browse image of orbit 17403 (270 KB JPEG)
Particulate air pollution is a complex mixture of particles of varyingorigins and compositions. Determining the type and abundance of tinyairborne particles, known as aerosols, is needed for monitoring airquality and for understanding climate change. During the last weeks ofMarch 2003, unusually high and widespread aerosol pollution was detectedover Europe by several satellite-borne instruments. The Multi-angleImaging SpectroRadiometer (MISR) instrument aboard NASA’s Terrasatellite determines aerosol amount and information about particleproperties by examining the variation in scene brightness at differentview angles. These images and data products illustrate the amount ofaerosols on two dates over parts of Central and Eastern Europe, from theBaltic Sea in the north to the Adriatic Sea in the south.
Two groups of three panels are shown. Within each group, the left andcenter views are natural-color images from MISR’s vertical-viewing(nadir) and most obliquely forward-viewing cameras, respectively, andthe right-hand panel is a map of retrieved aerosol amount, parameterizedby a quantity called the optical depth. A color scale is used torepresent this quantity, and high aerosol amount is indicated by yellowor green pixels, and clearer skies are indicated by blue pixels. Theleft-hand group of panels is comprised of data acquired on February 23,2003, when most of the land area was still partially frozen. Theright-hand group of panels portrays the same area about one month later,on March 27. The nadir camera enables surface features to stand out mostclearly, whereas MISR’s oblique cameras enhance sensitivity to even thinlayers of aerosols. In the March image, the only strong indications ofhaze from the nadir view are the thin tendrils of grayish pixels overthe dark waters of the Baltic Sea.
Although aerosols are conventionally difficult to discern over brightsurfaces, MISR is able to produce an aerosol abundance map for both theearlier snow-covered scene and for the later date, though fewersuccessful retrievals were obtained in the winter data. Skies wererelatively clear in the earlier view, and the high optical depthsimplied by the red pixels are probably blunders due either to thehomogeneity of the underlying snow-covered surface or the presence ofunscreened clouds. In contrast, the March data show a thick haze overmost of the lower-elevation parts of the observed area. Optical depthsare relatively lower over the Julian Alps and the mountains of westernCroatia (just north of the Adriatic), whereas higher abundances areobserved to the north of the mountains and over eastern Croatia. Thereis a gradual transition from higher optical depths in western Poland tolower optical depths in Lithuania and along the eastern coast of theBaltic. Higher optical depths are also indicated over much of Hungary,Slovakia and eastern Austria. Places where clouds or other factorsprecluded an aerosol retrieval are otherwise shown in dark gray.
An overview of the haze extent and meteorological conditions forMarch 28, 2003 is also available from the Sea-viewing Wide Field-of-viewSensor (SeaWiFS) sensor.
The Multi-angle Imaging SpectroRadiometer observes the daylit Earthcontinuously and every 9 days views the entire globe between 82 degreesnorth and 82 degrees south latitude. The MISR Browse Image Viewer provides access tolow-resolution true-color versions of these images. These data products were generatedfrom a portion of the imagery acquired during Terra orbits 16937 and17403. The panels cover an area of about 380 kilometers x 1775kilometers.
References & Resources
Image courtesy NASA/GSFC/LaRC/JPL, MISR Team. Text by Clare Averill (Acro Service Corporation/JPL)
