Spring imagery Spring imagery has been found most useful from the stand point of distinctive patterns in soil moisture and vegetation development, using geobotanical methods. This is a time of year when vegetation phenology and soil moisture conditions reflect subtle differences in soil texture and organic content, in land slope and aspect, and in land cover or agricultural practices. Sun position is at or near its highest elevation of the year, which provides for maximum illumination and minimum shadow effects. This is also a good time of year to see surface drainage and lake patterns clearly. The standard false-color composite image is quite effective for displaying geobotanical aspects of the landscape.
Geomorphic features are usually less distinct on such summer images.
Autumn imagery Autumn is again a time of year when vegetation phenology reflects geomorphic variations in the landscape, as certain plants become dormant or die and crops are harvested during the season. Soils are usually drier, and consequently lakes and streams are often lower. In semiarid or arid regions, shallow lakes may partly or completely dry up, leaving bare mud flats or salt deposits. Drought conditions may enhance certain geomorphic features revealed on autumn images. Sun elevation is significantly lower, compared to spring images, which imparts a moderate topographic shadow effect.