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I'm learning to use eCognition (8.1) and my teacher has provided me with some example tif files to segment and classify. The tif files have multiple layers, each of which are supposed to represent a light spectrum (Red, Green, Near-infared, etc). The problem is that I'm not always given descriptions of what spectrum each layer is supposed to be.

My question is, is it possible tell what spectrum a layer is supposed to represent?

  • Welcome to GIS Stack Exchange! One thought though is that this question may be more suited to the Signal Processing Stack Exchange. – PolyGeo May 24 '13 at 2:07
  • Alright, cool, I'll try there. Thanks for the advice and welcome! :) – Robbie Redfearn May 24 '13 at 2:13
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    It's a remote sensing question should it should be on topic here as well. – R.K. May 24 '13 at 2:53
  • As remote sensing is "joined in marriage" with GIS, this is a very appropriate question for this forum--perhaps more so than the SP site. – Aaron May 24 '13 at 3:17
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Look at the Layer Values in the Image Object Information window. From here you will be able to determine the pixel value/DN/radiance/reflectance (or whatever your image format is). You will have to add these Layer Values from the Feature View window:

Feature View > Object Features > Layer Values > Mean > [right-click] Layer... > Display in Image Object Information

Simply select a pixel or segment within the viewer and the values for each of the bands will appear for that region of interest. For example, in this screenshot I selected a very "green" object in an ag area. My imagery has 4 bands (R, G, B, nIR). nIR has very high reflectance values off of healthy green vegetation, so you can see that layer 4 is clearly nIR. Conversely, nIR will have very low values when you select an object over water, as water has very low reflectance at nIR. The red band is also very easy to determine strictly from looking at the layer values. Since healthy green vegetation exhibits low reflectance in the visible red, values here will be the lowest among the 4 bands. Blue also has lower reflectance off vegetation, while green has higher reflectance off vegetation.

In sum, you can see that layer 4 = nIR band, layer 1 = red band, layer 2 = blue band and layer 3 = green band.

enter image description here

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    This is EXACTLY what I was looking for! Thanks so much, that'll save me opening and loading images into Arcmap. – Robbie Redfearn May 24 '13 at 3:56
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You'd need to know the actual data source for that. You might want to ask your teacher what sensor the image came from. Is a SPOT image? LANDSAT? QuickBird? Once you know that, you'll be able to identify what spectrum each band is supposed to be as those are documented.

  • Awesome! Okay, well I know it comes from a LANDSAT sensor, and I've found some documentation about the wavelengths of different bands. As for finding the wavelengths of the layers, I can do that with Arcmap and ENVI.. Do you know how I could find that in eCog? :) – Robbie Redfearn May 24 '13 at 3:18
  • I think the correspondences between bands and wavelengths are the same, regardless of software. So for example, if band 2 corresponds to blue in ArcGIS then it should be the same as well in eCognition. – R.K. May 24 '13 at 3:42
  • Glad to be of help :) – R.K. May 24 '13 at 3:53

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