Triana complements current and planned missions for both low and geosynchronous orbit Earth observation, and for space weather monitoring. This mission will be a pathfinder; discovering new and better ways to observe our Earth system from deep space.

The Triana spacecraft will orbit the Lagrange-1 (L1) neutral gravity point, a point one million miles from Earth where the pull of Earth's gravity matches the pull from the sun. While there have been sun observing missions at L1, Triana will be the first Earth science satellite stationed there.

This unique vantage point provides a continuous view of the Sun-lit side of the Earth, as the planet slowly revolves about its axis. In contrast, Earth-observing satellites in low Earth orbit only sample a small and changing area while even geostationary satellites only view a portion of the Earth at any time.

The full disk, Sun-lit view of the Earth afforded by the L1 location has tremendous potential for Earth science. Triana will the first mission to explore that potential.

Triana will use an SMEX-Lite spacecraft developed by the NASA Goddard Space Flight Center. The scientific payload will consist of two Earth science instruments; the Scripps-NISTAR advanced active cavity absolute radiometers, and the Scripps-EPIC, a ten-channel telescope, plus a solar monitoring Plasma-Mag instrument package.

The instrumentation has been carefully chosen and specified to answer important questions about Earth science, and to maximize their potential to complement science data being collected from low and geosynchronous satellites. A brief summary of the Earth science to be addressed by Triana is provided below.

Earth Science Objectives

• Radiation and Climate Solar radiant energy is a major driver of the Earth's climate. The reflection, absorption, and re-emission as infrared radiation (heat) of that energy, via clouds, aerosols, atmospheric composition, oceans, ice and land surfaces, determines the response of the Earth system to the incoming energy. Triana's advanced radiometers will measure the radiances of reflected and emitted energy over a critical angle range with unprecedented accuracy. Such accurate measurements are needed to refine and test our understanding of climate, climate change and the Earth's radiative processes. Furthermore, future deep space observatories distributed around the Earth would be able to simultaneously sample radiances from a variety of scattering angles with consequent further improvement in radiative balance estimates.

• Cloud Microphysical Properties Ice crystal shape and size determine the basic radiative properties of cirrus clouds. By routinely combining the Scripps-EPIC instrument data with reflectances measured with the Earth Observing System, geostationary, or other satellites at corresponding wavelengths, we can improve our capability to monitor cloud particle shape at all latitudes and times of day. These results will be valuable for further constraining climate models in their critical calculations of cloud interactions with solar radiation.

• Ultraviolet Radiation Atmospheric Ozone shields the surface of the Earth from much of the lethal ultraviolet radiation emitted by the Sun. Triana's Scripps-EPIC instrument will serve as an important complement to the Total Ozone Mapping Spectrometer (TOMS) instruments on other Earth science satellites, providing data on the full sunrise to sunset changes in ozone, clouds, and aerosol amounts that influence not only climate but also the amount of UV radiation reaching the surface.

• Clouds. Cloud cover is the key factor affecting UV exposure at the ground. Measurements of cloud reflectivity at 380 nm have been used to determine cloud transmittance, and have been shown to be accurate using data acquired by TOMS. Unlike TOMS, Triana will measure the clouds throughout the day at a given location giving an accurate picture of the UV reduction by clouds, and therefore the UV exposure of humans and plants. Only the GOES-type geostationary satellites have similar coverage for clouds, but without the closely correlated ozone and aerosol amounts needed to understand the penetration of UV radiation through the atmosphere.

• UV Radiation at the Surface. As researchers have learned to do with TOMS data, monitoring of UV radiation reaching the Earth's surface will also be possible with data from the Scripps-EPIC instrument. Triana's sunrise to sunset view of the full disk of the Earth will enable hourly estimates of surface UV over the entire globe.

• Aerosols Particles suspended in the atmosphere, called aerosols, impact climate directly by absorbing and scattering solar and infrared radiation, and indirectly by modifying the microphysical structure of clouds. The magnitude of the aerosol forcing of climate is highly uncertain because aerosol concentration and composition exhibit substantial spatial and temporal variability on scales ranging from regional to global. Triana's Scripps-EPIC instrument will be the first to combine visible and UV viewing channels, enabling scientists to derive measures of particle size distributions as well as aerosol optical depth. With much greater resolution than TOMS (8 Km vs 100 km), Scripps-EPIC data will also be better able to track aerosol plumes from fires, desert-dust sources, and volcanoes. Data concerning volcanic ash is important to the FAA for aircraft routing, and smoke plume data are important to the US Forest Service and others who manage large areas of fire-prone lands or monitor air quality.

• Vegetation Canopy Measurement
  Due to its location near the Sun-Earth L1 point, Triana will acquire images of the Earth in and near the solar retro-reflection direction, also known as the hotspot direction. Changes in amount of vegetation-leaf structure, or fraction of covered land area can be detected by this method. As a minimum, Triana data will provide the radiometric calibration for hotspot and other related data.

The Triana satellite will also have a sun-observing instrument, the Plasma-Magnetometer. It will provide early warning for solar flares and other extreme solar events that could allow utility companies and satellite operators to execute timely procedures to protect their assets. It might also provide some warning to manned space missions such as the space station or shuttle. These capabilities have already been demonstrated by the plasma magnetometer instruments on the Advance Composition Explorer (ACE), a space science satellite currently operating at L1 which is nearing the end of its design lifetime. Triana's Plasma-Mag instrument suite is an advanced, smaller version of the ACE instrumentation, and should arrive at L1 in time to continue this valuable service. NOAA, the US agency with responsibility for space weather forecasting, is already preparing to receive Triana data, as they do now with ACE.

Educational Opportunities

Finally, a most exciting and significant payoff for the Triana mission may be in the area of education. Under the sponsorship of NASA, a separate educational enhancement follow-on project will involve professional educators in developing high quality educational products. These efforts will start with the inspirational views of the full sunlit Earth, and will lead to up-to-date educational materials that can be shared over the Internet. We see this enabling students to work on and experience science issues such as global changes in ozone, cloud cover, weather patterns, tracking of pollution plumes and seasonal changes. We will support new and innovative inquiry based learning that involves multiple disciplines, such as mathematics, geography, computer technology, and physical sciences.

Summary

If an objective view of Triana is taken, it should be evident that significant new Earth and space science can be derived from this important mission. The science instruments have been designed to complement existing Earth and space science satellites, while addressing new and unique questions that could not be answered without the deep space viewing position. We fully expect that the results will lead to additional Earth observing missions from deep space. Triana science, coupled with the educational opportunities that can be developed around the Triana data will make this a most exciting and effective mission.