Free Remote Sensing Data

I am always amazed at the amount of remote sensing data available for free from a wide variety of different satellite and aerial platforms. A major watershed moment in the remote sensing community occurred in 2009 when the USGS made their Landsat satellite image archive freely available over the internet. The availability of remote sensing data at no cost certainly didn't start in 2009 (EOS Aqua/Terra comes to mind) but since the Landsat decision there has been a philosophical shift amongst government missions and research organization programs with a trend towards making data freely available (either to the general public or a specific subset of users).
 
This trend continues with programs such as Suomi National Polar-orbiting Partnership (NPP) making the data from sensors such as VIIRS freely available with more recent examples such as the European Space Agency (ESA) providing free distribution of the data from the Copernicus/GMES Sentinel missions. Much of this free data can be found on website-based data portals such as USGS EarthExplorer or NASA Reverb | ECHO. Furthermore, there are a wide variety of commercial industry sources such as Esri's Landsat imagery services.
 
Making remote sensing data freely available certainly helps scientists perform research and collaborate with one another on a wide variety of projects. Applications in the realm of environmental assessment alone include land use, forest fires, volcanic ash clouds, flooding, tropical storms, air quality, water resources, climate change, coral reef health, oil spills, agricultural monitoring, ecological forecasting, algal blooms, polar ice, dust storms, tornado damage, drought analysis, etc..  In addition to supporting scientific research, freely available data also supports "citizen scientist" objectives that some missions have as an outreach requirement.  For example, NEON will be making all of its long term HSI, MSI, LiDAR, aerial photography and field data available on a public portal.
 
Since I have a hard time keeping all of these website resources organized in my web browser bookmarks/favorites, I started collecting the links and some brief searchable text descriptions in a whitepaper document that I'll share with you in the link below:
 
http://www.exelisvis.com/portals/0/pdf/6-14_Geospatial_Imagery_Raster_GIS_Data_Sources.pdf
 
I use the term "whitepaper" loosely. This document is really nothing more than a bulleted list of URL links.
 
The resources in this whitepaper definitely lean towards EO/IR imagery, SAR data, LiDAR point clouds, digital elevation model (DEM) and spectral library data sources. Furthermore, in many circumstances the data available from the free sources may not have the spatial resolution, geographic coverage, temporal revisit, or radiometric & geometric accuracy required for certain applications. Consequently, within this whitepaper I have also tried to include some links to satellite and aerial data providers that are also a great source for remote sensing data (albeit usually at-cost).
 
This whitepaper is by no means designed to be a comprehensive list of geospatial data servers or providers, as such a list would be hundreds of pages long and require almost constant maintenance. My hope is that some of you may find this document to be a useful resource as you tackle your remote sensing projects, as the wealth of freely available remote sensing data is certainly something we should take advantage of as often as possible.