PROGRAM TITLE:  	Earth Probes Program
ACTIVITY STREAMS:	Observations & Data Management
SCIENCE ELEMENT:	Climate and Hydrologic Systems
				Biogeochemical Dynamics
				Ecological Systems and Dynamics
				Solid Earth Processes          
				Solar Influences

NATIONAL AERONAUTICS AND SPACE ADMINISTRATION

SCIENTIFIC MERIT:   The centerpiece of NASA's contribution to 
understanding global climate change is the Earth Observing System 
(EOS) Program, a series of polar orbiting platforms for long-term 
global observations of the Earth's land, biosphere, atmosphere and 
oceans.  The Earth Probes (EP) Program includes low-to-moderate 
cost missions designed to complement EOS by acquiring observations 
that require specific orbits and/or timeliness that cannot be met by 
the EOS Program.  Earth Probes contribute to all U.S. Global Change 
Research Program (USGCRP) goals and objectives, and the scientific 
basis for the missions results from priorities and requirements of the 
scientific community, including recommendations of the National 
Academy of Sciences.  As an ongoing series, the individual spacecraft 
and instruments will be implemented as the funding, scientific 
priorities, and readiness permit.  Currently, the EP Program includes 
three missions:  the Total Ozone Mapping Spectrometer (TOMS), the 
NASA Scatterometer (NSCAT), and the Tropical Rainfall Measuring 
Mission (TRMM).  Each of these approved missions are part of 
international cooperative projects.  

The TOMS instrument missions (planned for 1994, 1996 and 1998) 
will continue the high-resolution global mapping of total 
stratospheric ozone which began in 1978 with the TOMS instrument 
on Nimbus-7 and followed in 1991 with the TOMS instrument on the 
Soviet Meteor-3 weather satellite.  TOMS measurements are vital to 
the continuing effort to monitor and understand the dynamics of 
stratospheric ozone depletion.  This is part of the research in 
biogeochemical dynamics, specifically changes in the atmospheric 
processes.  Research using this data is directed to the detection of 
total ozone trends and to the verification of chemical models of the 
stratosphere used to predict future trends.   

The NSCAT instrument mission (planned for 1996) measures ocean 
surface wind velocity and provides data on air-sea interactions 
crucial to understanding oceanic uptake of carbon dioxide and other 
gases.  NSCAT addresses fundamental processes in which the oceans 
and the atmosphere play a role in moderating the Earth's climate.  
Surface marine winds modulate the fluxes of momentum, heat, and 
moisture between the atmosphere and ocean.  These fluxes drive 
both the atmospheric and oceanic circulations, and are critical to 
understanding and developing accurate coupled atmosphere/ocean 
circulation models needed for short- and long-range climate 
forecasting.  NSCAT will contribute the single most important missing 
factor for advancing the understanding of wind-driven ocean 
circulation--the lack of systematic high-resolution wind observations 
over the ocean.

The goal of the TRMM mission (planned for 1997) is to obtain a 
minimum of three years  of climatologically significant observations 
of rainfall in the tropics.  TRMM will play a significant role in global 
change studies, especially in developing an interdisciplinary 
understanding of atmospheric circulation, ocean-atmospheric 
coupling and tropical biology.  General circulation models require 
detailed data on the latent heating of equatorial air masses, and the 
forcing and propagation speed of waves involved in the 30- to 60-
day tropical oscillations.  TRMM data on tropical clouds, evaporation, 
and heat transfer will be used to understand the larger scale 
coupling of the atmosphere to oceans, especially in the development 
of El Nino events, and in the more general understanding of ocean-
atmosphere circulation.  Tropical rainfall is also closely coupled to 
tropical forest processes.  Convective mixing of trace gases, including 
carbon dioxide and methane, provides a direct link between tropical 
rainfall and the global biogeochemical cycles that regulate life on 
Earth.

NASA's long range plans include additional Earth Probes addressing 
specific Earth science investigations.  Several mission categories have 
been identified to provide critical Earth science measurements not 
provided by the international constellation of satellites.  NASA 
intends to pursue collaborations with domestic and/or international 
partners in the following disciplines: gravity and magnetic fields, 
solid earth topography, and ocean topography.

STAKEHOLDERS:  TOMS will fly on a U.S.-launched free-flyer in 1994, 
on the Japanese ADEOS mission in 1996, and on an international 
mission of opportunity in 1998.  The TOMS ozone data are of wide 
interest to a large international scientific community, and is 
coordinated with the UN Environmental Program (UNEP) and through 
the World Meteorology Organization (WMO) with participation by the 
National Oceanic and Atmospheric Administration (NOAA) and the 
Environmental Protection Agency (EPA) for global ozone change 
monitoring in accordance with the Montreal Protocol.  NSCAT will 
also fly on the Japanese ADEOS mission in 1996, and the data will be 
a key contribution to major international ocean/atmosphere research 
programs, including the World Ocean Circulation Experiment (WOCE) 
and the Tropical Ocean Global Atmosphere (TOGA) program, both of 
which are components of the World Climate Research Program 
(WCRP).  The TRMM mission in 1997 is a joint mission with  Japan 
who will provide the launch vehicle and the Precipitation Radar 
instrument.  There will also be broad international participation in 
the ground-based validation of the TRMM measurements.  The Global 
Energy and Water Cycle Experiment (GEWEX), an initiative of the 
WCRP, will also employ and validate TRMM data.  Other international 
programs, such as the International Geosphere-Biosphere Program 
(IGBP), will also use TRMM data for investigation of hydrologic 
processes important to global change. 

POLICY RELEVANCE:	
Primary	- Climate Change and Global Warming
		- Stratospheric Ozone and UV-B Radiation  

Secondary	- Ecological & Biodiversity
		- Seasonal and Interannual Prediction

PROGRAM CONTACT:	Lenwood G. Clark                      
				Office of Mission to Planet Earth
				NASA Headquarters, Code YF    
				tel: 202-358-0786
				fax: 202-358-2769
				E-mail:  L.CLARK.NASA/omnet