Skip Navigation

University of Nebraska–Lincoln

  • Virtual Nebraska Logo

Virtual Nebraska

Educational Modules

A Guide to the Practical Use of Aerial Color-infrared Photography in Agriculture

Agricultural Applications of Color-infrared Film

Crop Inventory and Analysis

CIR aerial photography is used widely for general crop inventory and analysis. It is often important for a resource manager or agriculturist to record and/or map the distribution of crop types within a certain study area; for example, a county or natural resources district. Of course, the scale and type of photography flown for inventory purposes is generally different than that acquired for monitoring one farm or a few particular fields. For regional crop surveys, workable scales are between 1:40,000 and 1:80,000 (sometimes even up to 1:120,000), while the film format is generally 9 inches by 9 inches.

One very important aid in the identification of crop types from aerial photography is the agroclimatic calendar, or more commonly, the crop calendar. A crop calendar summarizes the general planting, reproduction, and harvesting periods for crops located in specific growing areas. An example of a crop calendar for the Nebraska panhandle for five specific crops is shown in figure 7.

Fig. 7

An understanding of the crop calendar for a particular area is critical to the correct identification of agricultural crops from CIR aerial photography. The interpreter must be aware that the photographic tone on specific color "signature" of a crop changes as its life-cycle stage changes. An example of the change in image signatures as seen at different points in time in southeastern Nebraska is illustrated in figure 8. Notice in figure 8 that the corn and wheat are easily distinguished by referring to the multi-date CIR imagery, but separating corn from milo or corn from soybeans is much more difficult.

June 15, 1983 August 15, 1983
Fig. 8

Aerial color-infrared photographs of the University of Nebraska South Central Research and Extension Center, near Clay Center, Nebraska. Notice how the CIR tone of the fields has changed through the growing season (from June 15 to August 15). The specific crops are identified as follows: "W" = winter wheat; "F" = summer fallow; "M" = milo; "SBL" = late-planted soybeans; "SG" = silage sorghum, "SF" = sunflowers; "C" = corn. Some variations in signatures are apparent between and among fields of the same crop, for example, in the case of corn (lower right). These variations generally indicate cropping experiments. A good example is the two small corn fields (lower center) that are planted in north-south rows while the other corn plots are planted in east-west rows. The arrow on the August 15 image points to a parked car, which may be used as a reference for scale.

Through an understanding of the crop calendar for a particular area, one can also plan the CIR aerial-photo missions for the maximum interpretive separation of crops on the resulting images. Critical points in the life-cycle of each crop can be identified and the air-photo mission planned accordingly.

While crop species are generally discernible to an experienced interpreter of multi-date CIR photography, differentiating crop varieties is much more difficult. For example, the area in figure 8 designated as wheat is actually made up of small plots representing many different varieties of that crop. Notice that it is possible, in some cases, to detect subtle differences in signature among the wheat plots.

Remote-sensing research has shown that sometimes it is possible to correlate the density of a crop canopy (biomass) as shown on CIR film with the eventual yield obtained from the field. Such research generally involves instrumentation for converting the film into a computer-readable format (digitizing) and subsequent statistical analysis by computer.