4. Instrument Operations

Fig. 4-1
SCIAMACHY’s scientific observation modes: 1 = nadir, 2 = limb, 3 = occultation. (graphics: DLR-IMF)
Fig. 4-2
An orbit with planned limb/nadir matching on the dayside of the orbit. The sequence of nadir and limb states in a timeline is arranged so that limb ground pixels (blue), defined by the lineof- sight tangent point, fall right into a nadir ground pixel (green). At the beginning and end only limb or only nadir measurements are executed. (graphics: DLR-IMF)
Fig. 4-3
ENVISAT’s yaw steering, the yaw steering correction of limb states and the resulting SCIAMACHY yaw steering. Between ENVISAT and SCIAMACHY yaw steering an orbital shift of 27° exists which reflects the observation geometry when looking to the horizon in flight direction. (graphics: DLR-IMF)
Fig. 4-4
SCIAMACHY’s monthly lunar visibility occurs between 1 and 2 over the southern hemisphere (lunar phase > 0.5). The hatched area illustrates the limb TCFoV of 88°. Visibility at smaller lunar phases over the northern hemisphere between 3 and 4 is not used because it coincides with solar occultation. (graphics: DLR-IMF)
Fig. 4-5
The rising moon seen from a spacecraft in a low- Earth orbit. Differential refraction distorts the lunar disk. (photo: NASA)
Fig. 4-6
SCIAMACHY reference orbit with sun/moon fixed events along the orbit. The events define orbital segments which are filled with timelines. State duration is not to scale. (graphics: DLR-IMF)
Fig. 4-7
The pattern of ground pixels in a nadir measurement for an integration time of 1 sec (left) and 125 msec (right). Only the forward scans are shown. This causes the along-track gaps between consecutive scans which vary in width due to a projection effect. Across-track extent is defined by the integration time while along track the size reflects the dimension of the IFoV with only a small contribution of the integration time. (graphics: DLR-IMF)
Fig. 4-8
Calibration & monitoring scenarios from orbital to monthly timescales. In the top row the individual measurements and their targets, e.g. sun, moon, lamps, are listed. The states used in each calibration orbit, referring to the definitions in table 4-2, are outlined below. All states unrelated to the sun or the moon can be executed several times at any position along the orbit. (graphics: DLR-IMF)
Fig. 4-9
Information flow during timeline execution. Timelines are started by macrocommand and end when the last state in the timeline has run to completion. (graphics: DLRIMF)
Fig. 4-10
Example of the seasonal temporal variability of orbital segments. The time interval between end of SO&C window and start of eclipse varies only slightly over a year (yellow). In the monthly moon visibility periods, the time between end of MO&C window and start of eclipse shows a much higher variation (red curves). The blue segments indicate lunar visibility phases where moonrise occurs on the nightside, i.e. those which can be used for occultations. (graphics: DLR-IMF)

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