[1] In 1926, he and Albert H. Taylor worked out several basic characteristics of the ionosphere, including the distribution of its electron density and dependence on solar elevation, by studying the propagation of radio signals in the atmosphere.
They collaborated with Gregory Breit and Merle Tuve in the development of the ionosonde device used to study the ionosphere.
Hulburt also studied how solar X-rays and extreme ultraviolet radiation were responsible for ionization in E- and F-regions of the upper atmosphere, with the use of V-2 rockets captured from Germany at the end of World War II to make high-altitude observations.
[1][2] During World War II, he advised the United States Navy on camouflage designs for its ships.
[1] His honors and awards included the Frederic Ives Medal of the Optical Society of America (1955),[2] the John Adam Fleming Medal of the American Geophysical Union (1964), and the degree of Doctor of Humane Letters from Johns Hopkins University (1980).