS)

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. The TRMM/VIRS fire product is revealing very clearly the seasonal patterns of biomass burning in the tropics and subtropics. The two images below compare the location of fires in July and December, 2000.

July 2000. Note that in the region of detection (the blue band), fires are burning principally below the equator. Burning of biomass, whether it be savanna, brushland or forest, is carried out during the drier season. Within the tropics, the ITCZ (and the rain associated with it) migrates north and south with the solar equator. In July, the ITCZ is generally north of the equator, and biomass burning is likely to take place south of the equator. This pattern is especially noticeable in Africa. 

 

December 2000. In this data set, fires in Africa are taking place in the sub-Saharan region, north of the equator. By this time of year, the solar equator has migrated south toward the Tropic of Capricorn, and the ITCZ, and its rains, have moved along with it. Biomass burning of savanna and woodland is now more likely to occur north of the equator.