IEEE Geoscience and Remote Sensing Magazine - March 2016 - 31

multi-Angle imAging SpectRoRAdiometeR
Launched in 1999 aboard NASA's Terra satellite, the
Multi-Angle Imaging SpectroRadiometer (MISR) acquires
global multiangle imagery on the daylit side of Earth, providing accurate measurements of the brightness, contrast,
and the color of reflected sunlight [19]. The MISR provides information for scientists studying Earth's climate,
such as the partitioning of energy and carbon between
the land surface and the atmosphere and the regional and
global impacts on the climate of different types of atmospheric particles and clouds.
The instrument consists of nine separate digital cameras,
each recording data in four wavelengths (i.e., blue, green, red,
and near-infrared). The cameras are aimed at fixed angles
ahead of, directly down, and behind Terra's flight path.
The change in reflection at different view angles allows distinguishing different types of atmospheric particles (i.e., aerosols), cloud forms, and land surface covers. Combined with
stereoscopic techniques, this enables the construction of threedimensional (3-D) models and the estimation of the total
amount of sunlight reflected by Earth's diverse environments.
oRbiting cARbon obSeRvAtoRy-2
Carbon dioxide is the most significant of the humanproduced greenhouse gases and is the principal humanproduced driver of changes to Earth's climate. The latest
in NASA's ongoing studies of the global carbon cycle is
the Orbiting Carbon Observatory-2 (OCO-2), NASA's first
remote sensing mission dedicated to studying atmospheric
carbon dioxide [20], making global scale observations as
illustrated in Figure 6. OCO-2 measures the molecular
emissions of oxygen (found in the deep red) and carbon
dioxide (two bands in the near infrared) for its column
measurements of these gases.
NASA launched the OCO-2 in July 2014. Combined with
other ground and aircraft measurements and satellite data,
OCO-2 will answer important questions about the processes that regulate atmospheric carbon dioxide and its role
in the carbon cycle and climate (e.g., [21]). The mission also
serves as a pathfinder for future long-term carbon dioxide
monitoring satellites.
oceAn SuRfAce topogRAphy miSSion
on the JASon-2 SAtellite
The Ocean Surface Topography Mission on the Jason-2
satellite (OSTM/Jason-2) is a follow-up to the Jason-1 mission [22]. It was launched on 20 June 2008. OSTM/Jason-2
combines radar altimetry for altitude, radiometry for tropospheric delay, and GPS positioning to map the topography
of the ocean surface to within a few centimeters. Accurate
observations of variations in ocean surface topography tell
a larger story about the ocean's most basic functions-how
it stores vast amounts of energy from the sun and how it
moves that energy around the globe through ocean currents that circulate in enormous gyres around regions of
raised or lowered sea level-including the hills and valleys
march 2016

ieee Geoscience and remote sensing magazine

OCO-2
Atmospheric Carbon Dioxide
Concentration (Sept. 2014-Sept. 2015)

Parts per Million by Volume
390 392 395 397 400 402 405

Global Level 3 Data
1-15 June 2015

FIGURe 6. The global average carbon dioxide concentrations

as seen by NASA's OCO-2 mission on 1-15 June 2015. (Figure
courtesy of JPL.)
of ocean surface topography (see Figure 7). Understanding
where this heat is and how it moves within the ocean as
currents and into the atmosphere is critical to understanding global climate.
JPL provided the advanced microwave radiometer
(AMR) instrument for measuring vertical delay induced by
the wet troposphere and an experimental GPS system for
orbit determination. The mission is a partnership between
NASA and the French Space Agency (CNES).
Soil moiStuRe Active pASSive
Launched on 31 January 2015, the Soil Moisture Active Passive (SMAP) is designed to measure and map Earth's soil
moisture and freeze/thaw state to better understand terrestrial water, carbon, and energy cycles [23]. Using a unique
configuration of a large spinning L-band radar and radiometer, the satellite peers beneath clouds, vegetation, and
other surface features to monitor water and energy fluxes,
helping to improve flood and drought predictions. SMAP
data will play a crucial role in understanding changes in
water availability, food production, and other societal
impacts of climate change.
The radar was designed such that synthetic aperture processing (SAR) could improve the resolution of the overall
measurement by combining real-aperture radiometer measurements with the finer resolution SAR data. Though the
radar is no longer operational due to an anomaly in July
2015, several months of combined data are available for
studies, and the radiometer-based science mission continues. Figure 8 presents global radar and radiometer maps
from early in the mission.
SMAP is designed to measure global soil moisture over
a three-year period, every two to three days. This permits
changes around the world to be observed over time scales
ranging from major storms to repeated measurements of
changes over the seasons.
31

Table of Contents for the Digital Edition of IEEE Geoscience and Remote Sensing Magazine - March 2016