Satellite Research

CERES Working FTP Directory Research Links MODIS Images From SSEC CERES Programmable Azimuth Plane Scans MODIS Image & Glint vs Wind Speed (pdf) Deep Ocean Cholrophylls(pdf)

Submitted by Martial Haeffelin

    The TERRA spacecraft passes over the Chesapeake Lighthouse in daylight
once or twice per 24 hours. If the CERES instrument scans in the cross-track 
direction only one footprint will contain the Chesapeake Lighthouse at each 
overpass. The rotating azimuth capability of the CERES instrument can be used 
to adjust the scan plane such that the Chesapeake Lighthouse remains within the 
scan swath as the spacecraft moves along its orbit.

Figure 1 shows the azimuthal direction of the scan plane, represented by 
arrows directed towards the Lighthouse, as TERRA proceeds on its descending orbit. 
The direction is shown once per minute. The colors represent separate days. On 
day3 and day5 CERES is able to observe the Lighthouse from two consecutive orbits. 
On average the Lighthouse can remain in the CERES scan swath for about 7 minutes 
per orbit, which, with proper adjusments to the CERES scan pattern could yield 
more than 100 observations each day!

Figure 2 shows the distribution of viewing zenith and relative azimuth angles 
sampled during one week of operation. Note that the relative azimuth angles are 
uniformely sampled. Large viewing zenith angles are preferentially sampled because 
they are used for all overpasses. Small viewing angles can only be obtained when 
the subsatellite point of TERRA is close to the Lighthouse.