Abstract
A major problem with calculating the uncertainties of measurements with
weather satellites is the fact that a full characterisation and
calibration of their instruments can only be carried out before launch.
The Moon, however, makes at least some of these activities possible in
flight as well by providing a reliable flux reference at a well-defined
position. We used serendipitous observations of the Moon with AMSU-B and
MHS on eight different satellites to measure pointing accuracy, spectral
channels coregistration, and beamwidth with unprecedented accuracy in
flight. In addition we compared these findings with the corresponding
values obtained on ground. By analysing more than a hundred Moon
intrusions in the deep space view we could determine the radiance of the
Moon as a function of its phase angle and distance from the Sun. The
difference in average brightness temperature of the lunar disk between
perihelion and aphelion amounts to $4.4 \pm 2.3$ K at
183 GHz. We compare the measured brightness temperature of the Moon as a
function of phase angle between $-85^{\circ}$
(waxing) and $+76^{\circ}$ (waning) with the
predictions from two models and find that one of them reproduces the
shape of this function very well.