Contents
How do you classify in ENVI?
The ENVI classification framework provides a powerful and flexible way to classify data. You can create and train a classification algorithm (or classifier) on one dataset and apply it to a similar dataset. Traditionally, classifiers are tied to a specific dataset.
How do you supervise classification in ENVI?
The Supervised Classification panel appears. Select the Algorithm tab, then select Spectral Angle Mapper from the drop-down list. Keep the default Maximum Spectral Angle setting of None. You can define training data from an existing ROI file, but for this exercise you will interactively create your own ROIs.
What is maximum likelihood in remote sensing?
The maximum likelihood classifier is one of the most popular methods of classification in remote sensing, in which a pixel with the maximum likelihood is classified into the corresponding class. The likelihood Lk is defined as the posterior probability of a pixel belonging to class k.
How is the maximum likelihood calculated in ENVI?
ENVI adds the resulting output to the Layer Manager. The rule images, one per class, contain a maximum likelihood discriminant function with a modified Chi Squared probability distribution. Higher rule image values indicate higher probabilities. The final classification allocates each pixel to the class with the highest probability.
How to choose the best ENVI classification approach?
For the data selected for the single year: Choose one supervised and one unsupervised classification approach (we recommend Maximum Likelihood and ISOData Theory: describe how the approaches work (noting similarities and differences) and relate this to the information content of your data. Cite literature as appropriate. [10%]
How to calculate maximum likelihood of an image?
ENVI implements maximum likelihood classification by calculating the following discriminant functions for each pixel in the image (Richards, 1999): p (ω i) = probability that class ω i occurs in the image and is assumed the same for all classes Reference: Richards, J. Remote Sensing Digital Image Analysis, Berlin: Springer-Verlag (1999), 240 pp.
Why is my ENVI Max likehood not working?
That is probably not working because atmospherically corrected images have reflectance values instead of Digital Numbers, which is what your 65535 refers to. Since you’re not dealing with pixel values anymore, it’s not gonna work. What version of ENVI are you using? Version 5.0 sets a default value of 1.0 for Max Likehood classification.