Even before the cover opened,
the Multi-angle Imaging SpectroRadiometer (MISR) instrument aboard NASA's
Terra spacecraft began making scientific measurements. The MISR cameras,
designed to detect visible light, are also sensitive to energetic protons
at high altitudes. With the cover closed, background levels of
protons stand out.
This map was created by specially processing MISR "dark" data taken between
3 February and 16 February 2000, while the cover was still closed. Data
from the red band of the most forward-looking MISR camera were geographically
projected over a map of Earth's land areas. Individual orbit tracks are
visible, and some tracks are missing due to data gaps, missing spacecraft
navigation information, or other early-mission processing problems. Each
picture element is a square measuring one-quarter of a degree in latitude
and longitude, and each contains hundreds to thousands of pixels from the
raw MISR imagery. The South Atlantic Anomaly (SAA) is a region of unusually
high proton levels. Because proton "hits" even in the SAA are relatively
infrequent, each picture element of the map shows the most extreme "outliers"
resulting from proton hits, rather than the average of all observations.
This accentuates the effect of the SAA.
|
