Terra: MISR

M		Multi-angle
I		Imaging
S		Spectro-
R		Radiometer

Most satellite instruments look only straight down, or toward the edge of the planet. To fully understand Earth's climate, and to determine how it may be changing, we need to know the amount of sunlight that is scattered in different directions under natural conditions. MISR is a new type of instrument designed to address this need—it will view the Earth with cameras pointed at nine different angles. One camera points toward nadir, and the others provide forward and aftward view angles, at the Earth's surface, of 26.1°, 45.6°, 60.0°, and 70.5°. As the instrument flies overhead, each region of the Earth's surface is successively imaged by all nine cameras in each of four wavelengths (blue, green, red, and near-infrared).

In addition to improving our understanding of the fate of sunlight in the Earth's environment, MISR data can distinguish different types of clouds, aerosol particles, and surfaces. Specifically, MISR will monitor the monthly, seasonal, and long-term trends in:

the amount and type of atmospheric aerosol particles, including those formed by natural sources and by human activities;

the amount, types, and heights of clouds; and

the distribution of land surface cover, including vegetation canopy structure.

These data will be used to investigate the influence of aerosol, cloud, and surface properties on the Earth's reflected radiation budget and climate. Spatial samples are acquired every 275 m. Over a period of 7 minutes, a 360 km wide swath of Earth comes into view at all nine angles. Special attention has been paid to providing highly accurate absolute and relative radiometric calibration using onboard hardware consisting of deployable solar diffuser plates and several types of photodiodes. To complement the onboard calibration effort, a validation program of in situ measurements is planned, involving field instruments such as PARABOLA III, which automatically scans the sky and ground at many angles, and a multi-angle aircraft camera (AirMISR). Global coverage by the space-based MISR will be acquired about once every 9 days at the equator. The nominal mission lifetime is 6 years.

MISR is being built for NASA by the Jet Propulsion Laboratory in Pasadena, California. The Principal Investigator is David J. Diner. For more information, check out the MISR Web Site at http://www-misr.jpl.nasa.gov.

MISR Instrument Characteristics

Swath width	360 km

Spectral bands	446, 558, 672, 866 nm

Cross-track pixel size	275 m off-nadir, 250 m nadir

Duty cycle	50% (day only)

Data rate	3.3 Mbps (avg), 9.0 Mbps (peak)

Mass	149 kg

Power	72 W (avg), 135 W (peak)

This computer-generated image shows the Terra spacecraft, with the MISR instrument on board, orbiting the Earth. Direction of flight is toward the lower left. The actual locations imaged by the 9 cameras, each with 4 color bands, along the Earth's surface are illustrated here with translucent surfaces. The background star field is also realistic (Shigeru Suzuki and Eric De Jong, Solar System Visualization Project, Jet Propulsion Laboratory). Click to enlarge

This pair of red/green/blue color composite images was taken by the AirMISR instrument on August 25, 1997, over the area surrounding Moffett Field, California. They each cover an area approximately 10 km on a side and were acquired from a NASA ER-2 aircraft flying at 20 kilometers altitude in an approximately southward direction. Radiometric scaling using preflight calibration coefficients and a simple line-by-line roll correction algorithm have been applied. The imaged area straddles the waters of San Francisco Bay near the inlet of Coyote Creek, mudflats, marshes, tidelands that are in part utilized as salt evaporation ponds, and urban areas of Mountain View, Sunnyvale, and adjacent communities that provide a grid of city streets, buildings, and freeways. North is toward the top of these images, and the sun is shining roughly from the south. For the bottom image, the camera was pointing at 26.1 degrees forward of nadir, whereas the top image was taken with the camera pointing 26.1 degrees aftward of nadir. The rivers and tidal areas are brighter in the forward-viewing (left) image, illustrating that these wet surfaces produce mirror-like reflections that are observable at this viewing geometry (MISR Team, Jet Propulsion Laboratory).