TERRA FIRST LIGHT IMAGES

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Final Terra Status Report

The two CERES instruments on Terra successfully opened their contamination cover doors on Friday, February 25. A few hours later, they began to scan the Earth, making measurements of the reflected solar flux and emitted terrestrial flux that make up the Earth’s radiation budget. Both instruments appear to be working very well. In normal operation one instrument will scan perpendicular to the Terra ground track, in order to spatially sample the Earth. The other instrument samples the angular distribution of radiation. These two Terra instruments join a previous CERES scanner on the Tropical Rainfall Measuring Mission (TRMM), which was launched on November 27, 1997. They complement TRMM by extending the observations to cover the globe and by improving sampling of the large diurnal cycle of radiation.

1. Reflected Solar Radiance from February 26, 2000

The first image shows reflected solar radiance emerging from the top of the atmosphere, as measured by the CERES Flight Model 1 (FM1) instrument on the Terra spacecraft. These preliminary (unvalidated) data show twenty four hours of measurements covering the entire Earth from North Pole to South Pole.

Reflected solar radiance (or brightness) is a quantity describing how much light energy is moving in a particular direction, in this case the direction between a position on the Earth and the Terra spacecraft. Terra from north to south in the individual orbital swaths that are sometimes visible on close examination of this image. Swath-related features appear most noticeable over the Eastern Pacific, which is just west of South America. There are four features spaced between the left edge of the image and South America that are probably related to the geometry of the scan pattern, where the east side of each swath is being observed at about 11:45 a.m., local solar time, while the west side of each swath is observed at about 9:45 a.m.

Where there are no clouds over the oceans, this image is very dark — as we can easily see in the Carribbean or the Indian Ocean between Saudia Arabia and the Indian subcontinent. Where the ocean part of the images is lighter, there are clouds reflecting sunlight back to the CERES instrument.

The tropical oceans near the Equator show intense thunderstorms. These are particularly visible between Africa and Australia, where the storms form part of the Intertropical Convergence Zone (ITCZ). Air ascends in the ITCZ and descends on the midlatitudes, where makes it harder to form clouds. Further away from the Equator, we can see large storms, such as the cold front west of the Appalachians and the storm over the Northwest Pacific Coast of the United States. The southern oceans show particularly striking patterns associated with huge storm systems circling the Antarctic continent.

Land reflects more sunlight than the oceans do. The Sahara Desert, in the center of this first image, is one of the most reflective large land targets in the world, along with the Saudi Arabian Peninsula. Other land areas of the Earth are darker — with the rain forests of South America and Africa being almost as dark as the oceans. In this image, the rain forests are covered by clouds, so these naturally dark regions do reflect a large amount of sunlight.

While this image is a beautiful reminder of the relationship between clouds and radiation, much work remains to be done in quantifying the uncertainty in the measurements. Other instruments on Terra will also contribute to determining the properties of the clouds, the state of the vegetation on the land, and the mixture of biological and chemical activities in the oceans.

2. Reflected Shortwave Flux from February 26, 2000

The second image shows the reflected solar flux emerging from the top of the atmosphere. The data are taken from an entire day of observations from the CERES Flight Model 1 (FM1) instrument on the Terra spacecraft. The quantity plotted is "reflected solar flux", which not only involves instrument calibration and geolocation, but also removes the angular dependence of the upwelling radiance field. Thus, these data are Level 2 data, which means that CERES has been able to get a reasonable "engineering" calculation of derived physical fields within a few days of opening its covers. The data shown come from Saturday, February 26, 2000, the first full day of FM1 scanning.

The latitude where the Sun is overhead is slightly below eight degrees south on this day. The upper portion of the globe, from about 80 degrees north to the North Pole, receives no sunlight on this day and reflects none. The CERES instrument sees an entire swath of the Earth from limb-to-limb as the satellite passes from North to South. The short black arcs that are regularly spaced near the Equator mark the edges of the scan swaths. Although the CERES instrument actually covers the Earth from one swath to the next, the image was made without taking the expansion of the instrument field-of-view into account.

Just to the left of the center of the image, we can see South America. The North American continent is off to the northwest, where it is obscured by a cold front east of the Appalachians and a storm striking the Northwest Pacific Coast. Africa, particularly the Sahara Desert, and Saudi Arabia are clearly visible to the right of center in this image. The Sahara is obscured to some extent because of clouds. Saudi Arabia is not obscured, so we can see the bright sands of the desert contrast with the dark ocean at the southern edge of the Arabian Peninsula.

