English: Graph shows the energy-density spectrum of outgoing thermal radiation from Earth at wave numbers ranging 400-1600 cm-1. Equivalent wavelengths of 6.3-25 microns are in the infrared band. Radiance data was measured on May 5, 1970 with NASA's IRIS instrument on the Nimbus 4 satellite.

This is one of the earliest observations of Earth's outgoing longwave radiation that have since become critical to monitoring our planet's energy balance.

Data Citation: Hanel, Rudolf A., et al. (1994), IRIS/Nimbus-4 Level 1 Radiance Data V001, Greenbelt, MD, USA, Goddard Earth Sciences Data and Information Services Center (GES DISC), Accessed: 14 October 2022, https://disc.gsfc.nasa.gov/datacollection/IRISN4RAD_001.html

Further info: Hanel R. A. and Conrath B. J., Thermal Emission Spectra of the Earth and Atmosphere from the Nimbus 4 Michelson Interferometer Experiment, Nature 228, 143–145 (1970). https://doi.org/10.1038/228143a0