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Landsat-1 (Originally named ERTS-A for Earth Resources Technology Satellite); Landsat-2 (called ERTS-B until few time prior to launch, and Landsat 3; and also Spot (Satellite Pour l’Observation de la Terre: Sattellite for Earth observation) prime focus was in terrestrial natural resurces (soils, crops, etc) Landsat was aimed to for geology an Spot for agriculture) Due communication limitations at that time (we talk about hundreds of megabytes by minute in the ’70s) they chose limitated number of bands to survey different spectral signatures, and due just few things got differences in blue band (beyond water) they chose to carry a more usefull close infrared band than the blue one. Regards. Art

Spot 6 has blue : http://www.satimagingcorp.com/satellite-sensors/spot-6/ maybe because SPOT aimed for object on land, so they dont need blue