Image Scaling¶

Image scaling now is A LOT EASIER with eemont! Let’s see how!

Before anything, let’s import our modules and authenticate in Google Earth Engine:

import ee, eemont

ee.Authenticate()
ee.Initialize()

Now, we are ready to go!

Overview¶

The eemont package extends the ee.Image and ee.ImageCollection classes with the following methods:

ee.Image¶

`getOffsetParams`(self)	Gets the offset parameters for each band of the image.
`getScaleParams`(self)	Gets the scale parameters for each band of the image.
`preprocess`(self, **kwargs)	Pre-processes the image: masks clouds and shadows, and scales and offsets the image.
`scaleAndOffset`(self)	Scales bands on an image according to their scale and offset parameters.

ee.ImageCollection¶

`getOffsetParams`(self)	Gets the offset parameters for each band of the image collection.
`getScaleParams`(self)	Gets the scale parameters for each band of the image collection.
`preprocess`(self, **kwargs)	Pre-processes the image collection: masks clouds and shadows, and scales and offsets the image collection.
`scaleAndOffset`(self)	Scales bands on an image collection according to their scale and offset parameters.

Supported Platforms¶

This method automatically scales ALL images from the Google Earth Engine STAC Catalog by using the List of Scale and Offset Paramaters from the GEE STAC Catalog Repository.

Usage¶

The scaleAndOffset() method scales each image according to the Scale and Offset parameters for each band of the image.

Let’s take the Sentinel-2 SR image collection as example:

S2 = ee.ImageCollection('COPERNICUS/S2_SR')

The spectral bands from Sentinel-2 have values close to the (0, 10000) range, but they’re unscaled. In order to get the real values, each spectral band must be multiplied by 0.0001, while AOT and WVP bands must be multiplied by 0.001. This scaling is automatically done by the scaleAndOffset() method, without any additional parameters:

S2.scaleAndOffset()

The Scale and Offset parameters vary according to the satellite platform and the scaleAndOffset() method detects the platform and do the scaling according to its parameters.

Let’s take now the MOD11A2 product from MODIS. The LST_Day_1km and LST_Night_1km bands must be multiplied by 0.02, the Day_view_time and Night_view_time bands must be multiplied by 0.1, the Emis_31 and Emis_32 bands must be multiplied by 0.002 and added by 0.49, while the Day_view_angl and Night_view_angl bands must be added by -65. All of this scaling is simply done by the scaleAndOffset() method:

MOD11A2scaled = ee.ImageCollection('MODIS/006/MOD11A2').scaleAndOffset()

The scale() method can be applied to single images as well:

MOD11A2scaled = ee.ImageCollection('MODIS/006/MOD11A2').first().scaleAndOffset()

Preprocessing¶

Additionally, if required, the preprocess() method can be used to scale and mask images and image collections:

S2 = ee.ImageCollection('COPERNICUS/S2_SR').preprocess()

Data Conversion Masking Clouds and Shadows