Featured Terra Image
Measuring Earth's Albedo
Sunlight is the primary driver of Earth’s climate and weather. Averaged over the entire planet, roughly 340 watts per square meter of energy from the Sun reach Earth. About one-third of that energy is reflected back into space, and the remaining 240 watts per square meter is absorbed by land, ocean, and atmosphere. Exactly how much sunlight is absorbed depends on the reflectivity of the atmosphere and the surface.
As scientists work to understand why global temperatures are rising and how carbon dioxide and other greenhouse gases are changing the climate system, they have been auditing Earth’s energy budget. Is more energy being absorbed by Earth than is being lost to space? If so, what happens to the excess energy?
For seventeen years, scientists have been examining this balance sheet with a series of space-based sensors known as Clouds and the Earth’s Radiant Energy System, or CERES. The instruments use scanning radiometers to measure both the shortwave solar energy reflected by the planet (albedo) and the longwave thermal energy emitted by it. The first CERES went into space in 1997 on the Tropical Rainfall Measuring Mission, and three more have gone up on Terra, Aqua, and Suomi-NPP. The last remaining CERES instrument will fly on the JPSS-1 satellite, and a follow-on, the Radiation Budget Instrument (RBI), will fly on JPSS-2.
The maps above show how the reflectivity of Earth—the amount of sunlight reflected back into space—changed between March 1, 2000, and December 31, 2011. This global picture of reflectivity (also called albedo) appears to be a muddle, with different areas reflecting more or less sunlight over the 12-year record. Shades of blue mark areas that reflected more sunlight over time (increasing albedo), and orange areas denote less reflection (lower albedo).
Taken across the planet, no significant global trend appears. As noted in the anomaly plot below, global albedo rose and fell in different years, but did not necessarily head in either direction for long.
Terra: the EOS Flagship
Terra explores the connections between Earth's atmosphere, land, snow and ice, ocean, and energy balance to understand Earth's climate and climate change and to map the impact of human activity and natural disasters on communities and ecosystems.
Terra collects data about the Earth’s bio-geochemical and energy systems using five sensors that observe the atmosphere, land surface, oceans, snow and ice, and energy budget. Each sensor has unique features that enable scientists to meet a wide range of science objectives. The five Terra onboard sensors are:
- ASTER, or Advanced Spaceborne Thermal Emission and Reflection Radiometer
- CERES, or Clouds and Earth's Radiant Energy System
- MISR, or Multi-angle Imaging SpectroRadiometer
- MODIS, or Moderate-resolution Imaging Spectroradiometer
- MOPITT, or Measurements of Pollution in the Troposphere
Because Terra's five sensors share a platform, they collect complementary observations of Earth's surface and atmosphere. These varying perspectives of the same event can yield unique insights into the processes that connect Earth's systems.