browse image of orbit 17403 (270 KB JPEG)
Particulate air pollution is a complex mixture of particles of varying origins and compositions. Determining the type and abundance of tiny airborne particles, known as aerosols, is needed for monitoring air quality and for understanding climate change. During the last weeks of March 2003, unusually high and widespread aerosol pollution was detected over Europe by several satellite-borne instruments. The Multi-angle Imaging SpectroRadiometer (MISR) instrument aboard NASA’s Terra satellite determines aerosol amount and information about particle properties by examining the variation in scene brightness at different view angles. These images and data products illustrate the amount of aerosols on two dates over parts of Central and Eastern Europe, from the Baltic Sea in the north to the Adriatic Sea in the south.
Two groups of three panels are shown. Within each group, the left and center views are natural-color images from MISR’s vertical-viewing (nadir) and most obliquely forward-viewing cameras, respectively, and the right-hand panel is a map of retrieved aerosol amount, parameterized by a quantity called the optical depth. A color scale is used to represent this quantity, and high aerosol amount is indicated by yellow or green pixels, and clearer skies are indicated by blue pixels. The left-hand group of panels is comprised of data acquired on February 23, 2003, when most of the land area was still partially frozen. The right-hand group of panels portrays the same area about one month later, on March 27. The nadir camera enables surface features to stand out most clearly, whereas MISR’s oblique cameras enhance sensitivity to even thin layers of aerosols. In the March image, the only strong indications of haze from the nadir view are the thin tendrils of grayish pixels over the dark waters of the Baltic Sea.
Although aerosols are conventionally difficult to discern over bright surfaces, MISR is able to produce an aerosol abundance map for both the earlier snow-covered scene and for the later date, though fewer successful retrievals were obtained in the winter data. Skies were relatively clear in the earlier view, and the high optical depths implied by the red pixels are probably blunders due either to the homogeneity of the underlying snow-covered surface or the presence of unscreened clouds. In contrast, the March data show a thick haze over most of the lower-elevation parts of the observed area. Optical depths are relatively lower over the Julian Alps and the mountains of western Croatia (just north of the Adriatic), whereas higher abundances are observed to the north of the mountains and over eastern Croatia. There is a gradual transition from higher optical depths in western Poland to lower optical depths in Lithuania and along the eastern coast of the Baltic. Higher optical depths are also indicated over much of Hungary, Slovakia and eastern Austria. Places where clouds or other factors precluded an aerosol retrieval are otherwise shown in dark gray.
An overview of the haze extent and meteorological conditions for March 28, 2003 is also available from the Sea-viewing Wide Field-of-view Sensor (SeaWiFS) sensor.
The Multi-angle Imaging SpectroRadiometer observes the daylit Earth continuously and every 9 days views the entire globe between 82 degrees north and 82 degrees south latitude. The MISR Browse Image Viewer provides access to low-resolution true-color versions of these images. These data products were generated from a portion of the imagery acquired during Terra orbits 16937 and 17403. The panels cover an area of about 380 kilometers x 1775 kilometers.
Image courtesy NASA/GSFC/LaRC/JPL, MISR Team. Text by Clare Averill (Acro Service Corporation/JPL)