Organization: National Aeronautics and Space Administration (NASA)

Research Title: Tropical Rainfall Measuring Mission (TRMM)

Funding Level (millions of dollars):

FY94 72.6
FY95 57.8
FY96 30.1

Committee on Environment and Natural Resources (CENR) Component:
(a) Subcommittee: Global Change Subcommittee (100%)
(b) Environmental Issue: Natural variability (50%) Global change: exploratory research with broad focus that is not primarily in another category (20%); Water availability and allocation (10%); Impacts of natural hazards on human and natural environments (floods and droughts) (20%)
(c) Research Activity: System structure and function: Observation (100%)

Organizational Component:
TRMM Program
Flight Systems Division Office of Mission to Planet Earth
NASA Headquarters, Code YF
Washington, DC 20546

Point of Contact:
Cheryl Yuhas
Phone: 202-358-0746

Research Goals:
(a)To advance our understanding of the global energy and water cycles by means of observing the distribution of rainfall and inferred latent heating over the global tropics and subtropics. (b) To understand the mechanisms through which tropical rainfall and its variability influence the global circulation. (c) To model these processes in order to predict the global circulation and rainfall patterns on monthly and longer time scales.

Research Description:
The research effort has several components: fundamental experimental research into the characteristics of the remote sensing of rainfall; retrieval algorithm development; instrument calibration and validation; cloud modeling of rainfall processes and their interactions with the radiative transfer affecting remote sensing; statistical sampling studies to assess the errors associated with observing rainfall from one satellite.

Fundamental experimental research into the characteristics of the remote sensing of rainfall. (25%): Experimental passive and active microwave sensors are flown aboard NASA aircraft together with visible-infrared imagers to measure rainfall in conjunction with ground-based radar and rain gauge networks. The purpose is to observe, understand, and quantify the variables which are important in retrieving rainfall rates remotely. Variables include characteristics of the underlying surface (land/sea/roughness/ etc.) rainfall rate, total rainfall, raindrop-size distribution, freezing level height, cloud height and type, air mass type, ice-liquid phase mix, vertical humidity profile, rain polarization characteristics, etc.

Retrieval algorithm development..(20%): Algorithms to translate the remotely sensed information into rainfall rates are developed. Varying physical and thermodynamic conditions require the use of different algorithms to optimize the retrievals. The most effective retrievals result from the combination of multifrequency observations. Thus algorithms utilizing multiple channels and sensors are expected to provide the most accurate retrievals.

Instrument calibration and validation...(25%): Ground based observations of rain from radars and rain gauge networks are compared and statistically analyzed. A validation standards facility is utilized to compare various types of rain gauges with rain attenuation measurements in order to establish a standard measurement technique. A statistical rainfall data base is being acquired to characterize various types of rain according to the type of clouds, the season, and the geographical location involved.

Cloud modeling of rainfall processes and their interactions with the radiative transfer affecting remote sensing (20%): Time dependent cloud models including the dynamics, thermo-dynamics, ice-liquid-vapor mixed phases of water, and the radiative transfer as it is affected by these characteristics has been developed to study the remotely sensed signals seen by a space-borne sensor(s). Model runs are used to interpret the experimental observations and independent observations are used to validate the model. The model also provides the means to determine the vertical profiles of latent heating which result form the phase changes of water in the clouds.

Statistical; sampling studies to assess the errors associated with observing rainfall from one satellite (10%): Theoretical and simulation studies using surrogate satellite data are conducted to understand the errors involved in estimating total rainfall for a given grid area from a single satellite as a function of the sampling period and the size of the grid area.

Program Interfaces:
The cited Physical Climate Branch is an integral part of Mission To Planet Earth Program which is addressing climate change issues through a coordinated effort with other federal agencies in the U.S. Global Change Research Program and internationally through bilateral and multilateral agreements with the space agencies other countries and agencies such as, for example, the U.N. World Meteorological Organization's World Climate Research Program.

Program Milestones:
February, 1994: selection of a U.S.-Japanese mission science team through a joint research announcement. December, 1994: draft mission science operating plan completed. Late 1995: final science operating plan completed. Mid 1996: preliminary sensor algorithms completed. August, 1997: mission launch.

Policy Payoffs:
Improved understanding of the distribution and variability of rainfall and improved climate models which accurately account for rainfall patterns and the latent heating which they generate. Rainfall enters into every aspect of human endeavor, from the provision of fresh water to the production of food and fiber to industrial uses of water to the generation of renewable electric power. Rainfall in its extremes causes floods or droughts (natural hazards) and the latter is more costly in terms of the number of human lives lost than all other hazards combined. Thus the ability to monitor and predict droughts has enormous potential in terms of avoiding human suffering and death. This has very important policy and even national security implications.