Orbit and Swath


The measurement principle of TROPOMI is illustrated in Figure 1. The instrument images a strip of the Earth on a two dimensional detector for a period of 1 second during which the satellite moves by about 7 km. This strip has dimensions of approximately 2600 km in the direction across the track of the satellite and 7 km in the along track direction. After the 1 second measurement a new measurement is started thus the instrument scans the Earth as the satellite moves. The two dimensions of the detector are used to detect the different ground pixels in the across track direction and for the different wavelengths. The light is separated in the different wavelengths using grating spectrometers. TROPOMI has four different detectors for the different spectral bands. Note that the nominal observing time for the shortest UV wavelengths is 3 seconds instead of 1 second, and the corresponding ground pixel size in the flight direction is 21 km.