The Tropical Rainfall Measuring Mission (TRMM) was a joint space mission between NASA and JAXA designed to monitor and study tropical rainfall. The term refers to both the mission itself and the satellite that the mission used to collect data. TRMM was part of NASA's Mission to Planet Earth, a long-term, coordinated research effort to study the Earth9832124766 as a global system. The satellite was launched on 27 November 1997 from the Tanegashima Space Center in Tanegashima, Japan. TRMM operated for 17 years, including several mission extensions, before being decommissioned on 15 April 2015. TRMM re-entered Earth's atmosphere on 16 June 2015.
Background Tropical precipitation is a difficult parameter to measure, due to large spatial and temporal variations. However, understanding tropical precipitation is important for weather and climate prediction, as this precipitation contains three-fourths of the energy that drives atmospheric wind circulation. Prior to TRMM, the distribution of rainfall worldwide was known to only a 50% of certainty. The concept for TRMM was first proposed in 1984. The science objectives, as first proposed, were:
To advance understanding of the global energy and water cycles by providing distributions of rainfall and latent heating over the global Tropics. To understand the mechanisms through which changes in tropical rainfall influence global circulation and to improve ability to model these processes in order to predict global circulations and rainfall variability at monthly and longer timescales. To provide rain and latent heating distributions to improve the initialization of models ranging from 24-hour forecasts to short-range climate variations. To help to understand, to diagnose, and to predict the onset and development of the El Niño, El Niño–Southern Oscillation, and the propagation of the 30- to 60-day oscillations in the Tropics. To help to understand the effect that rainfall has on the ocean thermohaline circulations and the structure of the upper ocean. To allow cross calibration between TRMM and other sensors with life expectancies beyond that of TRMM itself. To evaluate the diurnal variability of tropical rainfall globally. To evaluate a space-based system for rainfall measurements. Japan joined the initial study for the TRMM mission in 1986. Development of the satellite became a joint project between the space agencies of the United States and Japan, with Japan providing the Precipitation Radar (PR) and H-II launch vehicle, and the United States providing the satellite bus and remaining instruments. The project received formal support from the United States Congress in 1991, followed by spacecraft construction from 1993 through 1997. TRMM launched from Tanegashima Space Center on 27 November 1997.
Spacecraft The Tropical Rainfall Measuring Mission (TRMM), one of the spacecraft in the NASA Earth Probe series of research satellites, is a highly focused, limited-objective program aimed at measuring monthly and seasonal rainfall over the global tropics and subtropics. TRMM is a joint project between the United States and Japan to measure rainfall between 35.0° North and 35.0° South at 350 km altitude.
Mission extensions and de-orbit To extend TRMM's mission life beyond its primary mission, NASA boosted the spacecraft's orbit altitude to 402.5 km in 2001. In 2005, NASA director Michael Griffin decided to extend the mission again by using the propellant originally intended for a controlled descent. This came after a 2002 NASA risk review put the probability of a human injury or death caused by TRMM's uncontrolled re-entry at 1-in-5,000, about twice the casualty risk deemed acceptable for re-entering NASA satellites; and a subsequent recommendation from the National Research Council panel that the mission be extended despite the risk of an uncontrolled entry. Battery issues began to limit the spacecraft in 2014 and the mission operations team had to make decisions about how to ration power. In March 2014, the VIRS instruments was turned off to extend the battery life. In July 2014, with propellant on TRMM running low, NASA decided to cease station-keeping maneuvers and allow the spacecraft's orbit to slowly decay, while continuing to collect data. The remaining fuel, initially reserved to avoid collisions with other satellites or space debris, was depleted in early March 2015. Re-entry was originally expected sometime between May 2016 and November 2017, but occurred sooner due to heightened solar activity. The probe's primary sensor, the precipitation radar, was switched off for the final time on 1 April 2015 and the final scientific sensor, LIS, was turned off on 15 April 2015. Re-entry occurred on 16 June 2015 at 06:54 UTC.
Instruments aboard the TRMM
Precipitation Radar The Precipitation Radar (PR) was the first space-borne instrument designed to provide three-dimensional maps of storm structure. The measurements yielded information on the intensity and distribution of the rain, on the rain type, on the storm depth and on the height at which the snow melts into rain. The estimates of the heat released into the atmosphere at different heights based on these measurements can be used to improve models of the global atmospheric circulation. The PR operated at 13.8 GHz and measured the 3-D rainfall distribution over land and ocean surfaces. It defined a layer depth of perception and hence measured rainfall that actually reached the latent heat of atmosphere. It had a 4.3 km resolution at radii with 220 km swath.
… excerpt ends here. Continue reading the full article.
