Over the course of the day, the number of fires (indicated with red dots) burning across the central African Sahel and savannas can increase as much as three-fold. For example, on December 16, 2002, fires increased from just over 1,000 at the time of the Terra MODIS overpass to close to 4,000 by the time Aqua MODIS passed over in the afternoon. The ability to monitor the diurnal pattern of fire is one of the many benefits of having two iterations of a sensor flying aboard "sister" satellites. These images were acquired by the Terra and Aqua MODIS instruments in mid to late December 2002 and early 2003. In the images from December 24, Lake Chad is barely visible at the upper left hand corner. In the false-color images, vegetation is bright green and burned areas are reddish brown.