NCO is three things: a geoscience data analysis toolkit, an
open-source software project, and an academic enterprise that embodies
fundamental new (research-level) algorithms for geoscience data
analysis. Successful academic research depends upon peer-evaluation,
dissemination, and explicit acknowledgement of prior work and original
results. The accepted way to convey acknowledgement to NCO for ideas
or assistance in workflow processing is to cite its peer-reviewed 
description and or its User Guide. We encourage users and data science 
researchers to cite NCO for another reason, too: it helps funding
agencies track the impact of the work they fund.

The recommended citation for NCO software is

Zender, C. S. (2008), Analysis of Self-describing Gridded Geoscience
Data with netCDF Operators (NCO), Environ. Modell. Softw., 23(10),
1338-1342, doi:10.1016/j.envsoft.2008.03.004. 

or

Zender, C. S. (2014), netCDF Operator (NCO) User Guide, Version 4.4.3,
http://nco.sf.net/nco.pdf. 

Use the former when referring to overall design, purpose, and
optimization of NCO, and use the latter when referring to specific
features and/or the Users Guide itself.

Additional information on citing NCO is in the User Guide at
http://nco.sf.net#ctt
A complete list of NCO publications and presentations is at
http://nco.sf.net#pub
This list links to the full papers and seminars themselves.
