MultiSpectral Instrument (MSI) Overview
The design of the Multispectral Instrument (MSI) on-board SENTINEL-2 has been driven by the requirement for large swath high geometrical and spectral performance of the measurements.
The MSI measures the Earth's reflected radiance in 13 spectral bands from VNIR to SWIR (Table 1). The Bandwidth (nm) is measured at Full Width Half Maximum (FWHM).
Table 1: Spectral bands for the SENTINEL-2 sensors (S2A & S2B)
Figure 1 (below) shows the S2A spectral response functions (SRF) and transmission due to vertical column Water Vapour (WV) absorption for subarctic winter atmosphere (light blue, lowest WV content) and tropical atmosphere (darker blue, highest WV content). WV transmission data comes from MODTRAN.
Note: In order to better view the Figure, right click on the image, and select 'View Image'.
Figure 1: SRF and transmission due to vertical column WV absorption
The MSI is designed and built by Airbus Defence and Space, France, and is based on a push-broom concept (Figure 1).
MSI instrument features
Figure 2: The MultiSpectral Instrument (Airbus Defence and Space)
Figure 3: MSI Internal Configuration
The 12 detectors on each focal plane are mounted in a staggered formation (Figure 4) to cover the whole 20.6o instrument field of view, resulting in a compound swath width of 290 km on the ground track. As illustrated in the figure below, due to the staggered positioning of the detectors on the focal planes, a parallax angle between the two alternating odd and even clusters of detectors is induced in the measurements, resulting in a shift along track of approximately 46 km (maximum) inter-detector. Likewise, the hardware design of both the VNIR and SWIR detectors imposes a relative displacement of each spectral channel sensor within the detector resulting in an inter-band measurement parallax amounting to a maximum along track displacement of approximately 14 km.
Figure 4: Staggered Detector Configuration and Inter-Detector / Inter-Band Parallax Angles (parallax figures derived from MSI instrument documentation)
Due to the particular geometrical layout of the focal plane, each spectral band of the MSI observes the ground surface at different times.
Table 2: The temporal offset (in seconds) between selected Bands