Figure 7.30. Pioneer 10 and 11 trajectories. Courtesy of NASA.

the first detection of helium on Jupiter and enabled the first estimation of the H2/He ratio.

Imaging photopolarimeter

The imaging photopolarimeter had a single 0.5mrad FOV and used the spinning motion of the spacecraft to build up images. Each rotation of the spacecraft provided one line of the image, and a pointing mirror was then adjusted before the next line was recorded and so on. The pointing mirror allowed the instrument to view at angles between 27° and 170° of the rotation axis. The imaging photopolarimeter could record images in two spectral channels: red (595-720 nm) and blue (390-500 nm), and could also determine the polarization of the light.

IR radiometer

The IR radiometer had a FOV of 17.4 x 5mrad and had two channels covering the spectral ranges (14-25 ^m) and (30-56 ^m), respectively. Since both spectral regions are dominated by the collision-induced absorption of hydrogen and helium, temperature sounding was achieved by viewing a location on the planet at multiple emission angles, allowing a range of weighting functions peaking at different altitudes.

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