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Accessing Open Satellite Data

Most satellite data is free and open to the public. This section details the primary portals used to download raw remote sensing datasets.

1. Copernicus Data Space Ecosystem (CDSE)

The Copernicus Data Space Ecosystem (CDSE) is the primary portal for European Space Agency (ESA) satellite datasets.

  • URL: dataspace.copernicus.eu

  • Available Data: Sentinel-1 (SAR), Sentinel-2 (Multispectral), Sentinel-3, and Copernicus DEM.

  • Search Tools: Allows filtering by geographic area (drawing polygons), cloud cover threshold, acquisition date, and sensor type.

  • API Access: Supports script-based downloading via OData and SpatioTemporal Asset Catalog (STAC) protocols.

2. USGS EarthExplorer

The primary portal maintained by the United States Geological Survey.

  • URL: earthexplorer.usgs.gov

  • Available Data: Landsat (1-9), SRTM DEM, ASTER DEM, and global land cover products.

  • Search Tools: Allows searching by address, coordinate list, or Shapefile upload.

  • Bulk Download: Supports downloading multiple scenes using the USGS Bulk Download Application.

3. NASA Earthdata

The portal for NASA's Earth Observing System Data and Information System (EOSDIS).

  • URL: search.earthdata.nasa.gov

  • Available Data: MODIS products (Evapotranspiration, Snow Cover, LST), GPM precipitation data, and soil moisture grids (SMAP).

  • Usage: Best for downloading large-scale, daily global climate datasets.

4. SpatioTemporal Asset Catalog (STAC) API

The SpatioTemporal Asset Catalog (STAC) specification provides a common language to describe geospatial datasets, making them easily searchable and indexable. Instead of downloading heavy raw images manually, analysts can programmatically query STAC APIs to inspect metadata and stream assets directly.

  • STAC Structure: Organized into Catalogs (entry points), Collections (related datasets, e.g., Sentinel-2 L2A), and Items (individual scenes representing a specific time/location with links to raster assets).

  • API Client Libraries: Python clients such as pystac-client allow querying endpoints via geographic bounding boxes, date ranges, and cloud cover criteria.

5. ObservEarth

A satellite imagery analytics platform designed to simplify access, preprocessing, and analysis for developers and environmental researchers.

  • URL: observearth.com

  • Key Features: ObservEarth aggregates public datasets (such as Sentinel-1, Sentinel-2, and Landsat) and integrates them with automated preprocessing pipelines to output analysis-ready data.

6. Digital Elevation Model (DEM) Sources

Digital Elevation Models are the baseline files for hydrological delineation (slopes, stream networks, and basins).

  • SRTM (Shuttle Radar Topography Mission):

    • Resolution: \(1\) Arc-Second (\(\sim 30\text{ m}\)) resolution.
    • Access: Available via USGS EarthExplorer (under the Digital Elevation section) or programmatically via Google Earth Engine (USGS/SRTMGL1_003).

  • Copernicus DEM (GLO-30 / GLO-90):

    • Resolution: \(30\text{ m}\) (GLO-30) and \(90\text{ m}\) (GLO-90) resolution. It is currently one of the most vertically accurate, void-filled global DEMs.
    • Access: Downloadable through the Copernicus Data Space Ecosystem (CDSE) catalog or GEE (COPERNICUS/DEM/GLO30).

  • ALOS World 3D (AW3D30):

    • Resolution: \(30\text{ m}\) global surface model generated by the Japan Aerospace Exploration Agency (JAXA) from \(5\text{ m}\) optical stereo imagery.
    • Access: Free registration and download via the https://search.asf.alaska.edu/

7. Precipitation & Rainfall Sources

Gridded rainfall datasets are critical inputs for water balance models and regional rainfall-runoff calculations:

  • CHIRPS (Climate Hazards Group InfraRed Precipitation with Station data):

    • Resolution: \(0.05^\circ\) (\(\sim 5.5\text{ km}\)) resolution. Daily, pentad, and monthly rainfall data from 1981 to present.
    • Access: Directly from the UC Santa Barbara CHG FTP server, the QGIS Climate Data Store Plugin, or GEE (UCSB-CHG/CHIRPS/DAILY).

  • IMERG (Integrated Multi-satellitE Retrievals for GPM):

    • Resolution: \(0.1^\circ\) (\(\sim 11\text{ km}\)) resolution. High-accuracy half-hourly and daily rainfall estimations from 2000 to present.
    • Access: Downloadable through NASA Earthdata Search (under the GES DISC portal) or GEE (NASA/GPM_L3/IMERG_V06).

