The Earth straylight program is performed with both the P2 detector at 25 
micron, where the emission by the Earth has a maximum, and the C200 detector
at 170 micron, the channel which is most sensitive to any kind of straylight,
as representative detector subsystems. The measurement is a differential one 
by comparing the absolutely calibrated surface brightness of a relatively dark 
background level at 3 different illumination angles of the inner side of 
ISO's sunshade by the Earth. For stability monitoring of the detector 
conditions each time a dark and a measurement of a secondary sky standard are 
performed. In order to have similar constellations for both P2 and C200 the 
measurements are performed on two subsequent revolutions. Revolutions 819 and 
820 offer good constellations of Earth, Sun and Moon. The observations are
performed with AOTs (PHT-05//PHT-03//PHT05 - PHT-03 for P2 and 
PHT-25//PHT-22//PHT-25 - PHT-22 for C200). The total measurement time is 6.1 
hours.

History:
21/01/98				UK, RJL	Instantiation and delivery

.TDT 23205
.OTT 20805