Attempting thermal difference analysis in Google Earth Engine?

Question

I am attempting to do a means of NDVIS and a means of Thermal thermal for Summer (July &August) 2016.

When I run the annotated code below the error I get in the side console panel is: Use print (...) to write to this console. And in the red box right below: "image" is not defined in this scope.

What's wrong with my code?

//specify a portion of Landsat archive to work with as image collection
var collection = ee.ImageCollection('LANDSAT/LC08/C01/T1_TOA')
  .filterDate('2016-07-01','2016-08-31')
  .filterBounds(ee.Geometry.Point(-95.32287567601213,29.79395929049292));

//add a function for NDVI calculation & apply it to the collection using collection.map():
var addNDVI = function(image) {
  return image.addBands(image.normalizedDifference(['B4', 'B3']));
};
var ndviCollection = collection.map(addNDVI);

//add a function for NDVI calculation & apply it to the collection using collection.map():
var addIR = function(image) {
  return image.addBands(image.normalizedDifference(['B10', 'B11']));
};
var ndviCollection = collection.map(addIR);

//normalize difference
var addNDVI = image.normalizedDifference(['B4', 'B3']);
var addNDVI = image.normalizedDifference(['B10', 'B11']);

//calculate mean value of each band from the collection as a new multi-band image
var mean = ndviCollection.reduce(ee.Reducer.mean());

//select the mean NDVI band and Thermal band from this reduced image to visualize and display:
var vizParams = {bands: ['nd_mean'], min: -0.5, max: 1, palette: ['FF0000', '00FF00']};
Map.setCenter(-95.32287567601213,29.79395929049292);
Map.addLayer(mean, vizParams, 'NDVI');

Map.addLayer(addIR,{min:0,max:700}, 'IR');

Answer 1

The first part is fine, although I would rename the NDVI band..

//specify a portion of Landsat archive to work with as image collection
var collection = ee.ImageCollection('LANDSAT/LC08/C01/T1_TOA')
  .filterDate('2016-07-01','2016-08-31')
  .filterBounds(ee.Geometry.Point(-95.32287567601213,29.79395929049292));

//add a function for NDVI calculation & apply it to the collection using collection.map():
var addNDVI = function(image) {      
  // I'd rename the NDVI band to be more specific
  return image.addBands(image.normalizedDifference(['B4', 'B3']).rename('NDVI'));
};
var ndviCollection = collection.map(addNDVI);

Before computing IR, notice that redefining the ndviCollection variable, you loose the NDVI computation. You have two options:

1. Make a new irCollection and have two collections at the end, or
2. include the IR band in the images of ndviCollection (I'll show you this option)

//add a function for IR calculation & apply it to the collection using collection.map():
var addIR = function(image) {
  return image.addBands(image.normalizedDifference(['B10', 'B11']).rename('IR')); // also renames IR band
};
ndviCollection = ndviCollection.map(addIR);

The following part of the code is what's making the error come up:

//normalize difference
var addNDVI = image.normalizedDifference(['B4', 'B3']);
var addNDVI = image.normalizedDifference(['B10', 'B11']);

because you are working with collections, not with an image, in fact, the log says there is no image variable (you haven't define image anywhere), just erase that portion.. then

//calculate mean value of each band from the collection as a new multi-band image
var mean = ndviCollection.reduce(ee.Reducer.mean());

//select the mean NDVI band and Thermal band from this reduced image to visualize and display:
var vizParams = {bands: ['NDVI_mean'], min: -0.5, max: 1, palette: ['FF0000', '00FF00']};
Map.setCenter(-95.32287567601213,29.79395929049292);
// visualize NDVI band
Map.addLayer(mean, vizParams, 'NDVI');

And the last issue in the code is that you are trying to visualize a function (addIR), not an image, and also the range you are using for stretching is irrelevant, change that line for

Map.addLayer(mean, {bands:['IR_mean'], min:0,max:0.01}, 'IR');

complete code here