  • ERA5 Reanalysis (ECMWF):

    • Resolution: \(0.25^\circ\) (\(\sim 31\text{ km}\)) resolution. Hourly and daily atmospheric, surface, and hydrological variables from 1940 to present.
    • Access: Query and download via the Copernicus Climate Data Store (CDS) using the https://cds.climate.copernicus.eu/

  • PERSIANN-CCS (Precipitation Estimation from Remotely Sensed Information using Artificial Neural Networks - Cloud Classification System):

    • Resolution: High spatiotemporal resolution (\(0.04^\circ\) or \(\sim 4\text{ km}\), hourly and daily).
    • Access: Download via the CHRS Data Portal or access in GEE (UCIRVINE/CHRS/PERSIANN-CCS). Developed by the Center for Hydrometeorology and Remote Sensing (CHRS) at UC Irvine, it is highly useful for convective storm and flash flood modeling in complex mountainous terrain.

8. Surface Water Sources

  • JRC Global Surface Water:
    • Resolution: \(30\text{ m}\) resolution. Standard global dataset maps temporal surface water patterns (occurrence, intensity, seasonality, transition) over 35+ years.
    • Access: Interactive maps via the JRC Global Surface Water Explorer or imported directly in GEE (JRC/GSW1_4/GlobalSurfaceWater).

9. Land Use / Land Cover (LULC) Sources

LULC determines runoff coefficients and land surface resistance in hydrological modeling:

  • ESA WorldCover:

    • Resolution: \(10\text{ m}\) global land cover map based on Sentinel-1 and Sentinel-2 data (available for 2020 and 2021).
    • Access: Download maps from the ESA WorldCover Viewer website or GEE (ESA/WorldCover/v100 and v200).

  • Dynamic World:

    • Resolution: \(10\text{ m}\) near-real-time global land cover dataset containing 9 land classes with pixel-level probabilities, updated continuously matching Sentinel-2 revisits.
    • Access: Queryable dynamically using Google Earth Engine (GOOGLE/DYNAMICWORLD/V1) or downloadable in tiles from the Dynamic World App.

10. Evapotranspiration (ET) Sources

Actual Evapotranspiration (\(ET_a\)) is the largest loss component in watershed water balance equations:

  • FAO WaPOR:

    • Resolution: \(100\text{ m}\) (Africa and Middle East) and \(300\text{ m}\) (global) resolution.
    • Access: Download via the FAO WaPOR Portal or search and import directly in QGIS using the QGIS WaPOR Plugin.

  • MOD16 (MODIS Evapotranspiration):

    • Resolution: \(500\text{ m}\) resolution. 8-day and monthly actual evapotranspiration (\(ET\)) and potential evapotranspiration (\(PET\)) grids.
    • Access: Download through NASA Earthdata Search (AppEEARS tool) or GEE (MODIS/061/MOD16A2).

  • SSEBop (Operational Simplified Surface Energy Balance):

    • Resolution: \(1\text{ km}\) thermal-based actual ET dataset developed by the USGS.
    • Access: Download from the USGS FEWS NET Data Portal or access directly in GEE (USGS/MEaSUREs/HEX/SSEBop/ETA/V4).

11. River Networks & Hydrological Vector Basins

Delineated river vectors and sub-watersheds are crucial for routing streamflow:

  • HydroSHEDS:

    • Description: Global hydrographic database providing flow direction, flow accumulation, river networks, and watershed boundaries derived from elevation data.
    • Access: Download vectors and rasters directly from the HydroSHEDS portal (hydrosheds.org).

  • HydroRIVERS:

    • Description: A global vector line dataset representing all river reaches with attributes including catchment area, stream order, and estimated annual discharge.
    • Access: Download from the HydroSHEDS downloads directory.

12. Administrative Boundaries & Basemaps

  • OpenStreetMap (OSM):

    • Description: Crowd-sourced global map database containing vector elements like roads, waterways, structures, and land boundaries.
    • Access: In QGIS, download raw vector features directly via the QuickOSM plugin (running Overpass queries) or download pre-cut national shapefiles from Geofabrik.

  • GADM (Database of Global Administrative Areas):

    • Description: High-resolution spatial boundaries representing national (Level 0), provincial (Level 1), and district (Level 2) limits.
    • Access: Download files by country in GeoPackage, Shapefile, or RDS formats from gadm.org.

13. Open Data Policies and Citations

When using satellite datasets in public commission reports (such as WECS studies), it is essential to follow licensing and citation guidelines:

  • Copernicus Data: Free for reuse under Creative Commons licenses. It should be cited as: "Contains modified Copernicus Sentinel data [Year], processed by [Author Name]."

  • USGS/NASA Data: Public domain. Cite the specific mission and acquisition year (e.g., "USGS Landsat 8 image courtesy of the U.S. Geological Survey, [Year].").