Most of the patterns visible away from the Equator are large storm systems, where clouds reflect a large fraction of the incident sunlight. To the right of center, we can see much of the Indian subcontinent, although a large and very bright storm over the Himalayas extends to obscure the Pacific coast of China. Between India and Australia (visible just below the Equator on the lower right of the image), we can see a series of large thunderstorms that form the clouds in the Intertropical Convergence Zone (ITCZ). Far to the south, we can also see the high reflectivity of the Antarctic snow and ice emerge from the mixture of cloudy and clear areas over the Southern Atlantic and Pacific.

3. Emitted Longwave Flux from February 26, 2000

The third image shows the energy being lost from the Earth and the atmosphere by thermal emission. This process, familiar to most of us as the heat radiated by electric stove elements, involves light with wavelengths invisible to the eye. Again, these data are Level 2 data from Saturday, February 26, 2000.

In this image, blue values come from cold scenes with low thermal emission, while red values come from hot ones with high emission. As we might expect, the colder regions near the poles are blue, while the much warmer tropics are red.

Near the center of the image, in red, we can see the Saudi Peninsula standing in contrast with the warm waters of the Indian Ocean, which appear a lighter shade. The land is hotter than the ocean, as we might expect from having the Sun shining on the Earth under clear skies at about 10:45 a.m. local time. Surprisingly, the Sahara Desert appears to have fairly extensive cloud cover, particularaly near the Mediterranean.

Along the Equator from the Amazon Basin in South America, across the Atlantic to the Congo Basin, and then over the Indian Ocean, we can see the tops of very high, thunderstorms in the Intertropical Convergence Zone. These appear in the image as very dark blue or black features that we typically associate with huge cirrus anvils. The temperature of the atmosphere declines with altitude, so that the tops of these tropical thunderstorms are actually colder than the surface of the Earth at the wintertime pole.

The red features in this image are primarily clear areas, where we see through to the Earth’s surface without much impediment from clouds. In addition to the Indian Ocean, we might expect central Mexico and a large area of the Western Pacific to be relatively cloud free.

The prominent green and blue features away from the Equator are typically large storm systems. Over the United States, we can see a frontal system west of the Appalachians that brought a moderate amount of rain to the Ohio Valley and the Northeast. We can also see a massive storm system depositing rain (and snow) on the Northwest Pacific Coast.

MOPITT measures radiances in several channels to determine the amount of carbon monoxide (CO) and methane in the atmosphere. Channel 1 Difference radiances, shown here, are sensitive to the temperature of the earth's surface, the temperature of the atmosphere, and the amount of CO Of these, the first two effects dominate. Thus, we see red colors, indicating high radiances and high surface temperatures from the subtropical deserts (Sahara, Arabian, Rajastan and Kalahari). The blues indicate low surface temperatures (polar regions) or high clouds, as the line of clouds of the intertropical convergence zone at about 10 South.

The intuitive nature of these results, the correspondence of variations with coast-lines, and their similarity to expected values, indicate that the MOPITT instrument is functioning very well.

To recover the amount of CO, it is necessary to combine difference measurements like these with other MOPITT measurements of the radiation from the earth's surface, and independent data on the atmospheric temperature, to remove these effects and get at the subtle effects of CO. This effort is now underway.

First light over James Bay, Ontario, Canada, acquired by NASA's Multi-angle Imaging SpectroRadiometer on February 24, 2000, shows this winter landscape from three of the instrument's nine cameras. The image at left captures the opening of MISR's cover and was recorded by the most oblique forward-viewing camera, which images the Earth at 70 degrees relative to a vertical plane. Several islands, including the crescent-shaped Akimiski Island, are visible in the frozen bay. The center image, acquired a few minutes later, was taken by the nadir camera, which looks straight down, and the image on the right, acquired seven minutes after first light, was taken from the most oblique aftward-viewing camera.

"These first pictures illustrate many of MISR's new and unique capabilities," said JPL's Dr. David J. Diner, MISR principal investigator. "The instrument, operations system, and science data processing software are performing extremely well and the quality of the images, particularly at the very challenging oblique angles, is outstanding."

An increased blue tint at the oblique angles is the result of scattering of light in the atmosphere. Contrast reversals and other color and brightness variations from one angle to another are also apparent, and most likely due to variegated surface geometries and textures. Observing such changes in image content and detail from space, over a wide range of angles and with near-simultaneity, is an unprecedented approach for characterizing surface, atmospheric, and cloud properties. Capturing swaths 400 kilometers wide, MISR can detect objects as small as 275 meters in diameter.