Google Earth Engine

Google Earth Engine (GEE) is a cloud-based platform for planetary-scale environmental data analysis. It hosts a vast collection of satellite imagery and other geospatial datasets, enabling users to perform large-scale data analysis.

This module can be used to extract remote sensing satellite data directly from Google Earth Engine.

soil

1. Configuration file breakdown

This module uses a configuration file in yaml format to extract data from google earth engine. This configuration file defines the global parameters, satellite collections, and derived variables . Below is a detailed explanation of each section.

# filename: config.yml

# Global parameters
global_scope:
  time_range: ['2016-01-01', '2021-12-31']
  variables: ['nir', 'red', 'green', 'ndvi', 'lai_ndvi']  
  resolution: 10

# Specify Earth Engine collections and their respective variables
collections:

  le07:
    collection: LANDSAT/LE07/C02/T1_L2
    select:  (b('QA_PIXEL') >> 6) & 1
    variables:
      nir: b('SR_B4')*0.0000275 - 0.2
      red: b('SR_B3')*0.0000275 - 0.2
      green: b('SR_B2')*0.0000275 - 0.2

# Derived variables
derived_variables:
  ndvi: '(nir - red)/(nir + red)'

i. Global Parameters

The global_scope section contains general settings applicable to the entire data extraction process.

time_range: Specifies the period for which the satellite data should be fetched.
variables: Lists the key variables to be extracted. These are typically satellite bands or derived products such as vegetation indices.
resolution: Defines the spatial resolution (in meters) for the output data.

ii. Satellite-Specific Parameters

Each satellite dataset is defined under its own subsection. The key components are collection, select, and variables. Multiple satellite dataset can be given. If data from multiple satellites are present for the same time period, the module will return the mean of the variables across all satellites.

collection: Refers to the specific Google Earth Engine dataset for LANDSAT 7.
select: Defines a masking condition for the data selection.
variables: Specifies the bands to extract, along with any scaling factors.

iii. Derived Variables

Derived variables are calculated from the raw bands using mathematical expressions and functions available in numpy package.

2. Fetching the Data

You can use the following command line to fetch satellite data from Google Earth Engine and store it in a CSV file:

geo-epic gee <config-file> --fetch <input> --out <output-path>

i. Input options

The input for fetching data can be provided in three formats:

Latitude and Longitude: Use direct coordinates (latitude and longitude)

geo-epic gee ./landsat_lai.yml --fetch 40.56773135493621 98.55058401654036 --out ./out/sample.csv

Shapefile (.shp): A shapefile containing the region of interest. It must contain a SiteID or FieldID column. The data will be stored in the name of FieldID or SiteID.
```
geo-epic gee ./landsat_lai.yml --fetch ./input/region.shp --out ./out
```
CSV File: A CSV file must contain a SiteID or FieldID column. Additionally, if using a CSV, it must include lat, lon columns. The data will be stored in the name of FieldID or SiteID.
```
geo-epic gee ./landsat_lai.yml --fetch ./input/region.csv --out ./out
```