Examples: Example 3
 

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Introduction

Using Remote Sensing

  1. Obtaining
  2. Linking
  3. Subsetting
  4. Compositing
  5. False coloring
  6. Ratioing
  7. Supervised classification

Examples

Pre-post test

Example #3 Are farmers rotating crops?

Using images part B: 

Composite subset: NW OH April 2004 and April 2005

In this example, a small section of farmed fields in NW Ohio from the same month in 2004 and 2005 are analyzed as a combined image. (Compositing and subsetting two successive years of the same area.) The following is a subset of Ohio LANDSAT path 20 row 31. It covers the Bowling Green Water Treatment Pond (black rectangle) and the Maumee river in the upper left corner (black). There are 4 fields of interest labeled 1,2,3,4, and the water treatment pond labeled 5. Vegetation reflects very high in band 4 and very little in band 3. This means that an image with a low band 3 value and a high band 4 value would indicate vegetation. Therefore, we will focus on these two bands for now. The software program, Multispec, makes it possible to look at all or any bands from 2 images at once by assigning a band to a channel. In this composite, channels 1-6 correspond to bands 1,2,3,4,5,7 of April 2004 and channels 7-12 correspond to bands 1,2,3,4,5,7 of April 2005. This display colors band 4 of April 2004 red and colors band 4 of April 2005 green. If the surface has high reflectance in both years, the pixel will be yellow. If the surface has low reflectance in both years, the pixel will be dark. The Selection Graphs show the values of all 6 bands for both years (12 channels). What determines whether a farmer rotates his crops?

Interpretation of image:

Field one:

The Selection Graph for Field # 1 shows lower reflectance value in bands 3 and 4 for both years (channels 3, 4 and 9, 10). Therefore, field 1 is probably bare at this time for both years and winter wheat is not being grown there either year.

Field Two:
The Selection Graph for Field # 2 shows a higher reflectance value in band 4 (channel 4) in April 2004 than in band 4 in April 2005 (channel 10).  Band 3 shows low reflectance in both years. Therefore, field 2 probably has winter wheat growing in April 2004 and not in April 2005. Crops in this field were rotated. 

Field Three:

The Selection Graph for Field #3 is very similar to the Selection Graph for Field #1.

Field Four:

The Selection Graph for Field #4 shows a lower reflectance value in band 4 (channel 4) in April 2004 than in band 4 in April 2005 (channel 10). Band 4 in April 2005 has a higher value indicating vegetation. Therefore winter wheat is probably growing in April 2005 and not in April 2004. The crops were rotated.

Pond

The Selection Graph for the pond has low values for 3 and 4 both years as one would expect. Band 2 is often used to detect sediment in the water. One might conclude from the Selection graph that there is not much sediment in the  Maumee river and in the pond at this time.  The pond water is water from the Maumee river.