Opposition between Eastern and Western Margins

Opposition Between Eastern and Western Margins (does not apply to ERTS or to one Nimbus 5 radiometer) 

The zone traversed and usable extends for about 30° longitudinally, corresponding to a time difference of two hours. Other things being equal, it should be understood that the thermal contrasts are quite large and, in the daytime, the energy reflected cannot be compared between the two extemes of the zone covered, since the angle of incidence of the Sun s rays at the two extremes differs too much. 

Practically the same situation could occur since radiation picked up by the instruments on board the satellites is a function of that part of the energy accumulated during the daytime that is reemitted during the night. This nocturnal radiation begins as soon as the Sun sets, i.e., two hours earlier in the east than in the west. 

Daytime NORTHBOUND Q2 o clock satellite Nighttime SOUTHBOUND 

Each area scanned by the instruments on board the satellite is obviously perpendicular to the axis of orbital motion, the two margins being at different latitudes. When a map is made of the data received from the satellites, the time difference is increased by about one minute between two points situated at the same latitude on either side of the map (from E to W), the point in west having been seen a little later than its corresponding point in the east. This fact is recorded for general information only, as it has no practical importance. 

---