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Earth_Engine_Data_Overview.md

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Earth Engine Data Overview

Version 0.1.0 | 5 Aug 2022

Introduction

Through the Google Earth Engine API, the AgReFed Data-Harvester provides access to the following satellite products:

Note that Earth Engine is still under active development. Download and access limits apply, including a maximum download size of 32 MB (but, ~50MB raw). The Data Harvester uses the geedim package to overcome this ceiling but cloud processing limits (e.g. during compositing of images) will continue to limit the amount of data that can be downloaded.

Landsat

The USGS/NASA Landsat Program provides satellite spectral and thermal data of the Earth from 1972. Collection 2, Tier 1 products in the catalog represent data of the highest available quality with inclusions of corrections for improved geometric accuracy, digital elevation modeling and radiometric calibrations. Strips of collected data are packaged into overlapping "scenes" covering approximately 170 km x 183 km using a standardized reference grid.

Coverage: See coverage here

Resolution: 15/30/100 m

Period (y-m-d):

  • Landsat 9 : 2021-10-31 – present
  • Landsat 8 : 2013-03-18 – present
  • Landsat 7 : 1999-05-28 – 2022-04-06
  • Landsat 5 : 1984-03-16 – 2012-05-05

Updates: Daily

Revisit frequency: 16 days

Attribution: tbd

Sentinel-2, Level 2A

Sentinel-2 is part of a constellation of satellites in the Copernicus Program and surface reflectance images have been available from 2017. Level 2A images provide orthorectified and atmospherically corrected surface reflectance data. Each Level 2A product is composed of 100 km^2^ tiles in cartographic geometry (UTM/WGS84 projection).

Coverage: See coverage here

Resolution: 10/20/60 m

Period (y-m-d): 2017-03-28 – present

Updates: Daily

Revisit frequency: 5 days

Attribution: tbd

Functionality

The following functionality are supported:

  • Selecting image(s) based on date(s)
  • Automatic cloud masking, shadow masking, using eemont and geedim
  • Automatic scale and offsetting, using eemont
  • Image compositioning/reduction
  • Automatic calculation of spectral indices (via Awesome Spectral Indices)
  • Interactive map previews, with automatic pixel stretching, using geemap and geetools
  • Download image(s) using split-download-assemble method to overcome size limits, using geedim