There are several spectral transformation methods in Earth Engine. These include instance
methods on images such as normalizedDifference()
, unmix()
,
rgbToHsv()
and hsvToRgb()
. The latter two methods are useful
for pan sharpening. For example:
// Load a Landsat 8 top-of-atmosphere reflectance image. var image = ee.Image('LANDSAT/LC08/C01/T1_TOA/LC08_044034_20140318'); Map.addLayer( image, {bands: ['B4', 'B3', 'B2'], min: 0, max: 0.25, gamma: [1.1, 1.1, 1]}, 'rgb'); // Convert the RGB bands to the HSV color space. var hsv = image.select(['B4', 'B3', 'B2']).rgbToHsv(); // Swap in the panchromatic band and convert back to RGB. var sharpened = ee.Image.cat([ hsv.select('hue'), hsv.select('saturation'), image.select('B8') ]).hsvToRgb(); // Display the pan-sharpened result. Map.setCenter(-122.44829, 37.76664, 13); Map.addLayer(sharpened, {min: 0, max: 0.25, gamma: [1.3, 1.3, 1.3]}, 'pan-sharpened');
Spectral unmixing is implemented in Earth Engine as the image.unmix()
method.
(For more flexible methods, see the Array Transformations
page). The following is an example of unmixing Landsat 5 with predetermined urban,
vegetation and water endmembers:
// Load a Landsat 5 image and select the bands we want to unmix. var bands = ['B1', 'B2', 'B3', 'B4', 'B5', 'B6', 'B7']; var image = ee.Image('LANDSAT/LT05/C01/T1/LT05_044034_20080214') .select(bands); Map.setCenter(-122.1899, 37.5010, 10); // San Francisco Bay Map.addLayer(image, {bands: ['B4', 'B3', 'B2'], min: 0, max: 128}, 'image'); // Define spectral endmembers. var urban = [88, 42, 48, 38, 86, 115, 59]; var veg = [50, 21, 20, 35, 50, 110, 23]; var water = [51, 20, 14, 9, 7, 116, 4]; // Unmix the image. var fractions = image.unmix([urban, veg, water]); Map.addLayer(fractions, {}, 'unmixed');
The unmixing result should look something like Figure 1.
