GIScience (Geographic Information Science)

Welcome to the Earth, Water, Fire, Air, and Space open data portal page. Here, themed elements have been used to loosely categorize each data providers' research area. 
Note: Given the multidisciplinary nature of GIScience, there is understandably overlap between efforts. In these cases the first focus of each data provider was used for categorization.

Earth

United States Geological Survey (USGS) Science Data Catalog (SDC)
A multitude of datasets of the United States landscape, including natural resources, and natural hazards.
https://data.usgs.gov/datacatalog/

United States Department of Agriculture (USDA)
An authoritative source of publicly available data related to agriculture in the United States.
https://www.usda.gov/content/usda-open-data-catalog

Earth Engine Data Catalog
The Google Earth Engine provides a platform for working with satellite data online. This system allows access to petabytes of geospatial data going back to the 1980s.
https://developers.google.com/earth-engine/datasets/catalog

Living Atlas of the World 
An extensive collection of curated geographic information from around the globe. An ArcGIS online account is required to access much of the data.
https://livingatlas.arcgis.com/en/home/

Climate

National Centers for Environmental Information (NCEI) Paleo Data Search
A subgroup to NOAA, the NCEI Paleo data portal provides paleoclimatic proxy data and paleoclimate reconstructions data derived from tree rings, ice cores, corals, and submerged sediments.
https://www.ncdc.noaa.gov/paleo-search/

Water

National Oceanic and Atmospheric Administration (NOAA) Data Discovery Portal
Containing weather, climate, oceans and fisheries data generated by NOAA.
https://data.noaa.gov/dataset/

National Snow and Ice Data Center
Encompasses data about the Earth’s cryosphere (snow, ice, glaciers, frozen ground, and climate interactions). 
https://nsidc.org/

HYDROSHARE
HydroShare provides an open source platform for sharing hydrologic data. 
https://www.hydroshare.org/search/

Fire

Wildland Fire Decision Support System (WFDSS) Data
These data are made available to assist fire managers and analysts in making strategic decisions for fire incidents.
https://wfdss.usgs.gov/wfdss/WFDSS_Data.shtml

LANDFIRE
Get access to many layers relevant to understanding forest files and their potential.
https://www.landfire.gov/getdata.php

Canadian National Fire Database (CNFDB)
A GIS database containing forest burned areas in Canada since 1986.
https://cwfis.cfs.nrcan.gc.ca/datamart

Air

National Center for Atmospheric Research (NCAR) Research Data Archive (RSA)
A diverse collection of meteorological and oceanographic observations, model outputs, and remote sensing data.
https://rda.ucar.edu/

NCAR University Corporation for Atmospheric Research (UCAR) Climate Data Sets
Over 200 datasets each spanning multiple years.
https://climatedataguide.ucar.edu/climate-data

NOAA's Physical Sciences Laboratory (PSL) Data and Imagery
Includes a wide range of data, from gridded climate datasets hundreds of years in length to single point real-time wind data.
https://psl.noaa.gov/data/index.html

Cooperative Institute for Research in the Atmosphere (CIRA)
Air quality, weather and model data collected and produced at CIRA.
https://www.cira.colostate.edu/imagery-data/

Environmental Protection Agency (EPA) Air Quality System (AQS) database 
Accessed via REST API using a freely created user account, various air quality measurements from across the nation can be downloaded.
Note: these data are updated every couple of months and downloaded data requires an understanding of the JSON file formate.
https://aqs.epa.gov/aqsweb/documents/data_api.html

PurpleAir
A citizen science initiative where community members install twin units of laser particle counters (Plantower PMS5003) to form a dense air quality sensor network roughly measuring Particulate Matter 2.5 μg/m3 (PM2.5).
https://www.purpleair.com/map

The PurpleAir data download is on the right.

Space

National Aeronautics and Space Administration (NASA) Open Data Portal
Access data collected by NASA satellites. It helps to be familiar with the satellites orbiting the earth and what they are measuring to make the most of this portal.
https://data.nasa.gov/browse

NASA Earth Data Search
A true data discovery platform allowing filtering, visualization, and access to all the Earth science data holdings at NASA. A free account must be created prior to downloading the data.
https://search.earthdata.nasa.gov/search

European Space Agency (ESA) Earth Online
Similar to NASA's data portal but more approachable for the uninitiated.
https://earth.esa.int/eogateway/search?text=&category=Data&subFilter=data%20download

NOAA Satellite Data Access by Datasets
Supported by NOAA's Climate Data Record (CDR) Program this collection includes long-term, high-quality satellite data products.
https://www.ncdc.noaa.gov/data-access/satellite-data/satellite-data-access-datasets

Miscellaneous

Avenza Maps
While more geared towards selling maps, this site does have plenty of free ones too.
https://www.avenzamaps.com/maps/search.html

GISGeography
A nicely organized collection of remote sensing, and cartography datasets.
https://gisgeography.com/category/data-sources/

If you have an open data resource you'd like to see listed here, please email Kevin[dot]Worthington[at]colostate.edu.